Plasma progesterone secretion during gestation of the captive short-beaked echidna

Abstract

This study describes the progesterone profile during pregnancy in sexually mature female captive short-beaked echidnas (Tachyglossus aculeatus aculeatus). Echidnas were monitored daily by video surveillance to confirm key reproductive behaviour. Plasma samples were collected and pouch morphology was assessed three times a week. The pouch of the female echidna only develops during gestation and it was possible to create a four-stage grading system using the most distinguishable characteristics of pouch development. Maximum pouch development was associated with declining progesterone concentrations, with the pouch closing in a drawstring-like manner at oviposition. Control of pouch development in pregnant echidnas is not yet clear but later pouch development is associated with a decrease in progesterone and pouch closure and may be under mechanical influences of the egg or young in the pouch. The length of pregnancy was 16.7 ± 0.2 days with a 15.1 ± 1.0 days luteal phase followed by an incubation period in the pouch. Eggs could be detected in utero at least 4 days before oviposition. Plasma progesterone peaked at 10.5 ± 0.9 ng/mL within 12 days of mating but then declined to basal levels within 1 day of oviposition and remained basal throughout egg incubation, confirming that progesterone is elevated throughout pregnancy and that gestation does not extend beyond the luteal phase. After the loss of an egg or pouch young, most females entered a second oestrous cycle and ovulated, suggesting echidnas are seasonally polyoestrous. The duration of the luteal phase in the echidna corresponds with that observed in other mammals.

Optimizing captive short‐beaked echidna (Tachyglossus aculeatus) fecal sample identification and hormonal analysis

“…An iterative process was used to calculate baseline hormone metabolite concentrations using the hormLong package (Fanson & Fanson, 2015) in "R" (version 3.6.2), as described by Dutton-Regester et al (2021).…”

“…The average weight of female and male echidnas was 4.4± 0.04 and 5.2± 0.04 kg, respectively. The echidnas were housed and maintained as previously described by Dutton-Regester et al (2021). The echidnas were obtained and maintained under the Queensland Government EPA scientific purposes permit WISP153546614 and the experiment was conducted with the approval of the University of Queensland Animal Ethics Committee (SAFS/334/17).…”

Reproductive behaviour before and after oestrus and oviposition in the captive short-beaked echidna (

“…Oestrus in the female echidna remains elusive, at least to human observers, due to a lack of overt behavioural cues and the difficulty of detecting biologically meaningful changes in plasma oestrogen (Dutton-Regester et al 2021) and/or faecal oestrogen metabolites (Dutton-Regester et al submitted to General and Comparative Endocrinology). It is possible that female echidnas undergo a 'silent' behavioural oestrus, communicaingt their receptivity by means of chemical signals (i.e.…”

“…Once the female has ovulated and the influence of presumed systemic oestradiol on behaviour has abated, progesterone secreted by the corpus luteum associated with the luteal phase of pregnancy increases (Dutton-Regester et al 2021), heralding the possibility of further changes in behaviour. In the case of the monotremes, gestation terminates in oviposition (egg laying).…”

Maternal care and juvenile development of captive-bred short-beaked echidnas (

“…in New Guinea, and studies of echidnas in Tasmania (Morrow et al 2009;Morrow and Nicol 2013) have identified some significant variations, such as males mating with females in deep hibernation, and a shorter lactation period than that of other subspecies. In the wild, breeding is seasonal, occurring from June to mid-September, with females producing a single egg 16-24 days after mating (Beard and Grigg 2000;Rismiller and McKelvey 2000;Nicol and Andersen 2007;Dutton-Regester et al 2021). The egg is incubated in the pouch of the female for 10-11 days before hatching and the young is carried and suckled in the pouch for a further 23-63 days, before being deposited in a nursery burrow (Griffiths 1989;Abensperg-Traun 1989;Beard and Grigg 2000;Rismiller and McKelvey 2000;Morrow and Nicol 2013).…”