Promiscuity and the evolutionary transition to complex societies C. Cornwallis, S. West, K. Davis & A. Griffin Nature; 2010

CK Cornwallis et al. Nature 466, (2010) doi: /nature09335 Making sense of the diversity.

Methods Avian Supertree: Created from 966 published trees between 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

CK Cornwallis et al. Nature 466, (2010) doi: /nature09335 The monogamy hypothesis. Negative relationship found between helper-offspring relatedness and female promiscuity.

Evolution of Monogamy Eusocial Insects is the ancestral condition of strict lifetime monogamy leading to irreversible transitions to societies with sterile worker cast Monogamy in Vertebrates is far more rare and Non-breeding helpers retain reproductive potential during transitions to cooperative breeding. 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)

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 non- cooperative 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?

Very High or Very Low Promiscuity  Weak Kin Selection Intermediate Promiscuity  Stronger Kin Selection Experimenters found that…

CK Cornwallis et al. Nature 466, (2010) doi: /nature09335 Kin discrimination and rates of promiscuity. Intermediate promiscuity leads to greater kin selection