Testosterone and tusks: maturation and seasonal reproductive patterns of live, free-ranging male dugongs (Dugong dugon) in a subtropical population

Abstract

Knowledge of male reproductive status and activity in free-ranging animals is vital to understanding reproductive patterns and population dynamics. Until now, almost all information regarding reproductive behavior of the dugong, a cryptic marine mammal, has relied on post-mortem examination. We examined the relationships between body length, tusk eruption (secondary sexual characteristic), seasonality, and group association on fecal testosterone metabolite concentrations in 322 free-ranging dugongs (159 males, 163 females) in subtropical Moreton Bay, Australia. Fecal testosterone concentrations demonstrated biologically meaningful differences in testicular activity between sexes and across reproductive/age classes, and were correlated with circulating concentrations in serum. Male dugongs have a pre-reproductive period that persists until a body length of 240 cm is achieved. Puberty apparently occurs between 240 and 260 cm body length when fecal testosterone levels increase fourfold (O500 ng/g) over juvenile levels, and is associated with tusk eruption. However, social maturity may be delayed until male dugongs are larger than 260 cm with well-developed tusks. In mature males, the lowest (!500 ng/g) fecal testosterone concentrations occur in the austral autumn months with maximal concentrations in September-October, coincident with the onset of a spring mating season. During spring, solitary mature males had fecal testosterone concentrations double those of mature males sampled within groups, potentially suggesting a mating strategy involving roving of reproductively active males. This study demonstrates that single-point physiological data from individuals across a population have value as indicators of reproductive processes. Our approach provides an efficacious non-lethal method for the census of reproductive status and seasonality in live male dugongs.

Seasonal variation in urinary and salivary reproductive hormone levels in Amazonian manatees (Trichechus inunguis)

“…Pimentel (1998) also did not find a difference in the faecal androgens of captive T. inunguis males among the seasons evaluated, similar to our results. However, for other sirenians, reproductive seasonality has already been observed in dugongs (Dugong dugon; Marsh et al 1984aMarsh et al , 1984bBurgess et al 2012) and Florida manatees (T. manatus latirostris; Hernandez et al 1995). Burgess et al…”

Bacterial Community Structure in the Hindgut of Wild and Captive Dugongs (Dugong dugon)

“…To obtain a representative sample of wild dugongs of both sexes and varying size classes, faecal samples from four dugongs of each size class and of both sexes were randomly selected (N = 32). Size classes were based on total body length measurements as follows: non-neonatal calf in second or later season accompanied by cow, ≤ 200 cm; juvenile, 201 to 240 cm; subadult, 241 to 260 cm; and adult, > 260 cm (Lanyon et al, 2010;Burgess et al 2012aBurgess et al , 2012b.…”

Population Structure and Dynamics

“…In this same study, a captive male dugong reached puberty at age nine, his tusks erupted at age 11, and he was confirmed to be sexually mature at age 12.8 years. Hormonal monitoring in the wild suggests that males reach puberty when they are approximately 240-cm long, coincident with tusk eruption; but they are unlikely to be socially mature until they reach 260 cm and have fully developed tusks (Burgess et al 2012). Sexual maturity in female Californian and Alaskan sea otters occurred at an average age of 4 years (Riedman and Estes, 1990;Jameson and Johnson, 1993).…”