Unravelling the complex reproductive tactics of male humpback whales : an integrative analysis of paternity, age, testosterone, and genetic diversity

• Main Author: Eichenberger, Franca
• Other Authors: Garland, Ellen C., Rendell, Luke, Carroll, Emma Louise, Garrigue, Claire, University of St Andrews. School of Biology, Louis M. Herman Research Scholarship, Royal Society (Great Britain), National Geographic Society, Carnegie Trust for the Universities of Scotland, British Ecological Society
• Format: Doctoral or Postdoctoral Thesis
• Language: English
• Published: The University of St Andrews 2024
• Subjects: Reproductive success; Baleen whales; Sexual selection; Population recovery; MHC; Epigenetic ageing; Gametic-mark recapture; Mate choice; Population age structure; Endocrinology; QL737.C424E5; Humpback whale > Reproduction; Humpback whale > Endocrinology; Sexual selection in animals; Courtship in animals; baleen whales; Humpback Whale
• Online Access: http://hdl.handle.net/10023/29070; https://doi.org/10.17630/sta/706

How the underlying forces of sexual selection impact reproductive tactics including elaborate acoustic displays in cetaceans remains poorly understood. Here, I combined 26 years (1995-2020) of photo-identification, behavioural, (epi)genetic, and endocrine data from an endangered population of humpback whales (New Caledonia), to explore male reproductive success, age, physiology, and population dynamics over almost a third of the lifespan of a humpback whale. First, I conducted a paternity analysis on 177 known mother-offspring pairs and confirmed previous findings of low variation in reproductive success in male humpback whales. Second, epigenetic age estimates of 485 males revealed a left-skewed population age structure in the first half of the study period that became more balanced in the second half. Further, older males (> 23 years) more often engaged in certain reproductive tactics (singing and escorting) and were more successful in siring offspring once the population age structure stabilised, suggesting reproductive tactics and reproductive success in male humpback whales may be age-dependent. Third, using enzyme immunoassays on 457 blubber samples, I observed a seasonal decline in male testosterone in the population over the breeding season. Testosterone levels appeared highest during puberty, then decreased and levelled off at the onset of maturity, yet were highly variable at any point during the breeding season and across males of all ages. Lastly, I investigated the influence of genetic diversity at the major histocompatibility complex (MHC) class I and class IIa (DQB and DRB-a) on patterns of male reproductive success in humpback whales. Mating pairs shared fewer alleles than expected under random mating at MHC class I and IIa, thus, providing evidence of an MHC-mediated female mate choice in humpback whales. This thesis provides novel, critical insights into the evolutionary consequences of commercial whaling on the demography, patterns of reproduction and sexual selection of exploited ...