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

Abstract

The Amazonian manatee (Trichechus inunguis) is a threatened aquatic mammal endemic to the Amazon basin. The aim of this study was to evaluate the urinary and salivary reproductive hormone levels of captive Amazonian manatees collected during two seasons of the year. Salivary samples from four males and urinary and salivary samples from three females were collected during two seasons (March-June and September-November) over two consecutive years. Salivary testosterone in males was measured by radioimmunoassay and reproductive hormones in females (salivary progesterone and oestradiol and urinary progestogens, oestrogens and luteinising hormone) were measured by enzyme immunoassay. The data were analysed in a 2×2 factorial design, where the factors were year and season. There was no effect of year or season for salivary testosterone. All female hormones showed a seasonal effect (higher hormone levels during March-June than September-November) or an interaction between year and season (P<0.05). These results strongly indicate the existence of reproductive seasonality in Amazonian manatees; however, apparently only females exhibit reproductive quiescence during the non-breeding season. Further long-term studies are necessary to elucidate which environmental parameters are related to reproductive seasonality in T. inunguis and how this species responds physiologically to those stimuli.

Evaluating suitability of saliva to measure steroid concentrations in grey seal pups

“…Commercial ELISA kits may thus be suitable for estimating estradiol in grey seal pup plasma, however efforts need to be made to minimize between plate variation and ensure inter-plate confounds are minimized, because small biologically important differences might be too small to detect, especially when intra and inter assay variability are high. Saliva and plasma estradiol concentrations measured here were comparable with those reported previously in other marine mammals (Amaral et al, 2015;Theodorou and Atkinson, 1998). However, the range of steroid concentrations in blood vary more between studies than concentrations reported in saliva.…”

Advances in the knowledge of the biology and conservation of the Amazonian manatee (Trichechus inunguis)

“…The species shows reproductive seasonality, with the copulation and births occurring during the rising-water period of rivers, the time when food availability is greatest (Best, 1982). Reproductive seasonality also is reported in captivity (Amaral et al, 2015b) suggesting an environmental trigger other than food availability on the control of reproductive seasonality in this species.…”

Conservation of Amazonian manatee (Sirenia: Trichechidae): the case of Extractive Reserve Verde para Sempre, Brazil

“…Best (1982) reported reproductive seasonality in Amazonian manatee and observed a higher frequency of mating and calving in the rainy season, when rivers are flooding, and the abundance of food favors the survival of the calf. Captive females also exhibit re-productive behavior during the rainy season (Amaral et al 2015). According to Amaral et al (2015), the reproductive cycle could be primarily triggered by photoperiod or daytime light intensity, while food availability would act as a temporal fine-tuner of reproduction.…”

“…Captive females also exhibit re-productive behavior during the rainy season (Amaral et al 2015). According to Amaral et al (2015), the reproductive cycle could be primarily triggered by photoperiod or daytime light intensity, while food availability would act as a temporal fine-tuner of reproduction. However, the relation between photoperiod and the reproductive seasonality of wild manatee has yet to be confirmed.…”