Timing of parturition in two species of viviparous lizard: influences of β-adrenergic stimulation and temperature upon uterine responses to arginine vasotocin (AVT)

Abstract

The southern snow skink Niveoscincus microlepidotus is a viviparous alpine lizard with biennial reproduction, in which embryos are fully developed before winter but parturition is delayed until spring. We aimed to determine whether, in this species, in vitro uterine preparations are responsive to arginine vasotocin (AVT) and prostaglandin (PGF(2alpha)) in autumn and spring, and whether pre-treatment with the beta-adrenergic agonist isoproterenol decreases the effectiveness of AVT in stimulating uterine contractions. Using the spotted snow skink (Niveoscincus ocellatus), an annually breeding species, we aimed to determine influences of temperature and the beta-adrenergic system upon the response to AVT in vivo. In both N. microlepidotus and N. ocellatus females are more responsive to AVT than to PGF(2alpha), and that the response to AVT is decreased, but not prevented, by beta-adrenergic stimulation. In N. microlepidotus, uteri are equally responsive in both seasons to the hormones administered. In N. ocellatus environmental conditions, specifically, temperature, modulate the response to AVT in vivo with the time to parturition increasing as temperature decreases. We conclude that in these viviparous squamates the endocrine cascade leading to parturition is modulated by the beta-adrenergic system, and that this may reflect the mechanism by which the timing of parturition is tied to suitable environmental conditions.

Experimental evidence of early costs of reproduction in conspecific viviparous and oviparous lizards

“…Previous studies on reptiles have successfully used this drug to induce parturition in viviparous lizards, at very different concentrations across species (Guillette et al. , 1991; Atkins et al. , 2006).…”

“…At the same period, we used Arginine vasotocin (AVT; Sigma-Aldrich, V0130) to induce parturition in viviparous females. Previous studies on reptiles have successfully used this drug to induce parturition in viviparous lizards, at very different concentrations across species (Guillette et al, 1991;Atkins et al, 2006). Based on prior tests, we injected intraperitoneally 60 lL of AVT diluted in PBS (0.02 lg lL )1 ).…”

An Experimental Study of the Gestation Costs in a Viviparous Lizard: A Hormonal Manipulation

“…Previous studies on reptiles have successfully used this drug to induced parturition in viviparous lizards, at very different concentrations across species (Guillette et al 1991;Girling et al 2002;Atkins et al 2006;Bleu et al 2012a). Females were randomly allocated to each treatment group: AVT-injected females ( ) and unmanipulated control females ( ).…”

“…The hormones oxytocin in mammals and the arginine vasotocin (AVT) in Reptilia are appropriate for these types of experiments because they induce early parturition or oviposition when injected into pregnant/ gravid females (Guillette and Jones 1982;Guillette et al 1991;Feldman 2007). Depending on species, on concentrations and on the timing of the injection, AVT will induce partial or full parturition (oviposition) in viviparous (oviparous) squamates (e.g., Guillette 1979;Summers et al 1985;Atkins et al 2006).…”

Effects of luteectomy in early pregnancy on the maintenance of gestation and plasma progesterone concentrations in the viviparous temperate lizard Barisia imbricata imbricata

“…Parturition has been widely studied in several mammalian species (for review, see [41,42]); however, few papers have addressed this process in reptiles (for review, see [13,34,12,43,44]). Nevertheless, several authors agree that the stimulation of uterine contraction associated with parturition involves a complex interaction between several hormones steroids (P 4 and estradiol 17β), arginine-vasotocine (AVT) and prostaglandins [45,46].…”