Local resource competition. Sex allocation Is the differential allocation of investment in sons vs. daughters to increase RS. Local mate competition

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1 Sex allocation Is the differential allocation of investment in sons vs. daughters to increase RS Local resource competition Biased against the competing sex Fisher: Genetic model predicts 1:1 sex ratio at a population level due to mixed ESS But, there can be biases when: Relatives interact There are variable environments that promote one gender over the other Galago Local mate competition As before, bias is against the sex that would compete most for mates Environment determines bias Maternal condition sons gain more in RS when times are good Fig wasps 1

2 Environment determines bias Maternal condition sons gain more in RS when times are good Environment determines bias Mothers should have more sons when she s mated with a particularly sexy male Environment determines bias Environmental sex determination by temperature Do animals ever change their gender over their lifetime in order to increase their LRS? Sequential hermaphroditism Can a temperature provide a good male environment or female environment? 2

3 Sex change in individuals Protandry and Protogyny Depending on ecology, it can be best to be female at large size or male at large size Protandry Protogyny males females males females Protogynous sex change Common in harem-forming reef fish Often, change controlled by the local situation: when a male dies, largest local female changes sex cleaner wrasse blue-headed wrasse Protandrous sex change Ex: Anemone fish (clownfish) monogamous due to anemone size male success not size dependent. Again, local situation triggers sex change Finding Nemo: the shocking truth 3

4 So why don t animals like elephant seals change sex with age and size? M F Categories of social interaction Recipient Actor _ mutualism, cooperation altruism selfish, parasitic spitefulness Are humans ever truly altruistic? 4

5 Altruistic behavior is, for the most part, only seemingly altruistic Social parasitism cooperation actually induced by the recipient to the donors disadvantage. brood parasitism (fish, birds, insects) kleptoparasitism induced regurgitation in insects What else can explain seemingly altruistic acts? Kin selection (Hamilton, 1964) Mutualism Reciprocity (Trivers, 1971) induced regurgitation kleptoparasitisism warning calls cooperative breeding Food sharing Kin selection Cooperative acts are directed toward kin. Proportion of your genes in future generations can be increased indirectly by helping relatives Hamilton s Rule: Kin selection An altruistic trait is selected for if benefit B is large enough so that: Br > C or Br C > O r = coefficient of relatedness (ranges from 0 to 1) W.D. Hamilton 5

6 Determining r (Box 11.2) Inclusive fitness Parentoffspring I would be prepared to lay down my life for the sake of 2 brothers or 8 cousins J.B.S. Haldane Avoid double counting when considering kin selection. I found this on a course website: For example, suppose that on average a human has two offspring in its life. But you are given the chance to help your sister with her offspring. She has 9 kids. If your act of altruism towards your sister was controlled by a gene, it would spread through the population because 9/2 > 1/(0.25). B/C > 1/r Calculating inclusive fitness Joe s RS Joe s brother s RS O O O O O O O O O O Strip away the effects of helping O O O O O O O O Modify according to effects of helping O O O O O O O O This avoids double counting young Joe s inclusive fitness = 3(0.5) + 3(0.25) = 2.25 Not help 4(0.5) = 2 Help

7 Using Hamilton s rule A version of H s rule for when you are forgoing your own offspring B r (donor to own offspring) 3.5 > > C r (donor to recipient) 1.25 Helpers at the nest in Florida scrub jays Without With helpers helpers Fledglings per pair Extra offspring due to helping: = 0.58 Average # of helpers = /1.18 =.49 extra young per helper r Inclusive fitness of helpers =.49 (0.43) = 0.21 m f h Predictions and tests of kin selection Altruistic acts should be given to relatives Black-tailed prairie dogs Probability of calling in presence of relatives or non-relatives. Tricky to measure B and C Male turkey coalitions Dominant males w/partner have 6.1 more offspring than solitary males r =.42 Solitary males have 0.9 offspring (.42 x 6.1) 0.9 > 0 rb C > > 0 partner 7

8 Using Hamilton s rule A version of H s rule for when you are forgoing your own offspring > > B r (donor to own offspring) C r (donor to recipient) (0.5) 6.1(0.42x 0.5) (0.5) > 0 For kin selection to work, you need: Ways to signal relatedness or gene similarity Relatedness signal can be detected by others Altruistic acts are directed towards those with closest relatedness signals 1.7 > 0 This predicts kin recognition Theoretical Green beard effect Dawkins An allele codes for all three things Susceptible to false beards Kin recognition Ex: Mexican free-tailed bats pups are placed in a crowded creche. Pups are recognized via olfactory and vocal cues. 400 pups per square foot 8

9 Ideally, you d want genetic markers to be directly detected and acted upon Individual slime molds were related by either 1 or 0 Animals trying to direct help toward kin can face same mistakes as brood parasite hosts Aggregations avg r = 0.8 Or at least some way of knowing family Types of cues Chemical - genetic or environmental? Visual Chemical cues When the environment is very heterogeneous, then environmental cues can work well Treat anyone home as kin (or imprint) Genetic cues work better in homogenous environments (ex: within the same beehive, some aquatic habitats) Sound 9

10 Chemical cues: environmental Environmental cue examples: Most social insects use chemical labels to identify nestmates Ex: Paper wasp larvae absorb nest odor onto their cuticle during development Chemical cues: genetic MHC genes are highly polymorphic and often used as recognition cues The major histocompatability complex is a set of genes used for the recognition of self as a part of the immune system. MHC determine glycoproteins on cell membranes Chemical cues in use Honeybees can not only identify nest mates via environmental cues, but can also discriminate half vs. full sisters Chemical cues in use Belding s ground squirrels also use environmental and genetic cues Aggression b/w various pairs of ground squirrels Freq. of fight Freq. of help Fig

11 Visual cues in use Chimpanzees can pair mothers with their sons Sound cues in use Dolphins, Orcas each have unique whistles Colonial seabirds young are in creche and parents find them by call 11