Delayed parturition: constraint or coping mechanism in a viviparous gekkonid?

Abstract

The extended gestation of fully developed embryos in viviparous reptiles can be the consequence of a lack of appropriate environmental conditions and/or an adaptive contribution to increased offspring viability. I examined the cause and effects of extended gestation in a gekkonid lizard Hoplodactylus maculatus, which delays parturition of developed embryos for up to 9 months from autumn into a second spring. Comparisons of microhabitat temperatures showed that thermal opportunities were equally conducive to birth in autumn and spring. The responsiveness of females to a hormonal stimulant for parturition also did not differ between these seasons. Multiple offspring traits were measured, including body size, locomotory ability and lipid reserves, and were found not to increase with extended gestation. Incorporating these results with previously published evidence for microhabitat thermal variation, I discuss whether delayed parturition may be an adaptive mechanism maintained by the selective pressures of an uncertain thermal environment on components of reproduction, including vitellogenesis, maternal birthing cues and neonatal survival.

Maternal basking regime has complex implications for birthdate and offspring phenotype in a nocturnally foraging, viviparous gecko

“…These potentially include a reduced physical burden, an earlier resumption of feeding at normal rates, and an earlier return to warmer T sel , all of which potentially enhance maternal growth. In this species with invariant clutch size, larger maternal size is associated with larger offspring size, both within our population (Rock and Cree, 2003;Preest et al, 2005;Rock, 2006; present study) and among populations . Thus, faster maternal growth would mean more rapid attainment of a size favouring larger offspring (and thus, potentially, lifetime reproductive success).…”

“…Husak, 2006; but see Hare et al, 2012). Although the survival value for nocturnally foraging geckos is unknown, rapid locomotion might reduce predation risk when basking (Gibson et al, 2015) and when moving between daytime retreats (Rock, 2006). With regard to induced births, our intervention produced the intended difference in mean gestation length compared with spontaneous births, with no interaction between delivery mode and regime.…”

“…These long-lived geckos (30+ years; Sheehan et al, 2004) are nocturnal foragers that thermoregulate by day within rock retreats (Rock et al, 2002;Rock and Cree, 2008); they also bask cryptically in the field (Gibson et al, 2015) and laboratory Rock and Cree, 2003). At Macraes Flat, pregnancies begin in spring and embryos are fully developed by autumn, but birth does not occur until the following spring, meaning that most females reproduce biennially (Cree and Guillette, 1995;Rock, 2006; S. Penniket, Trends in body size and female reproductive frequency with elevation and temperature in a primarily nocturnal, viviparous gecko, MSc thesis, University of Otago, 2012). In contrast, females in most lower-elevation populations appear to reproduce annually, with births in autumn after a 3-5 month pregnancy (Cree, 1994;Girling et al, 1997;S.…”

Timing in a fluctuating environment: environmental variability and asymmetric fitness curves can lead to adaptively mismatched avian reproduction

“…Conservative bet-hedging has frequently been invoked in the evolution of timing traits in animals and plants, for example, the timing of bolting in monocarpic perennials [42], diapause in copepods [43], parturition in viviparous lizards [44], and laying dates in woodland passerines [32]. Variance in fitness reduces the geometric mean relative to the arithmetic mean, and thus bet-hedging is typically assumed to involve processes that minimize fitness variance across generations, potentially at the expense of reduced arithmetic mean fitness [13,45].…”

First Observation of the Parturition and Peripartum Events in a Harbor Porpoise (<I>Phocoena phocoena</I>)

“…Parturition (i.e., the process by which the fetus is expulsed from the uterus to the extra-uterine environment [Challis et al, 2000]) and peripartum events are generally difficult to observe among wild animals because they generally tend to hide or move away from potential disturbances (Fedak et al, 2009). In some cases, females can even voluntarily delay parturition if environmental conditions are not favorable (Rock, 2006). Parturition in some marine mammals species has been documented, but mostly for pinnipeds that usually give birth on land (Ronald & Thomson, 1981;Stewart et al, 1981;Frank et al, 1985;Lawson & Renouf, 1985;Eliason et al, 1990;Layna et al, 1999;Blanchet et al, 2006;Acevedo et al, 2008).…”