3T03 Midterm 1 Content (Q&A)

Lecture 3 – Pillars of Behavioural Ecology

09.01.2025

·        Levels of analysis

o   Behavioural studies address two types of questions:

o   1. Proximate or immediate cause questions (“how” questions)

§  Mechanism (physiological, cognitive)

§  Ontogenic process (development)

o   2. Ultimate or long-term cause questions (“why" questions)

§  Effects on fitness

§  Evolutionary origins

o   Within each of these two general types of questions there are different kinds of answers, termed levels of analysis

·        E.g. jellyfish mostly swim upwards in the daytime

o   How? As the sun rises, they move upwards towards light = they have phototaxic cells, when stimulated they’ll move upwards; photosensitive neurons stimulatd by light, stimulating muscles

o   Why? They have symbionts (zooanthelles) living in them, providing amino acids, glycogen; the better they do, the better the jellyfish do; jellyfish that maximize the productivity do better

·        Niko Tinbergen class “4 questions” (1963)

o   First to propose that there are four basic mode/levels of analysis that explain behaviour

o   Mechanism/causation/mechanisms of control

o   Ontogeny/development

o   Phylogeny/evolutionary history

o   1) what is it for? Function/adaptive significance/current utility

§  How does the behaviour contribute to survival and reproduction (what are the fitness effects)?

§  Functional question, why is it maintained by natural selection

o   2) how did it evolve? Phylogeny

§  how did the behaviour evolve?

§  Functional question: what were the evolutionary antecedent behaviours? When did the behaviour first appear or originate in evolutionary time?

o   3) how did it develop? Ontogeny

§  How does the behaviour develop within an individual?

§  Proximate: how does it develop during an individual’s lifetime

o   4) how does it work? Causation

§  What mechanisms cause the behaviour?

§  Proximate question: how does it work physiologically? Cognitively?

o   Interaction among these questions

o   Answers complementary but not mutually exclusive

o   Niko’s ideas were a breakthrough and are an enduring legacy

·        How and why do birds sing?

o   Increasing daylight has hormonal affects on brains, relating to control of song; modulate singing behaviour. HVC (higher vocal center) is important, connected to (RA), connected to nXIIts, sends to sarynx (analogous to larynx). We know these centers are important to birdsong

§  Some areas for song production vs song learning

o   How does birdsong develop over a lifetime

§  Output and complexity increase overtime due ot learning; they must hear song from parents of conspecifics during a specific developmental window, otherwise they don’t earn properly

§  Males ZZ, females ZW chromosomes

§  Male birds have estrogen produced in the brian, females do not; under estrogen, HVC neurons (song center) grow; if you give females estrogen, they will be able to produce song later in life

o   How does bird song contribute to fitness?

§  Larger song repitoire = larger clutch size

§  Attracts mates and tells competitors to stay away

o   How did birdsong evolve?

§  Primitive birds don’t sing, just squawking calls; innate

§  Song learning occurs in parrots, hummingbirds and Passeriformes

§  What makes more sense? Evolving 3 times independently or once and then disappeared in many times

§  If evolved separately, it would work differently in the brain; this is the case; differently location of learning centers

§  But also regulated by the same gene

§  So we don’t know which way it happened

·        Tinbergen wanted these questions to be addressed together

·        Homework/Practice

o   In wood frogs, at night males gather together in large aggregations and acoustically court females

o   Using the levels of analysis framework, make up 4 different types of explanations to explain this group calling in wood frogs

o   No marks

·        Costs and Benefits

·        Trade-offs

o   Hawk wants high calorie food, fast; Get the most calories and spend the least time and energy

o   “behaviours will only evolve if the benefits are greater than the costs” B>C

·        Optimality

o   Mother stink bug guarding clutch vs getting food?

o   Optimality = minimize costs, maximize benefits

·        How loud should a male sing

o   Singing loudly is beneficial; attracting mates and repelling predators

o   Louder can attract predators

o  

o   There is a spot that minimizes cost and maximizes benefits (i.e. you want the distance between the lines to be bigger

·        Optimality – where it is advantageous to engage processes with a maximal beneficial effect and a minimal cost under given constraints

o   Optimality models force us to be explicit about the tradeoffs

·        Kestrels

o   Flight hunting vs perch hunting

o  

o   Flight hunting is way more profitable than perch hunting

o   Only using flight hunting the majority of the time, why do they even perch hunt??

o   This data is only winter

o   Illustrates that minmaxing can help us understand animal decision making

·        Optimality modeling – what to eat?

o   A model of choice between big and small prey

o  

o   A) if it encounters prey 1, it should always eat it = choice of more profitable prey 1 does not depend on abundance of prey 2

o   B) if it encounters prey 2,it should eat it provided

§  Gain from eating prey 2 is greater than the gain from rejecting and searching for more profitable prey 1

§  i.e

§  choice of less profitable prey 2, depends on the abundance of the more profitable prey 1

§  predator should eat prey 2 if:

o   predictions

§  predator should either eat prey 1 (specialize) or eat both prey and prey 2 (generalize)

§  the secision to specialize depends on S1 not S2

§  the switch from specializing on prey 1 to eating both prey should be sudden and should occur only when S1 increases

o   this type of thinking leads us to new insights:

§  species with short handing times and long search times should usually be generalist and include a wide range of items in their diets

§  specialists are expected to have a longer handling times and short search times; they are choosy

§  animals should be generalists in unproductive environments and specialists in productive environments

o   now that we know about search times, handling time etc. what might we predict prey do to avoid being eaten?

o   Prey can make themselves less profitable by

§  Camouflage or crypsis (e.x. looking like stick or leaf) (S^)

§  Polymorphism (S^): multiple colour/size morphs; harder to develop search image

§  Anti-predator defences (H^): porcupine spine, claws, teeth

§  Toxins (H^):

·        Prey adaptations and predator counter adaptation (co-evolution: arms races)

o   Optimality theory – forces us into a trade-off framework. An elegant way to consider how to minimize costs and maximize benefits associated with a behaviuor. Makes testable predictions

·        Three most important variable in optimality approach

o   Decisions: what are the alternative possible strategies available to the animal? Should the animal take time to eat this bug now or keep searching for a bigger one?

o   Currency: what is being maximized? What are the means used to establish the value of alternative decisions? Time, energy, risk, how are these maximized or minimized

o   Constraints: what are the organism’s limits? The intrinsic and extrinsic constraints on an animal (physical or psychological limitations; temperature or available light, bill size/shape)

Lecture 4 – Game Theory, The Evolution of Sex

13.01.25

·        3rd pillar: Game Theory

o   There is not always just one optimum in nature

·        Bull frogs

o   Many males call for females; but calling can attract predators (frog eating bats)

o   Some males are silent and simply stick around large males and will try to grab a female as she moves towards a large male

o   What solution you come up with depends on what oterhs are doing

·        Evolutionary game theory

o   Frequency dependent

o   Playing a dynamic game – strategies can change (dyadic or against populations)

o   Co-evolutionary (strategies within a population can change and the best solutions depend on what others are doing)

·        Game theory and evolutionary game theory

o    John von Neumann – invented game theory 1928; developed game theory for economics;

o   John maynard smith: brought game theory to evolution; helped understand sex, , , ,  => evolutionary game theory

·        Evolutionary stable strategies

o   Can alternative invade?

o   If they can not then the strategy being played is an evolutionary stable strategy (ESS)

o   An ESS is a strategy that resists an invasion, and is a nash equilibrium

·        The hawk-dove game

o   Two animals want a resource with value V

o   The winner’s fitness is increased by V

o   Animals can adopt one of two strategies: hawk or dove

o   Hawks: escalate and continue to fight until inured or opponent retreats

o   Doves: display, retreat at once if opponent escalate, one or both wll be injured. Injury reduced fitness by a cost C

·        Hawk-dove game payoff matrix

o  

·        Conditionary for an ESS

o   If a strategy is stable, it must be that if almost all members of the population adopt it, then the fitness of members is greater than of any possible mutant

o   Otherwise a mutant could invade, and so the strategy would not be stable

o   Is playing hawk or dove while in a contest an ESS?

·        Hawk-dove game

o   Dove is not an ESS

o   Hawk is an ESS if ½(V-C)>0 i.e. if V>C

o   If V<C, if the costs of injury is high relative to the reward, we expected mixed strategies

·        The stoplight game

o   Imagine two cars are heading towards eachotehr and come to a light

o   It makes sense for the one with the gren light to go and the one with the red light to stop

o   This is an example of a nash equilibrium because any other option is worse

o   è if they both go then they will crash into eachother. That is very bad an both players ose fitness

o   If they both stop then they will be both just wait around and be delayed. They lose a little fitness (-1)

o   If one goes at the green light while the other car stops at a red light, no one will crash

o   The car that waits is delayed but not by much (0)

o   Fit these values into a payoff matrix

o  

o   So when two cars meet eachother at a traffic light or stoplight, it makes the most sense for the one with a greenlight to go and the one with a redlight to stop

o   This is the best solution. No other strategy can better it by adopting a different strategy

·        Nash equilibrium

o   A nash equilibrium is a set of strategies, one for each player, such that no player has incentives to change his or her strategy given what the other players are doing.

o   A nash equilibrium is a way to behave that everyone would want to adopt

·        Payoff matricies question

o   Student question: how do behavioural ecologists decide numerical amounts for values and costs in real life environments? Do they actually work with specific numbers?

o   Yes… they actually measure these things and fit in values that have been measured in nature

o   E.g. benefit: size and nutritional analysis of prey fish of bald eagles, cost: how likely they are to lose feathers

·        Lecture 3 summary:

o   Pillars of ecology

§  Levels of analysis: mechanism, ontogeny/development, function, phylogeny

§  Optimality, tradeoffs, costs and benefits

§  Game theory, hawk-dove game

Lecture 4

·        I. What is Sex

o   Recombination – a process where genetic material is broken down and brought together with other genetic material. A shuffling of the genes which ensures that offspring will differ genetically from their parents and usually from eachother

o   Reproduction – can be sexual or asexual and coupled or uncoupled with recombination

o   Sexual reproduction – it is a form of reproduction that has (a) the production of haploid gametes by meiosis, (a reduction division), and then (b) the fusion of these gametes produces a zygote that restores the full diploid complement of chromosomes. It involves creating new genetic combination (through transfer of genetic material, known as crossing over)

o   Asexual reproduction – is the production of new individuals without creating new gnetic combination (parthenogenesis). It a form of reproduction which does not onvovle meiosis, ploidy reduction or fertilization. Asexual reproduction only takes on parent. It is quick and easy!

·        II. Why sex?

o   We often assume that reproduction requires two individual

o   But for many organisms this is not true

o   Lots of single celled organisms and some plants and fungi and even some animals reproduce asexually

o   Life originated with asexual reproduction, so sexual reproduction is something that ahd to evolve

·        Amazon molly (poecilia Formosa)

o    All female species; reaches sexual maturituy after 1-6 months; 20-100 young, every 30-40 days; offspring are all gnetic clones of their moms. To reproduce, femlaes mate with males of a different species. She doesn’t take the genetic material but the sperm is needed to trigger embryogenesis

·        Whiptail lizard

o    All female; produce eggs through parthernogenesis, asexual

o   Ovulation spured by mating with other females; pseudocopulation

·        Zebrashkar, California condord, Komodo dragons

o   Can reproduce parthenogeneically

o   Can reproduce with males but are capable of parthenogenesis

·        Why did sex evolve? It is very costly! Why is it costly?

o   seems like a crazy strategy; turns out there is a 4x cost of sex

§  1) cost of breaking up co-adapted gene complexes: sex and recombinantion mix up and “co-adaptation” that a genotype might have to a particular environment; why disturb if its is adaptive

·       

§  2) cost of making males: there is a cost of meiosis associated with putting genes into males that cannot produce eggs. Asexual individual don’t have to look for mates! Asexual populations can grow faster

·       

·        Eg. yeast can reproduce sexually (8 hours) or asexually (1 hour). So in 8 hours a sexually reproducing cell has made 2 new cells. While an asexually reproducing one has made 256 – sexual reproduction is highly inefficient

§  3) cost of sexually transmitted diseases (STDs) – in some specie sthe longer they mate the more likely the female is to contract a venereal disease

§  4) Cost of finding a mate and mating (predation risk, time, energy)

o   Yet in the majority of plant and animal species reproduce sexualy

·        Why has sex evolved and why is it maintained?

o   Over 20 hypotheses that fall into 2 classes

o   1.  SEX CLEARS DELETERIOUS MUTATIONS. Genetic reshuffling (recombination) that occurs during meiosis and the fusion of male and female gametes allows new, potneitally advantageous combinations of genes to come together, a harmful mutation to be elimination or masked

o   2. SEX HELPS SPECIES GREAT A WIDER ARRAY OF OFFSPRING GENOTYPES than does asexuality (Lottery hypothesis. Sex assists species to evolve in response to variable environmetns (with temporal and spatioal unpredictability

o   Sexual reproduction increases genetic variation

o   Recombination benefits a species by increasing the rate of evolution or the rate at which adaptation can occur

o   Evolutionary benefit of increased genetic variability is to enhance the adaptability to adapt to changing environments

·        Sex can help species deal with environmental change

o   There is a constant arms race between host and pathogens or prey and prey and predators, as each treis to gain the upper hand. This idea is called the red queen hypothesis

o   Asexual forms all have the same vulnerability genes and so can be wiped out. Sexual forms are genetically unique

·        Sex must be advantageous

o   1. Over evolutionary time

§  Because sex is so common and ancient asexual lineages are rare (exception bdelloid rotifers)

·        Females reproduce exclusively through parthenogenesis; have been around for millions of years

·        Go into dormant stage for long time; very resistant to ionizing radiation; resistant to dna damage?

o   2. Over ecological time

§  Because some species that have asexual reproduction can and will flip into sexual reproduction (e..g many aphids and plants do both)

§  New zealand mud snaisl: can do both sex and asexual, ~230 young per year

·        Can get infected by parasitic worms, which also need ducks to complete their ife cycle

·        Depending on whether ducks and snails come together, reproduction affected

·        In shallow areas, mud snails reproduce sexually

·        In deeper water without ducks, mud snails don’t have parasitic worm and can reproduce asexually

·        They are invasive too, and there aren’t parasites so they grow really fast

Summary of paper: sex ration patterns can be affected by the ability of the parent to predict the offspring’s environment

Lecture 5 – Evolution of Sex, Sex Allocation

15.01.25

·        III Sex must be advantageous

o   Over evolutionary time

o   Over ecological time

·        IV Gender and Evolution of Dimorphic gametes

o   Gamete = cell that fuse with other cells during sexual reproduction

·        Males make many gametes, females make few

o   Human females are born with 1-2 million follicles that can become eggs

§  Most of these die – at 12, most females have only 400 00 left

§  About 1000 are lost each menstrual cycle and only about 400-500 ever mature into a proper egg

o   Human males produce 100 million sperm in every ejaculate

·        Start with isogamy (equally size gametes)

o   Parker-baker-smith model for the evolution of male and female gametes (1972)

o  

·        Model has 2 assumptions :

§  1) trade-off between gamte size and number

·        (more gametes = smaller gametes)

§  2) zygote fitness increases with size

o   With these assumptions, competition to fertilize eggs (the bigger gametes) leads to disruptive selection on gamte size, and the evolution of large (‘female’) gamtes and small (‘male’) gametes

o  

o   Large gametes selected because eof increase in fitness

o   Small gamtets selected because more cells could be made and will compete to find  alarge gamete to parasitize (join with or “fertilize”)

·        Evolution of anisogamous sex from isogamous sex = evolution of male (sall) and female (big) gametes from a situation of intermediate size of gametes

o   Isogamy = equal sized gamtes

o   Anisogamy = gamtes of differen sizes

o   Disruptive selection

o  

o   Disruptive selection can lead to the evolution of a cell type that specializes in swimming (small) and another than specializes in providing energy (large)

o   Selection against fusion between the two small cells (not viable)

o   Fusion between the large cells rare (or also disadvantageous)

o   The small cells (or the individuals making them) compete for access to the large cells (or the individuals making them) = sexual selection

o  

o   Tiny gamete = energentically inexpensive to produce in large numbers

o   Large gamete = energetically expensive to produce but with sufficient cytoplasm fir early embryogenesis

o   Intermediate = too large to produce a lot but too small to support early embryogeneis without additional cytoplasm

·        V. Evolution of anisogamy: differences in gametic investment

o   Males often have  asmaller gametic investment, gamester are smaller, mobile and devoid of nutrient

o   Females produce large, immobile, nutritionally rich

·        Summary: Evolution of Sex

o   Prevalence of sex is paradoxical

o   Costs are high relative to its known benefits

§  – Time

§  – Energy

§  – Disease

§  – Slower production, making males is wasteful

§  – Recombination of co-adapted gene complexes

·        • Gene combinations that were successful in the parents are broken apart, and only half of each parent’s genes are passed along

·        Review of topics discussed in this lecture

o   1.Sexual vs Asexual Reproduction

o   2. Costs of Sexual Reproduction

§  a. breakup of co-adapted genes

§  b. costs of making males

§  c. disease

§  d. finding mates takes time and energy

o   3. Advantages of sex

§  a. clearing deleterious mutation,

§  b. creates variability-helps adapt to changing environments, Red Queen Hypothesis

o   4. What is a male? What is a female?

o   5. Evolution of anisogamy from isogamy (Parker’s 1972 model)

o    

Sex Allocation & Sex Ratio

·        Sex ratio = % of M to F

o   Primary = ratio at conception; slight male biased in humans

o   Secondary = ratio at birth; slightly male biased in humans 107:100 males:female

o   Tertiary = ratio at sexual maturation (post-puberty); slight female biased 96:100 M:F

§  Amles more susceptible to disease, die at higher rates

o   Sex allocation = investment in M vs F; depends on environment, mating  system and how reproduction is carried out within a preeding system

·        In most species, males and femlaes are produce din approximately equal numbers. Why?

o   Fisher’s 1:1 Sex Ratio Rule

o   Fisher’s (1930) sex allocation theory

§  How will selectio shape parental allocation of resources between daughters and sons?

§  Fisher showed that the only stable strategy is to invest equally in the two sexes

·        Fisher’s sex ration principle; explains why the sex raito of most species is approx. 1:1

o   1. Suppose males births are less common than female

o   2. A newborn male then has better mating prospects than a newborn female, and therefore he can expect to have more offspring.

o   3. Therefore parents genetically disposed to produce males will tend to have more than average numbers of grandchildren born to them.

o   4. Therefore the genes for male-producing tendencies will spread, and male births will become more common.

o   5. As the 1:1 sex ratio is approached, the advantage associated with producing males dies away.

o   6. The same reasoning holds if females are substituted for males through-out. Therefore 1:1 is the equilibrium ratio

o   AN EVOLUTIONARY STABLE STRATEGY (ESS)

§ 

·        II. Departures from Equal Sex Ratios              

·        i. Local mate competition (LMC)

o   competition among relatives can affect selection on the sex ratio

o   selection favours a rex ratio biased towards the sex experiencing the least amount of kin competition

o   Fig wasps

§  Clutch of eggs; incest where brothers have sex with sisters then brothers die; females go off to reproduce

§  No competition between sisters, but lots between brothers

§  Fitness in making more sons is wasted, because when they compete only one son reproduces

o   Selection makes the ratio biased towards the sex that isn’t competing with relatives (i..e experiencing the least amount of kin competition)

o   == 1:1 is an ESS but only if there is random mating in a large population

·        ii. Local resource competition

o   south African prosimian, Otelemur crassicaudatus – strong male bias sex ratio

§  sons disperse, daughters do not

§  local competition for food with daughters reduces their value

§  really strong male bias; maybe even only one daughter in a mothers’ lifetime

§  females compete with moms for resources

·        iii. Maternal condition (trivers-willard hypothesis)

o    polygenous species, where males mate with many females

o   Red deer; link between maternal condition and sons reproductive success

§  Quality and amount of milk received from his mother will determine how big a male will grow (not effect females)

§  Bigger males win contests

§  Winners hold the best territories and biggest harems of females

§  Winners also mate with the most females

§  Many males don’t mate at all

o   Make high pay-off sex when in good condition and make low pay-off sex when in poor condition (when they “know” = not conscious)

o   Relative fitness costs and benefits of producing sons or daughters may vary according to parental condition

o   Selection would favour parents to ‘individually optimize’ the sex ratio accordingly

o   Fisher’s theory says that only equal investment in the sexes can be evolutionarily stable

o   But preferential investment in one sex could still be optimal for some parents in particular circumstances

§  Consider a polygynous animal with a litter size of 1, e.g. a red deer.

§  Expected fitness of sons is more variable than that of daughters

§  If pre-weaning parental investment has a big impact on a son’s expected fitness, but affects daughters less, a hind in poor condition might prefer a daughter over a dud son, whereas one in good condition can expect more grandchildren from a son.

o   Trivers and Willard hypothesis expanded the strategy set

§ 

§  Assumptions:

·        1) parental condition influences offspring condition

·        2) differences in offspring condition persist into adulthood

·        3) good condition influences the mating success of one sex more than the other

o   Tim Clutton-Brock examined lifetime reproductive success of red deer on the Isle of Rhum as a fuction of sex and mother’s dominance status in year of one’s birth

§  Found: expected fitness of songs is more variable than that of daughters

§  MM , but not FF , reproductive careers are strongly influenced by mother’s dominance status

§  Island studies are great because you can follow every individual for their lifetime, there’s no immigration/gene flow and your subjects don’t leave

o   Costs and benefits of producing sons or daughters can vary according to parental condition

o   Selection would favour parents to individually optimize accordingly

o   Lifetime reproductive success of red deer depends on sex and mother’s dominance status

o  

o   Premise of T-W theory satisfied: a male’s reproductive career is strongly influenced by mother’s dominance status. A female’s is not.

o   Trivers willar effect: birth sex ratios of individual remale red deer differ in relation tosocial rank over their life span

o  

·        iv. Sex ratio disorders

Lecture 6 – Sex Allocation

16.01.2025

·        II. Departures from Equal Sex Ratios

o   Local mate competition

o   Local resource competition

o   Maternal condition

o   4. Sex ratio distorters (SRDs): heritable elements that modify the sex ratio of their host to promote their own development

·        Sex ratio distorters in Nasonia vitripennis

o   The “lab rat of sex ratio research – is a tiny wasp that parasitizes blowfly pupae

o   In studies in the facultative control of sex ratio, distorters have been discovered serendipitously

o   1. MSR (maternal sex ratio) - a maternally transmitted factor that causes females to fertilize all eggs, thereby produce broods that are virtually100% daughters

o   2. SK (Son Killer) – an infectiously transmitted bacterium that kills unfertilized (those that would have developed as sons)

o   PSR (Paternal Sex ratio) chromosomes – a paternally transmitted” factor. They convert diploid fertilized eggs (which would normally develop into females) into haploid males that carry a PSR chromosome.

o   Wolbachia – inherited bacteria (present in eggs), feminizes males, induces parthenogenesis and produces sperm incompatibility

·        III. More Examples

·        How do animals manipulate sex ratios?

o   Sex ratio manipulation occurs in many taxa, but the mechanisms underlying the phenomenon remain largely unknown

o   Exception: hymenoptera

o   In wasps, bees, ants, termites (collectively called hymenoptera) and some mites, sex is determined by how many chromosomes your mother decides to give you. Fertilized eggs get two sets of chromosomes (one from each parent) and develop into diploid females. Unfertilized eggs get only one set of chromosomes (from mom) and develop into haploid males. èThis phenomenon is called haplodiploidy.

o   If a fig wasp can smell that she’s the first present, she’ll lay 90% females and only a few sons

o   If other wasps have already laid eggs, she’ll lay more males because they’re no longer a waste; there are other females for the males to mate with

·        Do mammals and birds manipulate sex ratios?

o   Dogma: sex determination is based on chance, a X vs Y sperm reaching the egg (or W vs Z in birds)

o   View is being challenged by a growing number of studies

o   White crowned sparrow

§  Low maternal condition and low food availability results in female biased clutched in a number of bird species

§  Females with high corticosterone (the primary stress hormone in birds) produce more daughters

§  Implanted corticosterone; increased proportion female babies

§ 

o   Lesser black-backed gull

§  Researchers kept taking eggs from birds

§  About equal proportions

§  As they kept taking them away, proportions biased toward females

§  Was nutritional stress; when they provided more nutrition the proportions were not affected

o   ==. Seems like stress hormones are really important, and they select for females, but its actually species specific

o   Different direction in different species; in chickens, corticosterone produces male bias

·        Mammals

o   Maternal testosterone hypothesis: testosterone levels (pre-conception) especially in the female’s follicular fluid appear to influence offspring sex ratio

§  Females with high testosterone have more male offspring

o   Good condition hypothesis

§  Maternal glucose levels (post-conception) and dietary fat appear to influence offspring sex ratio.

§  Females with high fat levels or high glucose in their diets have more male offspring

o   Still theories; not proven yet; contradictory evidence

·        Seychelles warbler

o   In 1960, the total world population of this species was <30 birds on the tiny (26 ha) island of cousin

o   Privately owned island, plantation

o   1959 census concluded there were only 26 left

o   1968 bird preservation council bought the island, reintroduced native vegetation

o   By 1982, there were 115 occupied territories and over 300 birds

o   Unusual reproductive behaviour for a small songbird:

§  Typical clutch consists of just one egg

§  The single nestling was often cared for by three adults

§  Young birds didn’t breed until they were at least 3 years old

o   Pairs don’t always breed alone

o   Helping (by grown offspring) is common

o   The number of young born, fledged and reaching 1 year depends on territory quality (more insects)

o    

Lecture 7 – Sex Allocation

20.01.25

·        Sex Allocation departure example

o   Seychelles warbler

o   Unusual reproductive behaviour for a small songbird

§  Typical clutch only 1 egg

§  Single nestling was often cared for by three (or more) adults

§  Young birds didn’t breed until they were at least 3 years old

o   Pairs don’t always breed alone — helping (by grown offspring) is common

o   Survey of insect abundance, quality

o   The number of young born, fledged and reaching 1 year depends on territory quality

o  

o   To protect the warbler populations two translocation experiments to other islands were planed

o   Aride: huge seabird colonies, already protected, larger (68 ha)

§  Similar habitat, vegetation to Cousin’s

§  29 birds, 16 M 13 F

o   Cousine

§  Also very similar

§  Used to have feral cats, but they were all trapped and removed

§  29 birds, 15M and 14 F

o   Originally mostly pairs. By 1993, as the new islands filled up, extra helping adults appeared on aride and cousine too

o   Both populations expanded rapidly, such that all suitable habitat was occupied by territorial birds within 3-4 years

o   Best territories filled up first (territory quality depends on insect density

o  

o   Females typically stay put males disperse out of their territory

o   Helping is costly for parents on poor territories because they have to compete with their grown helper offspring for food

o   Breeding warbler pairs on low quality territories produced 77% sons, while warbler pairs on high quality territories produced 13% sons

o  

o   Sex ratios BEFORE vs AFTER the translocation of warblers

o  

·        Sex allocation summary

o   Fisher’s sex allocation theory

o   Departures:       

§  Local mate competition, Local mate enhancement

§  Local resource competition

§  Condition-dependent sex allocation: trivers and wilard

§  Sex ration distorters: “selfish genetic elements”

o   How do animals manipulate sex ratios

o   Examples of sex allocation theory

Sex Roles, dimorphism, weapons and fights

·        Sexual selection: a form/subcategory of natural selection

o   Intrasexual selection: nivovle traits that help members of one sex compete with each other for mates

o   Intersexual selection: involve traits that make individuals attractive to the opposite sex

·        Timeline

o   1858 - Darwin & Wallace jointly present the theory of “natural selection”

o   1859 - Publication of “On the Origin of Species...” Darwin presents the evidence for natural selection and the germ of the idea of sexual selection.

o   1871 - Publication of “The descent of man and selection in relation to sex”, where Darwin develops the idea of sexual selection as that part of natural selection (differential reproduction of types) that is attributable to differential access to mates, and divides it into ...

§  1) selection for attributes that help individuals vanquish same-sex rivals in competition for mating opportunities (Mating competition or intrasexual selection)

§  And

§  2) selection for attributes that “charm” the opposite sex (mate choice or intersexual selection)

o   Natural selection becomes generally accepted as the unifiying theory of biology

o   Sexual selection is largely ignored and sometimes dismissed, especially true of mate choice

o   1971 - A symposium commemorating the centenary of “The descent of man...” revives interest in sexual selection.

o   1972- A volume results that includes an influential paper by Robert Trivers who explores of the implications of Bateman’s (1948) principle.

o   èSexual selection (especially mate choice) becomes a major focus of behavioural ecological theory and research

·        Sexual selection: a process whereby secondary sexual traits become elaborated because they increase their owner’s ability to gain access to mates

·        Factors influencing the direction and intensity of sexual selection

·        Anisogamy: differences in gametic investment

o    Females have way more investment

o   Fundamental asymmetry, females make few, males make many

o   E.g. female spotted kiwi weighs 1.3 kg and eggs weighting 300g

·        Bateman’s principle

o   Males: reproduction is usually limited by the number of eggs fertilized, which is dictated by number of females a male can mate with

o   Females: reproduction limited by number and quality of eggs produced, often limited by resources

o  

o   Principle

o   1) variance in number of offspring and mates in males exceeds that of females

o   2) males show a significant correlation between number of mates and number of offspring, whereas females do not **

·        Problems with bateman

o   Bateman’s did not monitor the flies’ behaviour or observe mating. He simply inferred who mated indirect inferences from visible single-gene mutations on fly offspring

o   Bateman ran his experiment 6 times, results from runs 1-4 were similar and 5-6 were similar. So he lumped the data from these runs into two graphs

o  

§  In 1-4, females still went up with successive matings, just not as much

o   Bateman’s idea about the two sexes were overly simplistic

o   He didn’t take into account:

§  That females also can vary in reproductive success because of differential access to resources

§  Social environments matter

§  Harassment avoidance

§  Mate choice

§  Sperm selection

·        Difference in parental investment

o   Males- more mating effort

o   Females – more parental effort

o   “where one sex invests in parenting considerably more than the other, members of the least investing sex will compete among themselves to mate with members of the sex investing the most” – Trivers, 1972

·        Gametic investment (bateman), parental investment (trivers) leads to sexual selection; who competes and who chooses? Direction and intensity

o  

·        Operational sex ratio (OSR) – ratio of receptive males to females in a population

o  

·        What about male parental investment? Or shared

o   Must consider reproductive rates; time to produce and/or recover

o  

o   Example: sticklebacks

§  Males care for 21 days, males accept 1-5 females clutches

§  Female slay 30-60 eggs every 10 days

§  Male reproductive rate > female reproductive rate

·        5 females x 60 eggs / 21 days = 14 young/day > 60 eggs / 10 days = 6 young/day

·        Normal

o  

·        When do you get sex role reversal?

o  

o   Species where you get the opposite: males put more energy into parental care, more into gametic investment, males reproduce slower, are less common, males are more “choosy”/females more competitive, etc

·        Intrasexual selection – process selecting for traits that help members of one sex compete with each other for mates

·        Intersexual selection – process selecting for traits that help members of one sex determine which members of the opposite sex to mate with

·        Intrasexual selection

o   Sexual dimorphism

o   Evolution of weapons

o   Fighting and contests

o   Alternative reproductive tactics

o   Sperm competition

Lecture 8 – Sex Roles, Dimorphism, Weapons and Fights

22.01.25

·        Why was darwin’s ideas on intersexual selection ignored for 100 years until trivers?

o   Intrasexual selection is more easily observed: showy, bloody, loud = conspicuous

·        Intrasexual Selection

o   Sexual dimorphism

o   Evolution of weapons

o   Fighting and contests

o   Alternative reproductive tactics

o   Sperm competition

·        1. Sexual dimorphism – males and females of different sizes

o   Potential causes

§  Natural selection

·        Sometimes females can be larger – e.g. larger female birds, fish etc can lay more eggs

§  Competition between males and females (disruptive selection)

·        If males and females compete for the same resources, disruptive selection can work to move them into different feeding niches so they no longer compete

·        E.g. woodpecks males are bigger, larger beaks è they have different feeding ecology

§  Sexual selection

·        Most common

·        Sexual selection

o   The elephant seal is the most sexually mimorphic of mammals

o   3000kg males, remain on beach competing for matings and fasting for up to 4 months

o   A female who is ready to mate (weaned her pup already) typically weigh about 450kg

o   Males have to live much longer than females and grow much bigger before they can reproduce. No male copulates before 6 years of age, and almost no paternity goes to males < 9 years old, whereas females typically conceive their first pup at age 2

o   Highly polygenous – female produces one pup a year, and up to 12 in a lifetime

o   But a very dominant male can sire dozens of pups in one year

o   A few males win big. Most are total losers

o   Estimated 11% of weaned males ever sire a pup, whereas 35% of weaned female produce at least one

o   Winning fights depends on larger body size = selective pressure for larger size

o   The prize for which male elephant seals compete is maternal investment

o   A pregnant female arrives at the beach weighting 700gk

o   She delivers a 50kg pup, and nurses it while fasting for 4 weeks

§  By the time of weaning, mom is 450kg, pup is 200kg

§  Asonighingly efficient transfer of mass

o   Mother mates, conceives next years pup

o   Successful males may produce many more surviving offspring than the most successful female, but most males are also more likely than females to die without reproducing at all.

o   Males have a higher variance in fitness.

o   High within-sex variance favours the evolution of intense and dangerous competitive tactics.

o   As the victor’s prize gets bigger, and the pool of competitors who have nothing to lose by escalating competition with dangerous tactics gets larger, the more competition there will be.

o   Costly investment in boyd growth can only be sexually selected if there are exceptional reproductive rewards to be gained by being a good fighter

o  

§  Species where there is higher levels of size dimorphism occur when the size allows them to have a larger harem

o   Strong significant relationship between harem size and sexual size dimorphism across mammals (phylogenetically controlled)        

§  Male/female ewight contrasts vs harem size

·        Different typed of sexual size dimorphism F>M or M>F

o   There are several reasons why sexual size dimorphism may exist

o   If sexual dimorphism is a result of male-male competition (intrasexual selection) then dimorphism will be greatest in species where the variance males in RS (reproductive success) is greatest

·        2. Evolution of weapons

o   Horns and antlers are secondary sexual traits that have evolved for male-male competition

o   Horns are never lsot, aren’t branched

o   Antlers are lost yearly, sually branched

o   Weaponry: traits that have evolved for male-male ocmpetitino

o   Insect exoskeletons often modified into weapons – in scarb and dung beatels, males fight with their horns, females mate with winners (not based on horn size)

·        Dung beetle / scarab

o   About 5000 species, feed on feces

o   Many species roll feces into a ball – drag and bury the ball into brood chambers, or tunnlers will lay eggs in dung, dwellers just live in it

o   Dr douglas Emlen - Son of the guy who though of operational sex ratios

o   Males with different horn lengths

o   Males that exceed a critical body size develop a pair of long, curved horns on their heads, while smaller males remain hornless

o   Type i – honred, larger

o   Type 2, hornless, smaller

o   Horn size varies greatly within a population

o   Males fight for tunnels

o   Males with larger hors win the fights

o  

§  Bimodal distribution = small and norless, large and horned, few intermediates

o  

§  Staged fights between individuals with same body size but different horn size

§  Individuals with larger horns won 22/27 fights

§  Proportion of fights won increased with disparity

§  Males were defnding tunnels with females so they could mate with her when she exited

o   Why do hornless males persists?//?/

§  They have a completely different strategy

§  They are pacifists

§  Sneak into tunnels

§  Horns help in fights but reduce agility in tunnels

o   èDiscrete morphological variation within a sex related to reproductive strategies

o   If you have intermediate horns, you’re crap at tunnels and fighting

·        Properties of weapons

o   Weapons are structures used in combat with rivals

o   Among species, weapons diverge in size, shapes and the habitats in which they are used

o   Weapons evolve when one sex (usually males) are able to defend spatially restricted critical resources

o   Weapons are usually the most variable morphological structures and the variation honestly reflects individual differences in boyd size or quality

§  ***Why is so different between species is a big unanswered question

·        Fighting is costly; could be injured or die

o   Animals want to avoid it as much as possible

·        Intense fights and contests

o   Fighting is a purposeful, sometimes violent, conflict to establish dominance over a competitior and get resources. High degrees of mating competition select for ntesne fights and onctests

·        Why do aniamls fight/

o   Limited resources

o   Food, mates, shelter, territories

o   Contest over indivisible (monopoliizable resources)

·        Horseshoe crab

o   Scramble competition, not fighting

·        Fish tangenika

o   In nature they don’t fight over food

o   They feed on zooplankton in water column; no reason to fight over food

o   Its ephemeral

o   But down on substrate, they mouth-fight (rip eachotehrs lips off) è fight over shelter

§  Limited and monopolizable

·        Costs and benefits of fighting

o   Benefits

§  Win resource (territory, mate, food etc)

o   Costs

§  Energy

§  Time

§  predation risk

§  Injury

§  Death

·        Dominance or social hierarchies

o   Strategy to minimize fighting

o   In animals that live in groups, esp permenant, depresses the amout of fighting

o   Bc smaller fight establishes dominance longer term so they avoid fight in the future

·        Or ritualisex fighting – dampen frequency / risk

o   Assessment tacticts

o   Threat displays

o   Non-contact behaviour

o   Lower costs

o   E.g. elephant seals intimidation displays before actual fight

o   Usually occur before contact or overt aggression begins

·        Fight rules

o   Threats and assessment only (no contact) progress to assessment and contact, then later all out fight (increase in intensity)

o   But when should an individual give up?

·        Factores that influence contests and when to give up

o   Resource holding power (RHP)

o   Resource value (V)

§  E.g. important of meal when starving vs already fed

o   Aggressiveness

·        Resource holding power or potential (RHP)

o   RHP is the absolute fighting ability of the individual, a measure of the size, strength, weapins etc which would enable an animal to win an escalated contest

o   If they are well match, the fight will last longer

o   If big asymetery, very short fight

o  

·        Resoruve value (V)

o   Subjective value; motivation state (internal)

o  

o   Territory owners have higher resource value than intruders è they’ve already invested into the territory, they’ve got more knowledge, build residency etc

o   The longer they’re owner, the longer they’l fight

·        Aggressiveness / daring

o   Readiness of an individual to engage, risk an encounter or dare to escalate, inherent property of the individual

o  

·        How do aniamls fight in the real world

o   Minimize costs

o   Threat displays and assessment

o   Dominance hierarchies

o   Ritualization

o   RHP, V and aggressiveness rules

o   Injuries happen often but acutllay deadly behaviour is rare

·        Lecture 7 summary

o   Intra vs intersexual selection and Darwin

o   Bateman’s principle and triver’s sex differences in parental investment help explain why males are usually more competitive and females are usually more choosy

o   Sexual size dimorphism and weapons have evolved as a means to win contests for femaes

o   Fights have costs and benetifs. Constst duration and intensity are influenced by RHP, V and aggressiveness

·        How measure aggressiveness

o   Have a stimulus like a one-way mirror

o   Put the individual in, measure how many times they will try to fight the opponent

o   Some will fight much more or less

o   Do it again a week later

o   The one that is consistently more aggressive if more aggressive

o    

Lecture 9 – ARTs & Sperm Competition

23.01.2025

·        Intrasexual Selection

·        Orangutan

o   Most reproductive male should territories

o   Males form pair bond with females for weeks/months

o   Secondary sex characteristics – cheek pads help amplify call, + throat sacks make them look more threatening

o   Not all mature orangutans make these long calls, not all have cheek pads (flanges), long hair or throat sacks – instead they force copulate female already in a concertship

§  Subordinates can grow them if a dominant dies; become territorial male

·        Alternative Reproductive Tactics (considered polymorphism if not related to reproduction)

o   Refer to the alternative ways that members of one sex obtain fertilization and reproduce

§  Finding different solutions to reproductive competition

o   Alternative refers to traits with a discontinuous distribution

§ 

o   Individuals allocate resources to either one or the other (mutually exclusive) way of achieving reproduction

§  Large males will call for females

§  Small males are silent and try to grab a female as she moves towards a large male

·        Marine isopod

o    

o   Found in sponges along California coast, intertidal zone

o   Females look very much alike

o   Males come in three very distinct sizes

o   Alpha males -large, hold/own territory

o   Gamma – tiny, stealth to mate with females, alpha males can grab and throw them out no fight

o   Beta male – female mimic, male allows them in thinking he will mate with them

·        Bluegill sunfish

o   Three male reproductive tactics

o   Territorial male

o   Satellite males – smell, look and pheromones like female; cuckold the territorial male

o   Sneaker males

o  

o   Very different trajectories for the different tactics

o   Territorial males become parental at year 8, whereas cuckolder males beging as snakers at year 2, then become the satellite males at year 5ish

o   Females start producing at 5-6 years

o   Satellite males’ offspring were bigger, had bigger eyes è faster growing fish, possibly higher quality, are from cuckold type

§  Big eyes are helpful = more light, visual acuity

·        Ruffs, a shorebird with a plumage (feather) dimorphism

o   Satellite and territorial males on ruff breeding ground

o  

o   85% are darker, territorial

o   Lighter non-territorial satellite males 15% of male population

o   This is genetically inherited = you are what your dad was

o   There is a third tactic – tiny proportion, less than 1% - faders; female mimics

·        Two or more discrete male phenotypes that reproduce in different ways are widespread across the animal kingdom

o   Different terminologies in literature

o  

o    Often there are behavioural, morphological and physiological differenced btw tactics

·        Alternative reproductive tactics are an evolutionary puzzle

·        Most traits are continuous: for example, human male height; normally distributed

o   But if males with certain traits get more or the bulk of mating, then adopting alternative ways to reproduce may pay-off

·        When do ARTs evolve?

o   When ther is fitness to be gained by pursuing different reproductive tactics

o   When there is investment to be exploited by same sex competitors

o   When intermediate expression of a trait is not possible or is selected against

o   Disruptive selection / diversifying

§ 

§  Bimodal distribution in male phenotypes

·        How do ARTs evolve?

o   Polymorphic genotypes  = Frequency dependent selection

§  Alternatives have equal lifetime fitness

o   Monomorphic genotypes = condition dependent selection

§  Tactic adoption depend on condition, status or maternal condition

§  Best a bad job

§  Alternative don’t have to have equal fitness

o   Strategy vs tactic

·        Frequency dependent selection

o   Fitness of a trait depends on how common it is in the population

§  Positive – fitness increases at the trait becomes more common

§  Negative – fitness dec

o   An evolutionary process where the fitness of a mating tactic or strategy is dependent on its frequency relative to other tactics in a given population. The idea is that two or more mating phenotypes/strategies can co-exist because of negative frequency dependence. In negative frequency dependent selection, the fitness of a phenotype increases as it becomes less common. There will be a point where the fitness of each tactic is equal

o  

·        Condition dependent selection

o   Despite the same genetic architecture, tactics adopted by individuals differ due to diverging conditions

o   If resources vary strongly during development, then adopting a tactic may depend on passing a threshold

o   No assumption of equal fitness

o   Condition dependent selection: mating tactic depends on individual condition. So you use one mating tactic if you are in good condition and the other if you are in poor condition

o   Tactics could change (plastic) throughout an individual’s life depending on condition continuously or they might be determined (fixed) at one point in development depending on condition

·        Conditional model: making the best of a bad job

o   Hypothesis: there’s just one conditional strategy

o   One tactic leads to greater reproductive success and is preferred, but playing it successfully is somehow more demanding, such that only some individuals can pull it off.

§   E.g. cost of waiting to be bigger and older for territorial fish

o    The second, lower-payoff tactic has lower reproductive success, and hence played/adopted, only if you can’t “afford” the superior tactic.

o    

·        These are still theories; most people think that most species have condition dependent selection (preferred theoretical model) but there are a few known examples of frequency dependent

o   Limited in how many species either has been studied in

o  

·        Strategy vs tactic

o   A strategy – is a genetically based decision rule. Difference btw strategies (e.g. fight vs sneak) are due to difference sin genes.

§  Examples: ruffs and isopods

o   A tactic is a behavioural pattern played as part of a strategy. There is only one set of genes but two or more alternative tactics within one conditional strategy (fight if big, sneak if small). The tactics result form bad luck not bad genes

§  E.g. you know its not genes; you feed beetle more food and its switches to growing horns

§  E.g. ear wigs and dung beetles

·        Summary 1. When do ARTs evolve?

o   Evolves when intermediate expression of a trait is not possible or is selected against

o   Whenever there is investment to exploit and fitness can be gained by pursuing a divergent reproductive tactic

o   Privileged access to females is costly and sneakers do not pay these costs

§  Parasitize the territorial / guarding / conventional males

·        Sperm competition: competition between the sperm form two or males for the fertilization of a female’s eggs

o   Why females mate with multiple males

§  Ensure some of their offspring are from a good male

§  Diversify offspring; you want offspring with both genotypes

§  Cooperation within a group; convince more males to help with the group; social

·        Sperm competition

o   Theoretical predictions

o   Across species

o   Alternative male reproductive tactis

o   Sperm competition and ejaculate expenditure

·        Male-male competition is obvious/noisy

·        Vs sperm competition

o   Very subtle; took a long time for anyone to realize it was going on

o   Basically, just post-copulatory male-male competition

·        The might yellow dung fly

o   Lay eggs on cow dung

o   Females mate with several different males – sperm must be competing for which gets to fertilize eggs

o   Males tried to hold onto female after mating to prevent other males form being able to mate with her

·        Some strategies

o   Mating plugs – gelatinous material that hardens in female reproductive tract; allows sperm to be inside for a duration of time to make sure eggs get fertilized

o   Mating guarding – hold onto mate, don’t let anyone else near them

o   Release substances so the females can’t mate – toxic chemical that prevents female from laying eggs after his

o   COMMON: dilute rivals’ sperm

·        Sperm number and fertilization success

o   Greater sperm concentrations increase fertilization success

o   Males ejaculating greater sperm concentrations should increase fertilization success

o   Selection should act on increased sperm production

o   ? in species with sperm competition, they produce higher concentration of sperm

Lecture 10 – ARTs in the Round Goby, Sperm Competition

27.01.25

·        Competition

o   intra-sexual selection

o   E.g. antlers=weapons, size=elephant seals

o   More valuable resource = more likely to invest

·        Male alternative reproductive tactics

o   Individuals within a sex adopt a different approach to achieve fertilization/reproduction

o   E.g. guarder males = defend nest and court females

o   Cuckholder: sneakers males=sneak paternity “unnoticed”, satellite males = pretend to be female

·        The round goby

o   Two male phenotypes

o   Guarder male

§  Bigger, secondary sex characteristics (e.g. buffy cheeks, dark coloration)

§  Courtship, partental care

o   Sneaker male

§  Smaller

§  Sneak fertilizations

·        Research questions: what is the timeline of reproduction in the round goby?

·        Spawning behaviour (record behaviour continuously for months)

o   Nest preparation

§  Turns from mottled to dark black indicating readiness for spawning

o   Spawning

§  Female lays eggs in nest, with guarder male insiade

§  Females invert, lay eggs on ceiling

§  Guarder male inverts, releases sperm onto eggs (external fertilization)

§  Sneaker sneaks in a fertilizes in a couple seconds

o   Paretnal care period

§  Fanning = move water inside nest to keep eggs ventilated/oxygenated

·        Does the presence of a sneaker male affect the guarder male behaviours?

o   Prediction: increase in guarder male agression

·        Set up:

o   Guarder male + three females, switch out one female with sneaker after spawning

o   Or guarder male + two females +one sneaker the whole time

o   Record, compare behaivour

·        Guarder male aggression vs stage

o   Slight mingrease in spawning stage in no-sneaker condition

o   Similar pattern but much larger increase when there is a neaker = 200% increase e..g 1 vs 3 agression per minute

·        Why high aggression during spawning?

o   Snekar males approach nest most often during spawning

·        è yes, increase in aggression

·        Male reproductive behaviours (summary)

o   Sneakers approach the nest once every 30 seconds during the spawning period

o   Guarder males respond aggressively

o   Sneaker males spend about 20 seconds in the next

o   = what is the difference in paternity?

·        Do the two male types have equal reproductive success?

o   Prediction: no, sneakers should have lower success because less opportunity

·        Paternity analysis

o   Set up artificial nests in the wild

o   Collect guarder male and eggs

o   Perform DNA extraction

o   Run microsatellite analysis; compare fathers to offspring

o   Assign parentage

o   Predict guarder 90-95%; sneaker males 5-10%

·        = no results yet!

·        Ecological threat; why

o   Invasive to NA; native to black and Caspian sea

o   Aggressive, outcomepete native species like sculpin for e.g. shelter

o   Feed on other species eggs

o   Long reproductive season; females can reproduce multiple times ina  summer so once introduced they can grow very rapidly

o   Vector for contaminants and diseases

·        The big picture

o   Understanding reproductive success to predict effect on native species

o   Help to develop management strategies

·        Questions

·        Aggressive behaviours?

o   Chasing, biting, ramming

o   Display behaviours, not very common, less aggressive

o   Weighted average

·        Only guarder male and eggs were collected; sneaker males don’t stay in nest after spawing

·        Does one type of male pose a greater ecological threat?

o   Not really?

o   We want to understand the reproduction to find a way to control them e.g. will population crash if you target all the gobies of a certain size

o   Or will sneakers become guarders

·        Don’t know if this is a strategy or tactic

·        Estimation of proportions was based on studies on other gobies

·        How record?

o   Manually check tank to see when spawning has occurred

o   Once it has, check footage of spawning

·        Having sneakers enhances population density

o   Resilience

·        In Hamilton harbour, lots of steel mills dumped in lake

o   Tons of contaminants

o   In areas with mills/contaminants, there are more sneaker males

Sperm competition

·        Mating plugs, mating guarding, release substances so that females can’t mate

o   Most common = dilution

o   Dilutes rivals sperm and increases your all-around fertilization success

·        Males invest different amounts in sperm competition

o   Theory predicts that increased sperm competition will lead to increase

o   Sperm number

o   Relative testes mass

o   Sperm density

o   Ejaculate volume

·        Sperm morphology

o  

o   Longer tail = fast

o   Longer tailed sperm in species with more sperm competition

·        Drosophila bifurca

o   Sperm 6 cm long when uncoiled

o   20 times longer than its body size

o   Very costly to make sperm; might actually have higher male investment

·        Sperm morphology

o   Flagellum length

§  E.g. can be two tailed

o   Head design

§  Apical/hooked heaks

§  Bird =corkscrew head

o   Midpiece length

o   In species with more multiple maitng, the sperm were more hooked

o   But, within one spcies, they selected for hooks          

§  One line monogamous

§  One line multiple mating

§  But there was no change in hook-ness

o   Maybe the hooks let them linkn together into a train and move faster together???

·        Sperm swimming speed – motility

o   Swimming speed

o   % motile cells

o   Longevity

o   Path type

o   Theory predicts that increased sperm competition will lead to increased… swimming speed, longer duration of swimming

·        Theoretical predictions from sperm competition

o  

o   All should increase theoretically?

·        Applying sperm competition theory across species

o   Diversity in mating systems

§  Monogamous vs polygamous

§  Polyandrous species (two males), polygyandrous (both males and females multiply amte), promiscuous species

§  Mating system can influence the level of sperm competition experienced by a male

§  E.g. female do not multiple mate = low competition; fmelae often mate multiply = high

·        Larger testes are associeated with spermcompetition across species

o   Longer tails when competition except for fish

·        Lake Tanganyika

o   When controlled for phylogeny, comparing species with low vs high sperm competition; relative tests size was higher in males that had competition

o   i.e. species exepreienceing sperm competition have larger testes

o   CONTRARY TO OTHER STUDY, species experiencing sperm competition have longer sperm!!

o   Species experiencing sperm competition have faster swimming speed

§   

·        How does sperm competition influence reproductive investment within species?

o   Sneakers are always mating ni the presence of another male, so they have relatively more sperm competition

o   Guarder males invest in growth, courting, defence of resource

o   Sneaker males invest everything into reproduction

o   è consequently, guaders experience lower sperm competition (but still some)

·        More investment in testes and sperm by cuckolding males

o  

o   Body size ~ with gonad size linearyly for guarders, 1% of body mass

o   Sneakers = 3-5% of body mass, but way less size overall

§  Sneakers<satellites

o   much higher sperm density

·        plainfin midshipman guarders and sneakers

o   big: large and vocal, compete and court, build nests, care for young; use sound to attract females

o   little: small and silent, no physical competition, cannot make sounds, no care, sneak in and out

o   sneaker males invest more in testes (mass % body weight)

o  

§  Sneakers are swimming bags of testes

o   Sneakers have faster swimming sperm

§ 

o   Sneaker males produce more sperm-rich ejaculates and sperm with more helical heads

o  

§  Sneakers had more helical sperm heads – don’t really know why – maybe to get through thick fluid

Lecture 11 – Sperm Competition and Intersexual Selection

29.01.25

·        Sperm Competition and Ejaculate Expenditure

o   Strategic sperm allocation

·        Strategic sperm allocation – when sperm competition is present how do males distribute sperm stores?

o   Ejaculates are costly and finite

·        Strategic sperm allocation in European bitterling

o  

o    Males fight and one becomes dominant / subordinate

o   How many times do males try to ejaculate?

o   Males try to inseminate more often in the presence of a rival

·        Strategic sperm allocation in humans

o   Males may also adjust their sperm quality depending on cues of sperm competition

o   In a fertility clinic males were given sexually explicit material representing

§  No sperm competition risk treatment

§  High sperm competition risk treatment

o   = males viewing images depicting sperm competition had significantly more motile sperm (52.1% vs 49.3%)

·        Summary 2. Sperm competition

o   Males experiencing greater levels of sperm competition invest more in:

§  Testes size and sperm number

§  Sperm tail length

§  Sperm swimming speed and duration

o   Males strategically allocate sperm number and quality based on cues of sperm

o   Smoking, drinking had an impact

o   More sexually active men had more sperm

Mate Choice – intersexual selection

·         Females usually have more to lose if they mate with low quality males.. so although both sexes can exercise choice, female choice is often more important as a selective force, than male choice

o   But female choice for what?

o   1. Mate choice for direct benefits

§  Maternal or economic benefits such as nuptial gifts, paternal care, good territories with resources – have direct consequences for female RS

o   2. Mate choice in the absence of direct benefits

§  Indirect or genetic benefits, genetic quality

·        1 a) choice for male resources

o   Males use food to convince females to mate with them. Females prefer males with igger food items. Males with bigger food items get to mate for longer e.g. courtship feeding

o   Spermatophore – gift that she eats – the bigger it is the longer she takes to eat it – the longer he has to mate with her

·        1 b) choice for resources held by males

o    

o   If males are larger, they hold territories that have less  vegetation = less predation from leeches

o   Also less shade = warmer water = faster development

·        1 c) choice for parental ability

o   Female choice for caring fathers

o  

o  

§  Males can be polygenous – if they’re really good at courtship feeding they can have up to 5 females

o  

§  Settling order

§  Vegetation quality

§  But male provisioning rates were the most consistent factor in female settling rates

o  

o  

o   Females all went to the tiles with the biggest male, (tile size didn’t matter)

o   Probability of hatching increases with mate size =

§  Better at defending against predators?

§  Better at gathering resources?

§  = females prefer to go to nests that already have eggs, evidence of other females choosing that spot and the males choose to look after the other eggs

o  

o  

§  Courtship behaviour (excitement of males towards female) was equal in both treatments

§  Having a mate may have changed their courting behaviour = this was not the case

§  Male with eggs preferred in 13/15 cases

o  

§  Males sing a lot

§  Also they feed the chicks

§  Males have drastic differences in song repertoire size

§  Females can hear males sing

§  Males that have longer, more complex, larger song repertoire are better at feeding, providing care

·        Choice for resources and parental care

o   Addition of rocks —> increased previously unsuccessful males reproductive success

o   Removal of rocks —> decreased previously successful males reproductive success

o  

o   Larger male = more rocks (resources) + more time spent guarding

·        1. Mate choice for direct benefits

o   A) choice for resources defended by males

o   B) choice for parental ability

o   C) choice in relation to both resources and paternal care

o   When should females trade-off paternal care for resources?

§  Prefer resources when there are not many

o   When should females trade-off direct vs indirect benefits?

§   

·        2. Mate choice in the absence of direct benefits

o   Wise choices still important for females

o   Genetic quality of father influences offspring quality

·        African redcollared widowbird

o   Female choice for plumage

o   The normal male tail is apparently an impediment (drag and predation) and hence a costly signal

o   Do females prefer long tails?

o   The manipulated birds retained their territories and courted females as they arrived

§  Superglued tails to extend them

o  

o   Females prefer long tailed males in red-collared widow bird

o  

o   All of them had about the same number of mates before

o   Manipulates tails -glue or chop

§  Control 1 – no change to tail

§  Control 2 – cut and reattatch tail

·        Control for effects of handling, manipulation of tail length, effects of glue

·        The song sparrow: female choice for song

o   Males have btw 4-14 song types

o   Females prefer mating with males with larger repertoires

o   BC island near Vancouver island, between Canada and US; small, uninhabited so great to study like isla daphne

o   Independent = they’ve left the nest, no longer relying on parents

o   Recruited = become part of the breeding population

o   Males with larger repertoire have more independent (i.e. fledgling) and breeding offspring, and grand offspring

·        Elaborate plumage, elaborate song, elaborate courtship

·        Female choice for courtship activity - Bowerbird

o   Male builds display nest for courtship that isn’t actually used for eggs

o   E..g blue bowerbird collects blue itmes, decorates bower to impress female

o  

Lecture 12 – Mate Choice

03.02.25

·        Difference between frequency dependent selection and condition dependence

o   frequency dependent selection: there are (at least) two traits, and when they’re balanced between the two frequencies, they get equal lifetime reproductive success

o   condition dependent selection: at some point in development, if you pass a certain threshold you go to one tactic, if not then you don’t try for it. Equal fitness is not assumed – not everyone can afford to try the “better” tactic; its better to do the inferior strategy than try to do the better tactic and completely fail

·        Cryptic female choice

o   Females influence fertilization success as well through post-copulatory control of fertilization

o   E.g. differential ejection of sperm (gallus gallus domesticus)

§  Pecking order or dominance hierarchies in chickens

§  Dominance is heritable

§  Females gain from mating with more dominant males

§  Sperm ejection was non-random wrt status = female feral fowl eject subordinate male sperm

§ 

§  B) removed some males – pushed social status to change; some moved up and down. Those that became more dominant through restructuring they were less likely to be rejected i.e. if their status went up, their sperm was kept

§  è evidence that its because of the social status, not phenotypical traits

o   Post-copulatory mate choice; female behaviour, physiology and morphology can influence male success/paternity success