Sex steroid correlates of female-specific colouration, behaviour and reproductive state in Lake Eyre dragon lizards, Ctenophorus maculosus

Abstract

In some species, females develop bright colouration to signal reproductive status and exhibit behavioural repertoires to incite male courtship and/or reduce male harassment and forced copulation. Sex steroids, including progesterone and testosterone, potentially mediate female reproductive colouration and reproductive behaviour. We measured associations among plasma profiles of testosterone and progesterone with variation in colour expression and reproductive behaviour, including unique courtship rejection behaviours, in female Lake Eyre dragon lizards, (Ctenophorus maculosus). At onset of breeding, progesterone and testosterone increased with vitellogenesis, coincident with colour intensification and sexual receptivity, indicated by acceptance of copulations. As steroid levels peaked around the inferred ovulation time, maximal colour development occurred and sexual receptivity declined. When females were gravid and exhibited maximal mate rejection behaviours, progesterone levels remained consistently high, while testosterone exhibited a discrete second peak. At oviposition, significant declines in plasma steroid levels, fading of colouration and a dramatic decrease in male rejection behaviours co-occurred. Our results indicate a generally concordant association among steroid levels, colouration, behaviour and reproductive events. However, the prolonged elevation in progesterone and a second peak of testosterone was unrelated to reproductive state or further colour change, possibly suggesting selection on females to retain high steroid levels for inducing rejection behaviours.

Effect of stress on female-specific ornamentation

“…Sex steroid hormones have been the focus of most work examining the hormonal regulation of lizard coloration, with evidence suggesting androgen regulation of male color (Cox et al, 2005;Rand, 1992) and (primarily) progesterone regulation of female-specific reproductive color (reviewed by Cooper and Greenberg, 1992;Jessop et al, 2009). However, these studies did not examine glucocorticoids.…”

Has contemporary climate change played a role in population declines of the lizard Ctenophorus decresii from semi-arid Australia?

“…To quantify the extent of dehydration imposed by our treatments, we measured plasma osmolality (the solute concentration of blood) by taking a blood sample from each lizard at the end of the treatment period, accessed from the sinus angularis at the corner of the mouth (Jessop et al, 2009). These blood samples were immediately centrifuged at 10,000 rpm for 2 min and the separated plasma stored in a freezer at -80°C until analysis.…”

Why are females ornamented? A test of the courtship stimulation and courtship rejection hypotheses

“…First, females may be physiologically unable to uncouple color expression and reproductive condition (Cooper 1984). In C. maculosus as in other lizards, color expression is associated with plasma steroid concentrations (Jessop et al 2009). Rather than decreasing after ovulation, plasma concentrations of progesterone and testosterone remain high until oviposition (Jessop et al 2009).…”

“…In C. maculosus as in other lizards, color expression is associated with plasma steroid concentrations (Jessop et al 2009). Rather than decreasing after ovulation, plasma concentrations of progesterone and testosterone remain high until oviposition (Jessop et al 2009). Because females maintain high steroid concentrations throughout the reproductive cycle and steroid concentrations are associated with color expression (Jessop et al 2009), females may be physiologically unable to reduce color expression when unreceptive.…”