Transcript 26_Helpers
Announcements Number of eggs / size of litter Hatching order / Asynchrony in hatching Sex of offspring Parental favoritism Likely occurs when resources are variable and adults have more young than they can raise (bet hedging) Females can invest in eggs differently (even choose sex in some species). Young can be fed preferentially. Seychelles warbler Parental favoritism Honest signals of quality in offspring? barn swallows Asynchrony in hatching (birth order) can promote or reduce sibling conflict and parental favoritism great egret Can parents control sex of offspring? Seychelles Warbler Can parents control sex of offspring? Haplo / diploid organisms (like ants, bees and wasps) fertilized egg = female ; un-fertilized egg = male Temperature Dependant Sex Determination (TSD) many reptiles Genetics basis for mating systems / parental care. prairie voles Monogamous, male parental care meadow voles polygynous, no male parental care In male prairie voles, vasopressin and dopamine in the forebrain regulate affiliation between mates (bond formation). Vasopressin receptor is expressed at higher levels in monogamous species than polygynous species. Lim and colleagues, used a viral vector to transfer the vasopressin receptor gene from the monogamous species into the polygynous species. With this change in a single gene, the polygynous species essentially became monogamous. Helpers at the nest In some animals, juveniles stay to help second nesting effort. More often female juveniles. Both direct and indirect benefits. Direct (learning about maternal care) Indirect (inclusive fitness by helping rear related offspring voles magpie jays Helpers at the nest Leads to overlapping generations Key step in the evolution of sociality? Overview for next few lectures Some of the costs & benefits of cooperation. Altruism & selfishness. Relatedness & kin selection. The Major Transitions 1. Replicating molecules ---> Molecules in protocells 2. Independent replicators ---> Chromosomes 3. RNA as gene and enzyme ---> 4. Bacteria (prokaryotes) ---> Eukaryotes (organelles) 5. Asexual clones ---> Sexual populations DNA genes, protein enz 6. Single-celled organisms ---> Multicellularity 7. Solitary individuals ---> 8. Primate societies ---> Eusocial colonies Human societies (language) Maynard Smith & Szathmáry 1995 The Major Transitions 1. Replicating molecules ---> Molecules in protocells 2. Independent replicators ---> Chromosomes 3. RNA as gene and enzyme ---> 4. Bacteria (prokaryotes) ---> Eukaryotes (organelles) 5. Asexual clones ---> Sexual populations DNA genes, protein enz 6. Single-celled organisms ---> Multicellularity 7. Solitary individuals ---> 8. Primate societies ---> Eusocial colonies Human societies (language) Maynard Smith & Szathmáry 1995 Potential benefits of sociality Pooled resources/shared defenses. Division of labor. Increase indirect fitness (by helping relatives reproduce) Potential costs of sociality Shared resources Parasitism Cheaters Solitary individuals to social groups Dispersal is risky Death Finding resources (food, home) Finding mate When the costs of ecological constraints are high, offspring do better by staying home. Family-based social groups Risks of not dispersing: Competing with relatives Limited resources Inbreeding Conflict over reproduction So an individual’s decision should be determined by the balance of these costs and benefits. Remember, most organisms not social! Individuals becoming helpers only after best territories are taken. Florida Scrub Jays Nests that lost helpers (experimental) had fewer surviving offspring cichlid fish Neolamprologus pulcher cichlid fish Neolamprologus pulcher Brouwer and colleagues, 2005, Behavioral Ecology Mexican jay Hormone prolactin thought to play critical role in parental care. Conflict over reproduction Reproductive skew - the distribution of reproduction across members of a group. high skew = one or few individuals reproduce. low skew = everybody reproduces equally. Dominants control who breeds. Subordinates control whether they stay or go. Reproductive Skew Factors affecting skew: • Expected success of breeding independently. • Expected success of the group if the individual stays. • The relatedness among group members. • The probability of beating a dominant for a share of reproduction. Skew should increase with: • higher ecological constraints • higher relatedness • low fighting ability Reproductive Skew Dominant (reproductive) individuals can offer incentives to entice subordinates to stay (if there is a benefit to the dominant). • Staying incentives - subordinates get a share of reproduction for not leaving. • Peace incentives - reduce aggression toward dominants for a share of reproduction. An example: The dwarf mongoose (Helogale parvula) • Social groups of 7-10 individuals. • Dominant pair suppresses reproduction by subordinates. Photo: Ralf Schmode Packs do better when subordinates stay and help. As individuals age, their probability of successfully dispersing increases. Therefore, the dominants should (and do) offer staying incentives to older subordinates, but not younger ones.