New horizons in the reproductive biology of Chinese pangolin (Manis pentadactyla) using the gonadal hormonal profile

Abstract

The reproductive uniqueness of pangolins has been documented through diverse biological reports with discernible data discrepancies in gestation, copulation, and pregnancy. These mechanistic reproductive differences have yet to be endocrinologically quantified, which could assist in optimizing natural breeding in zoos to recover endangered species. The present research characterizes the Chinese pangolin's annual seasonal reproductive pattern by measuring immunoreactive estrogens and progestagens in 34 captive females and testosterone in 29 captive males. Our results showed that Chinese pangolins are seasonal breeders, with most births witnessed during Sept-Dec, overlapping with the field records. Females exhibited spontaneous ovulation and post-partum ovulation. Pregnant females exhibited a higher P4 level for ~ 9 months (Jan-Sept) and decreased before parturition (Oct-Dec). The circulating E2 is maintained at the baseline in pregnant females year-round. Contrastingly, in non-pregnant females, P4 is maintained at the baseline, apart from a slight elevation in January, and E2 demonstrates a sudden hike from November and remains elevated until February, suggesting the onset of ovulation. The serum testosterone concentration in males peaked during October, which is in sync with the female ovulation period. As a result that their major reproductive events, ovulation, mating, and parturition, all transpire in November-March. Evidence also supports that Chinese pangolins exhibit signs of postimplantation (pregnancy) ranging only from 5 to 6 months (May-Oct), preceded by possible facultative delay implantation triggered by lactation. The provided data not only fill in the knowledge gap for this critically endangered species but can also assist in making informed decisions, which can directly affect the successful breeding of this species in captivity.

Figure 1

Annual serum endocrinological pattern of sex steroid E2 in pregnant and non-pregnant female pangolins. The dotted line represents the non-pregnant females, and the solid line represents the pregnant females. The grey boxes indicate the total number of samples obtained per month from non-pregnant females, and the white boxes indicate the total monthly serum samples obtained from pregnant females.

Figure 2

Annual serum endocrinological pattern of sex steroid P4 in pregnant and non-pregnant female pangolins. The dotted line represents the non-pregnant females, and the solid line represents the pregnant females. The grey boxes indicate the total number of samples obtained per month from non-pregnant females, and the white boxes indicate the total monthly serum samples obtained per month from pregnant females.

Figure 3

Annual serum endocrinological pattern of the sex steroid testosterone in male pangolins. The white boxes indicate the total number of monthly samples from different male pangolins.

Figure 4

Summarization of major reproductive events in Chinese pangolin (Manis.pentadactyla).