Seasonal variations in reproductive hormones in free-ranging echidnas (Tachyglossus aculeatus): interaction between reproduction and hibernation

Investigating the utility of using fecal hormone metabolites as a reproductive management tool for captive short-beaked echidnas (Tachyglossus aculeatus)

This study demonstrates the utility of the analysis of fecal hormone metabolites as a reproductive management tool for captive short-beaked echidnas. Over three breeding seasons daily fecal samples were collected from female echidnas (n = 8) that were monitored continuously by video surveillance to confirm key reproductive events. Fecal progesterone metabolite concentrations were elevated above baseline values (448.0 ± 156.3 ng/g) during pregnancy and the luteal phase. However, compared to plasma progesterone the rise in fecal progesterone metabolite concentrations after copulation was delayed (3.3 ± 0.4 versus 8.3 ± 0.6 days, respectively), such that pregnancy was more reliably detected in its latter half when using fecal samples. Mating and oviposition were observed for 14 of the 19 pregnancies resulting in an estimated gestation of 16.7 ± 0.2 days (range 16.0-18.1 d). The estrogen enzyme-immunoassays tested (n = 3) in this study were not suitable for the fecal samples of the echidna. Fecal progesterone metabolites are an effective tool for confirming the timing and occurrence of estrous cycles in captive echidna colonies and can assist zookeepers in identifying possible causes of sub-optimal reproductive success without the unnecessary stress of repeated capture and anaesthesia for blood collection.

Can spines tell a story? Investigation of echidna spines as a novel sample type for hormone analysis in monotremes

The short-beaked echidna (Tachyglossus aculeatus) is a monotreme endemic to Australia and New Guinea, and is the most widespread native mammal in Australia. Despite its abundance, there are considerable gaps in our understanding of echidna life history such as reproductive cycles in both sexes, patterns of stress physiology, and possible seasonal changes in metabolism. Slow-growing integumentary sample types comprised of keratin (hair, claw, etc.) have been used in other wildlife to assess these questions via analysis of longitudinal patterns in steroid and thyroid hormones that are deposited in these tissues as they grow. Hairs and spines comprise the pelage of echidnas, the spines being keratinized structures homologous to hair. Thus, echidna spines could be a viable sample type for hormone analysis contributing to a better understanding of the biology of echidnas. The aim of this work was to determine whether steroid hormones are detectable in echidna spines, to perform assay validations, and to establish a protocol for extracting and quantifying hormones in echidna spines using commercially available assay kits. We also inspected cross-sectioned spines using light and electron microscopy for any evidence of annual growth markers that might enable inferences about spine growth rate. Corticosterone, progesterone, estradiol, and testosterone were detectable in all samples, and echidna spine extract passed standard assay validations (parallelism and accuracy), indicating that commercially available assay kits can quantify hormones accurately in this sample type. No visible growth marks were identified in the spines and thus spine growth rate is currently unknown. Echidna spines show promise as a novel matrix from which hormones can be quantified; next steps should involve determination of spine annual growth rate, possible seasonal changes in growth rate, and persistence of spines over time in order to perform physiological validations, i.e., relationship between physiological status and hormone concentrations in spines.

Tachyglossus aculeatus (Monotremata: Tachyglossidae)

Tachyglossus aculeatus (Shaw, 1792) is a monotreme commonly called the short-beaked echidna. Although considered Australia’s most common native mammal because of its continent-wide distribution, its population numbers everywhere are low. It is easily distinguished from all other native Australian mammals because of its spine-covered body, hairless beak, and unique “rolling” gait. The five subspecies, one of which is found in Papua New Guinea, show variations in fur density, spine diameter, length, and number of grooming claws. The Kangaroo Island short-beaked echidna Tachyglossus aculeatus multiaculeatus is listed as “Endangered” but all other Tachyglossus are listed as “Least Concern” in the 2016 International Union for Conservation of Nature and Natural Resources Red List.

Spurs, sexual dimorphism and reproductive maturity in Tasmanian echidnas (Tachyglossus aculeatus setosus)

We present data from an 18-year study of a wild population of Tasmanian echidnas, which show that the presence of spurs in an adult are a reliable indicator of sex, and that there is a slight but significant sexual dimorphism in size, with a male to female mass ratio of 1.1. Minimum age at first breeding in the wild for Tasmanian echidnas was 5 years, as has been found on Kangaroo Island, compared with 3 years in captive echidnas. It is often assumed that although the echidna is distributed throughout Australia, New Guinea and off-shore islands that all aspects of its basic biology are the same in all populations, but comparisons of our results with data from other populations suggest that there may be differences in size and sexual dimorphism.

Frozen embryos? Torpor during pregnancy in the Tasmanian short-beaked echidna Tachyglossus aculeatus setosus

We studied the interaction between torpor and reproduction in free-ranging female Tasmanian echidnas using a combination of techniques including urogenital smears, hormone analysis, ultrasonography, external temperature loggers and camera traps. Male echidnas initiated mating activity by locating hibernating females. All females that mated or were disturbed by males prior to July 27 re-entered hibernation, including many that were pregnant. Pregnant females only entered hibernation in early pregnancy when plasma progesterone concentrations were about twice basal and progesterone then remained constant during torpor. By re-entering hibernation pregnant females extended their gestation period and delayed egg-laying. Progesterone peaked 4-6days before egg-laying, then dropped rapidly.

Hormonal regulation of platypus Beta-lactoglobulin and monotreme lactation protein genes

Endocrine regulation of milk protein gene expression in marsupials and eutherians is well studied. However, the evolution of this complex regulation that began with monotremes is unknown. Monotremes represent the oldest lineage of extant mammals and the endocrine regulation of lactation in these mammals has not been investigated. Here we characterised the proximal promoter and hormonal regulation of two platypus milk protein genes, Beta-lactoglobulin (BLG), a whey protein and monotreme lactation protein (MLP), a monotreme specific milk protein, using in vitro reporter assays and a bovine mammary epithelial cell line (BME-UV1). Insulin and dexamethasone alone provided partial induction of MLP, while the combination of insulin, dexamethasone and prolactin was required for maximal induction. Partial induction of BLG was achieved by insulin, dexamethasone and prolactin alone, with maximal induction using all three hormones. Platypus MLP and BLG core promoter regions comprised transcription factor binding sites (e.g. STAT5, NF-1 and C/EBPα) that were conserved in marsupial and eutherian lineages that regulate caseins and whey protein gene expression. Our analysis suggests that insulin, dexamethasone and/or prolactin alone can regulate the platypus MLP and BLG gene expression, unlike those of therian lineage. The induction of platypus milk protein genes by lactogenic hormones suggests they originated before the divergence of marsupial and eutherians.

Examining the role of testosterone in mediating short-term aggressive responses to social stimuli in a lizard

Hormones have been suggested as a key proximate mechanism that organize and maintain consistent individual differences in behavioural traits such as aggression. The steroid hormone testosterone in particular has an important activational role in mediating short-term aggressive responses to social and environmental stimuli within many vertebrate systems. We conducted two complementary experiments designed to investigate the activational relationship between testosterone and aggression in male Egernia whitii, a social lizard species. First, we investigated whether a conspecific aggressive challenge induced a testosterone response and second, we artificially manipulated testosterone concentrations to examine whether this changed aggression levels. We found that at the mean level, plasma T concentration did not appear to be influenced by an aggression challenge. However, there was a slight indication that receiving a challenge may influence intra-individual consistency of plasma T concentrations, with individuals not receiving an aggression challenge maintaining consistency in their circulating testosterone concentrations, while those individuals that received a challenge did not. Manipulating circulating testosterone concentrations had no influence on either mean-level or individual-level aggression. Combined with our previous work, our study adds increasing evidence that the relationship between testosterone and aggression is not straightforward, and promotes the investigation of alternative hormonal pathways and differences in neuro-synthesis and neuroendocrine pathways to account for species variable testosterone - aggression links.

Advances in the captive breeding and reproductive biology of the short-beaked echidna (Tachyglossus aculeatus)

Captive breeding of the short-beaked echidna (Tachyglossus aculeatus) has proven a difficult challenge; as recently as 2009, there were fewer than 10 echidnas born in captivity. We present observations of captive reproductive behaviour following video surveillance and measurements of body temperature collected from six captive female echidnas over a six-year period. In the first series of observations (2009–10) we examined the efficacy of artificial burrow boxes as possible aids for reproductive success. Females with access to burrow boxes had significantly higher levels of reproductive activity (P = 0.001), there was coincidental improvement in the production of eggs or pouch young (two eggs, one unhatched and one offspring). During 2009–10, a range of reproductive behaviours (courtship, copulation and postcopulation) were documented and analysed, as were new observations of oestrous cycle activity. Female body temperature was characteristically stable during egg incubation during this study and has the potential to be used as a tool for the assessment of reproductive status. Following initial observations, burrow boxes and infrared lamps were implemented as standard husbandry in our echidna breeding facility and the effects on reproductive success were monitored, albeit less intensively, for a further four years (2011–14). Although no direct causal effect could be ascribed, the use of burrow boxes and heat lamps coincided with a total of 13 young being born to four females in the last four years (2011–14). These female echidnas were found to be receptive at intervals throughout the breeding season, both before and after presumed incubation phases, suggesting that captive animals exhibit polyoestry. In 2012 and 2014, the same female showed evidence of producing two young from one breeding event.

Endocrine control of embryonic diapause in the Australian sharpnose shark Rhizoprionodon taylori

The reproductive cycle of the Australian sharpnose shark, Rhizoprionodon taylori, includes a temporary suspension of development at the commencement of embryogenesis termed embryonic diapause. This study investigated levels of 17β-estradiol (E₂), testosterone (T) and progesterone (P₄) in plasma samples of mature wild female R. taylori captured throughout the reproductive cycle and correlated them with internal morphological changes. Levels of T were elevated through most of the embryonic diapause period, suggesting a role of this hormone in the maintenance of this condition. Increasing plasma T concentrations from late diapause to early active development were associated with a possible role of androgens in the termination of embryonic diapause. As in other elasmobranchs, a concomitant increase of E₂ with ovarian follicle size indicated a direct role of this hormone in regulating vitellogenesis, while a peak in P₄ suggested this hormone is associated with preovulation and ovulation. Additionally, significant correlations between photoperiod or water temperature and maximum follicular diameter and hepatosomatic index suggest that these abiotic factors may also play a role triggering and regulating the synchrony and timing of reproductive events.

Observations of breeding behaviour and possible infanticide in a wild population of Tasmanian echidnas (Tachyglossus aculeatus setosus)

We describe field observations of Tasmanian echidna behaviour, including possible infanticide, where males damaged and entered nursery burrows. We also present the second report of a female producing a second offspring within a single reproductive season after the loss of her first young at an early stage.

Environmental endocrinology

The rapidly evolving discipline of environmental endocrinology is briefly reviewed from the 'heroic era' to the present. Environmental endocrinology has developed in response to the need to understand how hormones modulate and control physiological processes in animals exposed to the exigencies of their particular, natural, environment. This has only been made possible through spectacular developments in hormone assay techniques which now make feasible hormone measurements on microlitre volumes of body fluids. The results of some recent research programmes working on animals in the field are reviewed. These include the reproductive responses of migratory birds in the Arctic, the role of antidiuretic hormone in the survival of desert rodents and marsupial wallabies, some interesting behavioural effects of glucocorticoids in reptiles, and the dynamic interplay between hormones and social status in primates.

Rewarming rates and thermogenesis in hibernating echidnas

We measured body temperatures (T(b)) in 14 free-ranging echidnas (Tachyglossus aculeatus) using implanted data-loggers. An average of 1020+/-744 days of T(b) data was recorded from each animal. The average maximum T(b) was 35.3+/-0.7 degrees C (n=14), and the lowest T(b) was 4.7 degrees C. Detailed analysis of rewarming events from four echidnas showed rewarming time to be dependent on initial T(b) (rewarming time in hours=15.6-0.41T(initial), n=31) with an average rewarming rate of 1.9+/-0.4 degrees C h(-1). Based on an hourly sampling rate, the peak rewarming rate was found to be 7.2+/-0.8 degrees C h(-1) (n=12), which was measured at a mean T(b) of 26.2+/-2.4 degrees C. This rate of heating was calculated to be equivalent to a peak oxygen consumption rate of 1.4+/-0.2 ml O2 g h(-1), approximately 9 times the basal metabolic rate. We found that a plot of rate of change of T(b) against T(b) for the entire data set from an individual echidna provided a useful summary and analytical tool.