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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) - PowerPoint PPT PresentationTRANSCRIPT
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
magpie jaysvoles
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
Maynard Smith & Szathmáry 1995
1. Replicating molecules ---> Molecules in protocells2. Independent replicators ---> Chromosomes
3. RNA as gene and enzyme ---> DNA genes, protein enzymes4. Bacteria (prokaryotes) ---> Eukaryotes (organelles)
5. Asexual clones ---> Sexual populations6. Single-celled organisms ---> Multicellularity7. Solitary individuals ---> Eusocial colonies
8. Primate societies ---> Human societies (language)
The Major Transitions
Maynard Smith & Szathmáry 1995
1. Replicating molecules ---> Molecules in protocells2. Independent replicators ---> Chromosomes
3. RNA as gene and enzyme ---> DNA genes, protein enzymes4. Bacteria (prokaryotes) ---> Eukaryotes (organelles)
5. Asexual clones ---> Sexual populations6. Single-celled organisms ---> Multicellularity7. Solitary individuals ---> Eusocial colonies
8. Primate societies ---> Human societies (language)
Potential benefits of sociality
Pooled resources/shared defenses.
Increase indirect fitness (by helping relatives reproduce)
Potential costs of sociality
Parasitism
Cheaters
Division of labor.
Shared resources
Dispersal is riskyDeathFinding resources (food, home)Finding mate
When the costs of ecological constraints are high, offspring do better by staying home.
Solitary individuals to social groups
Competing with relativesLimited resourcesInbreedingConflict over reproduction
Risks of not dispersing:
Family-based social groups
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 fishNeolamprologus pulcher
cichlid fishNeolamprologus pulcher
Brouwer and colleagues, 2005, Behavioral Ecology
Hormone prolactin thought to play critical role in parental care.
Mexican jay
Conflict over reproduction
Reproductive skew - the distribution of reproduction across members of a group.
low skew = everybody reproduces equally.high skew = one or few individuals reproduce.
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 offerincentives 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 towarddominants for a share of reproduction.
An example:The dwarf mongoose(Helogale parvula)
Photo: Ralf Schmode
• Social groups of 7-10 individuals.
• Dominant pair suppresses reproductionby subordinates.
As individuals age, their probability of successfullydispersing increases.
Packs do better when subordinates stay and help.
Therefore, the dominants should (and do) offer staying incentives to older subordinates, but not younger ones.