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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.