Investigating reproductive biology of female mugger crocodiles (Crocodylus palustris) by using behaviour and endocrine measures

Abstract

Reptiles are one of the most speciose groups of tetrapods, however, they are often neglected in conservation research. In this manuscript, we studied a focal population (20 females and 2 males) of captive mugger crocodiles to investigate their reproductive behavioural patterns and underlying endocrine correlates, a basic knowledge that was lacking in understanding the biology of the mugger crocodiles. Our study population exhibited three distinct phases of behavioural activities: a) mating phase, with only mating eventsb) mixed phase with a few mating events and high occurrences of parental carec) non-breeding phase, where reproductive activities were absent. Ethogram analysis demonstrated a fixed behavioural repertoire during mating (n = 165), including 13 behaviours exhibited by both males and females. Due to low sample size (n = 2), we excluded males from further statistics. Female-female aggression was prevalent in all three phases and did not vary significantly (P > 0.05). To investigate endocrine correlates, scats (n = 138) were collected to measure (averaged across phases, Mean±SE, ng/g dry faeces) fecal progesterone (fPm=2421.4 ± 316.5), oestrogen (fEm=406.9 ± 34.8), and testosterone (fTm=2386.6 ± 245.4) metabolite levels in females. Hormone-behaviour associations in females showed that fEm and fTm levels did not vary significantly (P > 0.05) across phases, but fPm levels were significantly higher (P < 0.05) during mixed phase when compared to mating and non-breeding phases. Though our research had a few limitations (low sample size of males and included a single reproductive season only), it is the first to investigate reproductive behaviour and physiology of the female muggers. This work also successfully validated fecal measurements of three reproductive hormone metabolites, progesterone, testosterone and oestrogen for the mugger crocodile species. Overall, the current study presents fundamental work on the reproductive biology, including both behaviour and endocrine correlates, of vulnerable muggers, which will contribute towards improving ex-situ as well as in-situ conservation and management strategies for the species