Postcopulatory selection for dissimilar gametes maintains heterozygosity in the endangered North Atlantic right whale

• Published in: Ecology and evolution Vol. 3; no. 10; pp. 3483 - 3494
• Main Authors: Frasier, T. R., Gillett, R. M., Hamilton, P. K., Brown, M. W., Kraus, S. D., White, B. N.
• Format: Journal Article
• Language: English
• Published: England John Wiley & Sons, Inc 01-09-2013; Blackwell Publishing Ltd
• Subjects: Animal behavior; Animal reproduction; Aquatic mammals; Calves; Cetacea; Endangered & extinct species; Expected values; Fertilization; Fisheries; Gametes; Gene pool; Genetic diversity; Genetic drift; Genetic incompatibility; genetic variation; Heterozygosity; Hypotheses; Inbreeding; mate choice; mate incompatibility; Mate selection; Microsatellites; Offspring; Original Research; Paternity; Population; Populations; right whale; Success; Whales & whaling; Canada; AN, North Atlantic; right whale; genetic variation; Genetic incompatibility; mate incompatibility; mate choice
• ISSN: 2045-7758; 2045-7758
• DOI: 10.1002/ece3.738

Although small populations are expected to lose genetic diversity through genetic drift and inbreeding, a number of mechanisms exist that could minimize this genetic decline. Examples include mate choice for unrelated mates and fertilization patterns biased toward genetically dissimilar gametes. Both processes have been widely documented, but the long‐term implications have received little attention. Here, we combined over 25 years of field data with high‐resolution genetic data to assess the long‐term impacts of biased fertilization patterns in the endangered North Atlantic right whale. Offspring have higher levels of microsatellite heterozygosity than expected from this gene pool (effect size = 0.326, P < 0.011). This pattern is not due to precopulatory mate choice for genetically dissimilar mates (P < 0.600), but instead results from postcopulatory selection for gametes that are genetically dissimilar (effect size = 0.37, P < 0.003). The long‐term implication is that heterozygosity has slowly increased in calves born throughout the study period, as opposed to the slight decline that was expected. Therefore, this mechanism represents a natural means through which small populations can mitigate the loss of genetic diversity over time.
Pedigree information for the endangered North Atlantic right whale shows that successful fertilizations/pregnancies are biased towards dissimilar gametes. This has resulted in a slight increase in heterozygosity over time, instead of the expected erosion of genetic diversity expected for a small population.