Download 26_Helpers - life.illinois.edu

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.