Lecture 1-10 (Midterm 1 - Psych 3T03)

Ethology

the study of behaviour under natural conditions, pioneered by Tinbergen, Lorenz and Von Frisch

Behavioural ecology

the scientific study of behavioural phenomena in the light of ecological and evolutionary theory;

Things that affect behaviour or are affected by behaviour, such as endocrine systems, developmental processes and choices/preferences

Adaptation

the evolutionary process by which organisms fit better into their environments or habitats

Adaptive Traits

properties of organisms that enhance the probability of surviving and reproducing

What are the two traditions of behavioural ecology?

Ethology and Evolutionary biology

Evolutionary biology

the study of how organisms have come to be, particularly how their features have been designed by natural selection

Why did Tinbergen, Lorenz, von Frisch win the Nobel Prize in 1973?

for starting the field of behavioural ecology

Niko Tinbergen (work)

-Can only understand animals by studying them out in nature

-Came up with scientific method: observations, alternative hypothesis, creating expected results if hypothesis is correct

Konrad Lorenz (work)

Imprinting – importance of very early experience – got grey geese to imprint on him – they followed him and treated him like their mom; and in later life, the adults courted humans, not geese

Karl von Frisch

-Realized there was communication in movement, in bees - gave each other information on location/direction of sugar by their dance

Great insights of classical ethologists

just as each species has its own characteristic anatomy physiology and biochemistry, so too each species has its characteristic behaviour

Behavioural traits can be analyzed in the same way as physical traits, including the study of their evolution

Richard Dawkins (Tinbergen’s student)

wrote ‘the selfish gene’; argues the unit of selection is the gene.

Marian Stamp Dawkins (Tinbergen’s student)

Filmed hens from above, seeing how much they move, how much space they need, compared to battery cages they are kept in.

= pioneer of animal welfare. We just need to know what animals need and what they want

Iain Douglas Hamilton (Tinbergen’s student)

Studied the social behaviour of African elephants via aerial survey, to understand their decisions making i.e. where do they go and why; tells us what their needs are

Desmond Morris (Tinbergen’s student)

popularized how humans are like other apes/monkeys. “the naked ape”

Alfred Russel WAllaece

Independently thought of natural selection; when Darwin read his work he writes the origin of species based on previous letters

Natural selection occurs because of…

variation within populations, heredity and differential reproduction

Variation within populations (natural selection)

individuals differ in characteristics that influence their survival and reproduction

Heredity

parents pass on some variation/distinctive characteristics to their offspring

Differential reproduction

because of their distinctive inherited characteristics some individuals will have more surviving offspring that others

Natural selection

when differential survival and reproduction are related to individual differences and these individual differences are heritable, evolution can ensue

Why do was say evolution can ensure what requirements are met?

even if all 3 conditions are fulfilled, selection is often stabilizing: if a trait is already optimal (because of past selection), current selection tends to prevent it from evolving (“drifting”) away from that optimum

Darwin’s finches

11 species of tanningers in the Galapagos islands, much more diverse in bill morphology, diet and behaviour than is typical within a genus of songbirds

Why did Darwin’s finches diversify so much?

Arriving first at the newly formed volcanic islands of the Galapagos, they “radiated” to fill unoccupied ecological niches that other songbird genera occupy in south America and elsewhere

David Lack (Darwin’s finches)

Realized it wasn’t just each type of finch was on a different island; but that each type had a different type of beak, optimized based on food handling; 5 months

How long was Peter Grant’s study?

50 years!

Unusual aspects of Peter Grant’s study (4)

Very long term (>50 years) vs months or a few years

Every individual was marked and tracked. So LRS (lifetime reproductive success) was known and the traits beneficial for fitness could be assessed (very rare)

Natural environmental perturbations (droughts) allowed the grants to observe strong episodes of natural selection in a relatively short time period

Tame birds because no one had ever been there; so you can capture and measure them very easily

Medium ground finch 1976-77

Drought cause population crash and change in seed abundance (from more evenly spread to mostly large and hard, which not all MGF could open

produced direction selection on peak size as a result of differential survival of the drought

Adaptation

the process of change by which organisms change to better fit their environments; adaptations contribute to the survival and fitness of individuals

Natural selection

a mechanism of evolution; process by which traits become more or less common in a population because of differential reproduction

What is the difference between natural selection and evolution?

evolution is gene frequency change across generations vs natural selection is differential reproduction, measured as fitness, that predictably leads to adaptation

LGF and MGF (2004 drought)

Another drought occurred but because LGF was present and disincentivized larger seeds, character displacement occurred on MGF beak size and beak size decreased

Similarities between 1977 and 2004 droughts

both were droughts that led to seed bank depletion and crashing finch populations due to starvation

What island did the Grants’ study happen on?

Isla Daphne

Why did 1977 and 2004 droughts have different effects?

critical difference was the presence of LGF that produced character displacement

Character displacement

divergence in traits caused by competition between species where differences become exaggerated by interselective competition

Character release

greater overlap in trait when each species is found alone (allopatric) than when sympatric

i.e. they are released from competition so they can occupy the same niche

Example character release MGF and SGF

In the absence of competition from the SGF, the MGF on daphne had smaller beaks than is typical on other islands; producing greater overlap in beak size

Levels of analysis

proximate and ultimate

Proximate questions

immediate cause (“how”)

1. mechanism (physiological and cognitive)

2. ontogeny (development)

Ultimate questions

long-term “why” questions

1. effects on fitness

2. evolutionary origins

Jellyfish mostly swim upwards in the daytime - how?

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

Jellyfish mostly swim upwards in the daytime - 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

Tinbergen’s 4 questions

function/adaptive significance, phylogeny, ontogeny, causation

Tinbergen’s 4 questions - function/adaptive significance

What is it for? How does the behaviour contribute to survival and reproduction? What are the fitness effects? Why is it maintained by natural selection?

Tinbergen’s 4 questions - Phylogeny

how did the behaviour evolve? what were the evolutionary antecedent behaviours? When did the behaviour first appear or originate in evolutionary time?

Tinbergen’s 4 questions - Ontogeny

How does the behaviour develop within an individual/lifetime?

Tinbergen’s 4 questions - Causation

how does it work physiologically/cognitively? what mechanisms cause the behaviour?

Tinbergen’s question - how does birdsong develop over a lifetime?

• Output and complexity increase overtime due to 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 brain, females do not; under estrogen, HigherVocalCenter neurons (song center) grow; if you give females estrogen, they will be able to produce song later in life

Tinbergen’s questions - How does bird song contribute to fitness?

Larger song repertoire = larger clutch size

Attracts mates and tells competitors to stay away

Tinbergen’s questions - How did birdsong evolve?

unknown - could have evolved 3 separate times in parrots, hummingbirds and passerines but also regulated by the same gene

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

Optimality

maximize benefits and minimize costs

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

Trade-offs

behaviours will only evolve if the benefits are greater than the costs … B>C

Optimality - how loud should a male bird sing?

Singing loudly is beneficial; attracting mates and repelling predators

But…louder can attract predators

Find spot that minimizes cost and maximizes benefits

Optimality - flight hunting vs perch hunting

Flight hunting is way more profitable than perch hunting but only in winter, in summer both is more?

If E1/H1 > E2/H2

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 if gain from eating prey 2 is more than rejecting to look for prey 1

What causes switch from specializing on prey 1 to eating both prey 1 & 2?

depends on S1 - should be sudden and only occur when S1 increases

profitability equation

= energy / handling time

Generalists prefer…

species with short handling times and short search times

Specialists prefer…

species with longer handling times and long search times - they are more choosy

How does environment dictate generalist vs specialist?

animals should be generalists in an unproductive environment and specialists in productive environments

How to increase search time?

Camoflage/crypsis

Polymorphism: multiple colour/size morphs make it harder to develop a search image

Important variables in optimality? (3)

Decision: what are the alternatives?

Currency: what is being maximized/minimized? time, energy, risk

Constraints: What are the intrinsic and extrinsic constraints on an animal? (physiological/psychological limits, temperature or light availability, bill size/shape)

Who invented game theory?

John von Neumann developed game theory for economics in 1928

Who brought game theory to evolution? What for?

John Maynard Smith; to help understand sex

Nash equilibrium

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

ESS

a strategy that, if adopted by a population, cannot be invaded by any alternative strategy (type of nash equilibrium)

Conditions of an ESS

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

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

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

Types of reproduction

can be sexual or asexual and coupled or uncoupled with recombination

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

=involves creating new genetic combination (through cross-over)

Asexual reproduction

the production of new individuals without creating new genetic combination (parthenogenesis);

does not involve meiosis, ploidy reduction or fertilization.

only takes one parent

What was the original type of reproduction?

asexual - sexual had to evolve

e.g. Amazon molly (reproduction)

all female species that reproduces parthenogenically (offspring are clones of mothers)

But, female must mate with males of a different species because sperm is needed to trigger embryogenesis (no genetic material taken)

e.g. whiptail lizard (reproduction)

all female species that produces eggs through parthenogenesis

Ovulation spurred by mating with other females (pseudocopulation)

e.g. zebra shark, California condor, komodo dragon

can reproduce with males but are also capable of parthenogenesis

4x cost of sex

breaking up co-adapted gene complexes

cost of making males

cost of STDs

cost of finding a mate and mating

4x cost of sex - 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

4x cost of sex - cost of making males

cost of meiosis - half the population is dedicated to producing males, who cannot produce eggs themselves. i.e.half the reproductive potential is “lost” to males.

vs asexual populations all individuals capable of producing offspring. This allows them to potentially grow twice as fast as sexual populations

4x cost of sex - cost of STDs

in some species, the longer they mate the more likely the female is to contract a venereal disease

4x cost of sex - cost of finding a mate and mating

includes predation risk, time and energy

Why has sex evolved and why is it maintained? 2 classes of hypotheses

Sex clears deleterious mutations

Sex helps create a wider array of offspring genotypes

Why sex? Sex clears deleterious mutations

Recombination allows new, potentially advantageous combinations of genes to come together, by eliminating or masking harmful mutations

Why sex? sex helps speceis create a wider array of offspring genotypes

Lottery hypothesis: Sex assists to evolve in response to variable environments with temporal and spatial unpredictability

Red queen hypothesis

organisms must constantly evolve to maintain their fitness in a co-evolutionary arms race, where adaptations in one species drive counter-adaptations in others, essentially "running to stay in place"

Red queen hypothesis - sexual reproduction

sexual reproduction is favoured because it allows species to evolve rapidly, enabling them to keep pace with co-evolving parasites and pathogens, thus maintaining genetic diversity and resilience

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

3 pillars of ecology

I. levels of analysis

II. optimality

III. game-theory

Sex must be advantageous over … time; why

ecological time: sex is so common and ancient asexual lineages are rare

over ecological time: some species can do both but will flip between them

e.g. bdelloid rotifers

exception - a rare, ancient asexual lineage where females reproduce exclusively though parthenogenesis; have been around for millions of years

e.g. new zealand mud snail (reproduction)

can reproduce sexually or asexually

they can get infects by parasitic worms, which need ducks to compelte their life cycle

so, in shallow areas mud snails reproduce sexualy

but in deep areas without ducks, they don’t have worm and so can reproduce aseuxally

Parker-Baker-Smith model for the evolution of male and female gametes 1972 (assumptions)

1) trade-off between gamete size and number (more gametes = smaller gametes)

2) zygote fitness increases with size

Parker-Baker-Smith model

competition to fertilize eggs (the bigger gametes) leads to disruptive selection on gamete size, and the evolution of large (‘female’) gametes and small (‘male’) gametes

Parker-Baker-Smith model - why is each size selected on?

Large gamete specialize in providing energy = increase in fitness

Small gamete specializes in swimming = select for quantity (inexpensive to produce)

Evolution of anisogamy (Parker-Baker-Smith model)

initially isogamy, but since pairing of large an small is favoured, distribution of size becomes bimodal, creating protosperm and protoovum

Primary sex ratio

ratio at conception; slightly male biased in humans

secondary sex ratio

ratio at birth, slightly male biased in humans

tertiary sex ratio

ratio at sexual maturation; flight female bias in humans

why does sex ratio flip at matruity in humans?

males are more susceptible to disease, die at higher rates

Sex allocation

investment in M vs F; depends on environment, mating system and how reproduction is carried out within a breeding system

Fisher’s 1:1 Sex Ratio justification

posits that in a population, if one sex becomes rarer, individuals of that sex will have a greater reproductive advantage, leading to a shift in the sex ratio towards equality; suggests that this is an ESS