Disentangling the mechanisms of mate choice in a captive koala population
Brandies, PA , Grueber, CE, Ivy, JA, Hogg, CJ & Belov, K 2017, PeerJ Preprints (Not Peer Reviewed).
Successful captive breeding is a major contributor to the conservation of many threatened species; however, the sustainability of several captive breeding programs is limited by pair incompatibility. If captive breeding is to be both successful and sustainable, an understanding of the behavioral and genetic drivers of pair incompatibility is essential. To determine what behavioral and genetic drivers influence pair incompatibility of captive koalas, analyses of 28 years of pairing data from the studbook for the San Diego Zoo koala colony and genetic analyses of 70 banked koala DNA samples from the same colony were performed. Both behavioral and genetic determinants were found to contribute to captive koala mating success.
Copulation success was found to be significantly associated with male age. Young males were found to a have a copulation success rate of approximately 20%, which increased to 40% at 12 years of age and decreased to 35% at 17 years or older. Female age did not appear to contribute to reproductive success. Familiarity was also found to positively influence breeding. Pairs that had lived together for five or more years had success rates greater than 50% whereas those that were never placed together before the breeding attempt had only a 34% reproductive success rate. All koalas were genotyped at both MHC-linked and non-MHC-linked microsatellite markers and standardised heterozygosity was determined. A negative relationship between genetic dissimilarity and copulation success was found; that is, the more genetically similar the pair were, the more successful copulation was.
Many studies, including this one, support the hypothesis that female koalas prefer to mate with older males. This is likely because older koalas have lived longer, and thus are likely to have high quality genes that have contributed to their survival and longevity. Familiarity also appears to promote reproductive success in captive koalas. It is suspected that female koalas are more likely to encounter the territorial scent marks of nearby koalas, and thus are aware of their capacity to defend a territory, making them a desirable mate choice. Generally, female animals are attracted to genetically dissimilar males and heterozygosity has been associated with increased reproductive success. Genome-wide heterozygosity was not found to influence mating success in the captive koala colony studied here; instead, a positive correlation between genome-wide similarity and breeding success was determined. It is suggested that pairing of similar individuals may protect koalas from infectious diseases, although this hypothesis requires further research.
Pair incompatibility is likely to be the explanation for several failed captive breeding programs. The age of males, familiarity of the breeding pair and genome-wide similarity all contributed to mating choice and success of captive koalas in this study, and these findings may inform similar captive breeding programs.
Summarised by Alexander Hendry
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