Nov 25 Social Class 2

With haplodiploidy:: 

With haplodiploidy: A worker’s genes are passed on more quickly through sisters than offspring b/c of higher degree of relatedness (inclusive fitness ) Females should increase inclusive fitness more by rearing female siblings (r=.75) vs. producing their own offspring (r=.5) hence, sterile worker caste Also, have ability to recognize closest kin and selectively care for them (sisters vs. brothers)

Haplodiploidy Hypothesis: 

Haplodiploidy Hypothesis Workers’ investment should be skewed towards raising female sibs (r=.75) vs. male sibs (r=.25); predict 3X investment in female sibs Trivers & Hare (1976): worker ants invest in female sibs 3:1, except in “slave-making” species, ratio 1:1 Supports kin selection/haplodiploidy hypothesis as explaining eusociality

Problems w/ Haplodiploidy Hypothesis:: 

Problems w/ Haplodiploidy Hypothesis: Assumes 1 queen and 1 male mating Queens mate multiple times (reduces relatedness among sisters) Some eusocial species have multiple queens “local mate competition” may cause bias in sex ratio if males compete for matings

Problems w/ Haplodiploidy Hypothesis:: 

Problems w/ Haplodiploidy Hypothesis: Some eusocial species are diploid (e.g., termites, naked mole rats) – thus, r=.5 to sibs and offspring Not all Hymenopterans are eusocial, despite being haplodiploid Thus, haplodiploidy is neither necessary nor sufficient for eusociality Note: When present, haplodiploidy does not maintain eusociality – through evolution, it is obligatory (i.e., bees need the hive, etc.).

Eusociality without Haplodiploidy: 

Eusociality without Haplodiploidy The naked mole rat - 2 castes: “workers” – Non-reproductive adults: dig tunnels, find food “non-workers” – Reproductive female (queen) and several reproductive males: breed, keep young warm Native to Africa, droughts common, live in underground tunnels and eat tubers, can only dig when wet, need many individuals to dig to find enough food – ECOLOGY promotes eusociality (Fig. 19.18)

Other Explanations…: 

Other Explanations… Eusociality among kin may evolve due to same selection pressures as with sociality, e.g.,: Family associations in food-rich habitat Slow development High-risk dispersal Opportunities for inheritance (e.g., nest, harem) Advantages of group defence and foraging

Helpers at the Nest: 

Helpers at the Nest In some bird species (e.g., Florida scrub jays, pied kingfishers), offspring from previous years help their parents – feed and protect younger siblings instead of reproducing; (sometimes low r kin help) Beneficial: Number of young fledged goes down if helpers removed Altruism through kin selection? Or, beneficial to individual (selfish)?

Helping at the Nest: 

Helping at the Nest Why help vs. have your own offspring? Habitat “saturated” with breeders (no room) May be better to wait for a high quality territory (inherit it), than leave for a low quality one May not be able to leave group location (e.g., limited food resources elsewhere) No mates available Life history characteristics: Small clutch size and low adult mortality

How Do Helpers Benefit?: 

How Do Helpers Benefit? Increase inclusive fitness if helping kin Enhance likelihood of future breeding (gain mate if primary male dies - unrelated males) May increase own survivorship (access to resources, lower risk of predation in a group) May gain useful reproductive experience (care of young) & may be reciprocated in future So, kin selection may explain helping through increased inclusive fitness, but many other factors

Evolution of Human Social Systems: 

Evolution of Human Social Systems Are evolutionary explanations of human social behaviour valid in any sense? Possible evidence for kin selection: Violence against step-children (Daly & Wilson, 1981-1996) 76/98 murders were committed by non-relatives living in the home (usually spouse) Step-children also more often victims of child abuse and child homicide than genetic offspring “blood” relatives 10x less likely to kill each other

Cooperation in Non-Kin: 

Cooperation in Non-Kin Types: Reciprocal altruism (reciprocity) Recipient benefits, donor’s fitness decreased; later, roles reversed e.g., vampire bats Model: Prisoner’s Dilemma Mutualism (and/or symbiosis) Mutually beneficial e.g., symbiotic fish

Reciprocal Altruism in Vampire Bats: 

Reciprocal Altruism in Vampire Bats Can survive only two days without feeding If unsuccessful, will beg food from a roost-mate If willing, altruist will regurgitate blood for recipient Later, will repay favour

Reciprocal Altruism (RA): 

Reciprocal Altruism (RA) Kin selection cannot account for cooperation in non-kin… How could RA in non-kin have evolved? A “cheater” could beg blood, then refuse to return the favour = donor may die (unless it finds another donor), cheater lives Why don’t individuals evolve to act selfishly?

Reciprocal Altruism (RA): 

Reciprocal Altruism (RA) Axelrod & Hamilton (1981), others… “Game theory” – two players interact with goal of maximum individual gains Model for evolution of reciprocal altruism = “Prisoner’s Dilemma”

Prisoner’s Dilemma: 

Prisoner’s Dilemma 2 criminals brought in for questioning (separated) Police have evidence of minor crime (2-yr sentence) Criminals also suspected of major crime (10-yr sentence) Both are offered a deal…

Prisoner’s Dilemma: 

Prisoner’s Dilemma Testify against other (“defect”) and gain immunity (0 yrs), other serves 12 yrs (major+minor) If both deny knowledge of major crime (cooperate w/ other) each serves 2 yrs (minor) If both accuse each other, each get 10-yr sentence (major)

Prisoner’s Dilemma: 

Prisoner’s Dilemma If neither squeals (cooperation), get a “reward” (R) = 2 years, for minor crime only (saves 10 years) If both squeal (defection), both get a punishment (P) = 10 years, for major crime only (saves 2 years) If one cooperates and one defects, defector (the “rat”) is set free and gets best possible reward (T) = 0 years, T = temptation to defect. Other prisoner gets sucker’s payoff (S) = 12 years (combined sentence for both crimes)

Altruism in Non-Kin: A model: Prisoner’s Dilemma: 

Altruism in Non-Kin: A model: Prisoner’s Dilemma Player A’s Payoffs below(“points” = years saved /12). Note T > R > P > S

Prisoner’s Dilemma: 

Prisoner’s Dilemma On a single encounter, best strategy is to defect; because if other player cooperates, T>R, and if s/he defects, P>S Player A defects, player B cooperates A = 12 points, B = 0 points However, not true for multiple encounters: Once bitten, twice shy… Next encounter, A defects, B defects A = 2 points, B = 2 points

Prisoner’s Dilemma: 

Prisoner’s Dilemma On third encounter, A defects, B defects A = 2 points, B = 2 points Over 3 “turns”: A = (12+2+2) = 16 points, B = (0+2+2) = 4 points What if they had cooperated each time? 10 points each x 3 turns = 30 points each In long run, (w/ multiple encounters), better to cooperate…but not be taken advantage of!

Evolution of Reciprocal Altruism: 

Evolution of Reciprocal Altruism So, best strategy for solving Prisoner’s Dilemma is: “Tit-for-tat” strategy – start off “nice” and do what other does; do not tolerate cheating (retaliate); but be quick to forgive if other cooperates in future May be an evolutionarily stable strategy (always do better than just defecting or just cooperating) Shows how reciprocity based on cooperation in an asocial group can come about

Evolution of Reciprocal Altruism: 

Evolution of Reciprocal Altruism Requires these conditions: Longer-lived animals, such that future opportunity for repayment likely (multiple encounters) Altruist and recipient must be able to recognize one another; identify and refrain from helping cheaters Benefit to recipient greater than cost to altruist (but both individuals benefit in the long run)

Mutualism (a form of symbiosis): 

Mutualism (a form of symbiosis) Cooperation between 2 different species Both benefit, neither harmed Therefore, not considered altruism (fitness of both organisms is increased) Consider how the following complex relationships could have evolved…

Slide24: 

Clownfish (genus Amphiprion) dwell among the tentacles of tropical sea anemones. Protects anemone from anemone-eating fish In turn, stinging tentacles of anemone protect fish from its predators (a special mucus on fish protects it from getting stung).

Slide25: 

Honeypot ants feed and care for aphids, “milk” them for their honeydew secretions (by stroking them gently with their antennae) Ants protect aphids, aphids feed ants Charles Kingery/Phototake NYC

Mutualism: Goby Fish + Shrimp: 

Mutualism: Goby Fish + Shrimp Goby fish sometimes live together with a shrimp Shrimp digs & cleans up a burrow in the sand in which both the shrimp and the goby fish live Shrimp is almost blind (vulnerable to predators when above ground) In case of danger, goby fish touches shrimp with its tail to warn it. Both the shrimp and goby fish quickly retract into the burrow.

Slide27: 

shrimp Goby fish Goby fish

Slide28: 

A Spur-winged Plover finds nourishment cleaning a Nile Crocodile's teeth of leeches, first recorded by Herodotus in 440 BC, by J. M. Cook in 1876 and illustrated  in "Popular Natural History" by Henry Scherren in 1909.

Mutualism: Plover + Crocodile: 

Mutualism: Plover + Crocodile The Egyptian Plover, Pluvianus aegyptius, a.k.a. Crocodile Bird Crocodiles lay on the shore with their mouths open, and the plovers fly into the crocodiles' mouths…!!! Feed on bits of decaying meat that are lodged between the crocodiles' teeth. Crocodiles do not eat the plovers, as the plovers are providing the crocodiles with greatly-needed “dentistry” (prevents tooth decay!).

Cleaner wrasse cleaning shark’s gills: 

Cleaner wrasse cleaning shark’s gills

Slide31: 

Wrasse inside mouth of predatory species

Mutualism: Evidence for Creationism??: 

Mutualism: Evidence for Creationism??