Midterm

Why has copulatory suicide evolved in redback spiders?

1) Productivity hypothesis: converting males into food increases the overall rate of egg production; populations with suicidal males expand and replace populations without suicidal males 2) Reproductive restraint hypothesis: copulatory suicide helps prevent overpopulation and local extinction by reducing the overall egg fertilization rate • Cheater problem: If non-suicidal males fertilized more eggs than suicidal males, then suicidal populations would rapidly be taken over by non-suicidal genotypes (within populations). For group selection to work, suicidal populations would have to colonize areas where non-suicidal populations went extinct faster but this not likely if non suicidal populations produced more offspring Production hypotheses: 1) Paternal effort hypothesis prediction: suicidal males contribute nutrients to their own offspring (no) 2) Mating effort hypothesis prediction: suicidal males fertilize more eggs (yes) • From a genetic standpoint, copulatory suicide appears to be a selfish act in redback spiders. In general, natural selection favors any trait that gives individuals an advantage in passing on their genes.

Dan gives up a chance to marry and have a family in order to go to work in a distant country. Had he married, he would have had 2 surviving offspring. He sends money back to his sister, who as a result produces 5 surviving offspring instead of the 2. 1. What was the cost (in units of direct fitness) of his altruism to Dan? a. 1 b. 1.5 c. 2 d. 3 2. What was the benefit (in units of inclusive fitness) of his altruism to Dan? a. 0.5 b. 0.75 c. 1.5 d. 3 3. Dan's decision was a. adaptive. b. maladaptive.

1. A - 2 * (0.5) = 1 2. B - 3 * (0.25) = 0.75 3. B - Brb < Crc

Summary Kin Selection

1. Eusocial insects we see extreme altruism where workers rarely reproduces and the members are closely related 2. Inclusive fitness = direct + indirect fitness 3. Kin Selection organisms attempt to ensure the survival of their own genes by protecting or helping closely related individuals

Lecture 6 Summary - The Evolution of Habitat Selection, Territoriality, and Migration

1. Ideal free distribution theory - animals can assess habitat and choose a location based on best fitness 2. Defense of habitat only evolves when individuals gain substantial benefit from the territory 3. Residents are most likely to win but the amount of time on the territory matters 4. Dear enemies effect - familiar neighbors stop fighting 5. Major benefit to dispersal is avoiding inbreeding 6. Migrations allow for access to more resources 7. Conditional strategy explains coexistence of both residents and migratory behavior for animals with behavior flexibility - choose the option with highest fitness

Adaptive Behavior and Maladaptive Behavior

Adaptive behavior - a behavior that increases the fitness of the individual performing it, relative to a nearby alternative. Maladaptive behavior - a behavior that reduces the fitness of the individual performing it, relative to a nearby alternative.

Ideal Free Distribution Theory

Key assumptions: 1) habitat suitability decreases as the density of individuals increases (except at very low densities - Allee Effect) 2) all individuals settle in the habitat most suitable to them ("ideal") 3) all individuals within a habitat have identical expected fitness ("free") • The theory requires that individuals are able to move around and evaluate the quality of habitat • Animals will settle on a site to maximize success

Hamilton's Rule

An allele for altruism can spread in a population if: Br(subscript b) > Cr(subscript c) • B is the number of extra offspring produced by the recipient because of the donor's help* • r(subscript b) is the relatedness between the donor and the recipient's offspring • C is the direct fitness cost (offspring lost) for the donor • r(subscript c) is the relatedness between the donor and its own offspring *B can be negative if the donor causes a reduction in the recipient's direct fitness

Social Conflict: Policing

• "Policing" is found in social insects - Ex. Paper wasp nest females lunge at one another or bite opponents if a worker wasp lays an egg • Researchers tested whether sanctions imposed on workers force those workers to behave more altruistically - Policing colonies resulted in fewer insects developing ovaries and the eggs of workers were destroyed - Little chance of boosting inclusive fitness directly thus indirect route is superior - Graph: The better the workers are at destroying the eggs of their fellow workers, the less likely workers are to try to reproduce

Adaptation

• (process) - changes caused by natural selection leading to a greater fit between a population and its environment across generations. • (trait) - a trait that confers higher fitness on individuals that have it

Multi-strategy hypothesis (migration)

• A conditional strategy controls some migratory behavior • Multi-strategy hypothesis - animals achieve the same fitness by adopting the optimal migration patterns for their breeding site • A male might choose to leave for the winter to avoid competition and return in the spring to occupy territory made available by the death of some rivals • Migration begins when dominance contests are the most frequent • Older birds typically stay put possibly because they are more dominant and don't have to leave Predictions : 1. Ability to switch tactics 2. Dominant should pick the better option 3. The option should produce the best reproductive payoff

Comparative method

• A procedure for testing evolutionary hypotheses based on disciplined comparison among species of known evolutionary relationships • Usually the simpler scenario with the fewest transitions between ancestral & present state is the one that scientists accept

Adaptationist Hypotheses

• Adaptationists test whether a given trait enables an individual to propagate more effectively • All 4 modern species of hyena communicate via anal scent glands • Spotted hyena appear use this info to evaluate social rank • Erect penis in males signal interest to bond and not aggression • This communication was already in place and females that developed the pseudopenis might have been able to tap into this well established form of communication

Altruism in Vertebrates & Insects

• Almost all helper vertebrates retain the capacity to reproduce • Highly social vertebrates engage in facultative altruism (not given opportunity to reproduce), not obligate altruism (can't reproduce if they wanted to) • Hamilton's rule suggests that helpers are giving up very little because their ability to reproduce is low • Monogamy also promotes adaptive altruism - The more partners the fewer helpers

Why Do Gulls Mob? Distraction Hypothesis

• An animal is assaulting the potential predator in order to protect its young • Fitness cost - negative effect a trait has on surviving • Fitness benefit - positive effect trait has on reproductive success • Cost of mobbing - expenditure of energy • Benefit - social harassment protects their eggs and chicks

Sensory Exploitation or Retention of Ancestral Traits

• Artificial signals may elicit response because ancestors of the tested species used similar signals during courtship in the past and todays descendants retained the sensory preference • In the lizard Sceloporus virgatus when they were artificially painted blue, rivals were far more likely to back down - Blue used to be a sign of health and strength among these lizards

Parthenogenesis

• Asexual females that reproduce • Whiptail lizards are all females and each can reproduce without the help of a donor, however they still display courtship behavior • Females that engage in pseudo male sexual behavior are more likely to produce clutches • The behavior must be left over from when the species had males - example of holding onto ancestral traits

Creating a Phylogeny for Behavioral Communication in Bees

• Based on the complexity of the behavior, might expect it to start simple and evolve to become more complex - Possible phylogeny: simple alert, then loss of sociality and dances, then following, then giving directions • Based on large data set of molecular evidence, the dancing has arisen in separate lineages that are not the closely related. • Behavior can arise independently and disappear over time in different lineages. • You can't just depend on physical features or behavior to determine how closely related organisms are to one another; you need to use genetics.

Lecture 1 Summary of Key Points - Introduction to Animal Behavior

• Behavior evolves through the same processes as other organismal traits (e.g., morphology, physiology). • Natural selection can operate at different levels (gene, individual, group, population, etc). The vast majority of evolutionary biologists believe that selection at the level of the individual usually prevails. • There is no reason to invoke group-level benefits for traits that increase the fitness of the individual (e.g., parental care). • Most behaviors that seem selfless or altruistic have hidden benefits for the individual (e.g., copulatory suicide). • The behavior of animals in the wild is usually adaptive, notwithstanding some interesting exceptions (e.g., hosts feeding cuckoo chicks). • Most instances of maladaptive behavior can be explained by recent changes in the environment (evolution takes place on a multi-generation time scale).

Conspicuous Behavior

• But what about being conspicuous? Why make yourself known? The trait must have some substantial benefit Warning coloration thought to be adaptive because predators more easily learn to associate noxiousness with conspicuous color patterns than with cryptic ones • Predators may be innately leery of conspicuously colored prey • Caterpillars whistle to deter predators

Can altruistic behaviors evolve "for the good of the species"?

• By definition, altruistic behaviors reduce the fitness of an individual • For-the-good-of-the-species arguments were accepted uncritically by many biologists until Wynne-Edwards formalized the group selection hypothesis. • Ex. Birds laying fewer eggs than they were capable of Lemmings jump off cliffs to keep the species from using all resources • Behaviors that benefit the masses could evolve: even if they reduced the fitness of individuals, if selfish individuals go extinct more often than populations of altruists.

By-product hypothesis

• By-product hypothesis: An explanation for a maladaptive or nonadaptive trait that occurs as a byproduct of a genetics or physiology mechanism that has some other adaptive consequence for individuals. • Cooperation among scrub jay relatives - Perhaps helping occurs simply because it is adaptive for young adults to delay their dispersal from their natal territory. - If they stay at home and are exposed to nestlings - Begging behavior of the bird might trigger parental behavior of the nonbreeding adult - Exploiting a biases to want to care for one's own offspring - Research shows that in Mexican jays nonbreeding birds do produce an increase prolactin as do the parents

Flexible Behavior in Pied Kingfishers

• Can be primary helper (can't find mate so bring back food for siblings), delayer (don't help and delay breeding til next year), or secondary helper (assist at another unrelated nest) • Primary helpers raise their fitness indirectly through production of non-descendent kin - They reproduce less over a lifetime but are compensated genetically through indirect fitness • Secondary helpers are more likely to secure a mate in the second year and sometimes can inherit territory or sexual partners as a result of their help

Lecture 5 Summary - Avoiding Predators and Finding Food

• Convergent and Divergent behavioral characteristics can help explain if a behavior evolved as a result of the environment • Cost-Benefit approach to analyze traits in terms of fitness • Game theory - decisions as a game played by competitors, best strategy wins (most offspring) • Optimality Theory - traits that have the best benefit to cost ratio • Antipredator and foraging behavior must be considered when thinking about optimal foraging behavior • Frequency-dependent selection: occurs when the fitness of one strategy is a function of the frequency of the other • Conditional Strategy allows for flexibility of choices

Convergent Evolution, Divergent Evolution, and Shared Ancestry

• Convergent: Species from different evolutionary lineages that live in similar environments should be subject to similar selection pressures - These species might adopt the same solution and adaptations to deal with a particular environment - Swallow and Gull are distantly related but many lineages ground-nest and share distinct behavior • Divergent: Related species evolve different traits • Shared ancestry: a common feature can be traced back to a common ancestor

Dear Enemy Effect

• Cost of territory reduces with time, the neighbors are aggressive to the newcomers: - disputes over boundaries occurs - once things are settled, everyone calms down •African lizard will chase familiar neighbor much shorter distance than unfamiliar intruder • Dear Enemy Effect - once neighbors learn who is who, fighting significantly reduces (waste of energy) • Resident expends time and energy establishing boundaries - Male fiddler crabs may help their neighbors in fights against intruders since they save time, energy and injury risk from having a familiar neighbor as opposed to an aggressive newcomer (neighbors rarely fight)

Cost-Benefit of Migration

• Costs: - If you don't have sufficient reserves you won't survive the trip - You have to deal with new predators - You have to settle new territories • Even though migration is risky, there must be benefits that outweigh the costs • Benefits: - Additional resources - Better climate - Less competition

Cost-Benefit of Dispersal (leaving your habitat/territory)

• Costs: - Travel cost and exposure to new predators, need to establish new territory • Benefits: - Find it more advantageous to move away from samesex rivals they can't beat - Dispersal of juveniles in many species protect against inbreeding depression - recessive alleles may be expressed by closely related individuals • Male mammals usually disperse greater distances than females - Young male lions often leave when a new dominant male arrives - no opportunity for breeding there

Cowbird Parasitism and Evolutionary Lag Time

• Cowbird parasitism: cowbird eggs in another bird's nest, host parent feeds cowbird chick • Cowbird parasitism of many species in North America may be evolutionarily recent - a result of deforestation. • Grassland species tend to be cowbird egg rejectors while forest species tend to be cowbird egg acceptors. • Suggests that evolutionary time lag explains some of the variation in cowbird egg acceptance/rejection behavior. •Historical range of cowbirds was mid-western prairies, has expanded - Deforestation and agriculture • Grassland species share evolutionary history - Abandon their nest if it is parasitized by a cowbird - Build a new nest right on top of the old one, leaving the cowbird egg in the lower nest • But forest birds lack these responses - Actually give cowbird chicks preferential treatment

Cryptic Behavior

• Cryptic coloration depends on where the animal chooses to rest - The Australian thorny devil is camouflaged but only when the lizard is motionless in areas littered with bark and other varicolored debris, not on the road • Cryptic behavior - cost finding the right background - Black moth on white trunk would be obvious for predator

Maladaptive behavior: raising brood parasites

• Cuckoo drops its own egg into another bird's nest • Cuckoo chick must eject (throw out) the other host eggs cus the mother can't feed them all (mean but adaptive) • Hedge sparrow feeds cuckoo (nice but maladaptive) • However, when cuckoo drops egg into robin nest, robin rejects cuckoo egg (throws them out)

Altruism and Group Selection

• David Wilson argues that colonies with more self-sacrificing individuals will be favored by group selection, if groups with more altruists outcompete rival groups and so contribute more genes to the next generations

Dilution Effect

• Dilution effect- safety in numbers that comes from swamping the ability of local predators to consume prey - Cost-benefit approach to social defense • Harvester ants come together to mate for only few days each year - dense aggregation • Dragonflies & birds take advantage of prey saturation • But the odds any ant will be targeted is reduced • Advantages of social defense include shared vigilance, communal defense

Types of Fitness

• Direct fitness- measure of reproductive success based on individuals and their offspring • Indirect fitness- measure of genetic success of an altruistic individual • Inclusive fitness- Direct + Indirect fitness

Optimality Model: Reproductive Success

• Does more energy from foraging activity translate to achieving maximum reproductive success? • A key assumption of the standard optimality model • Then the behavior can spread through the population and by passed on through natural selection • In experiment with captive birds those with highest daily net caloric gain survived best, reproduced most, and began reproduction sooner • If a model only focuses on calories gained vs. calories expended and not predation then the model will likely not predict behavior • It makes sense that animals will sacrifice short-term caloric gain for long term survival - animals will move away from food and stop eating if predator is nearby

Redstart winter territoriality affects reproductive success

• Earlier departure from overwinter grounds infers more fitness --> higher # of fledglings • Reaching breeding ground early helps because they only have a few months to raise offspring

Chapter 3 Summary - Social Behavior

• Eusocial insects that engage in cooperative behavior gain fitness through indirect fitness and a high r value • In vertebrates few give up their reproductive ability but they will delay it if they are not likely to reproduce in that season anyway and helping might lead to future pay off • According to the prisoner dilemma cooperation should not occur • But cooperation does occur because of reciprocity behavior • Helpers can inherit valuable resources such as territory or access to mates resulting in direct fitness later • The closer social groups are related the more likely they are to engage in helpful behavior

Digger Bee

• Female bees tunnel into the ground creating a nest with chambers for their offspring • Males dig down below the ground and try to find a virgin female to mate with • Question: Why do males exhibit this digging behavior? 1. Females just mate once (based on the fact at other times the females are not pursued) 2. In other species that do mate several times and male meet their mates at flowers or nesting sites 3. Males are highly aggressive at digging sites (competition for females is first come, first serve)

Colony kin structure is linked to queen production in eusocial Melipona bees

• Female larva control their own fate - queen or worker • The higher the % of workers' sons in the colony, the less likely immature females try to become queens • The more workers that produce sons. the lower the coefficient of relatedness. the less likely females become queens • This shows that there needs to be a certain level of relatedness for the colony to operate efficiently

Firefly "femme fatales," and two explanations

• Females are nocturnal predatory insects genus Photuris, they respond to flashes by males of a different genus Photinus who are trying to find a mate • The male thinks he is going to get to reproduce but instead he is eaten - the female uses her victim's chemical defenses for her benefit • Novel environmental theory: the current environment is so different from that in which the behavior evolved that there is insufficient time for an advantageous mutation - no time to fix the problem • Net Benefit theory: sensory mechanism that results in loss for some individuals under circumstances overall results in a gain for most individuals - overall the mechanism is beneficial for the species - Firefly situation- males that avoid the deceptive femme fatale might live longer but they would most likely ignore females of their own species as well - Natural selections acts on those that reproduce those that exhibit cautious behavior, if they live a long time, leave few or no descendants and the behavior won't proliferate

Sexual Selection

• Form of natural selection where characteristics arise in a population from preference by opposite sex • How could certain traits have evolved that initially appear to lower the organism's fitness? - Darwin theorized that unique traits could evolve that lowered survival chances if they helped an individual gain advantage in acquiring mates - Males live shorter lives but reproduce (copulate) more - Display, aggressive behaviors, ornamental features spread through populations - Its not how long you live but how much you get to reproduce

What is free movement discouraged by?

• Free movement is discouraged by territorial males that attempt to monopolize high-quality sites and access to females • Forces the loser to look elsewhere for land • Benefit of territory is to utilize resources without interference (from other individuals)

Monogamy

• From chapter 2 we saw that monogamous insects help facilitate a complex social structure in which workers were willing to give up their own reproductive abilities to help produce more sisters. • In most vertebrate social animals do not give up their reproductive ability • But the lower the relatedness the less likely the individual is to benefit from helpers • "Promiscuous" behavior does happen but at the cost of cooperation in vertebrates • Kin Selection theory does explain vertebrate behavior

Game Theory

• Game Theory - decision making is treated as a game. Under one scenario one strategy works well, but an individual may come up short when matched against another individual using another strategy • Applied to evolution of animal behavior: - adaptive value in which the payoffs to individuals associated with one behavioral tactic are dependent on what the other members in the group are doing • Treat individuals as participants in a contest in which the success of one is dependent on what its rivals are doing • One strategy will work in certain situationsbut not be effective in other • Evolution game - winning means getting your genes in to the world relative to the fellow next to you - The best strategy wins

Social- Bonding Hypothesis

• Greeting could promote the formation of cooperative coalitions within clans • Coalitions within the clan are constantly shifting • After conflict some individuals initiate a greeting ceremony to reconcile their differences with previous opponents - Conflict resolution • Females dominate the social status • The enlarged clitoris make copulation really tricky and requires cooperation from the female • This gives a greater degree of control on selection of sexual partners • Rape is almost non-existent

Hamilton's rule

• Hamilton's rule: an allele for altruistic behavior will be favored and spread if Brb - Crc > 0 • Where B = benefit to recipient and C = cost to the individual • Unit of measurement for B and C is surviving offspring • Altruistic behaviors are most likely to spread when costs are low, benefits to recipient are high, and participants are closely related • Hamilton invented the idea of inclusive fitness.

Gang up on the territorial residents hypothesis

• Heinrich noticed that when a single bird or a pair feeding approached a carcass, they did not yell • Yelling only occurred when 3 or more ravens were present • Pairs of ravens defend territory and solo travelers will travel long distances to find food • Yelling could be a signal that attracts wanderers to the food bonanza (recruitment signal) • Multiples ravens that can overwhelm the defenses of the resident pair 1. Residents should never yell 2. Non residents should yell 3. Yelling facilitates a mass assault on carcass 4. Residents should be unable to repel a communal assault 5. Food should be eaten by either resident pair alone, a single bird, or by a mob

Honest Signal Hypothesis

• Honest Signals allow a fellow rival to assess the situation and avoid fights they do not have a good probability of winning • This is beneficial for both individuals involved because they can avoid injury and wasted energy

Waggle Dance in Honey Bees

• Honey Bees (Apis) perform dances when they return home • Round dance - food < 50 m • Waggle dance - food > 50 m • Longer the waggle the more distant the food source • Measure of the angle corresponds to the direction of the food source • Bees can note difference angle of flower, hive, and sun • If she waggles straight into comb: fly directly into sun • If she waggles 20 degree angle to the right of vertical comb - it is 20 degrees to the right of the line between the hive and sun

Theory of descent with modification

• Identify a distant ancestor state and then see what modifications have occurred over time • In this way you can potentially trace the history of attributes • Hughes created phylogeny of bees, ants, and wasps for 267 species • ancestral species at the base were monogamous • polyandry evolved independently among different lineages

Foraging decisions are affected by predator pressure

• If dugongs sense tiger sharks nearby, they will stop eating and move away (altering foraging strategies) • Introduction of wolves changed the foraging behavior of elk - Elk prefer open meadows for grazing, but when wolves are around they move to the forests - Fecal samples of elk suggest that when wolves are present they eat a quarter less and have fewer calves (more nervous)

The theory of sex role differences

• If the ratio of receptive males or females change over the course of a breeding season, the sexual tactics of the males and females should change as well • Australian katydid - when food is scarce the males are very choosy but when food becomes abundant then the behavior changes, females become choosy • Supply and Demand

Illegitimate receiver

• Illegitimate receivers - predators take advantage of signals that are provided by their prey • On the island of Kauai, field crickets no longer chirp to attract a mate - A parasitoid fly used the chirp as a guide to find the male and deposit her egg inside him such that he was eaten from inside out • The loss of the chirp took place in only 20 generations

Illegitimate signaler

• Illegitimate signaler - reduces the fitness of a species but it does not eliminate the fitness benefit • It is utilizing a generally advantageous signal - Manipulation of communication • The elbow orchid (leaves look like wasps) tricks a few species of thynnine wasps into thinking that it will be with a mate - instead it only gets a little pollen • Sometimes the male becomes so stimulated that he ejaculates - time, energy, and fluids • Why does he get tricked? - Access to female is limiting, so that's why it's still advantageous for male wasps - By exploiting the preexisting sensory bias th orchid gains an advantage

Inclusive Fitness Theory

• Imagine "you" have one offspring that survives to reproduce and you help your 2 siblings raise one offspring that couldn't have done it without your help - Direct fitness 1 x 0.5 - Indirect 2 x .25 = 0.5 - Inclusive fitness 0.5 + 0.5= 1 • An allele for altruism will become more common if the indirect fitness gained by the altruist is greater than the direct fitness lost as a result of self-sacrifice

Habitat selection is key factor in successful reproduction

• Individuals distribute themselves spatially in terms of fitness gains where individuals are free to migrate • If ideal habitat becomes too crowded and there is too much competition, secondary habitat provides higher fitness

Conditional strategy

• Inherited mechanism that give the individual the ability to alter its behavior adaptively in light of the conditions it confronts • Ruby Turnstones exhibit flexibility in foraging behavior, depending on their ranking - Push strands of seaweed around (least energy, so dominants do this) - Turn stones over - Probe sand for mollusks (subordinates do because dominants probably took all food from seaweed)

Deceptive Hypothesis

• Jumping spiders prey on flies, so it was hypothesized that tephritid fly imitated them - this is an example of a prey species gaining protection by mimicking a predator • Wing transplantation experiment showed that both the behavior and wing pattern of tephritids are required for the deception to work.

How does kin selection relate to eusociality and altruism?

• Kin selection most likely underlies the evolution of eusociality - monogamy with leads to high relatedness • Altruism seems to make a lot of sense when organism are closely related (which actually not true altruism but kin selection)

Reciprocity Hypothesis

• Reciprocal altruism - the individuals that are helped generally return the favor they receive (eventually) • The helper is not really sacrificing direct fitness over the long haul • Grooming behavior of primates is a classic example - The individual picks through the fur of a companion and will be repaid at a later date either by being groomed or by some other useful behavior • The problem with reciprocity is that individuals have to protect against "takers," individuals that take help and never return the favor

Does the resident territory owner always win?

• Residents always win when intruders fight them • But when experimenters captured the resident male butterfly and held him in a net until a new resident took over the area, when they released the old resident male, the two males would fight but eventually the new resident would always win. • However when put original resident in a cooler and retrieved it after finding replacement, 50-50 chance resident wins

Hamilton's selfish herd hypothesis

• Selfish herd - A group of individuals whose members use others as a living shield against predators • Individuals will jockey for a place in the center of the group • Bluegill nesting colonies: larger more dominant individuals occupy the central position forcing smaller subordinate males to the periphery

Sex Role Reversal

• Sex Role Reversal - where the male are choosy and the females are competing for mates • Can happen when males offer brood pouch that females compete to put their eggs in • Animals that give spermatophores (once a season) to females who produce a few clutches

Sexual Dimorphisms and Sex Roles

• Sexual dimorphism - any difference between males and females of the same species • "Sex roles" - species-typical sex differences in behavior (often assumed to be learned)

Why do antelopes leap into the air when threatened by a predator?

• Single gazelles stot - eliminates alarm signal hypothesis & confusion hypothesis • Gazelles stot in short grass - eliminates the ambush hypothesis • Single gazelle orients white rump to predator rather than group - eliminates social cohesion hypothesis • Only hypothesis that holds up is Honest Signal - gazelle messages to cheetah: it sees predator, has plenty of energy, will be hard to capture • Cheetahs are more likely to abandon hunt when gazelle stots • Honest signal between signaler and receiver: both benefit from information

The "Adaptationist" Approach

• Start by assuming that animals are well-adapted to their natural environment. • Come up with a hypothesis to explain why a particular trait has evolved through natural selection. • Collect data to test predictions made by the hypothesis. • If the data do not match the predictions, modify the hypothesis. This is a powerful approach, but it also has some pitfalls.

Submission Hypothesis

• Subordinate females and youngsters are more likely than dominate animals to initiate pseudo penile display • Sometimes a dominant female forces subordinates to engage in display or risk being attacked • Permission to remain may be granted if the female can accurately assess the physiological (hormonal) state of a subordinate female by inspecting the blood engorged clitoris - Really about communication hormonal state that helps to establish rank

What led Darwin to natural selection? And what was Darwin's crucial insight?

• The effects of selective breeding, also known as artificial selection - the term natural selection originally was used by animal breeders to refer to undesirable outcomes of selective breeding • The "struggle for existence" based on Malthus (1798) presented calculations showing that all species produce far more offspring than can possibly survive and reproduce • Darwin's crucial insight: - Any trait that gives the individual bearing it an edge in the struggle to survive and reproduce would be more likely to be transmitted to future generations.

Sensory Exploitation Hypothesis

• The evolutionary origin of sexual signals is largely debated • Communication signals originate in actions that activate sensory abilities that are already in place • Commonly accepted male signals can evolve in response to pre-existing sensory biases in females • This bias can be adaptive, if it evolves in another context than mating and through natural rather than through sexual selection (ex. foraging preferences) • The evolution of signals that happen to activate established sensory systems of signal receivers in ways that elicit response favorable to the signal sender • Natural Selection does not start from scratch but instead works on what already exists

Panda Principle

• The principle of imperfection where things don't have to be perfect to exist, they just have to be good enough to maintain the niche - The evolutionary principle using biological traits at hand to solve adaptive problems • In biology you are not starting from scratch or reinventing the wheel: new adaptations and behavior are created from preexisting ones • Pandas' thumbs are not real fingers but rather a modified wrist bone - They have 5 digits like most vertebrates + thumblike projection from the radial sesamoid bone - According to Dr. Gould, pandas evolved from carnivorous ancestors - the 1st digit became an integral part of the foot for running so they needed an additional digit for stripping leaves of bamboo as they developed an herbivore diet - Thumbs seem silly but they have adapted to use them

The Theory of Sex Differences

• The sexual behavior of males and females may differ because of the difference in parental investment that affect the rate at which individuals can produce offspring • The sex that can potentially leave more descendants gains from high levels of sexual activity, whereas the other sex does not • An inequality in the number of receptive individuals of the two sexes lead to competition for mates within in one sex, while the opposite can afford to be choosy • The sex that invests most is a limiting resource for the sex that invests least • Current view: gamete size and parental investment are just two of many factors that affect sex roles • Some other important factors: - operational sex ratio (sexually active males and females) - nuptial gifts (e.g., spermatophores) - population density (ease of finding mates)

The prisoner's dilemma

• There are two prisoners caught for a serious crime • The model predicts reciprocal cooperation should never evolve, because it is more safe to defect than to cooperate (less punishment) • If two players interact repeatedly... - Do unto others as they have done to you the last time you met - Back and forth cooperation adds up and exceeds the short term pay off of a single defector - In fact, accumulation of rewards can allow for "forgiveness" of the occasional defection to maintain long-term relationships - Organism can evolve to cooperate even if they are not related as long as they can recognize and remember who helped them last

Asymmetry Hypothesis

• Two individuals value a resource differently • Resident might derive greater payoff from maintaining control than a newcomer - Value is linked to familiarity with location and time spent on the location (residents have more time to appreciate and value the resource) • European robins - when the bird was kept away from the territory for a day he usually won the territory back, but when he was away for 10 days he usually lost - Residency gives a territorial advantage

Lecture 4 Summary - The Evolution of Communication

• You can't always tell why a trait developed but you can still identify what is beneficial about the trait - Adaptationist approach • Sensory Exploitation - exploit something already in place - food or an ancestral trait • Panda Principle - principle of imperfections • Threat displays can allow disputes to be solved without physical contact • Honest signals, Deception is an important tool organisms can use to catch their prey • Illegitimate signalers can persist if it does not eliminate the net fitness • Illegitimate receivers listen in on their prey and cause the loss of fitness by having the message reach the target • Communication system can only persists if both signaler and receiver gain benefit

Quality of Territory and Helpers

• Young birds that were raised on quality territory often stay put • Young birds raised on poor natal territory often left home and tried to find breeding territories of their own • The probability of dispersal was influenced by whether genetic parents were alive or if they had been replaced by stepparents - Helpers are much more likely to leave their home territory if they lose one or both parents they have been helping • Dispersal of helpers was more likely if relatedness had declined

Fitness

• relative number of gene copies contributed by an individual to the next generation (usually measured in terms of reproductive success [number of offspring] relative to the population average).

How can two strategies co-exist?

•Frequency-dependent selection: - occurs when the fitness of one strategy is a function of the frequency of the other - when the fitness of one type of behavior increases as it becomes rarer • When resources are scarce for fruit fly larvae, the fitness of the sedentary sitter vs the active rover depends on which of the 2 types is rarer

Evolution by natural selection requires:

1. variation among individuals in 2. heritable traits 3. that affect survival and reproduction • If these conditions hold, and they generally do, then evolution by natural selection is inevitable.

Should you forgo producing 2 children on your own to help your parents produce 3 additional children?

Brb = 3(0.5) = 1.5 - Benefit of altruism Crc = 2(0.5) = 1.0 - Cost to direct fitness Yes, assuming that you can help raise full siblings

Coefficient of relatedness (r)

Coefficient of relatedness (r) - proportion of identical genes that two individuals have in common, on the average. Parent-offspring 0.5 (exact) Full siblings 0.5 (on average) Half sibs 0.25 (on average) Aunts, uncles* 0.25 (on average) Nieces, nephews* 0.25 (on average) First cousins* 0.125 (on average) Unrelated 0.0 (on average)

Why do burrowing owls place cow dung around their burrow entrance?

Olfactory camouflage hypothesis: dung conceals burrow from predators • Prediction: burrows with dung suffer lower predation rates. • Experiment: 50 artificial burrows with quail eggs, half with and half without dung at entrance. •Result: nearly all eggs eaten by predators and no effect of dung treatment on time to predation event (survival analysis, P > 0.1). • Conclusion: hypothesis rejected. Baiting hypothesis: dung attracts prey • Prediction: owls with dung at burrow consume more beetles than owls without dung. •Experiment: remove dung from half owl burrow entrances; collect owl pellets; to see what they are eating. • Result: owls consumed 10 times more dung beetles when dung was present (paired t-test, P < 0.001). • Conclusion: hypothesis supported

Territoriality: Benefits and Costs

Possible benefits: • Access to resources • Spacing benefits (e.g., parasite avoidance) • Site fidelity benefits (familiarity with resources, refuges, etc.) Possible costs: • Time spent defending site • Energy spent defending site • Risk of injury, predation, etc. • Risk of losing the site to a superior competitor (vs. sharing)

Infanticide

• Lion males will attack and kill young infants of females in their own group • How can this be adaptive especially if they could end up hurting the female that is protesting her young? • Hrdy hypothesized: - Males will not kill their own progeny but attack the offspring of other males - Females that lose their infants resume ovulating - Males will be able to father their own offspring • Behavior is seen in some primates horses, rodents and bats

The Adaptive Value of Threat Displays

• Many animals so often resolve key conflicts with harmless threat displays - Animals show threat displays as an indicator of their strength - If one is clearly stronger, the submissive will back down

Novel Experiments

• Novel experiments can be designed that trigger responses from animals never encountered the stimuli before • Researchers - Played sounds to frog that had acoustic signals they had never heard in wild - Attached strips of yellow plastic pieces to male platyfish - Added feathers to the crests of auklets • In all cases artificial attributes elicited stronger reactions than natural ornaments

Optimality Theory

• Optimality theory - adaptations that have the best cost to benefit ratio will persist in the population over time • It looks at traits in terms of the net fitness to the individual that exhibits these traits • Best option compared to other options available • Ex. Northern bobwhite quail - in winter hangout in coveys with groups of 2-22 - Benefit - larger groups have more vigilance and react more quickly to danger - Cost - competition for food and more conspicuous • Studies show that there is an optimal size groups to gain the greatest benefit for the least cost - Results in highest survival

Parental Investment and Operational Sex Ratio

• Parental Investment - Time and energy and risk taken by parents to help their offspring grow and reproduce • Why do you think it is a better investment for female to take care of the offspring, but not so much for the male? - Females are relatively certain that they are taking care of their own genes - not always - Females have nothing to gain from copulating again after fertilization • Operational sex ratio - there are many fewer sexually active females than males at any given moment

Territoriality can be an expensive behavior

• Peaceful coexistence - Benefits (valuable resource) < Cost (defend that resource) • Yarrow spiny lizard - usually peaceful when females are not sexually active - males are non aggressive because it's cheaper to get along (territoriality and aggression expends a lot of energy) • females when ready to mate, change behavior

Polyandry and Monogamy

• Polyandry may have spread secondarily because of the benefit of high genetic diversity to resistance disease • Once workers were locked into their specialized role then polyandrous behavior may have arisen • Monogamy appears to have been essential for the evolution of sterile workers in Hymenoptera

Primary and Secondary Sexual Characters

• Primary sexual characters - necessary differences between sexes in reproductive organs • Secondary sexual characters (SS) - traits that differ between the sexes, neither required for reproduction nor related to sex differences in ecology • SS characters tend to be: - expressed more strongly in males than females - late maturing (e.g., not until puberty) - useless or costly in terms of survival

Why do birds fly in V-formation?

• V-formation, can confer energy savings to trailing individuals in a flock of migrating birds. • The effect, known as aerodynamic wash-up, happens when birds take advantage of updrafts created by the flapping wings of a preceding bird. •Reciprocal Altruism - The birds often worked in pairs, matching the time they spent in each other's wake by taking frequent shifts in the lead position.

Body condition affects the migratory route chosen by red-eyed vireos

• Vireo can take two routes - one across the ocean (shorter) or the other is to hug the land and travel through Mexico (longer) • If they weigh >5g then they take the direct sea route but if they weigh <5g then they take longer land route • The trans-Gulf light is shorter but if the bird can't make it all the way there is nowhere to make a pit stop

Kin Selection

• W.D. Hamilton (1964) showed that a gene for altruistic behavior could increase in frequency within a population if it caused individuals carrying it to help other individuals who likely carry the same gene. • Kin selection - a form of natural selection favoring behaviors that increase the survival or reproduction of relatives.

Who gets the territory? (butterflies)

• War of attrition - when the winner can outlast the loser in ability to continuously fly based on energy reserves • Resource holding power is sometimes based on size or energy reserves • But there are cases where physical fitness, beauty, or energy reserves do not explain the territory owner, indicating that there are still signals to be discovered... - Male with more fat reserves won - Older butterflies are more willing to persist in territory disputes than younger rivals (fight longer)

Examples of sensory exploitation

• Water mites: females pick up prey that bump into her, so males exploit that and bump into them, then give her a spermatophore - The male's behavior and its hereditary basis spread because it effectively activates a preexisting preydetection mechanism in females • Male cichlid fish have orange spots that resemble eggs --> females prefer them - Pre-existing bias is for carotenoid-rich - food like shrimps, algae and, notably, fish eggs indicative of foraging skills - Not bias for breeding (since non-brooding fish also preferred), as they resemble eggs

Darwin Puzzle

• When a trait appears to reduce the fitness of individuals, but is adaptive

Sexual Differences Theory

• Why do males build courtship displays? • Why do females evaluate their performance? - Males commonly try to mate with many females - Females commonly content mating only a few males • Females must choose carefully • Males produce many small sperm, while females produce only a few large eggs • A single bird egg constitutes up to 20% of body, a male might have up to 8 billion sperm at any given minute • Competition among males to access the limiting resource - females and their eggs

Dishonest Signals/Mimics

• Why not produce face signals that indicate dominance even if you're a subordinate? • Researchers noticed that the wasps occasionally test each other to see if the signals are synchronous with real fighting ability • Individuals who give dishonest signals are punished by their companions • If a mimic could easily display threats that do not accurately display their abilities, then natural selection would favor receivers that ignored the fake signal - Reduces the value of producing them • This would favor honest signals that could not be devalued by deceitful signalers • Signals should be easy for large males and difficult for small or weak males to imitate

Indirect Selection

• William Hamilton argues: - Individuals reproduce with the unconscious goal of continuing their family gene pool more successfully than others - If an individual helps organisms that are genetically similar (like brother/sister), survival to reproduction achieves the same goal indirectly - A trait becomes more common if the allele is promoted

Examples of social behavior

• Wolves coordinate attack on prey (group effort) • Cliff swallows nest side by side - improved foraging, yet attracts parasitic bugs and transient birds • Fish swim in schools (protection from prey) • Brown-necked raven hunts lizards in teams - one surprises animal out of its retreat and others attack retreat • Several bluegill males defend nesting colonies, and all males gain fitness cus nests are more likely to survive. • Several unrelated female social paper wasps work together to build nest - have a chance to inherit queen's nest

Classic contrasting views about group selection

• Wynne-Edward (1962): - Group-level selection usually trumps individual-level selection • G.C. Williams (1966): - Group selection is theoretically possible but it is usually much weaker than individual selection - Reproductive restraint and other forms of true altruism are illusions ("group-level adaptations do not, in fact, exist") • Reality lies somewhere between these extreme views, but probably closer to Williams'