Noninvasive Assessment of Testosterone Levels and Male Sexual Behavior in Sambar Deer (Rusa unicolor) as a Critical...

The role of testosterone in regulating the antler cycle and sexual behavior in temperate cervids is well documented. However, studies on tropical cervids, such as the sambar deer (Rusa unicolor), remain limited. This study aimed to measure testosterone levels and investigate their relationship with sexual behavior across different antler stages using a noninvasive approach. Eight sambar deer stags aged 3-5 years, housed in the Taman Rusa Zoo, Aceh, Indonesia, were observed. Fecal samples were collected 1-3 times per week from each individual, along with the behavior observation and antler stage assessments. Sexual behaviors were carried out using focal animal sampling and recorded using the all-occurrence sampling method. Levels of testosterone in feces were measured using the enzyme-linked immunosorbent assay technique. Data were analyzed using a linear mixed-effects model with antler stage as a fixed effect and individual identity as a random factor. Spearman's rank correlation test was used to examine the relationship between testosterone levels and sexual behavior. The results revealed a clear association between testosterone levels, antler stages, and male sexual behaviors. Levels of testosterone varied significantly among antler stages, with higher levels found during the hard and velvet stages compared to the casting stage (p < 0.01). Moreover, a strong positive correlation was found between testosterone levels and male sexual behavior during the hard antler stage (rs = 0.763, p < 0.01). Despite high testosterone levels during the velvet stage, male sexual behaviors, such as anogenital sniffing, anogenital licking, and flehmen, were significantly lower compared to the hard antler stage. These results suggest that testosterone may play additional roles beyond those related to male competition or mating during the velvet stage, which warrants further investigation. Understanding the dynamics of testosterone and male sexual behavior is crucial for the effective management and conservation of sambar deer populations in captivity.