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大學部 生態學與保育生物學學程 (必選) 2010 年 秋冬 團體生活,利他和合作 (Group Living, Altruism, and Cooperation) ─動物行為學 (Ethology) 鄭先祐(Ayo) 國立 臺南大學 環境與生態學院 生態科學與技術學系 教授 Ayo NUTN Web: http://myweb.nutn.edu.tw/~hycheng/ Part 3. 個體間的互動 生殖行為 (Reproductive Behavior) 親代照顧與交配體系 (Parental Care and Mating Systems) 溝通:管道與功能 (Communication: Channels and Functions) 溝通的演化 (The Evolution of Communication) 衝突 (Conflict) 團體生活,利他和合作 (Group Living, Altruism, and Cooperation) Ayo 教材 (動物行為學 2010) 2 17 團體生活,利他和合作 Living in Groups: from aggregation to structured societies Benefits of Group living Costs of living in groups Balancing costs and benefits The puzzle of altruism Individual selection and altruism Kin selection Reciprocal altruism manipulation Examples of cooperation among animals Ayo 教材 (動物行為學 2010) 3 An introduction to group living Ladybug beetles overwinter in aggregations of thousands of individuals They crawl inside rock crevices and houses for shelter They were introduced from Asia to control invasive pests Have become wildly successful and their numbers have soared They outcompete and even eat native ladybug species Ayo 教材 (動物行為學 2010) 4 Animal groups: simple to complex Ladybug groups are at the “simpler” end of the spectrum No evidence that ladybugs interact in complex ways Other species form groups Individuals respond to the same features of the environment The other end of the scale of animal groups: chimpanzees Ayo 教材 (動物行為學 2010) 5 After conflict, one chimpanzee opponent approaches the other, offering an open hand Ayo 教材 (動物行為學 2010) 6 Benefits of living in groups Societies: chimpanzees and other species are members of structured groups Fitness benefits accrue to animals living in groups Improved foraging Decreased risk of predation Conservation of water and heat Decreased energetic costs of movement Ayo 教材 (動物行為學 2010) 7 Cooperative hunting improves foraging Cooperative hunting in groups improves foraging success Harris’s hawks live and hunt in family groups In early morning, family members gather at one perch site The group splits into smaller subgroups The subgroups take turns flying through their family’s area Hawks employ different hunting tactics The surprise pounce(猛撲): hawks converge(聚集) on a rabbit Flush-and-ambush tactic: hawks flush the rabbit and other family members pounce on it Relay (換班) attack: family members chase the prey, with a new lead bird taking over each time Ayo 教材 (動物行為學 2010) 8 Cooperative hunters share prey For cooperative hunting to be favored by selection Individuals must average at least the same amount of food they would get by hunting alone Hunting success must be increased in groups Harris's hawks Ayo 教材 (動物行為學 2010) 9 In Harris's hawks, larger group size increases the chance of a kill Even with more individuals, the energy intake per individual from prey is higher in larger groups Ayo 教材 (動物行為學 2010) 10 Improved foraging: information sharing Animals improve foraging in groups by information sharing Individuals pay attention when conspecifics discover food They use this information to guide their own foraging Geese land nearer artificial geese with their heads down in a feeding position than to those standing erect Communal roosts or colonies can act as information centers Successful foragers return to the roost or colony and then return to the food site Seen in cliff swallows and honeybees Ayo 教材 (動物行為學 2010) 11 cliff swallows Ayo 教材 (動物行為學 2010) 12 Decreasing predation risk The many eyes hypothesis: better predator detection Animals in groups give alarm signals The dilution effect: an individual in a group has a smaller chance of becoming the next victim The selfish herd hypothesis: animals in the center of the group have a lower chance of being preyed upon Confusion effect: fleeing in different directions decreases a predator’s ability to track and kill any one individual Group members can band together to drive a predator away Ayo 教材 (動物行為學 2010) 13 Conserving heat and water By huddling together, animals reduce the surface area exposed to the environment Reducing the loss of heat or water Many mammals sleep or overwinter together in communal burrows Many birds perch snuggled (偎依) up next to one another The metabolic rates of penguins is reduced compared to isolated birds Even some slugs (蛞蝓) rest in contact with one another to reduce water loss Ayo 教材 (動物行為學 2010) 14 Conserving energy by moving together Drafting (riding close behind in the slipstream of another) Reduces the amount of energy needed to move Holds true for animal groups that travel together Schools of fish Flocks of birds Ayo 教材 (動物行為學 2010) 15 Pelicans (鵜鶘) flying in a V formation have lower heart rates than birds flying solo Ayo 教材 (動物行為學 2010) 16 Cost of group living: increased competition Individuals that live in groups often compete with each other For mates, nest sites, or food Some snails secret a mucous net that floats on water The snail draws the net in to eat the mucous and its catch When snails group, their mucous nets overlap and stick Snails adjust for neighbors by retracting their nets quickly Group-living animals might lose food to thieves Stealing can be considered a strategy There is a limit on how many “scroungers” (thieves) a population supports before the strategy becomes unrewarding Ayo 教材 (動物行為學 2010) 17 Costs of group living: increased disease and parasites Proximity to conspecifics presents an increased risk of infection Larger colonies of cliff swallows have more bloodsucking swallow bugs Which reduce nestling mass, and decrease survival Larger colonies have higher levels of glucocorticoid hormones, released in response to stress The stress response was caused by exposure to the parasites Ayo 教材 (動物行為學 2010) 18 Fending off(擊退) disease and parasites Group-living species have behaviors that help fend off disease and parasites Allogrooming: animals groom each other and pick off ectoparasites Social insects (honeybees, ants and termites) remove corpses and other waste from the colony And wall off or remove infected individuals Ayo 教材 (動物行為學 2010) 19 Costs of group living: interference with reproduction Extra-pair copulations (outside of the pair bond) are common Even among “monogamous” birds Males may take care for young that are not theirs A female may not notice when another female deposits an egg in her nest Allonursing: mammalian mothers nurse offspring not their own In shared roosts, reproducing communally or in a small space May provide fitness benefits to the nursing mother (e.g., feeding related young or the mother will reciprocate later) It may be misdirectedAyoparental care (mistaken identity) 教材 (動物行為學 2010) 20 Balancing costs and benefits Hunting success alone does not explain formation of prides in lions Benefits of group living include defense of food, young, and space against conspecifics Ayo 教材 (動物行為學 2010) 21 Costs and benefits of group living may differ across individuals Whirligig beetles form aggregations on the surface of fresh water Beetles at the outside edge are more likely to get food But are also more likely to get attacked Beetles weigh the tradeoff between predation risk and food availability Depending on how hungry they are Ayo 教材 (動物行為學 2010) 22 Hungry beetles move to the outside of the group, in spite of the risk Ayo 教材 (動物行為學 2010) 23 The puzzle of altruism Why do some animals help other members of their species? A Belding’s ground squirrel increases its risk of being spotted by an approaching predator when it barks an alarm Dwarf mongooses feed young of others and guard the den Eusocial insects (ants, termites, wasps and bees) care for their colony and rear young that are not their own Ayo 教材 (動物行為學 2010) 24 Wild turkey males form coalitions (聯盟) that court females and defend(保護) them, but only dominant males father offspring Ayo 教材 (動物行為學 2010) 25 Altruism Altruistic behavior appears to be costly to the altruist And beneficial to another member of its species Altruism is defined in terms of fitness It is a behavior that raises the fitness (number of offspring produced that live to breed) of another individual At the expense of the altruist’s direct fitness, measured by the number of offspring it leaves How could altruism evolve? Shouldn’t alleles that promote selfish behavior multiply more quickly than alleles that promote altruism? Ayo 教材 (動物行為學 2010) 26 Individual selection and altruism Behavior may appear to benefit others at a cost to the actor In fact, the actor might directly benefit from its behavior An animal that gives an alarm call may appear to be alerting others at is own expense But it improves its own survival by alerting the predator that it has been seen Some cichlid fish (慈鯛魚) adopt unrelated young into their own brood The parents gain: the adopted young reduce the predation risk of their own young Before assuming that a behavior is truly altruistic Determine if the actor benefits directly from the behavior Ayo 教材 (動物行為學 2010) 27 Kin selection Natural selection increases the frequency of an altruistic trait Individuals improve their fitness through their own offspring (descendent kin) And through the reproductive success of other relatives (nondescendent kin) Kin selection: family members other than offspring possess copies of some of the same alleles Because they inherited the alleles from the same ancestor Ayo 教材 (動物行為學 2010) 28 Kin selection duplicates alleles If family members increase their reproductive success The alleles that the altruist has in common with them are also duplicated Just as if the altruist reproduced personally Not all relatives have the same likelihood of sharing alleles Closer relatives (i.e. siblings) share more alleles than distant relatives (i.e. cousins) Coefficient of relatedness (r): the probability that particular pairs of relatives share the same allele through common descent Ayo 教材 (動物行為學 2010) 29 The coefficient of relatedness There is a 50–50 chance (probability of 0.5) that any particular allele will be found in an egg or sperm produced by the parent A parent and offspring have a coefficient of relatedness of 0.5 The value of r ranges from 0 (nonrelatives) to 1 (identical twins or clones) A family tree can be used to calculate the coefficient of relatedness between more distant relatives An animal shares 50% of its genes with a full sibling (r = 0.5) 25% with a half sibling or grandparent (r = 0.25) Only 12.5% with a first cousin (r = 0.125) Ayo 教材 (動物行為學 2010) 30 Calculating relatedness (r): a family tree Ayo 教材 (動物行為學 2010) 31 Coefficient of relatedness affects altruism When will the gene for an altruistic behavior increase? Hamilton’s rule: B 1 C r B = the benefit to the recipient: extra offspring that the relative produces because of the altruistic act C = the cost to the actor: the number of offspring it does not produce because of the altruistic act r = the coefficient of relatedness between the recipient and the actor 1/r = a value of 1 or greater (r ranges from 0-1) Ayo 教材 (動物行為學 2010) 32 Applying Hamilton’s rule When should an individual forgo (放棄) reproduction to help its sister? For siblings, r = 0.5, so 1/r = 2 The benefits of acting altruistically must outweigh the costs by 2:1 for an individual to help its sister reproduce Ayo 教材 (動物行為學 2010) 33 Stop and think A bird would have two offspring without help If her altruistic sister helps her by bringing food to the nest and driving off predators, she will have five offspring This behavior has a cost to the altruist The altruist will not have any of her own offspring Whereas if she did not help, she would have one Will altruism be favored by natural selection? Ayo 教材 (動物行為學 2010) 34 Expanding the definition of fitness Direct fitness: measured by the number of offspring that an individual has as a result of its own efforts Indirect fitness: the number of extra offspring that an individual gains by helping a relative Devalued by the genetic distance between the individual and the relative who was helped (in other words, multiplied by r) Inclusive fitness: the sum of direct and indirect fitness Ayo 教材 (動物行為學 2010) 35 Discriminating between kin and non-kin If animals can aid each other It should be evolutionarily advantageous to discriminate kin from non-kin Animals discriminate kin versus non-kin in four ways Location Familiarity Phenotype matching Recognition alleles Ayo 教材 (動物行為學 2010) 36 Kin vs. non-kin: location Individual animals are often found in predictable locations In mammals males generally disperse from home Females tend to remain in their natal area Female mammals that help conspecifics located near their home are likely to be helping relatives Even if they do not recognize them individually as kin They follow the rule of thumb “if you are a female, help those near home” which leads to increased inclusive fitness Ayo 教材 (動物行為學 2010) 37 Location as a mechanism for kin-biased behavior When a parent identifies its offspring as those young in its nest or burrow Parent birds feed any young in their nest When the young leave the nest The parent learns to recognize its young by its calls And rejects foreign young entering the nest Ayo 教材 (動物行為學 2010) 38 A bank swallow feeds any chicks inside its nest, but ignores its own chicks if they are moved to a nearby nest hole Ayo 教材 (動物行為學 2010) 39 Kin vs. non-kin: familiarity Young learn to recognize the individuals they are raised with, through their experiences during early development Later, they treat familiar and unfamiliar animals differently A young spiny mouse uses familiarity to distinguish its siblings Weanling pups huddle(聚在一起) in pairs And members of the pair are siblings Non-kin encountered during the learning process may be mistakenly classified as kin Ayo 教材 (動物行為學 2010) 40 Kin vs. non-kin: phenotype matching Animals identify kin, even if they have never met Through physical, behavioral, and physiological appearances One’s genetic inheritance has much to do with appearance Family members often resemble one another Animals can learn the “kin phenotype” By learning about the phenotype of familiar individuals Or by learning their own phenotype This template is then compared against strangers “He looks like my brother” or “He looks like me” Ayo 教材 (動物行為學 2010) 41 Learning the phenotype of familiar individuals Developing a template And then matching new individuals to that template Belding’s ground squirrels use both familiarity and phenotype matching Pups identify their siblings because they learn one another’s odors while still in the same nest burrow Juveniles and adults use phenotype matching to discriminate relatedness among individuals they have never encountered before Ayo 教材 (動物行為學 2010) 42 Paper wasps identify kin from non-kin By using the odor of hydrocarbons in the insect’s cuticle (skin) The odor comes from the nest When a wasp meets a nestmate away from the nest It can recognize it Since a colony consists of a queen and her worker daughters The nest odor is a reliable label of colony members as relatives Ayo 教材 (動物行為學 2010) 43 Paper wasps Ayo 教材 (動物行為學 2010) 44 An animal can use its own phenotype as a template Against which to compare strangers The “armpit (腋窩) effect:” imagine an individual sniffing (嗅聞) its own armpit And then that of a stranger Golden hamsters discriminate between odors of unfamiliar kin and unfamiliar non-kin Using their own odor to form a template Ayo 教材 (動物行為學 2010) 45 Kin vs. non-kin: recognition alleles This mechanism of kin discrimination is genetically based The allele endows its bearer with a recognizable label It enables the bearer to perceive that label in others The bearer behaves preferentially toward others with the label This recognition system is called the “green beard effect” The label could be any conspicuous trait (i.e. a green beard) As long as the allele responsible for it also causes its owner to behave appropriately to other labeled individuals Ayo 教材 (動物行為學 2010) 46 A green beard allele in the red fire ant Kin discrimination in fire ants is closely tied to genetics Memory (formation of a template) also plays a role The protein-encoding gene, Gp-9, controls social organization (The gene has two alleles, B and b) Workers encountering individuals with the b allele form a template Workers that come into contact with ants that bear b alleles when forming their template Accept only b-bearing queens (bb and Bb) Workers in colonies with BB individuals accept only BB queens Ayo 教材 (動物行為學 2010) 47 fire ants Ayo 教材 (動物行為學 2010) 48 Genetically-based recognition mechanisms Used to recognize a protein coded by a region of the DNA The major histocompatibility complex (MHC) The MHC region codes for molecules that allow the body to distinguish between “self” and “nonself” These genes may serve as direct cues of relatedness Allowing individuals to identify their kin Sea squirt (海鞘) larvae use MHC to discriminate kin Groups of siblings that share an allele in the MHC region Clump together when they settle on the sea bottom Ayo 教材 (動物行為學 2010) 49 Bluebell tunicates (Sea squirt) (海鞘) Ayo 教材 (動物行為學 2010) 50 MHC plays a role in kin recognition Especially in the context of mate choice and incest avoidance In amphibians and mammals (including humans) There is no evidence that MHC genes influence the perception of odor Necessary for MHC to be a “recognition allele” But the MHC system remains an interesting case of a close link between genes and kin recognition Ayo 教材 (動物行為學 2010) 51 Reciprocal altruism Helping relatives is favored by natural selection When the inclusive fitness of the helper is increased Natural selection also favors reciprocal altruism Altruism between nonrelatives Evolves if there is an opportunity for payback in the future “You scratch my back and I’ll scratch yours” The Prisoner’s Dilemma: in reciprocal altruism The costs and benefits to the altruist depend on Whether the recipient returns the favor Evolutionary game theory can handle situations such as this The best course of action depends on what others are doing Ayo 教材 (動物行為學 2010) 52 The Prisoner’s Dilemma An imaginary story: two suspects are arrested for a crime Kept in separate cells to prevent them from communicating One of them is guilty But sufficient evidence is lacking for a conviction The prosecutor offers each a deal Each prisoner is told that there is enough evidence To guarantee a short jail term Freedom can be obtained by providing evidence to send the other to jail for a long time If each informs on the other, they both go to jail for an intermediate length of time Ayo 教材 (動物行為學 2010) 53 Constructing a payoff matrix The strategies available to each player are: To cooperate (don’t squeal on your partner) To defect (squeal) The best strategy: defect while your partner cooperates Payoff = T (the temptation to defect) If both you and your partner cooperate the payoff is R (reward) If both partners defect, the payoff is P (punishment) If you cooperate and your partner defects You get the lowest possible payoff, S (for sucker’s payoff) The payoffs must be in the order T > R > P > S Ayo 教材 (動物行為學 2010) 54 The best strategy for Prisoner’s Dilemma Examine the payoff matrix Player 1: the best strategy if the opponent cooperates? Because T > R, it is better to defect—you will go free Similarly, if the opponent squeals Because P > S It is better to defect, rather than taking the rap In a single round of the game, it is always better to defect This is a “dilemma” If both players follow this logic, they will both defect, and will both do worse than if they both cooperated Ayo 教材 (動物行為學 2010) 55 Tit for tat (一報還一報) The Prisoner’s Dilemma implies that reciprocal altruism cannot evolve If the prisoners never meet again But individuals do interact, so reciprocal altruism may evolve The “tit-for-tat” strategy: repeated games of Prisoner’s Dilemma An individual begins by being cooperative In all other interactions: match the other party’s previous action Be “nice” (begin with cooperation) Retaliate immediately (if the partner defects, defect in return) Forgive immediately (“forget” a defection and cooperate if the partner later cooperates) Ayo 教材 (動物行為學 2010) 56 Reciprocal altruism can be an ESS If a population of individuals adopts this strategy It cannot be overrun by a selfish mutant that always defects When individuals have repeated encounters Reciprocal altruism can be an evolutionarily stable strategy (ESS) Cannot be invaded by another strategy Ayo 教材 (動物行為學 2010) 57 When reciprocal altruism is likely to evolve Conditions that favor reciprocal altruism: The benefit of the act to the recipient is greater than the cost to the actor The opportunity for repayment is likely to occur The altruist and the recipient are able to recognize each other These factors occur in a highly social species With a good memory Long life span Low dispersal rate Ayo 教材 (動物行為學 2010) 58 Reciprocal altruism in vampire bats Vampire bats bite large mammals and lap up the blood Consuming up to 50% of their body mass A bat that did not obtain a blood meal begs for food A receptive donor regurgitates blood Regurgitated food sustains the hungry bat until the next night When it may find its own meal Donors give blood to recipients that are not related to them Ayo 教材 (動物行為學 2010) 59 Vampire bats evolved reciprocal altruism The benefit to the recipient of the blood gift exceeds the cost to the donor The recipient gains 12 hours of life and a chance to find food The donor has two nights of hunting before it would starve Bats have the opportunity to repay favors and get favors repaid Most bats will need blood at some time They will encounter the same individuals again Individuals recognize each other Only bats who have had a prior association share food Pairs of unrelated bats regurgitated almost exclusively to each other Ayo 教材 (動物行為學 2010) 60 Manipulation Animals can coerce (迫使) others to help them Particularly between parents and offspring Because parents and offspring are not genetically identical Their interests are not always perfectly aligned Parents have an advantage in power struggles They are larger and more experienced than their offspring Because offspring are related to their parents Their motivation to resist(反抗) coercion is reduced If offspring forgo(放棄) their own breeding to help their parents reproduce They at least gain indirect fitness Ayo 教材 (動物行為學 2010) 61 Cooperation among animals: alarm calls When Belding’s ground squirrels spot a ground predator (badgers, snakes, coyotes) Their alarm call is a series of short sounds When they spot an aerial predator (hawks and eagles) Their call is a high-pitched whistle Are these calls directed at the predator to let it know it has been detected? Or are they directed at kin? Ayo 教材 (動物行為學 2010) 62 Individual selection in Belding’s ground squirrels Individual selection is behind aerial predator alarm calls When an alarm whistle is heard, pandemonium breaks out Others also whistle an alarm and all scurry(急趕) to shelter When a hawk is successful, the victim is usually a noncaller The most frequent callers were in exposed positions close to the hawk The alarm whistles directly benefit the caller By increasing its chances of escaping predation in the ensuing chaos (接踵而來的混亂) Ayo 教材 (動物行為學 2010) 63 Kin selection in Belding’s ground squirrels Individual selection is not behind the squirrels’ alarm trills Given in response to terrestrial predators In this case, the caller is assuming a risk More callers than noncallers are attacked Predators did not give up when an alarm call was sounded The caller was not manipulating its neighbors to its advantage Other squirrels sat up and looked at the predator Their reaction did not create chaos that might confuse a predator Ayo 教材 (動物行為學 2010) 64 Female Belding’s ground squirrels are genetically related Squirrels practice nepotism (任人唯親): favoritism for family members Females are more likely to sound an alarm with a ground This is consistent with kinship theory Females have nearby relatives that benefit from the warning Reproductive females are more likely to call Reproductive females with living relatives call more frequently Ayo 教材 (動物行為學 2010) 65 Expected and observed frequencies of alarm calls by Belding’s ground squirrels in response to aerial and terrestrial predators. Expected frequencies are those that would be predicted if the animals called randomly. The calls in response to aerial predators are close to the expected frequencies. However, the calls in response to terrestrial predators are more likely to be given by females with relatives nearby. Ayo 教材 (動物行為學 2010) 66 Evolution of alarm calls in rodents Alarm calling increases the caller’s own chance of survival Aids the caller’s offspring (i.e. Yellow-bellied marmots) Or aids other animals Social species are more likely to call than non-social species Diurnal (day active) species are more likely to call Evolution of diurnality precedes evolution of alarm calling In rodent species, alarm calling communicates with predators Benefits arising from kin selection are secondary Belding’s ground squirrels benefit from kin selection They live in high-density meadows near relatives Ayo 教材 (動物行為學 2010) 67 Cooperation in animals: acquiring a mate Males of some species cooperate in attracting a mate Some even relinquish (放棄) the opportunity to pass their alleles into future generations At least temporarily These males concentrate their efforts on making another male more attractive to females Seems to lower fitness But in some cases it can be advantageous Sometimes the benefits to cooperators can arise separately or in combination with each other Individual selection, kin selection, or reciprocal altruism Ayo 教材 (動物行為學 2010) 68 Cooperation among wild turkeys Most male wild turkeys in some Texas populations never mate A young male and his brothers form a sibling group Will be an inseparable unit until death Only the dominant male in each group mates Each male’s status is decided by the outcome of two contests Competition for dominance within the sibling group Endurance is the key to success: the last one able to fight is the winner Competition between rival sibling groups The groups fight until a dominance hierarchy is established The sibling group with the most members is victorious Ayo 教材 (動物行為學 2010) 69 Kin selection in wild turkeys Dominance hierarchies are stable: renegotiation of rank is rare When the breeding season begins, females visit meadows The brothers strut (高視闊步) in unison (和諧一致) Even though only the dominant male in the highest-ranking sibling group will mate Kin selection: the major driving force behind this behavior A subordinate male gains inclusive fitness by helping his brother perpetuate his alleles Without his assistance, the brother could not be successful Siblings must cooperate for their unit to become dominant Sibling strutting makes the dominant male more attractive Ayo 教材 (動物行為學 2010) 70 Cooperation among lions Male lions cooperate in acquiring mates Form coalitions (partnerships) to challenge males of other prides The larger coalition usually wins The reward is a harem of lionesses Females enter reproductive condition simultaneously Any of the males in the coalition may be the first to mate A female may change mates Ayo 教材 (動物行為學 2010) Coalitions drive out resident males and can involve fighting 71 Why do male lions form coalitions? Does kin selection underlie formation of coalitions? Coalitions usually consist of close relatives A male gains reproductive success indirectly by helping his male relatives mate with the female However, kin selection is not the entire story Because male coalitions contain unrelated males Ayo 教材 (動物行為學 2010) 72 Reciprocal altruism is not important: lions attack a stuffed lion regardless of the behavior of other lions Ayo 教材 (動物行為學 2010) 73 Coalition size affects reproductive success Male lions in larger coalitions have greater reproductive success A solitary male has little chance of reproducing And much to gain by joining a coalition By accepting an unrelated male, a small coalition may take over a pride The lifetime success of a male lion increases by cooperating with other males Even if all the males are not related Ayo 教材 (動物行為學 2010) 74 Males in larger coalitions have greater reproductive success. Ayo 教材 (動物行為學 2010) 75 Cooperation among long-tailed manakins Two or three males of this small bird species work together They call and perform visual displays to attract a mate In the up-down jump display: perching males take turns jumping up and down In the cartwheel display: one male jumps upward and backward over the second male Which then jumps up and over the first male One male leaves and the remaining male does a solo performance The female mates with him The same male always mates Ayo 教材 (動物行為學 2010) 76 Why does a subordinate manakin stay? It is not indirect fitness Because the two males are probably not related A subordinate’ chance of mating is not increased by deserting Solitary males cannot perform the courtship dance or mate A subordinate male that outlives his partner obtains a subordinate partner Then it will be his turn to mate and raise his direct fitness Also, singing (which impresses females) improves with age and practice The most likely reason for cooperative courtship in this species? Increased chances of obtaining future direct fitness benefits Ayo 教材 (動物行為學 2010) 77 Cooperation among olive baboons A male olive baboons enlists the help of a friend for a female Male A associates (consorts) with an estrous female Male B (with no female) covets (垂涎) this female Male B solicits the help of male C to challenge male A While the battle is in progress, male B mates Male C risked injury while assisting another to acquire a mate Reciprocal altruism: at some time in the future, he will enlist the help of male B to obtain his own female Ayo 教材 (動物行為學 2010) 78 An alliance between two male olive baboons. The two males on the right are cooperating to challenge the male on the left. At a later time, the male that was assisted will have to reciprocate to maintain the alliance. Ayo 教材 (動物行為學 2010) 79 Cooperative breeding Nonbreeding helpers can reproduce But stay to help their parents raise young Acorn woodpeckers fit the definition of cooperative breeding: Some individuals (helpers) assist in the care and rearing of another’s young Rather than producing offspring of their own Cooperative breeding it is quite rare Occurs in birds, mammals, insects and spiders Ayo 教材 (動物行為學 2010) 80 Acorn woodpeckers live in family groups containing nonbreeding helpers Ayo 教材 (動物行為學 2010) 81 Helpers provide food Helpers pitch in to feed offspring Anybody, not just parents, can collect and carry food Reduces the parents’ job and increases health and survival Mammalian mothers provide milk to their offspring Helpers deliver food by carrying it in their jaws or stomachs Feeding the mother allows her more time to remain with the pups instead of hunting Blackbacked jackals (黑背胡狼) Ayo 教材 (動物行為學 2010) 82 Blackbacked jackals (黑背胡狼) regurgitate food to pups and mothers Ayo 教材 (動物行為學 2010) 83 Helpers protect young and do other jobs Helpers provide extra protection for the young Florida scrub jays give alarm calls and mob predators Jackal families with helpers always have an adult on guard In fish, helpers protect but don’t feed offspring In some bird species, helpers may build and clean nests Or incubate and brood the nestlings Male helper saddle-backed tamarins (a small primate) carry offspring Mothers can obtain nourishment for herself and for an adequate milk supply Ayo 教材 (動物行為學 2010) 84 Is “helping” really helpful? In many species, the number of helpers correlates with the survival of the young, the survival of the breeders, or both Helpers have no effect on the number of eggs laid But increases the chance that the young hatch, leave the nest, and become independent birds Ayo 教材 (動物行為學 2010) 85 Breeding success for Florida scrub jay pairs with helpers exceeds that of pairs without helpers Ayo 教材 (動物行為學 2010) 86 Do helpers increase breeding success? Another factor, such as territory quality, may cause an increase in the number of helpers and breeding success Removing helpers reduces reproductive success Gray-crowned babbler nests where helpers were removed raised fewer young Superb fairy-wren helpers did not increase offspring survival But increased future survival of breeding females Ayo 教材 (動物行為學 2010) 87 Meerkat (狐獴) pups gained more weight when the number of pups was reduced but the number of helpers remained the same Ayo 教材 (動物行為學 2010) 88 Do breeders always want help? Not always Helpers might compete for resources Or increase the chance that the mate has an extra-pair copulation In pied kingfishers, helpers are tolerated only when their services are needed Primary helpers are older offspring Secondary helpers, which are unrelated, are permitted to stay when the additional fish they provide are needed Ayo 教材 (動物行為學 2010) 89 Ayo 教材 (動物行為學 2010) 90 Is it costly to help? Helping behavior has a cost Mongoose (貓鼬) helpers forgo feeding and stay at the burrow to baby-sit and guard pups from predators While the parents and others forage They lose weight Helping may even reduce survival Helpers among stripe-backed wrens that bring the most food die more quickly than other birds If it costly to help, why do it? (1) Why would an offspring delay dispersal? (2) Why would it help? Ayo 教材 (動物行為學 2010) 91 Mongoose (貓鼬) stripe-backed wrens Ayo 教材 (動物行為學 2010) 92 Stop and think: Imagine you are spending your graduate school years studying helping behavior in a little-known bird species You find that birds that remain behind on their natal territory to help their parents are far more likely to die than those that go off to breed on their own In your dissertation defense, you would like to make the argument that helping is costly How confident are you? What experiment(s) would you like to perform in order to increase your confidence? Ayo 教材 (動物行為學 2010) 93 Why should an offspring delay dispersal? Animals disperse to avoid inbreeding Or because of reproductive suppression by their relatives Or because of competition Animals exhibit philopatry because they are Adapted to the local conditions And familiar with the physical and social settings of home Dispersal is risky Small cichlid fish are eaten by predators when they disperse But, other options may be limited All available territories might be full Or all the available mates might be taken Ayo 教材 (動物行為學 2010) 94 Delayed dispersal: habitat saturation Florida scrub jays live in limited scrub habitat Every territory is filled A male acquires a territory by Inheriting a portion of his parents’ property Replacing his father after his death Subdivision of his father’s territory Defeating a breeder Successfully competing for territory of a breeder that has died If there is more than one son helping, the dominant one wins So, scrub jays help their parents because they are making the best of a bad set of circumstances Ayo 教材 (動物行為學 2010) 95 Territory availability and quality influences helping When no territories are available, juvenile acorn woodpeckers Remain at home and become helpers Not all territories are equal in quality It might be better to stay home if the only other choice is a poor-quality territory Some Seychelle’s warblers stay to help their parents rather than move to low-quality territories Ayo 教材 (動物行為學 2010) 96 Delayed dispersal: lack of mates Mates can also be a limited resource Splendid fairy-wren females suffer much greater annual mortality than do males Females are often in short supply Helpers tend to be males waiting for an available mate The wait can be as long as five years When females are scarce, male helpers are plentiful Ayo 教材 (動物行為學 2010) 97 Why should a helper help? Even if an animal does not have the opportunity to breed That does not automatically mean it will become a helper Many animals become “floaters” and wander around without a territory Even if an individual remains on its own territory It may not help There are other reasons beside lack of other opportunities that underlie helping behavior Helpers may get indirect fitness benefits Helpers may get direct fitness benefits Ayo 教材 (動物行為學 2010) 98 Helpers get indirect fitness benefits A helper benefits by increasing the production of relatives Older offspring help their parents raise siblings Kin selection can be important Helping in white-fronted bee-eaters did not provide direct benefits to the helpers (increased survival or chance of mating, and increased success in rearing young) But helping led to increased production of related young Pied kingfisher become secondary helpers when both their parents are dead Long-tailed tit helpers are failed breeders that help relatives Ayo 教材 (動物行為學 2010) 99 white-fronted bee-eaters Pied kingfisher Long-tailed tit Ayo 教材 (動物行為學 2010) 100 Helpers get direct fitness benefits A helper’s own lifetime reproductive success is increased by its actions Many groups have unrelated members Seychelle’s warblers help raise additional offspring Extra-pair copulation is common, so a helper may not have the same father as the offspring it helps Eggs may be deposited by other birds Indirect benefits are lower in this species Ayo 教材 (動物行為學 2010) 101 On the left is a nest built by a 4-year-old female Seychelles warbler with no experience. On the right is a nest built by a 4-year-old female that had experience in being a helper. Ayo 教材 (動物行為學 2010) 102 Direct fitness benefits for helpers They may add their own eggs to a nest They may be able to take over a territory budded off from the main territory They have a chance to practice their parenting skills They may mate with the original breeder later on Or if the original mate dies In pied kingfishers, secondary helpers (unrelated to the breeders) mate with the female they had previously assisted Ayo 教材 (動物行為學 2010) 103 Stop and think Helping behavior in humans has been studied from an evolutionary perspective Because human children are very dependent for years And mothers can give birth to children in rapid succession Most mothers require help from others In a review of studies across many cultures The presence of maternal grandmothers (the mother’s mother) and sibling helpers improves child survival Fathers improved child survival in only 1/3 of the studies What a hypothesis based on kin selection might explain this? Ayo 教材 (動物行為學 2010) 104 Bees are a eusocial (“truly social”) species Young worker honeybees feed the queen’s larval offspring Other workers maintain the hive and carry out the dead Older workers forage at flowers and communicate their location to their hive mates in an elaborate dance All workers are female Only one individual in the hive - a queen - lays eggs Eusocial species are defined by three characteristics Reproductive division of labor Cooperation in the care of young At least two generations share in the colony’s labor These characteristics also apply to some cooperative breeders Ayo 教材 (動物行為學 2010) 105 A eusociality continuum How evenly is reproduction is shared among group members? At one end, all or many of the group members breed At the other end, breeding is restricted to one or several group members Reproductive skew: describes the degree of eusociality The proportion of individuals that give up reproduction Eusociality is rare Occurs in ants, bees, wasps, termites, aphids, an ambrosia beetle, thrips, spiders and snapping shrimp Eusociality is extremely rare in mammals Ayo 教材 (動物行為學 2010) 106 Eusociality and cooperative breeding Predicted locations of cooperatively breeding species along the eusociality continuum • When reproduction is restricted to a single individual – Reproductive skew = 1 Ayo 教材 (動物行為學 2010) 107 Naked mole rats are eusocial Breeding is restricted to a single female - the queen Other adult females are smaller and don’t ovulate or breed Colonies contain overlapping generations of offspring Which are communally cared for Duties of nonbreeder members depend on their size and age Smaller member gather food and transport nest material Larger members clear the tunnels of obstructions The largest members dig tunnels and defend the colony Ayo 教材 (動物行為學 2010) 108 A queen naked mole rat, the only reproductive female of the colony, is resting on the workers that feed her and help care for the young. Ayo 教材 (動物行為學 2010) 109 Eusociality presents an obvious puzzle Members of eusocial species may relinquish all chances of reproduction Eusocial colonies can be described as “superorganisms” Members function efficiently together to ensure survival and reproductive success of the colony The most common feature of eusocial societies They are family groups What favors the evolution of eusociality? How do eusocial colonies function on a day-to-day basis? Ayo 教材 (動物行為學 2010) 110 Evolutionary origins of eusociality: haplodiploidy Haplodiploidy: an unusual genetic system in eusocial species The females are diploid, with two sets of chromosomes The males are haploid, with a single set of chromosomes Males grow from an unfertilized egg And produce sperm that are genetically identical to themselves When a male mates with a female The female offspring get a sampling of 50% of their mother’s DNA But all of the father’s DNA Ayo 教材 (動物行為學 2010) 111 Haploidiploidy changes coefficients of relatedness in a family Full sisters (share both a mother and a father) get half of their DNA from their mothers They share 50% of their maternally derived DNA Full sisters also get half their DNA from their fathers Because fathers are haploid and all sperm are identical This DNA is identical for every sister With the paternally and maternally derived DNA combined Full sisters share 75% of their DNA with one another (r = 0.75) Ayo 教材 (動物行為學 2010) 112 The genetic Ayo 教材 (動物行為學 2010) contributions of a male and female of a haplodiploid species to their offspring. Males are haploid and have only one set of chromosomes. They arise from unfertilized eggs. A female of a haplodiploid species shares more DNA with her full sister 113 The relationship between haplodiploidy and eusociality Haplodiploidy is not necessary for the evolution of eusociality Many eusocial species, such as termites, are not haplodiploid Haplodiploidy alone is not sufficient for the evolution of eusociality There are many haplodiploid species that are not eusocial Even in haplodiploid species that are eusocial Females very often mate with more than one male Multiple mating reduces the relatedness among sisters Ayo 教材 (動物行為學 2010) 114 Summary Benefits of group living: increased foraging success, decreased predation risk, conservation of heat, water and energy Costs: competition, disease, parasites, reproductive interference Altruism: performance of a service benefiting a conspecific at a cost to the one that does the deed - it is measured in units of fitness Hypotheses for the evolution of altruism: Individual selection: an individual receives direct benefits Kin selection: indirect fitness increases by helping kin Reciprocal altruism: the altruist’s final gain exceeds its cost Manipulation: animals can coerce others into helping them Ayo 教材 (動物行為學 2010) 115 Summary Relatives are identified through location, familiarity, phenotype matching, and genetics Reciprocal altruism occurs when: a recipient’s benefits exceeds the actor’s costs, future repayment arises, individuals recognize one another Cooperation in acquiring a mate: through displays, coalitions or alliances Cooperative breeding: altruism where a helper helps rear offspring not its own Eusocial species: an extreme example of cooperative breeding Division of labor, cooperation in caring for young, generational overlap in colony care Ayo 教材 (動物行為學 2010) 116 Summary Haplodiploid sisters are more related to each other than to their mothers or daughters By Hamilton’s Rule, kin selection is more likely to evolve Factors favoring evolution of eusociality: extended parental care, long-lasting sibling associations, sharing a central resource Eusocial individuals favor colony-mates that are more closely related Ayo 教材 (動物行為學 2010) 117 問題與討論 [email protected] Ayo 台南 NUTN 站 http://myweb.nutn.edu.tw/~hycheng/ Ayo 教材 (動物行為學 2010) 118