Phenotypic Plasticity in Reproductive Traits: Evidence from a Viviparous Snake

Abstract

A number of recent studies have indicated that life history characteristics (e.g., number of offspring, offspring size, age at sexual maturity) are strongly affected by proximate environmental factors such as prey availability. Evaluating this phenotypic plasticity will be crucial to a complete understanding of the evolution oflife history traits, because the occurrence of such variability casts doubt on the common assumption that the values of life history characteristics expressed in nature are the outcome of long-term natural selection. In this study, we manipulated the diets of a captive-bred colony of the viviparous snake Thamnophis marcianus to determine to what degree the reproductive characteristics of this species were determined by food intake. We found that both number of offspring and clutch mass were significantly affected by prey availability, but that relative clutch mass and offspring size were fixed relative to diet. Our data suggest that like other organisms, T. marcianus shows a gradient in phenotypic plasticity, with some traits more canalized than others. Therefore, intraspecific comparisons of life history characteristics should not be made without information on which traits are subject to phenotypic plasticity.

Allometry of cranial morphology, gape size and ingestion performance in the banded watersnake (Nerodia fasciata) feeding on two types of prey

“…Notable differences in slope between juveniles and adults that coincide with changes in diet have also been observed in a python (Morelia viridis) (Natusch and Lyons, 2012) and a pitviper (Agkistrodon piscivorus) (Vincent et al, 2004). A shift in prey type near maturity may be a corollary to energy demands for reproduction, in which prey with a higher energy content are selected (Santos et al, 2000), in turn increasing reproductive output (Ford and Seigel, 1989). Comparisons of the gape allometry across a broad range of snake taxa, that do or do not ontogenetically shift prey type, are necessary to confidently demonstrate and explain the non-linear relationship between gape and body length for N. fasciata.…”

When does a reproducing female viper (Vipera aspis) ‘decide’ on her litter size?

“…Thus, litter size in a female V. aspis is affected in a complex way by her body size, her pre-existing energy stores, and her food intake in the weeks immediately before ovulation. Experiments on the influence of energy input on reproductive output have provided valuable information in many vertebrate species (Arcese & Smith, 1988;Bolton, Momaghan & Houston, 1993;Monaghan & Nager, 1997 and references therein) including snakes (Ford & Seigel, 1989Seigel & Ford, 1991Gregory & Skebo, 1998). However, in a capital breeding species, the levels of pre-vitellogenic maternal reserves largely determine reproductive output (Bonnet, Naulleau, Shine et al, 2001).…”

“…If so, correlations between mass gain and reproductive output might reflect such additional factors, rather than a straightforward effect of enhanced feeding rates on litter sizes. Experimental manipulation of food supplies offers a direct and powerful approach to resolving such uncertainties (Ford & Seigel, 1989;Seigel & Ford, 1991Gregory & Skebo, 1998). To investigate the relative influences of the initial body stores and subsequent energy intake during vitellogenesis on the reproductive output of female vipers, they were maintained in captivity, their rates of prey consumption directly modified, and the effects of this manipulation on the numbers of offspring that they produced were examined.…”

Variation in vital‐rate sensitivity between populations of Texas horned lizards

“…Depredation of adults has increased in recent years at WR3 following human-induced habitat disturbance (Wolf et al 2013), or adult survival in the absence of humans could be even higher at WR3 compared to CWMA. Clutch size and hatchling health upon emergence may be affected by female nutritional condition and body size, which may in turn be affected by habitat quality and food abundance (Ballinger 1983;Ford and Seigel 1989;James and Whitford 1994), factors that managers can conceivably modify. Unfortunately, hatch rate may be largely determined by climatic conditions.…”