Kin Selection and Family Conflicts

Transcription

1 The Evolution of Sex and its Consequences HS 2011 Part II: Consequences Kin Selection and Family Conflicts Kin Selection: Altruism and Conflict Blue tit (Parus caeruleus) Burying beetle (Nicrophorus vespilloides) Human (Homo sapiens)

2 Kin Selection: Altruism and Conflict Sexual reproduction implies that parents are genetically not identical to their offspring (only half of the alleles are from a given parent; r = 0.5) Also, siblings are not genetically identical Nevertheless, the fact that parents and offspring, and siblings, are genetically related means that they have an evolutionary interest in the survival and reproduction of each other. But it is substantially reduced compared to clonal organisms But the interests are not completely shared Altruism (e.g. parental care) can evolve if r Parent Offspring B Offspring C Parent Family Conflict: Sibling Aggression Cattle egret (Bubulcus ibis) Mock & Parker 1997

3 Family Conflict Why did apparently selfish offspring behaviour evolve? Family Conflict Reason 1: Offspring of the same parents (i.e., siblings) are caught in a competitive arena. In general, a low-cost way to settle competition / aggression is to leave the resource patch and look for another resource patch with less competition (optimal foraging) This option is not available to offspring, because there usually is only a single resource (their parents)

4 Family Conflict : Conflict Battleground Reason 2: Siblings (and parents and their offspring) are genetically related, but not identical 4P * r = 0.5 selfish mutant wild-type P * -m P * -m P * +m P * +m r = 0.5 r = 1 Benefit (offspring survival) Cost to parent P * -m P * +m Parental provisioning per offspring Selfish mutant, that takes more than fair share (by amount m), has a survival advantage and spreads evolutionarily Family Conflict: Conflict Battleground Although the selfish mutant clearly enhances its spread through the enhanced survival of the individual bearer of the allele ( direct fitness), it also reduces its evolutionary success by reducing the number or potential bearers of the allele (siblings indirect fitness) by enhancing competition. Balance of direct fitness benefits to individual and indirect fitness costs to related individuals determine evolutionary success (Inclusive Fitness; Hamilton 1964) Likelihood that mutant is present in sibling through identity by descent ( degree of genetic relatedness) Selfish mutant that takes more than fair share spreads if B Offspring r Parent Offspring Inverse Hamilton s Rule C Parent

5 Family Conflict: Conflict Battleground Selection on parental care: offspring perspective (demand) Selection on parental care: parental perspective (supply) Benefit to offspring C Parent B Offspring r Parent-Offspring C Parent P * Parent P * Offspring Parental provisioning per offspring (P * : Optimum) Trivers (1974) Family Conflict: Conflict Resolution Hypothesis: Conspicuous and costly offspring begging and sibling aggression evolved due to selection from this parentoffspring conflict as a form of conflict resolution Scramble competition models (Parker et al ) Function of offspring begging: Outcompete siblings in signalling contest for access to parental resources. Needy offspring invest more in competition because they stand more to gain. Offspring control parental care. Honest signalling models (Godfray 1991,95; and others) Function of offspring begging: Signal need to parent, such that parent maximizes fitness returns on investment. Effect of condition: lowcondition offspring beg more because their fitness increases more steeply per unit investment, which in turn is why parents will feed them more

6 Family Conflict: Conflict Resolution Predictions: Conspicuous (costly) offspring begging evolves Begging should reflect variation in offspring need Parents should respond to offspring begging Offspring demand should evolve towards higher intensities when average relatedness among siblings is lower Family Conflict: Conflict Resolution Experiment: Support for prediction that begging should vary with offspring need Starling (Sturnus vulgaris) Kacelnik et al. (1995) Satiated Control Food deprived

7 Family Conflict: Conflict Resolution Experiment: Support for prediction that begging should vary with need Canary (Serinus canaria) Colour saturation (%) Food deprivation (h) Fig. 1. Effect of food deprivation and flush on gape colouration. White bars, before flush; hatched bars, after flush Kilner (1997) Family Conflict: Conflict Resolution Experiment: Support for prediction that begging should vary with need Canary (Serinus canaria) Kilner (1997)

8 Family Conflict: Conflict Resolution Experiment: But signals can also convey information about offspring quality American coot (Fulica americana) Lyon (1994) Family Conflict: Conflict Resolution Experiment: But signals can also convey information about nutritional quality European Earwig (Forficula auricularia) Solicitation pheromone ; Blend of non-volatile cuticular hydrocarbons C: control HF: high-food LF: low-food Mas et al. (2009)

9 Family Conflict: Conflict Resolution Comparative analysis: Support for prediction that demand should evolve towards higher intensity when sibling relatedness is lower Cuckoo Comparative studies on birds: Briskie et al. (1994) Family Conflict: Conflict Resolution Extreme case: Support for prediction that begging should evolve towards higher intensity when sibling relatedness is lower. Brood parasites, such as the common cuckoo (Cuculus canorus)

10 Consequences of Sexual Reproduction Female Sexual conflict: how often and with who should each mate? Male Family Conflict Paper to be read for next week Royle N, Hartley IR & Parker GA Begging for control: when are offspring solicitation behaviours honest? Trends in Ecology and Evolution 17: (