Seasonal variation in testes size and density detected in belugas (Delphinapterus leucas) using ultrasonography

Minimally invasive physiological correlates of social behaviour in belugas (Delphinapterus leucas) under human care

“…Whilst female-male association and courtship behaviour coincided with F1's breeding season, there was a weaker association with measures of male reproductive physiology. The seasonal timing of presumed courtship behaviour (primarily March through May) was consistent with previous observations of male beluga reproductive seasonality and the timing of conceptions in aquaria Richard, Schmitt et al 2017). The more frequent occurrence of courtship whilst testosterone and testes size were declining contrasts with spinner dolphins (Stenella longirostris; Wells 1984) and finless porpoises (Neophocaena phocaenoides asiaeorientalis; Wu et al 2010).…”

“…F1's preference for M1 during key times of the oestrous cycle may have occurred because M2 was likely immature during the study period. Whilst M2 had adult levels of testosterone, his testes were approximately half the volume of mature belugas in aquaria and the wild (Brodie 1971;Richard, Schmitt et al 2017). Most of the interactions between M2 and F1 occurred later in the breeding season and outside of inferred follicular phases.…”

“…Inferred ovulations must be separated by at least 30 days, given the inter-oestrous interval of 33-34 days (Steinman et al 2012). TTV was determined using ultrasonography performed with the voluntary cooperation of the whale as described by Richard, Schmitt et al (2017). Exams were conducted twice per month by a single operator using a convex 3.5 MHz probe (GE Logiq Book with 3C-RS transducer, GE Medical Systems, China).…”

“…Integrating the available information on beluga reproductive anatomy and physiology could help to elucidate potential mating strategies. Belugas have relatively low circulating testosterone concentrations (Høier & Heide-Jørgensen 1994;, small testes with reduced seasonal variation (Richard, Schmitt et al 2017) and small ejaculate volumes (O'Brien et al 2008) compared to other odontocetes, for example, bottlenose dolphin (Tursiops truncatus [Schroeder & Keller 1989;Robeck, Steinman et al 2005;Orbach et al 2019]). The female beluga reproductive tract is less complex (fewer vaginal folds and shorter cumulative length of vaginal folds) than several odontocete species known to engage in sperm competition, in which these folds may allow for sperm selection or limit penile penetration (Orbach et al 2017).…”

“…The female beluga reproductive tract is less complex (fewer vaginal folds and shorter cumulative length of vaginal folds) than several odontocete species known to engage in sperm competition, in which these folds may allow for sperm selection or limit penile penetration (Orbach et al 2017). In aquaria, most beluga conceptions occur after testes begin to regress and testosterone concentrations begin to fall (Robeck, Steinman et al 2005;Richard, Schmitt et al 2017), in contrast to convention in vertebrates, including other odontocetes (Wells 1984;Wingfield et al 1990;Wu et al 2010). Taken together, these observations suggest a reduced role for sperm competition or male contest competition relative to other species of cetaceans.…”