Animal Behavior Final

pre-existing trait hypothesis

signaler possesses a trait that already conveys informative cues to receiver; trait is then modified and extended through signal ritualization

features of ritualized signals

• redundancy (repetition; multiple signals with the same meaning)

• conspicuousness (opposite meanings are often dramatically different and exaggerated)

• stereotypy (distinctive form)

• alerting component (attention-getting portion at the beginning)

conspicuousness

(ritualized signal feature)

opposite meanings are often dramatically different and exaggerated

• ex: dog submissive + playful vs dominant + aggressive

• ex: spiders rear up before striking; submissive looks opposite - females willing to mate will be close to ground with abdomen raise (impossible for her to bite), unwilling will rear up with arms raised and fangs ready

sources of ritualized signals

• intentional movements (bird crouching before take off)

• motivational conflict (alternate between different behaviors - zig-zag of sticklebacks; ambivalent behaviors - threat displays composite of aggression and fear; displacement activities - preening, turf pulling, hair twirling, etc.)

• autonomic responses (piloerection of hair, baboon faces flushing red, canine urination, sweating, etc)

some traits favor reproduction, even if shorten lifespan

reproduction takes precedence when trading one for the other

ex: Adactylidium mite feeding on thrip egg

• females produce 5-8 female offspring and one male

• male mates with all daughters inside female’s uterus

• females eat their way out of their mother and kill her after she’s lived about 4 days

how many sexes

• slime molds + mushrooms 9-13,000 separate mating types

• male, hermaphroditic, and female individuals for many species (ex: nematodes, gastrotrichs, etc.)

• sex-role reversal (multiple genders) for each sex

• changing sexes (sequential hermaphroditism)

white-throated sparrow sexes

bird with 2 sexes or 4 sexes, or 2 sexes and 4 genders

• white-striped morphed = promiscuous, poor parental care, aggressive (territorial), tuneful; all traits usually associated with males, but both male and female do it

• tan-striped morph = monogamous, good parental care, protective, poor at singing; female behavior, but both do it

• paracentric inversion mutation in 1/3 birds (white = heterozygous) = supergene

• everyone wants to pair with tan stripes (good parents); 2 tans can’t hold territory

• associative mating - opposites pair with each other

mixed evolutionarily stable strategy (ESS) for 2 sexes/gametes

• fertilization specialists (male, sperm) have a higher number of fertilizations, and a higher survival rate, when small

• provisioning specialists (female, egg) have a higher number of fertilizations, and higher survival rate, when large

• opposite of bell curve - mid-sized are losers

parasitic gamete hypothesis for anisogamy evolution

• mixed ESS selects for extreme gamete size

• once either extreme is adopted, intermediate sized gametes cannot effectively invade the population

• 2 strategies result: fertilization specialists (males), energy and survival specialists (females)

battle for the cytoplasmic genome hypothesis for anisogamy evolution

• fusing gametes are favorable that maximize their cytoplasmic genetic contribution to the next generation

• selected for ever larger gamete size - continued until energetic investment became large and costly enough to make an alternative strategy possible - being exceptionally small

cooperative explanation for anisogamy evolution

• maximizes number of gametic contacts (fertilizations)

• parasitic gamete model, if severe enough, would cause reversion to asexual reproduction

• doesn’t present anisogamy as competitive, parasitic, or conflict-related

• proposed and supported by Joan Roughgarden

anisogamy and unequal gamete size and number

• asymmetry in gamete number between sexes leads to competition among males for access to a limited number of female gametes

• asymmetry in offspring investment leads to females being choosier regarding mates

sexual selection

a form of natural selection that occurs when individuals vary in their ability to compete with others for mates or to attract members of the opposite sex

• intrasexual - competition among same sex for access to mates

• intersexual - actively choosing among prospective mates

Bateman’s principle

variability in reproductive success is higher in males than females

• females and males have same average mating success, but variance in success is higher in males

• fruit fly experiment: female offspring number peaks after a certain number of matings; male keeps going up

Patty Gowaty replicates Angus Bateman’s study

• female multiple mating treatment - mate a bunch of female fruit flies twice with different males (females don’t mate more than 2x)

• male multiple mating treatment - mate a bunch of male fruit flies twice with different females (can mate more)

• measure the number of cases where the multi-mated female had more offspring than the multi-mated male (and vice versa)

• results: positive where offspring higher for females with multiple matings relative to males with same # matings; negative where males higher offspring relative to females with same # matings

• conclusion: no difference

• actual test: significantly higher offspring for males than females; indicates females can benefit from multiple matings

why are fruit flies bad sex-difference model organisms?

• many fruit fly species produce giant sperm

• male fruit flies produce sex hormones that inhibit female reproductivity after 2 matings

Triver’s parental investment theory

the sex that invests more in their offspring will be more selective choosing mates and will be a limiting resource to the other sex

• females usually invest heavily, providing resources to offspring (max resources and choose among males with best genes; control fertilization)

• males usually invest heavily in acquiring matings (fertilize as many eggs as possible, often = less offspring investment; control fertilization)

• sexual conflict - optimal reproductive strategy for each sex is different

sexual dimorphism female strategy

(resource maximizer)

• mate with males of highest genetic quality or viability (use male traits that honestly indicate)

• mate with males that provide resources for offspring

• allocate more time to foraging to increase fecundity

• invest little in ornamentation, weaponry, mate-seeking, or courtship

sexual dimorphism male strategy

(fertilization specialist)

• more highly developed senses for locating mates

• greater investment in locomotory structures for seeking out females

• greater investment in weaponry for fighting competing males

• greater investment in ornamentation and courtship to display genetic quality or body condition to females

• mature slightly before females to maximize chances of mating with unmated females early in the breeding season (more frequent in species with short lifespans or where females reproduce once - ex: fruit flies)

• court and mate with any female that has eggs to fertilize (not choosy about mates)

Pardosa milvina spiders sex differences derived from anisogamy

females produce large egg sacs (60-80% of weight)

• carry egg sac for up to 1 month, and offspring for up to 2 weeks

• eat 4-10 times more than males

• only 8.7% of females will mate 2+ times when given opportunity

males more active and better at detecting airborne chemical signals

• longer limbs = more energy into locomotory structures

• elaborate courtship displays

• ornaments present (large, dark pedipalps)

• no parental care (mate, leave)

• 40% will mate with 4+ females in one day when given the choice

Fisherian runaway selection

(sexy son hypothesis)

preference and trait become genetically linked

• benefit: females produce “sexy” sons

• trait may convey no useful info = just for show

• intersexual selection of females choosing males

• ex: peacock ornament display - female liked big feather display, mated with male, produced sons with big feather display and daughters that like big feather display

good genes hypothesis

(handicap model, viability indicator theory, parasite/immune system signal)

handicap principle where traits are an honest indicator of male quality and viability

• males with access to good resources can afford to create elaborate displays

• intersexual selection of females choosing males

• benefit: offspring with better viability; healthy mate principle

• ex: bowerbird courtship revolves around bower - larger brain size (intelligence); quality related to ectoparasite load; decorations w/ male body size; rump UV-patch-brightness = feather growth, body size, blood parasites; wing covert UV brightness = feather growth; overall plumage

• ex: red coloration in sticklebacks = parasite load

• ex: female pigeons prefer louse-free males

• ex: Pardosa spiders - courting carries a predation cost; poor condition males suffer more and court less successfully; courtship intensity honestly indicates overall health and viability - live longer

compatible genes hypothesis

traits are indicators of having different genes that are most compatible with a particular female’s genes. there are no universally “good genes.” instead, genes are “good” only relative to a particular genome

• explains diversity in attraction (not all females/males find the same individuals attractive)

• intersexual selection of females choosing males

• minimize # double copies of lethal genes

• infertility is genome specific

• benefit: most robust and diversified immune system

• solves “Lek paradox” or “why is there still genetic variation in male traits” problem

chase-away/ antagonistic seduction selection model

the reciprocal effects of males attempting to exploit female mate choice mechanisms (sensory exploitation) while females evolve resistance to these attempts

• intersexual selection of females choosing males

• benefit: NONE to female (only option like this)

contests

(mechanisms of competition and characters selected - intrasexual)

traits that improve success in fights (large size, strength, weaponry, agility, threat signals)

• most common in polygynous mating systems

• sexual dimorphism with males larger than females

• ex: big horned sheep

endurance rivalry

(mechanisms of competition and characters selected - intrasexual)

ability to remain reproductively active during large part of the season, improved longevity

• usually occurs when breeding season is long or lacking

scrambles

(mechanisms of competition and characters selected - intrasexual)

early search and swift location of mates, well-developed sensory and locomotory organs, early male maturity

• usually occurs when breeding season is short

• sexual dimorphism with males smaller than females common

sperm competition

(mechanisms of competition and characters selected - intrasexual)

mate guarding, sequestering, frequent copulation, production of mating plugs or other means of preventing additional mating

• ability to displace sperm, production of abundant sperm

• most common in promiscuous mating systems

measure strength of sexual selection/conflict

• relative parental investment of males and females (biased toward one/ other = more intense selection) (usually females)

• operational sex ratio (more biased toward one sex/ other= more intense selection) (usually males)

• relative time spent seeking mates (more time spent by one, more intense) (usually males)

• variance in (usually) male breeding success (higher = more intense)

• greater sexual dimorphism = more intense sexual selection

when is sexual selection limited?

• monogamous species with shared and equal parental investment (little to no sexual dimorphism)

• free-spawning in marine species (ex: starfish)

Trivers-Willard Effect

in polygynous mammals, healthy females should bias their offspring sex ratio toward sons, because their sons will mate more successfully and produce more grandchildren than sickly, small sons

• less healthy females should produce daughters, rather than competitively disadvantage sons, because receptive females are competed for by males

• primary sex ratio - male to female ratio at conception

• secondary sex ratio - male to female ratio in adulthood

• operational sex ratio - # males seeking mates to # females seeking mates

• ex: female red deer of higher social rank produce more sons, while lower social rank females produce more daughters

sex-role reversal examples

• Mormon cricket males give mates an edible nuptial gift (large spermatophores with nutrients - base simultaneously inseminates female while she eats everything else, turning nutrients into eggs)

• Kawanaphila katydid males produce spermatophores slowly with scarce food, quickly with abundance; male mate choice when scarce - don’t want to give spermatophore to skinny female who wouldn’t use it to make eggs

• hanging fly males give treat (killed prey) to female, mates while she’s eating - prevents cannibalism

• empid fly males advertise for mates - male enters female swarm and decides who to give prey item to; females display ornament (red puffed up abdominal sac); females mimic gravid female full of eggs (dishonest, so males think they have more eggs - sensory exploitation)

• Allocosa brasiliensis wolf spider - male produces sex pheromone, females court, males build burrow, smaller females wander looking for males, females have longer legs, males cannibalize females, sex ratio skewed toward females; female egg production limited by burrow availability (need burrow for viable offspring, females fight for burrow access)

sexual selection assumptions that are rarely tested

• sperm is cheap and males have an unlimited supply; willing to mate as long as a willing female is present (males are fully capable of running out of sperm in subsequent matings)

• males maximally court all females; courtship variation is mostly based on condition or genetic quality, not male choice

• male courtship is not strongly related to female behavior

• females passively assess males and do not court of advertise to males

why aren’t female sex pheromones considered courtship?

• thought to be metabolically cheap to produce

• assumed to be produced indiscriminately relative to presence/absence of male

• assumed to be produced indiscriminately relative to what male does

• not condition-dependent

• convey little predation costs like male courtship

• female cord silk deposition study (good condition females make more silk; unmated females make more silk - ornament?)

• female Pardosa increase silk deposition when they see a non-courting male

sexual selection after or during mating

• sperm competition (intrasexual selection)

• cryptic female mate choice (intersexual selection)

• both can generate sexual conflict between the sexes over control of fertilization

• evolutionary arms races between males and females can result in: bizarre reproductive systems, unusual genitalia (ex: kangaroo split penises for females’ 2 vaginas), inefficient matings and fertilization

female control of fertilization

• prevent intromission/ejaculation of male (clamps, hoods, vices, hooks)

• discard sperm of current or previous male

• mate with additional males (encourage sperm competition)

• biased sperm use (age out sperm, kill it, relocate it) - spermatheca (“sperm house,” store for later; birds house in uterus, voluntarily don’t stretch that part)

• create copulatory plugs for unacceptable males (glue; infertile eggs)

• remove copulatory plugs (own; placed by males)

• tortuous oviducts/vaginas (ex: female duck oviduct corkscrew shape = male duck penises are corkscrew-shaped

• rare: fail to mature or produce eggs; invest less in some male’s eggs; selective abortion

• ex: sperm competition in dunnock bird requires female cooperation (male sees female mate with another, she presents herself, he pecks cloaca until sperm from the last male releases, then mounts her)

• ex: female collared flycatchers could bias egg fertilizations in favor of extra-pair mate (EPC) - done when female is most fertile

• ex: adaptive mate-guarding by Seychelles warbler (males adjust mate guarding in relation to risk of losing paternity - lots of neighbors = more)

mate guarding

(male control of fertilizations)

• follow females after mating (ex: water striders clamp onto females for a while)

• insert copulatory plugs - glue/cement (ex: snakes, richardson’s ground squirrel, parnassias butterfly); parts of male genitalia (ex: male spider emboli threaded through female reproductive tract); entire male (ex: male fishing spiders spontaneously die during mating, male IS the plug; she sometimes eats him = more offspring)

• deform, break, or mutilate female genitalia associate with coupling

• prolonged copulation (capacitate sperm; prevent additional males from copulating; irritate female reproductive tract to induce swelling and prevent intromission of other males)

male control of fertilization

• ex: bean weevil penis - porcupine spikey thing (maintain engaged genitalia during copulation; stimulate female reproductive tract; irritate female reproductive tract to induce swelling)

• kamakazi sperm (prososperm)/ sperm trains, sperm polymorphism

• large sperm displace other males = harder for females to remove, tail may serve as copulatory plug (Drosophila)

• traumatic insemination

• coercive sex (water striders; male dolphin groups)

• eliminate competitors

• promiscuous species (lemur) have more ornamented penises; monogamous species are simpler (monkeys)

• male persuasion - resources for female (nuptial gifts; cannibalism; hold territory; help raise offspring)

• ornamentation, endurance, displays (good genes)

mate choice in simultaneous hermaphrodites

• ex: flatworms have hypodermic insemination - rear up and try to stab each other with penis; first to stab inseminates

• ex: bedbugs - genital product of conflict between sexes; male punctures female; female evolved spermaledge - thickened tissue area that screens some sperm; lower fertilization outside this area

satellite male mating tactics - conditional mating strategies

• male Panorpa scorpionfly guard dead stuff, swap spit, or steal a copulation - shift between opportunistically

• sexual interference from larger rivals - marine iguanas

• horn size differences in horned scarab beetles - invest in testes/gonad volume

• swordtail fish - large morph (courtship displays) and small morph (sneak copulations)

• two-spotted goby - sex-role reversal mid-season

• Lamprologus callipterus frmo lake Tanganyika fish - big male morph defends territory; small male morph finds extra large shells that are attractive, hides inside, when a large male takes it to territory for female to spawn inside, there’s already a male in there

species that show dimorphism, despite being monogamous

• ex: black Australian swans - both sexes have curled feathers and a bright side wing feather - maintain territories better and have higher aggression levels with more curls; socially selected-trait to determine dominance and resource holding potential (RHP)

• ex: white-necked Jacobin - female-limited polymorphism - female juveniles look like adult males

selection for extreme aggression can androgenize females

• ex: female star-nosed and Iberian moles with ovotestis - intersex to an extent, but produce non-functional sperm; highly aggressive species, almost always have a fight underground if they encounter another mole

• ex: female spotted hyena with pseudopenis - penile clitoris; often larger than males; males have to insert penis into pseudopenis, pups are born out of it after it splits open (very dangerous)

2 males mate with one female at the same time

Rabidosa punctulata wolf spider

Male benefits

• small/poor body condition males are more likely to partake - benefit as 2nd male

• avoid unreceptive female and sexual cannibalism

• conserve energy by not courting

• avoid attracting predators with courtship displays

Male costs

• guaranteed sperm competition

• genital fencing and other types of interference more likely

• extended mating time (4x longer than single matings)

Female benefits

• encourage sperm competition

• reduce harassment

• increased genetic diversity of offspring

Female costs

• less control over who fertilizes egg (poorer quality male is mating with you)

• prolonged copulation time

monogamy

neither sex monopolizes more than one member of the opposite sex

• second least common mating style

• social (one breeding season together); genetic (all offspring in one mating season from one pair); serial (multiple partners don’t overlap in time, but maybe in lifetime); dual-enforced (suppression of reproduction of others)

mate guarding hypothesis

(what drives monogamy?)

monogamy is a byproduct of extensive mate guarding

predictions:

• females should be receptive to males after mating

• females should be scarce and/or difficult to locate

• female receptive periods should be of short duration and infrequent

• females should not be very choosy about mates

• last-male fertilization priority should be prevalent

mate-assistance hypothesis

(what drives monogamy?)

need a partner to successfully raise young

predictions:

• species exhibits high levels of parental care

• food resources are scarce

• predation risk is high

• offspring mortality with one parent is very high

ex: American burying beetle parents both tend to larvae; yellow-breasted chat; starlings - males help incubate eggs

female enforced (combat) monogamy hypothesis

(what drives monogamy?)

male would mate with other females if he could, but the second he leaves the female opens herself to other males

predictions:

• females enforce monogamy through EPC threats

• males show paternal care of offspring

• males suffer attacks by mate while courting other females

• female eats the male after mating, loses genitals, etc.; can’t mate with another female after mating if dead or castrated (ex: banana slugs have genitals bit off)

seahorse monogamy

female injects eggs with a penis into male seahorse, where they’re internally fertilized

• takes a long time to brood offspring - about same length of time for a female to be ready to mate again with another egg yolk

• typically monogamous for life - synchronized after first mating

germline chimerism

give birth to offspring that aren’t genetically related to you, but are to your sibling

• common in marmosets

• germline = sperm or egg

• chimerism = have 2 genomes/sets of DNA

• mothers care for chimeric offspring less, dads spend more time; can smell how related

polygyny

males control access to more than one female

• ex: bowerbirds

• reduces female fitness in pied flycatchers - male splits time between mates and caring for both sets of young, reducing fledgling success

• benefits male yellow-bellied marmots without impacting female fitness

resource-defense polygyny

indirectly control access to females by monopolizing critical resources

• ex: African cichlid where females lay eggs inside special shells - males collect nice shells and guard them, waiting for females

female-defense polygyny

males control access to females directly because females are grouped for another reason

• requires tight grouping of females

• ex: marine amphipod - male collects females and glues them to his body to create a spatial grouping of females; up to 8; start with juveniles and wait for them to molt to sexual maturity, then mate, then wait, then drop them

male dominance (lek) polygyny

mate or resources are not monopolizable; females select mates from aggregations of males (leks) based on quality of the male’s display or other male trait

scramble polygyny

males actively search for mates without overt competition

• whoever is there first gets more matings

• ex: amphibians and ephemeral pools

polyandry

females control access to more than one male

• least common mating style

• skewed sex ratio toward males

• large differences in adult lifespan among males and females (males short, females long)

• ex: some insects (crickets, flour beetles, bees, etc.), some spiders (Erisids), some primates (some marmosets), 1% bird species, some pipefish

resource-defense polyandry

females control access to males indirectly by monopolizing critical resources

female-access polyandry

females don’t defend resources essential to males, but interact among themselves to limit access to males

male-enforced polyandry

self-sacrificing cannibalism, loss of male genitals during mating (bees, spiders) or other forms of self-castration

female-enforced polyandry

females castrate males or initiate cannibalism and eat the male

female benefits of multiple matings

genetic benefits

• ensure all eggs are fertilized

• encourage sperm competition

• increase genetic variation (sperm compatible with egg genotype; avoid extreme inbreeding/outbreeding; correcting poor mate-choice decisions)

material benefits

• acquire resources controlled by another mating partner (ex: Arctiid moth spermatophores)

• acquisition of parental care from mating partners (dunnock birds)

• improved foraging success via distraction of male foraging competitor (Sierra Dome spiders)

• reduced risk of sexual harassment from non-partners (water striders) - protection from other males, reduced predation, reduced risk of infanticide (uncertain paternity)

polygynandry

males and females both mate-multiply; neither sex controls access to the other

costs of promiscuous mating systems

• invest in larger gonads = slower evading predators

• STDs - ex: mantis fly parasitic STD of wolf spiders eat eggs; bacterial STD in arthropods Wolbachia infects insects = most common STD in the world - preferentially kills males in larval development)

lek

traditional display site that females visit to select a mate from among the males (often ornamented), displaying at their small resource-free arenas

• ex: turkeys; hammer-head bat

prerequisites:

• males provide no parental care

• males cannot monopolize resources to gain matings

• usually internal fertilization takes place

• mobility allows females to accept cost of searching for mating aggregations and for males to avoid increase in predation risk

• females must show mate choice while searching for mates

hypotheses for lek formation

• lower per capita predation risk for both sexes

• information sharing - more opportunity for mate-copying

• passive attraction - females respond to largest stimulus

• habitat limitation - patchy habitat or strict display requirements

• hotspot model - males settle in areas with high probability of encountering females; location drives it

• hotshot model - less attractive males parasitize attractiveness of one male; individuals drive it

• black hole model - females have less potential to leave a site without mating with a male

• reduced search costs to males - stay in one location, use energy toward displays, not risky locomotion

• easier for females to make direct comparisons

depreciable parental care

benefits of parental expenditure per offspring decline as brood size increases

• less and less given to young as brood size increases

• ex: feeding offspring, egg yolk provisioning, etc.

non-depreciable parental care

parental benefits do not decline with brood size

• some benefits are non up to a certain brood size, then become depreciable

• ex: vigilance, mouth brooding, stomach brooding, etc.

forms of parental care

• preparation of nests, burrows, territories

• yolk production (female)

• defend resources used by female

• nuptial gifts (usually male); glandular products (either)

• nutritious ejaculatory products (ex: stomatopods, lepidopterans, orthopterans) (male)

• males permit (?) themselves to be eaten by female (spiders, vinegarroons, amblypygids, scorpions, etc.) - calories go into eggs, usually seen in food-scarce environments

• care of eggs (if laid outside of body = either; inside = only female) - directly on substrate, attached to parent, retained in body/mouth/ stomach/under skin/etc

• removing parasites/fungus

• maintain ideal environmental conditions

• provisioning/feeding young (cannibalism, cannibalizing mother, trophic eggs made to be eaten, blood supplies, glandular secretions, after birth, cultured materials - plants/ fungus, predigested material - crop milk/ honey)

• care of offspring after nutritional dependence (gibbons until find mate; three-toed sloths surrender part of home range; drive competitors from offspring; retaliatory strikes between matrilines in macaques)

• social assistance to mature offspring (dominance hierarchy; share territory)

parent-offspring conflict theory (Bob Trivers, 1974)

parents and offspring should “disagree” over the amount of parental investment

• offspring should try to extract up to 2x resource as optimal for parent

• assumes: monogamous pairs; iteroparous species; full future siblings; parental expenditure/day is fixed

• more intense in polyandry/polygynandry - increased sexual conflict an kin selection

iteroparous species

multiple reproductive events over an animal’s life

• ex: humans

semelparous species

one single large reproductive event at the end of life

• ex: salmon, octopus

forms of parent-offspring conflict

• Excessive begging in bird offspring

• Conflict over weaning time in mammals

• Rodent pups actively resisting being removed from the breeding burrow by their mothers

• Young chimps (and humans) whose attempts to suckle have been frustrated throw weaning tantrums and attack their mothers

• Coots chase chicks away that they have just fed

• Juvenile macaques increase the frequency of their suckling attempts at the onset of the next breeding season

• Hyenas kill siblings of the same sex usually before the age of two

• Juveniles of social primates attempt to prevent males from mating with their mothers

• Pigs battle for the best teat with their teeth

• Pronghorns in the womb stab the next pronghorn further down in the womb

• Shark embryos cannibalize each other in utero (scorplings do the same)

• Spiderlings consume the eggs of their siblings while still in the egg sac

• Fig wasps sting and eat their brothers before mating with their emerging sisters (intrasexual selection too)

truncating offspring

best to do when young (higher residual reproductive value), resources are low (may be unable to feed all kids), and offspring is young (older invested in more)

• abandoning parasitized nests in birds and mud daubers

• withholding food from “runts” of the litter

• Bruce effect in mice - females mate with a male, another male comes into the scenario and she reabsorbs her embryos and mates with him - waste of time/energy to birth them if the male was just going to eat them

hypothesized evolutionary history of brood parasitism

• Loss of suitable nesting sites

• Facultative intraspecific brood parasitism

• Closely related species with similar nesting requirements and appearance

• Unrelated species

• Favors increased body size?

defense against brood parasites

• eject egg (count?)

• build new nest over egg (common; restart)

• abandon nest (common)

• “password” begging call learned as an embryo (superb fairy wrens) (rare; highly effective)

• counterstrategy - extortion or brood parasite mafiosa - threaten to destroy nest unless the owner cares for your young (ex: cowbirds patrol nests - smash eggs)

altruism

cooperative behavior that lowers the donor’s (altruist’s) reproductive success while increasing the reproductive success of the recipient of the altruistic act

• cooperation, delayed reciprocity, maladaptive altruism, adaptive altruism, spite, deceit and manipulation

facultative altruism

temporary loss of direct fitness, or reproduction is delayed, to raise indirect fitness

• ex: scrub jays - males stick around after they fledge, and older brothers help feed their new younger siblings when parents have more

obligate altruism

permanent loss of direct fitness - fitness can only be improved indirectly

• ex: worker honeybees and other eusocial worker animals (help queen reproduce, die without reproducing)

• ex: colonial marine invertebrates (sea squirts, coral, bryozoans, salps, etc.)

characteristics of eusocial animals

• Overlapping generations

• Cooperative brood care

• Philopatry (returning or staying where you were born)

• Reproductive altruism (improving indirect fitness at the expense of direct fitness)

• Division of labor (caste system)

coefficient of relatedness (r)

the probability that an allele in one individual is present in another because both individuals have inherited it from a recent common ancestor (measure of degree of relatedness)

• Hamilton’s rule: a gene for altruism will spread if rB>C

  • r = coefficient of relatedness

  • B = benefit gained by recipient of altruistic act

  • C = cost to the individual performing the altruistic act

Tit for Tat Rule

prisoner’s dilemma winning strategy by Anatol Rapoport

• never defect first (play nice) - start by cooperating; never cheat first

• retaliate quickly if defect occurs (copy defector in next round) - see cheating? cheat too

• forgive if the defector cooperates later - forgive earlier cheating

• seen in blue jays, guppies

antipredator benefits of sociality

• Reduced cost of vigilance (many eyes)

• Dilution effect

• Mobbing and group defense

• Confusion effect

• Selfish herd

• Aposematic coloration learning – in groups, learn more quickly about color warnings for danger

foraging benefits of sociality

• Information center for location of food

• Learning foraging techniques and prey capture methods

• Able to take down larger prey

• Reduced prey capture variance (more likely everyone gets to eat)

• Thwart antipredator responses of prey (ex: confusion effect)

mating benefits of sociality

• Mate copying opportunities (mostly female)

• Learn effective courtship methods (mostly male)

• Reduced searching costs for mates

• Reduced cost of mate assessment (especially females)

• Reduced predation costs of mate assessment, courtship, and mating

parenting benefits of sociality

• biparental/ shared parental care

• opportunities for non-parents to care for young (offspring, aunts, etc.)

• parasite removal/ allogrooming opportunities improved

other benefits of sociality

• Opportunities for kin-selection

• Reduced stress?

• Nesting or habitat modification benefits (ex: termite mounds, colonial webs, weaver bird colonies)

• Live in areas otherwise less accessible (hydrozoans, salps, etc.)

• Thermoregulatory benefits (homeotherms) (ex: bats in winter)

• Cultural memory, generalized learning

parenting costs of sociality

• Neighbor interference, aggression, egg consumption, infanticide, and cannibalism

• Egg dumping, intra- and interspecific brood parasitism opportunities (Ex: wood ducks)

• Competition for nesting material and nesting sites

foraging costs of sociality

• general food competition

• interference with prey ambush

• locomotory costs with resource depletion (migration more common)

other costs of sociality

• Attract predators

• Disease and parasite transmission (ex: ticks, lice)

• Signals of dominance and submission

• Cognitive costs associated with processing social information/ communication (social brain hypothesis)

• Increased risk of inbreeding

male-female sexual conflict in courtship

• Elaborate male courtship displays to reduce female threshold of sexual response

• Females evolve resistance to displays

male-female sexual conflict in copulation

• Male copulatory courtship, mate guarding, adding copulatory plugs after mating, irritating female reproductive tract

• Female termination of copulation, production of infertile eggs, and other female copulatory plugs, mating with additional males, removal of male copulatory plugs

male-female sexual conflict in fertilization

• Female reproductive tract “obstacle course” to select best sperm, age-out sperm, eject sperm

• Males attempt to bypass “obstacle course” with traumatic insemination, extended copulatory organs, etc.

male-female sexual conflict in gestation (placental animals)

• morning sickness

• gestational diabetes

• pre-eclampsia

• placental invasiveness (placental lactogen)

• miscarriage

male-female sexual conflict post-birth

• Male/female difference in infanticide context

• Male-females manipulating the other to enforce more parental care

• Offspring prolonging time before weaning

• Offspring interfering with subsequent matings of mother

• Manipulation of EPC threats, etc.

• Fetal micro-chimerism

value of additional offspring that are at risk of siblicide

• insurance policy against older sibling dying

• extra reproductive value if environment should turn favorable later

• common in birds (food competition, discrete packages of food, weaponry, competitive disparities, spatial confinement, we study them a lot)

parent-offspring conflict in humans

• prenatal morning sickness (HCG inhibit menstruation - large quantities = morning sickness)

• natural killer cells (NK cells) inhibit placental invasion

• gestational diabetes

• pre-eclampsia

• filicidal behavior (young, single mothers more likely to infanticide)

• sibling rivalries (half-siblings, step-siblings, more children, single parent)

• mate choice conflicts (offspring prioritize indicators of genetic quality, parents prioritize indicators of parental investment)

• inheritance laws (biased toward oldest offspring, degree of relatedness, negating resource inequities among offspring)

imprinted genes

genes that are expressed dependent on the parent-of-origin (mother or father)

• paternal genes switched on, maternal genes not

• female genes turned on = high birth weight

• male genes turned off = low birth weight

• IGF2 gene turned on = Beckwidth-Wiedmann syndrome

• Angelman syndrome, Prader-Willi syndrome

A female, monogamous species that breeds with a male polyandrous species.

Very large offspring (high birth weight)

Male monogamous species that breeds with a female polyandrous species.

Very small offspring (low birth weight)

Male polyandrous species that breeds with a female polyandrous species.

No difference in birth weight from non-hybrids

Male polygynous species that breeds with a female polygynous species.

No difference in birth weight from non-hybrids (same as monogamous)