The Antler Cycle and Fecal Testosterone of Male Sambar Deer Rusa unicolor unicolor at the Horton Plains National Park in Sri Lanka

Abstract

This study is aimed at evaluating the relationship between endogenous testosterone levels and antler development in male sambar deer (Rusa unicolor unicolor) inhabiting the Horton Plains National Park, Sri Lanka. Seven antler growth stages of sambar were documented based on phenotypic observations for the first time in Sri Lanka as (a) cast, (b) growing 1—single spike, (c) growing 2—antler fork into a Y as the second tine appears, (d) growing 3—velvet begins to harden as the third tine appears, (e) growth completed—velvet shedding begins, (f) hard antler, and (g) casting. Fecal samples were collected every month for a period of eighteen months from male sambar deer in different stages of the antler growth cycle, feeding in the wet patana grasslands of the park, and the fecal testosterone level was estimated by radioimmunoassay. Ten animals were randomly selected from each antler stage for the experiment. The results disclose that the highest concentrations of testosterone were recorded in the hard antler stage. Velvet shedding was preceded by an increase in the testosterone level, and it is the sudden drop in the testosterone concentration which triggers the antler casting. The casting stage corresponded with the lowest mean testosterone concentration. Although the study was able to conclude a clear relationship between the fecal testosterone levels of the male sambar deer in the Horton Plains National Park and their antler stages, there is no clear seasonality for the antler cycle.

Calreticulin Identified as One of the Androgen Response Genes That Trigger Full Regeneration of the Only Capable Mammalian Organ, the Deer Antler

“…Antlers and their antecedent pedicles are male secondary sexual characters and, as such, their development is strictly under control of androgen hormones ( Weerasekera et al, 2020 ). Surprisingly, except for pedicle initiation and antler calcification that require high levels of androgens, androgens seem to be detrimental to antler regeneration and growth.…”

Population dynamics and social organization of sambar (Rusa unicolor unicolor) in Horton Plains National Park, Sri Lanka

“…Sambar separated by <50 m were considered in the same social group (Harris et al, 2008). The gender and age class of individual animals were noted during the survey by following Weerasekera et al (2019) and deer were divided into five social units: single adult male; single adult female (with or without young); groups of adult males; groups of adult females with young; and mixed groups. Other than the social units, their sparring and mounting activities were recorded as behavioral events.…”

“…According to Weerasekera et al (2020), the group size of sambar herds in HPNP is directly related to the monthly percentage of males in different antler stages, except during the calving seasons. Antlers in male sambar are indicative of the status of breeding activity and are important in dominancy display (Savanth et al, 2011;Weerasekera et al, 2020).…”

“…Furthermore, the predator-prey dynamics between the apex predator leopard (Panthera pardus) and sambar, the largest herbivore of the plains may also play a key role in maintaining these grasslands of HPNP through regulating the sambar population. On the contrary, sambar has also been identified for its importance in the control of forest encroachment into grasslands, as they have been reported to browse (Padmalal et al, 2003) and cause tree bark damage even possibly leading to forest dieback (Ranawana, 2014;Weerasekera et al, 2022), in cloud forest habitats and forest-grassland edges of HPNP. Under such an ecological setup, the knowledge of the population dynamics of the sambar is pivotal in the management of the threatened wet patana grassland ecosystem of HPNP.…”

Variación estacional de testosterona fecal y desarrollo de astas en una subespecie tropical de venado cola blanca (Odocoileus virginianus) de la región Huasteca, México

“…En venados de zonas boreales, el aumento y disminución de la concentración de testosterona en plasma se presenta repentina e intensamente, ocasionando mineralización de astas, caída de terciopelo e incremento en espermatogénesis; las astas se conservan por un período de tiempo corto y la producción de esperma se suspende con la muda. En cambio, en regiones ecuatoriales la testosterona se incrementa y decrece lentamente, sin alcanzar niveles que detengan la espermatogénesis; las astas y la actividad sexual se mantienen por un periodo mayor en el año (Loudon y Curlewis 1988;Bubenik 1990;Pelletier et al 2003;Newbolt et al 2017;Stewart et al 2018;Weerasekera et al 2020).…”