Download Defining Cooperative breeding

Promiscuity and the evolutionary
transition to complex societies
C. Cornwallis, S. West, K. Davis & A. Griffin
Nature; 2010
Making sense of the diversity.
CK Cornwallis et al. Nature 466, 969-972 (2010) doi:10.1038/nature09335
Methods
Avian Supertree:
Created from 966 published trees between 1976-2008
Pruned to 267 Species for which had data on female promiscuity
Defining Cooperative breeding:
•helpers did not breed or had zero-to-limited opportunities to breed (genetic markers
to determine paternity)
•Typically retained natal's
•Present in at least 10% of nest in any part of their range
Minimizing Confounding Variables:
Gained maximum longevity data for 184 species
Tested weather any differences in latitude by entering breeding range
Definition of Monogamy: a prolonged association and essentially
exclusive mating relationship between one male and one female
Monogamy Hypothesis:
Monogamy, or low levels of promiscuity, leads to high relatedness in family
groups that favors the transition to cooperative societies.
Builds on Kin Selection Theory
Variables:
Genetic Benefit: In this case, helping to raise a sibling is equivalent to raising offspring
from the point of view of passing genes to the next generation
Ecological Benefit: Any small ecological advantage for cooperation can tip the balance in
favor of helping to raise siblings
Extent of Cooperation Varies from Obligate to facultative helpers
The monogamy hypothesis.
Negative relationship found between helper-offspring relatedness and female promiscuity.
CK Cornwallis et al. Nature 466, 969-972 (2010) doi:10.1038/nature09335
Evolution of Monogamy
Eusocial Insects is the ancestral condition of strict lifetime monogamy
leading to irreversible transitions to societies with sterile worker cast
generally involves the production of sterile members of the species,
which carry out specialized tasks, effectively caring for the
reproductive members. It can manifest in the appearance of individuals
within a group whose behavior (and sometimes anatomy) is modified
for group defense, including self-sacrificing “altruism”.
This is hypothesized to work evolutionarily because males are NOT
fertilized, so ALL females are 3/4 related to one another because
the males are haploid and can only give one set of genes each time. If
the queen in monogamous, it is in a female worker's best interest to
have fellow female siblings made instead of her own offspring(more
closely related)
Monogamy in Vertebrates is far more rare and Non-breeding helpers
retain reproductive potential during transitions to cooperative breeding.
Hamilton’s Rule
W. D. Hamilton who published, in 1964, the first formal quantitative
treatment of kin selection to deal with the evolution of apparently
altruistic acts.
rB > C
WHEN:
r = the genetic relatedness of the recipient to the actor, often
defined as the probability that a gene picked randomly from each
at the same locus is identical by descent.
B = benefit in terms of reproductive success to the
recipient of aid.
C = cost to the performer of a cooperative behavior.
Promiscuity and the transition
to and from cooperative
breeding.
• Avian Supertree “pruned”
from 6,219 to 267 species
• Promiscuity lower in noncooperative ancestors of
cooperative breeders
• Rate of transition was over
twice as high for ancestors
with low promiscuity
• Cooperative breeding evolved
33 times and was lost 20 times.
Kin Selection
Strategies in evolution that favor the reproductive success of an organism's relatives,
even at a cost to the organism's own survival and reproduction.
In systems with high levels of promiscuity relatedness can still be maintained by
helpers directing aid preferentially towards more related beneficiaries.
Birds cannot discriminate kinship using genetic cues
They can discriminate using behavioral cues such as vocalizations and breeder turnover.
Predictions for strength of kin
discrimination across species with
different levels of promiscuity?
Experimenters found that…
• Very High or Very Low Promiscuity  Weak Kin
Selection
• Intermediate Promiscuity  Stronger Kin Selection
Kin discrimination and rates of promiscuity.
Intermediate promiscuity leads
to greater kin selection
CK Cornwallis et al. Nature 466, 969-972 (2010) doi:10.1038/nature09335