144 Master Notes PDF

Optimality Western knowledge production and “science” ○ Positivist perspective – “knowledge” is derived from the scientific method – unbiased examination of natural phenomena and their properties and relations. ○ “Knowledge” is “objective” ○ BUT who asks t...

Optimality Western knowledge production and “science” ○ Positivist perspective – “knowledge” is derived from the scientific method – unbiased examination of natural phenomena and their properties and relations. ○ “Knowledge” is “objective” ○ BUT who asks those questions? What questions are asked? Optimality ○ Cost benefit analysis Every trait has the potential to yield both a fitness BENEFIT and a fitness COST to the actor ○ Costs ○ Female Ormia ochracea are attracted to singing male crickets ○ Once females locate them, females lay maggots on or near the singing cricket ○ 1. Risks inherent to the behavior e.g., flamboyant displays = risk of parasites ○ 2. Costs that arise because animals have finite amounts of: time energy Resources spent on one behavior necessarily means fewer resources available for other behaviors/tasks = TRADE-OFFS Trade offs ○ e.g., energy spent attracting mates = less energy available for foraging efforts = less energy to use for somatic repair and maintenance ○ e.g., time spent caring for young = less time available for foraging = less time to defend territory = less time available to find other mates Cost benefit analysis ○ ○ ○  ○ Optimality theory=adaptations ○ Assumes traits maximize fitness benefit and minimize fitness cost ○ Because evolutionary theory predicts traits seen in populations at equilibrium will be those that maximize lifetime reproductive success (LRS) ○ animal will **maximize** fitness benefit – fitness cost ○ applies to fixed traits (evolutionary or developmental decision) ○ also applies to behavioral traits (‘flexible’ decision rules with minute-to minute input from environment) Optimality theory ○ Derived from economics ○ Powerful predictive tool in behavior: ○ Four parts: 1) Identify behaviors & range of possible strategies ("decisions") 2) Determine a common currency for costs & benefits--which specific component of fitness is affected Benefits = Energy gain from food Costs = Energy lost from food (# of trips + height of trip) 3) Consider intrinsic and extrinsic constraints on performance 4) Test model predictions Example ○ Observations: Crows mostly pick large whelks (3.5- 4.4 cm long) Keep trying until whelk breaks (many trips) Fly 5 m up at each trip ○ Optimal drop height? ○ Benefit = energy gain from large whelk 2.0 kilocalories ○ Cost = energy cost of breaking large whelk = F(# of trips, height of trip) ○ Fly 5m each trip→model prediction fails  ○ ○ Why do crows fly to 5m instead of 5.6m? Extrinsic constraints on performance Competition Ability to find dropped whelk Constraints ○ Restrictions on decision making or implementation of decisions ○ imposed by internal or external factors Short term optimality ○ Focus on immediate solution to problem in absence of other considerations Long term optimality ○ Interaction of short term decisions on overall lifetime reproductive success ○ Solutions that maximizes LRS, combining all relevant decisions (& constraints) Optimality critiques ○ Competing demands may not be predictable (assumes optimality for isolated behaviors) ○ Assumes animals have perfect information about their situation ○ Imperfect information = non-optimal behavior even if the decision rule is perfect. ○ Optimality theory has too many assumptions Types of factors that may affect Costs & Benefits of a trait: ○ abiotic environment ○ social environment ○ individual genetic quality ○ individual condition ○ So, the behavior that maximizes net fitness will vary as a function of such factors… Why do crows fly to 5m instead of 5.6m? Competition?  ○ Back to cricket example ○ ○ Starved→higher cost→lower optimal time singing Cost benefit analysis–implication ○ even though trait value ‘S’ may yield the highest possible benefit of all possible alternatives: ○ 1. Everyone may not do “S” all the time ○ 2. Some individuals may never do “S” ○ The most advantageous behavior will vary across individuals, time & space!!!  Case study ○ ○ High parasites: sing→die ○ Crickets in Hawaii face huge parasitization rates! ○ On Kauai most male crickets have evolved to be silent in about 10 years! ○ Evolution has continued to come up with new forms ○ Increase in costs of singing has led to the evolution of different signaling phenotypes Communication and Honest Signals Signals evolve to modify receiver behavior Communication ○ the process by which senders use specially designed signals or displays to modify the behavior of receivers Sender sends message Receiver decodes meaning Why are signals honest 1. Unforced honesty a. Fitness interests of sender & receiver coincide b. sender is honest, no problem for receiver c. Dance language of honeybees i. forager returns to nest, communicates information on location of food patch to nestmates ii. Fitness of forager increases if nestmates help to forage in correct place iii. Fitness of nestmates increases if they find new patch of food quickly iv. Efficient foraging increases inclusive fitness of forager and nestmate v. d. Recruitment calls of non-resident ravens i. a raven intrudes on a territory. ii. calls to recruit other non-residents to food  iii. fitness of initial raven increases with the arrival of other intruders (otherwise evicted by territorial pair) iv. fitness of intruders increases with discovery of new food source 2. Fitness in interests of sender and receiver in conflict a. Forced honesty b. Sender might benefit from deception c. Over evolutionary time, receivers “force” honesty because they only pay attention to honest signals d. Does the receiver benefit from information from signals? e. Courtship signals i. Courters signal to choosers to persuade it to mate ii. Fitness of courters increases if chooser permits mating (regardless of phenotype) iii. Fitness of chooser only increases if it mates with the best mate iv. f. Threat displays i. One individual signals to another to warn it away from some disputed resource (e.g., food, territory, mate) ii. Fitness of signaler is increased if intruder is convinced signaler is a formidable enemy iii. Fitness of intruder is increased if it can accurately assess risk of fighting with signaler and act accordingly g. Physical constraint on deceit i. Deceit physically impossible =index ii. Direct material link between signal and some underlying aspect of the sender's state or condition iii. Eg. carotenoid pigments in house finches 1. Deceit physically impossible? a. YES! Carotenoids CANNOT be synthesized must be consumed 2. Direct material link between signal and some underlying aspect of the sender's state or condition? a. Carotenoids are difficult to find  b. Only high quality males find sufficient quantities to produce bright pigment iv. Eg. MHC genotype= major histocompatibility complex 1. highly polymorphic genes 2. control immunological self/non-self recognition 3. more variability = enhanced immune system 4. Females of some species prefer to mate with males with dissimilar MHC haplotypes 5. MHC signals are directly related to an individual’s genetic makeup–honest 6. 7. 8. Affecting hormonal patterns of attraction Strategic constraints on deceit ○ Handicap signals=signals are costly ○ General handicap = variation in benefits Same amount of money to invest, good gets more benefits  Barn swallow tails e.g. red deer roars (Clutton-Brock and colleagues) e.g. threat displays of lizards (Ord, Martins, and colleagues) More resources→longer tail feathers Both birds can produce feathers (costs similar) Higher quality individuals have enough resources (territory size/quality) to raise more offspring to adulthood (benefits different) ○ Quality handicap = variation in costs Traits cost more for poorer quality individuals, same benefits Individuals with more resources can “afford” to invest in traits Stalk eyed flies Males have elongated eye-stalks that are longer than female eyestalks Females prefer males with longer eye-stalks Hypothesis: Individuals with more resources will have longer eyestalks than ones with poorer resources Males and females were raised with different amounts of nutrition  Prediction 1: Male eye-stalks size will be affected by resource availability, higher resources, higher stalk Prediction 2: Eye-stalk size in females will not be affected by resource availability; other important traits will not be affected by resource availability ○ ○ What drives variation between individuals Predictions from handicap models ○ Signals are honest Grey tree frogs Males call Females approach and mate Females strongly prefer long duration calls Hypothesis: long duration calls are an honest signal of heritable high viability in males driven by variation in costs  Offspring of long-calling male had better performance than offspring of short-calling males ○ Signals have costs and benefits to productions Prediction 2: long-duration calls are more costly long-calling males attend fewer choruses /season long-calling males spend less time calling per night long-calling males alter absolute call duration as a function of competition Honesty despite conflict? ○ senders produce two types of signals ○ 1. Honest signal 2. Dishonest signal ○ Variation in response of receivers 1. Pay attention to honest signals, ignore dishonest 2. Pay attention to dishonest signals, ignore honest 3. Pay attention to all signals 4. Ignore all signals ○ over evolutionary time, selection will favor receivers that ignore dishonest signals… ○ EXPECT: “forced honesty” in signaling, despite conflicting fitness interests Examples ○ Female jacanas compete for mates (males choose based on female brightness) Brighter females lay more eggs Diet is not correlated with female brightness General handicap ○ Treehoppers compete for mates using horns Treehoppers raised on better diets have larger horns Treehoppers raised on better diets have no fecundity differences Variation of cost First look at if it is costly, then see variation  Honest signals will be favored Dishonest signals When will you find deceit? 1. Exploitation a. If it is not possible to distinguish deceitful from honest communication, b. receivers will still be selected to pay attention as long as the NET effect on fitness is positive i. low frequency of deceitful signals ii. costly to ignore those signals that are honest c. Femme fatale fireflies i. Female fireflies produce species specific flashing patterns that attracts mates ii. Female Photuris fireflies mimic the call of female Photinus fireflies iii. Male Photinus are attracted to female Photuris and are EATEN by deceitful females d. Deep sea angler fish i. “Lure” resembles small prey ii. Attracts hungry fish to within striking distance of predatory anglerfish  iii. Cost too much to ignore things that don’t resemble fish 2. Novel environment a. Responses to signals is maladaptive (beetles on the bottle) b. Female color (“brown”) is trigger for males to attempt mating c. Female’s color is now NOT unique d. Many human-made items (beer bottles) have similar color (= ‘illegitimate signalers') e. Males try to mate with beer bottles Mating Systems Paradise birds: leks ○ Males go to a lek, show off and mate with a group of females ○ No giving of resources Shrimp: monogamy Mating systems ○ The study of mating systems has historically recapitulated cultural biases about sex and gender roles ○ Every possibility is found in nature but we focus our attention on animals that are “like ourselves” and/or reinforce our biases ○ western, European, patriarchal Social mating system ○ based on observed interactions (mating, parental care) between individuals Genetic mating system ○ based on paternity and maternity patterns Monogamy, polygyny, polyandry, polygynandry  ○ Monogyny ○ Social mating–based on observed interactions (mating, parental care) between individuals ○ 90% of birds are socially monogamous ○ Only 3% of mammals are socially monogamous ○ Genetic mating–based on maternity and paternity 90% of 180 social monogamous species are genetically polygamous ○ Genetic monogamy is relatively rare in nature Prairie voles Clown shrimp Fiordland crested penguins Marmoset ○ Why would any individual be monogamous? Differential reproductive investment ○ How much does an individual invest in offspring? ○ Parental care (more on this later)  ○ Gametes ○ Other ○ For sexually reproducing animals, degree of reproductive investment drives the evolution of behaviors that maximize fitness If individuals differ in their degree of reproductive investment, behavioral differences between them may arise ○ Across animals, there is a vast diversity of reproductive investment Investment in gametes ○ Individuals that produce small gametes will be called male ○ Individuals that produce large gametes will be called female ○ Bateman principle ○ Individuals with relatively large gametes can often increase success by investing heavily in offspring favoring monogamy under certain conditions ○ Individuals with relatively small gametes can increase success by mating with many individuals with large gametes Male monogamy 1. Enforced monogamy ○ Individuals attack mates that attempt polygyny ○ Social & genetic monogamy ○ Mates attack their mates if they approach neighboring potential mates ○ If males try to attract further mates by releasing more pheromone, females attack males 2. Mate assistance hypothesis a. Individuals get net benefit from providing parental care b. Male care increases # of surviving offspring c. This hypothesis could explain why monogamy is so much more common in birds (90%) than mammals (3%) d. Birds: i. Males can incubate (brood) eggs & feed nestlings ii. Males can make significant difference in offspring survival  e. Mammals: i. Only females can gestate young ii. Only females can lactate iii. Thus positive effects of male care are more restricted to general supply and protection 3. Mate guarding a. Payoff for guarding is high i. last-male fertilizes most eggs ii. unguarded females frequently remate iii. Restrict access of other males b. Few other mating opportunities exist i. male-biased OSR ii. difficult to find females c. Australian black widows (redbacks) i. 85% male mortality during mate searching ii. Successful males commit self sacrifice (monogamous males!) iii. Female eats that male iv. Males that are eaten sire 90% of offspring 1. If male not eaten, females will remate 4. Mating systems 2 Monogamy? ○ Socially monogamous species may not be genetically monogamous if partners engage in Extra Pair Copulations (EPC’s) ○ Males that engage in EPC’s can increase fitness by siring offspring that will be cared for by other males (see differential reproductive investment) ○ While away from nest, female partner may be engaged in EPC’s of her own  ○ Good genes hypothesis ○ Blue tits ○ Mainly monogamous (socially) ○ 2 year study 39-43 nesting pairs 277 male visits to neighbors 206 female visits to neighbors ○ No foraging during visits Trying to find other mates? ○ Courtship or copulation with neighbor observed during visits ○ More attractive→females study Less attractive→females leave/cheat More attractive→less EPC ○ Females visit neighbors who have high parental care  ○ ○ No EPY(attractive males)-->get more female visits ○ Attractive male→no EPY (wife doesn’t leave)+more visits from neighbor females ○ Males that had fewer EPY were more likely to survive to the next breeding season = higher quality ○ Males that had fewer EPY had more surviving offspring in the following year ○ These data support the hypothesis that female blue tits engage in EPC’s to gain good genes benefits for their offspring General framework for understanding mating system evolution ○ Differential reproductive investment determines the extent to which polygamy increases reproductive success ○ Costs and benefits of defending benefits ○ Amount of parental care required for successful rearing of young  →mating system ○ These individuals can monopolize resources clump ○ Similar effects if potential mates clump due to benefits of group living  ○ Synchronous or brief receptivity ○ Insufficient time to mate with many mates ○ Low EPP Asynchronous or prolonged receptivity ○ Ample time to mate with many mates ○ High EPP Polygyny: females monogamous, males mate multiple One male mates with many females (females are socially monogamous) Expected where: ○ High EPP ○ Low benefit to male care of young Type of polygyny depends on ecology/biology: ○ female defense polygyny ○ resource defense polygyny ○ scramble polygyny ○ lek polygyny Female defense polygyny ○ Females form groups ○ Males control access to females directly ○ Elephant seals Female ‘haul out’ onto favorable shoreline to give birth Mate shortly after birth Resource defense polygyny ○ Males control access to females indirectly by monopolizing critical resources ○ Most often, males defend a feeding territory ○ Guanaco Social groups = 1 male and 15 females & offspring live on year-round feeding territory defended by male young males spend 3 -4 years in ‘bachelor’ groups, then challenge or establish own territory  Scramble polygyny ○ Males actively search for females without competition ○ Mate with as many females as possible in short time e.g., many frogs and rodents ○ Asynchronous or prolonged female receptivity ○ 13-lined ground squirrel Females sexually receptive for only 4 – 5 hours, but at different times in a 2 – 3 month breeding season Males search widely for receptive females & remember location of soon-to-be receptive females Timing is everything! 75% of female’s eggs fertilized by 1st mate Lek polygyny ○ Males defend small display territories (no resources) ○ Females approach leks and choose based on male display characteristics ○ Leads to some of the most extreme skew in reproductive success of any mating system ○ Asynchronous or prolonged female receptivity ○ Polygyny ○ One male mates with many females ○ Females are socially monogamous ○ Why would a female choose polygyny over monogamy? Polygyny threshold model  ○ ○ ○ Fitness is equal, poor but monogamy vs. good but polygyny ○ Polygyny threshold The point at which a female may do better to join an already-mated male with a good territory rather than joining an unmated male with a poor territory ○ Qualities vary Eg. food availability food quality amount of cover predation risk nest-building sites nest-building substrate Predictions of polygyny threshold model ○ 1. Females pay a cost for polygyny so would prefer monogamy if territory quality is equal (critical) ○ 2. Females will choose polygyny if polygynous territory quality is sufficiently high (critical) ○ 3. Female mate choice influenced by territory quality ○ 4. Polygyny more common in patchy environments than homogeneous environments More variation in territory quality Test #2. Red winged blackbirds ○ Territory quality depends on depth of water below nesting site ○  ○ ○ ○ Test #1 Individuals with relatively large gametes can often increase success by investing heavily in offspring favoring monogamy under certain conditions ○ Individuals with relatively small gametes can increase success by mating with many individuals with large gametes ○ Why should individuals that produce relatively large gametes be genetically polygamous? Female Polyandry Enforced polyandry  ○ Reduction of infanticide ○ Reduction of harassment Bet hedging ○ Fertility insurance ○ “Trading up” Increased resources Enforced polygamy ○ In water striders, the level of copulation attempts (“harassment”) varies with the operational sex ratio (OSR) Operational sex ratio is the proportion of breeding males to females ○ Accepting copulations is less costly in many situations (convenience polyandry) Females can hunt while copulating Copulating females attract less predators Indirect benefits–bet hedging ○ Mating multiply can increase reproductive success in situations where mates are selected sequentially Fertility insurance At least one male fertile Trading up – best mate possible over breeding season Always mate with the better male ○ Much increased response to a showy male after exposure to plain male ○ Cryptic female choice is a process where females “choose” the sperm of one male over another after they have already mated  Direct benefits ○ Cosmosoma myrodora moths acquire defensive compounds by feeding on poisonous plants ○ Males discharge filaments with defensive compounds during copulation which protects females from spiders ○ Male seminal fluid contains defensive compounds Why do females multiply mate ○ Enforced polyandry Reduction of infanticide Reduction of harassment Reduced costs of multiple mating ○ Bet hedging Increased indirect benefit Fertility insurance Trading up ○ Increased resources Increased direct benefits Polyandry One female, multiple males(males socially monogamous) Expected where ○ High EPP ○ Low benefit to female care of young High benefit of male care of young ○ Emancipation from care Ability to capitalize on EPP Types ○ Male defense polyandry  ○ Resource defense polyandry In birds, Female reproductive output is limited by # of offspring she can produce in a season 1. Frequent, unpredictable clutch failure 2. Variable food availability 3. Success decreases with number of eggs per clutch a. More eggs, less parental care, lose fitness Females can increase success by producing a large number of clutches, but can not provide care ○ ○ Male defense polyandry ○ Phalarope ○ Females brightly colored ○ Males dull–care for young ○ Females fight over males, produce up to 4 sets of eggs per breeding season ○ Exclusive male care of eggs (even when fertilized by other males) ○ High egg mortality (ground nesting), adult mortality due to starvation not uncommon  Resource defense polyandry ○ Jacana ○ Females setup+defend territories on floating mats of vegetation ○ Several males per territory ○ Exclusive male care of eggs ○ High rate of predation on eggs ○ Female infanticide at territory take-over Parental Care Why care? Parental investment ○ Benefits Increased survival and success of offspring ○ Costs Decreased likelihood of successful future reproduction Physiological costs Opportunity costs Foraging Other matings ○ Trade-off between current and future reproduction ○ Prediction of evolutionary theory: parental care will only evolve if it results in a net fitness increase Factors affecting level of investment (post birth) 1. Environmental factors a. K selected=stable environments b. Key factor affecting success of offspring: intense intraspecific competition c. Success elements i. Larger body size ii. Slower development iii. Longer lifespan d. Iteroparity i. Small # of young that receive intensive care ii. Relatively low mortality rate of young e. Produce offspring in successive bouts f. Parents’ strategy: intelligent, autonomous, but expensive offspring g. development of traits necessary for success after birth: learning physical abilities h. Development depends on food that is scarce/difficult to obtain i. High benefits for parental investment (large increase in success of current young) j. Altricial young i. Young born in relatively immature or helpless form  ii. Require care iii. K selected old world monkeys ○ Period of care: infancy: 18 – 40 months juvenile phase: 6 – 7 years 25% of lifespan !!! ○ Fitness depends on: Flexible behavior Large behavioral repertoire Functioning in complex social systems Large, developed brain African wild dogs ○ Fitness depends on: Functioning in complex social systems Group hunting Black eagles ○ Fitness depends on: Hunting ability Large body size ○ Juveniles fed by parents long after they could feed themselves 2. R selected=fluctuating environments a. Key factors affecting success of offspring: environmental fluctuations, predation b. Smaller body size c. Rapid development d. Shorter lifespan e. Semelparity i. large # young receive little or no care ii. relatively high mortality rate of young f. Production of offspring once in lifetime g. Parents’ strategy: large # of relatively cheap offspring h. Some may survive i. Low benefits for parental investment i. Little increase in success of current young j. Precocial young i. young born in relatively advanced developmental stage (relatively independent from birth) ii. Require relatively little care k. Coho salmon i. A single explosive breeding event then parents die ii. No care, large #’s of fry l. Redback spiders i. Thousands of offspring from one mother ii. Tiny, no care after hatching iii. High mortality rates for spiderlings iv. Spiderlings able to catch prey autonomously immediately These are gross simplifications ○ Continuum likely  ○ Exceptions ○ Amount of investment can change over time ○ But basic idea accurate: biotic/abiotic factors can affect selection on best traits for offspring some traits require care to develop Factors affecting level of investment ○ r-selected, K-selected ○ e.g., California gull ○ Relatively long-lived (15 years) ○ Food availability unpredictable year to year ○ Strategy = 1 or 2 offspring in each of many years ○ As parents age, they: lay more eggs feed chicks more food defend chicks more vigorously ○ likelihood of surviving for future reproductive bouts decreases with age = cost of parental investment decreases: SENESCENCE Residual reproductive value RRV ○ expected value of future reproduction ○ i.e., how many surviving offspring are you likely to have in the future? ○ older=Lower RRV=lower costs of parental investment ○ some factors affecting RRV: age health time of season (esp. for short-lived animals) Eresid spiders ○ High mortality of offspring→r-selected→hundreds of offspring ○ Precocial spiderlings ○ Spider adult longevity: max one summer ○ Time to produce only one egg sac→lower RRV ○ Suicidal maternal care Mother undergoes auto-digestion of internal tissues Offspring feed from leg joints Offspring consume female Who cares? In species with parental care: ○ Some have exclusive female care Some have exclusive male care Some have male OR female care Some have biparental care (simultaneous care from both parents) Hypothesis ○ 1. Sex with higher initial investment ○ 2. Sex with lower cost/benefit ratio Lower costs  Higher benefits Hypothesis 1: ○ Sex with higher initial investment ○ Females more likely to care because they have already made substantial investment in offspring (e.g., eggs) ○ (a) does not explain species with relatively large eggs but male care e.g., mallee fowl, some frogs & fishes ○ (b) logically incorrect: “Concorde fallacy” ○ Concorde fallacy British politicians justified continued (above budget) expenditure on supersonic aircraft to minimize wastage of previous expenditure But this was “throwing good money after bad”, NOT predicted by evolutionary theory Over evolutionary time, parents should develop decision rules to adjust current expenditure to prospective net fitness payoff, NOT past costs Hypothesis 2: sex with lower cost/benefit ratio–CORRECT ○ Care is costly to both sexes, but offspring need care ○ Net fitness payoff for some care is greater than for desertion ○ Prediction: Care will evolve in the sex for which care yields greatest net fitness increase ○ Costs opportunity costs - lost opportunity for additional matings Male fitness increases more with additional matings than females On average: cost to male >cost to female ○ Benefits–sperm competition In species where sperm competition is likely Female is guaranteed offspring are hers Male has some risk of investing in offspring of another male (no benefit) On average, benefit to male < benefit to female ○ Prediction: Female care should be more common in species with internal fertilization (male confidence of paternity is low) ○ But male care should be more common in species with external fertilization (male can see his sperm fertilize the eggs he cares for) ○ Can this hypothesis also explain flexible patterns of care? ○ Studies of St. Peter’s fish Mouth-brooding cichlid fish Biparental care Uniparental-female care Uniparental-male care(facultative)  Females take longer than males to spawn again after care-giving Cost to male < cost to female Both sexes lose weight as a result of care-giving body weight is closely related to gamete production→gamete production constrains female but not male reproduction (sperms in excess)  Why uniparental male care? overall, parental care is more costly for females than males in this species ○ What about uniparental female care? change in context can change relative cost of care for males Prediction: shift to female-biased OSR = more mating opportunities for males, inc male costs for caring, less male care Increased costs for males leads to increased desertion, female is left with brood care Additional notes: sometimes male care does not reduce mating opportunities ○ Stickleback males ○ Male defends nest with eggs ○ Females prefer to lay where eggs already present (honest signal of parental ability)  ○ Males can brood 10 clutches in nest (2 weeks) ○ Females can only produce 7 clutches in 2 weeks ○ So OSR still male-biased despite increased PI ○ Males benefit from caring for eggs Parental Care 3 Parent-offspring conflict–sibling rivalry Care for one offspring decreases care available for future (or other current) offspring Parent equally related to each offspring (r = 0.5), so care dispensed equally Offspring more closely related to itself (r = 1.0) than to sibling (r = 0.5), seeks more care than parent wishes to give ○ Siblings, parents r-0.5 ○ Aunts, uncles, niece 0.25 How much care ○ ○ 2 times because parent is half related to their offspring ○ Half sibling =4x Inclusive fitness ○ Fitness benefits Direct Fitness = fitness gained through your own personal reproduction Indirect fitness = fitness gained through your own kin’s reproduction ○ Inclusive fitness = the total genetic contribution of an individual (includes both direct fitness and indirect fitness) Number of offspring X relatedness of offspring  ○ ○ 1st S*: optimum for parent ○ 2nd S*: optimum for offspring Parent-offspring conflict ○ Gerbils juveniles resist being removed from breeding burrows by their mothers beat at mother with forepaws, resist being picked up. ○ Chimpanzees females may avoid breast feeding older offspring (weaning) juveniles who are repeatedly denied the chance to nurse have ‘tantrums’ (kick, scream, attempt to attack mothers) Sibling rivalry ○ Siblings can be in conflict over parental care ○ each infant favored to acquire as many resources as possible until indirect fitness costs outweigh direct fitness benefits (net increase in inclusive fitness) ○ Investment in current offspring decreases fitness of subsequent offspring  Siblicide ○ Sand tiger sharks Kill siblings during gestation ○ Spotted hyenas Kill or injure siblings ○ Blue footed booby Facultative siblicide(every now and then) Later in development 2 or 3 eggs laid hatch 4 days apart larger chick sometimes attacks and evicts smaller chick from nest over period of weeks ○ Black eagles Obligate siblicide Early in development 2 eggs laid hatch 3 days apart older chick begins attacking younger chick as soon as it hatches, kills it within days only 1 chick is reared to adulthood ○ When does siblicide occur 1. Resource competition 2. Food in small units (monopolizable) 3. Spatial confinement (e.g., womb, nest, den) 4. Weaponry(sharp teeth) 5. Competitive disparities Parental complicity ○ In siblicide birds, parents lay one more egg than the number of offspring that typically survive... …why do they do it?? doesn’t this set the stage for siblicide? ○ Insurance egg hypothesis 1. Obligate siblicide–siblicide has to happen 2. High risk of nest failure 3. Parental complicity–parents make situations easier for one sibling to kill the other 4. Siblicide unrelated to food limitation ○ Extra reproductive value hypothesis 1. Facultative siblicide–every now and then 2. Variable resources, and variable nest success 3. Parental complicity Easier to kill siblings 4. Siblicide related to food limitation Insurance egg hypothesis ○ Parents lay an extra egg because it provides reproductive insurance against the complete failure of a clutch  ○ Reproductive Insurance: against low hatching success (egg predation, low fertility) against early death of one chick ○ Prediction: obligate siblicide (whenever all chicks survive past hatching, inferior chick is killed) Parental complicity ○ Both hypothesis predict Parents should ensure that ‘winning’ siblings can kill competitor with minimal cost ○ parental behavior & physiology leads to competitive disparities between siblings 1. Asynchronous brooding a. eggs are laid over several days (α, β, then γ) b. parent begins brooding as soon as each egg is laid early-laid eggs hatch earlier = hatching asynchrony c. Early hatched chicks larger d.  e. f. Parents are hatching at optimal level to ensure maximal survival 2. Differential hormone provisioning of eggs a. testosterone increases competitiveness & aggression level in juvenile chicks b. c. Later eggs: less aggression Extra-reproductive value hypothesis ○ Siblicide should be more common under food limitation in facultatively siblicidal species ○ Test: deprive senior chick of food by taping neck observe aggression towards junior chick observe which chick is fed more  ○ ○ Less resources for senior chick→more aggressive Sibling rivalry ○ parent apparently prevents senior chick from killing junior chick ○ suggests: facultative siblicide increases parental fitness in this species, but chick may always do better with fewer competitors Territoriality and aggression Why be territorial? –Higher Benefits / Lower Costs! What determines aggressive contest success? Resource Holding Potential Resource Potential Value Arbitrary Rule ○ Bourgeois Strategy/ Desperado Effect What determines aggressive contest dynamics? Alternative Strategies Conflict resolution–what determines contest success 1. Resource holding potential RHP a. Ability of an animal to defend a resource b. What is RHP? i. Size, energetic reserves, mobility, weight, weaponry size c. Animal with larger relative RHP wins contest e.g. Red Deer d. Annual rut where males defend feeding territories e. Males fight by roaring and escalate to direct contests using their antlers f. Heavier animals more likely to win territorial contests g. 2. Resource Potential Value (RPV) a. “value” of resource determines ability of animal to defend resource b. State of animal often determines resource “worth” c. Animal who “needs it more” fights more aggressively and is more likely to win contest i. e.g. Juvenile jumping spiders ii. Fight harder to get valuable resources d. Spiders develop by molting e. Spiders are weak and immobile during and shortly after molting i. Molt in silken nests (territory) f. Nests are more valuable the closer a spider is to molting g. PREDICTION: Spiders closer to molting will be more likely to win territorial contests regardless of relative size, weight, etc.  h. 3. Ownership of resource a. Arbitrary rule – owner ALWAYS wins regardless of qualities of owner or intruder b. Predicted by game theory c. Ownership itself can be used to settle contests Evolutionary game d. Three players with three strategies Hawk – always attacks. Often hurt in attacks against other hawks Dove – never attacks. Never hurt, random winner against other doves Bourgeois – Always win when owner (hawk), always lose when not (Dove) e. f. Bourgeois strategy i. Male fight for sun-spot territories ii. Experiments demonstrated that owners ALWAYS won regardless of any other measured trait (Davies 1978) iii. BUT new evidence suggests that better males are usually the ones that are holding the territories. iv. Greater RHP/RPV and not arbitrary rule? (Kemp and Wikuld 2003) g. Desperado strategy i. Animals will fight to the “death” regardless of situation ii. Benefits of winning much (much) higher than costs of losing iii. No benefit to “living and fighting another day”  iv. Named after depiction of desperado’s in the American West v. Gladiator frogs vi. Males and females fight using thumb spine weapons vii. During breeding season, males and females fight for very limited breeding pools viii. Death and catastrophic injuries very common Contest dynamics How does an animal make decisions during contests? ○ What determines how long an animals persists? ○ What determines if an animal escalates aggression? Three different proposed models on animal contests 1. Mutual assessment 2. Self assessment 3. Cumulative assessment 1. Mutual assessment a. animal makes decision on whether to persist based on relative differences in resource holding potential b. Males defend territories in aerial battles Head width is a measure of RHP 2. Self assessment a. animal makes decision on whether to persist based on only on its own RHP Mutual vs self assessment ○ Mutual assessment is based equally on RHP of winners and losers ○ Self assessment based ONLY on RHP of loser ○ ○ Strong loser fight for a long time trying to win ○ The majority of animal contests follow self assessment rules Why? ○ Measure of one’s own ability is more reliable than estimating another's 1. Unreliable signals from opponents (opponents will often “bluff”) 2. Errors in assessing opponent RHP  3. Costs associated with evaluating opponents Mutual assessment ○ Self assessment ○ Males mount females and guard them from other males ○ Unpaired males attempt to pull of males from females Male weight measure of RHP ○ Winner no correlation 3. Cumulative assessment animal makes decision on whether to persist based on its own RHP BUT costs accumulate differently Higher RHP animals inflict relatively more costs Lower RHP animals bear relatively less costs Higher energy bars→loser persist longer  How do you tell the difference between Cumulative Assessment and Mutual Assessment? ○ In both models, same loser/winner duration pattern is predicted ○ Compare size matched contests Prediction: (1) In cumulative assessment models, fights between smaller size matched pairs will be shorter than larger size matched pairs(higher energy bars); (2) In mutual assessment, no relationship will be found between size-matched contests ○ Males defend feeding and nesting territories ○ Male claw size a measure of RHP Alternative strategies Dawn beetles ○ Some have long weapons/horns ○ Some don’t have horns Alternative mating strategies: guard vs. sneak How can alternative behaviors coexist in populations? 1. Conditional strategies=best of a bad job 2. Genetic polymorphism a. Evolutionary stable state 3. Mixed evolutionarily stable state Strategy ○ A genetically distinctive set of rules for behavior exhibited by individuals ○ May include several tactics Tactic ○ One of the options that may be exercised by an animal whose behavior is guided by a strategy  Payoff ○ Net benefit of a behavior Evolutionarily stable strategy ○ A strategy which when adopted by most members of a population cannot be invaded by an alternative mutant strategy 1. Conditional strategy a. Condition or environment-dependent strategy b. 1 strategy with 2n tactics c. Tactics usually do not have equal payoffs d. Maintained by condition or status-dependent selection e. f. Switch point: 2 lines cross 2. Genetic polymorphism a. 2n strategies b. Genetic basis, No change of strategies c. A proportion p use strategy A d. A proportion 1-p use strategy B e. Maintained by negative frequency dependent selection f. g. At EQ: equal payoffs=evolutionarily stable  h. i. Rare one has higher fitness j. EQ will be stable as long as i. Fitness lines cross ii. At least one strategy is negatively frequency dependent 3. Mixed evolutionarily stable strategy a. b. Rare have higher fitness c. Natterjack toad i. Males become satellites when they hear neighbors are much louder ii. Will call if neighbors disappear iii. Start to call once they grow larger Research lecture Sensory drive ○ “Sensory Drive” Hypothesis = Natural selection drives the evolution of signals that are designed to work effectively ○ Sensory drive works through selection on 1. Habitat Transmission: selection for signals that pass through the environment without degrading  2. Perceptual tuning: selection for sensory systems that are adapted to detect signals in the environment ○ The environment of an individual determines the effectiveness of its behavior The natural world is complex - animals that communicate via substrate borne vibrations may have many available signaling channels Signal design ○ Do different signaling strategies exist to deal with this channel complexity/heterogeneity? ○ Sensory drive ○ “Specialist” signaling strategy Increase signal reliability at the cost of signalling opportunity, as only a subset of possible sites within the habitat would be suitable Jumping Spiders ○ “Generalist” signaling strategy?