The assessment of reproductive function, behaviour and adrenal physiology in captive male southern hairy-nosed wombats (Lasiorhinus latifrons)

Abstract

Southern hairy-nosed wombats (SHNW; Lasiorhinus latifrons) rarely breed successfully in captivity, which has been primarily associated with a dearth of knowledge concerning their reproductive physiology and behaviour. One approach to better understanding those parameters that might influence captive wombat husbandry and management is the application of non-invasive techniques that facilitate evaluation of reproductive and adrenal hormones. Non-invasive urine samples are ideal for the assessment of both reproductive capacity and adrenal function in captive wildlife species but robust biological validation is initially required to confirm the reliability of this information. Once validated, animal behaviour can then be mapped in parallel with urinary hormone metabolites, and data from spermatorrhoea, to more precisely determine the success or otherwise of husbandry practices focused on reproductive success. This thesis examined the efficacy of using urinary testosterone and cortisol in the captive male SHNWs as means of understanding changes in hormone concentrations with respect to reproductive and adrenal function, breeding behaviour and social structure. Enzyme immunoassays (EIAs) were evaluated and validated for their potential to measure biologically relevant changes in plasma and urinary luteinizing hormone (LH), testosterone metabolites (UTM) and cortisol metabolites (UCM) in captive SHNWs. GnRH agonist and ACTH agonist challenges were conducted to validate urinary testosterone (male wombat only) and cortisol (male and female wombats) EIAs, respectively. Following intra-muscular injection of 8 - 12 g buserelin (n = 4 males) there was a significant increase in both plasma (P < 0.001) and urinary testosterone concentration (P < 0.001) 60 min and 21 h after administration, respectively. Plasma LH levels were elevated (P < 0.05) at 20 min but there was no significant increase found in urinary LH concentrations after injection. Intra-muscular injection of Synacthen® Depot (250 g) (n = 3 males, 3 females) resulted in a significant increase (P < 0.05) in plasma cortisol secretion after 15 min and in urinary cortisol concentrations 3 h post injection. Sex related differences in cortisol secretion were also reported in this study. These findings suggest that while urinary LH might not be an appropriate index for evaluating the reproductive status in captive male SHNW, UTM and UCM enzyme-immunoassays appear to be suitable for the assessment of captive southern hairy-nosed wombat testicular steroidogenic capacity and adrenocortical activity, respectively. Seasonal variation in physiology and social dynamics of a captive male population of SHNW (n = 6) were then evaluated using the validated assays. Seasonal changes in urinary testosterone metabolites (UTM), urinary cortisol metabolites (UCM), qualitative estimates of spermatorrhoea (QS), aggressive behaviour and reproductive behaviour were measured over an 11-month period. While there was no effect of month on QS (GLM ANOVA, P = 0.27), reproductive behaviour (GLM ANOVA, P = 0.19) or aggressive behaviour (Tukey pairwise comparisons), the secretion of UTM (GLM ANOVA, P = 0.051) was only marginally affected by season, compared to that reported for wild male southern hairy-nosed wombats. Mean UCM concentrations of July (0.927 ± 0.0729 ng/mg Cr) and August (0.941 ± 0.0876 ng/mg Cr) 2016 were significantly higher (Tukey pairwise comparisons) than those between October 2015 and January 2016 (October: 0.549 ± 0.0743 ng/mg Cr; November: 0.528 ± 0.0729 ng/mg Cr; December: 0.535 ± 0.0526 ng/mg Cr; January: 0.608 ± 0.0435 ng/mg Cr). To examine the physiology of a perturbation to social dynamics, two trials involving changes in animal location to different enclosure systems were implemented and behavioural data examined for each trial over a six week period; UTM, UCM and general behaviours (n = 27) were measured for each trial. Neither UTM nor UCM concentration varied significantly (P ≥ 0.45) before and after the relocation of wombats. “Scratching” decreased at the group level following the animal exchange in both trials, suggesting that this reduction in self-grooming may be a behavioural response to novel stimuli. UCM and UTM concentrations were both positively correlated with “standing still” and “body rub” behaviours which may reflect some form of hormonal control over what might be regarded as a “freezing response” to external stimuli in this species and marking behaviour, respectively. There was no evidence that changing the social dynamics affected reproductive or agonistic behaviour or hormone concentrations. It is concluded, therefore that captive male SHNWs show reduced seasonality compared to their wild conspecifics, and that while animal relocation created evidence of behavioural responses to novel stimuli, it was not sufficient to affect testosterone or cortisol secretion, within the context of my study.