Reproductive versus ecological advantages to larger body size in female snakes, Vipera aspis

Abstract

Bonnet, X., Naulleau, G., Shine, R. and Lourdais, O. 2000. Reproductive versus ecological advantages to larger body size in female snakes, Vipera aspis. -Oikos 89: 509-518.Body size can influence an organism's microevolutionary fitness either via ecological factors (ecological selection) or changes in reproductive output (sexual or fecundity selection). Published studies on sexual dimorphism in reptiles have generally focussed on sexual-selective forces on males, under the implicit assumption that the intensity of fecundity selection in females (and hence, overall selection on female body size) is likely to be relatively consistent among lineages. In this paper, we explore the degree to which larger body size enhances ecological attributes (e.g., food intake, growth, survival) and reproductive output (reproductive frequency, litter size, offspring size, offspring viability) in free-ranging female aspic vipers, Vipera aspis. The less-than-annual reproductive frequency of these animals allows us to make a direct comparison between females in years during which they concentrate on ''ecological'' challenges (especially building energy reserves) versus reproductive challenges (producing a litter). Because female snakes have limited abdominal space to hold the clutch (litter), we expect that fecundity should depend on body size. However, our data show that larger body size had a more consistent effect on ecological attributes (such as feeding rates and ''costs of reproduction'') than on reproductive output per se. Indeed, total reproductive output was maximised at intermediate body sizes. These results suggest that variation in female body size among and within species (and hence, in the degree of sexual dimorphism) may be driven by the ecological as well as reproductive consequences of body size variation in both sexes.

Fat Is Sexy for Females but Not Males: The Influence of Body Reserves on Reproduction in Snakes (Vipera aspis)

“…Although producing a large litter is more expensive than producing a small one (at least in terms of the energy content of the litter), the nonlinear relationship between reproductive effort and the sum of its associated costs may have favored the evolution of a high-body-condition threshold for reproduction. In female asp vipers, both the high survival and metabolic costs of reproduction are independent of the size of the litter (Bonnet et al, 2000c;Lourdais et al, 2001). Theoretically, the body-condition threshold enables females to save energy and to minimize survival costs during the 1-to 3-year phase of energy gathering between reproductive episodes.…”

“…Female vipers (Vipera aspis) experience high fecundity-independent costs of reproduction, both in terms of survival (Bonnet, Naulleau, and Lourdais, 2000a;Bonnet, Naulleau, Shine, and Lourdais, 2000c) and in terms of energetics during gestation (i.e., decrease in food intake) (Lourdais, Bonnet, and Doughty, 2001). Females reproduce on a 2-to 4-year cycle (Saint Girons, 1957;Naulleau, Bonnet, VacherVallas, Shine, and Lourdais, 1999).…”

Shelter availability, stress level, and digestive performances in the aspic viper

“…Previous studies provided important background (Saint Girons, 1957;Bonnet et al, 1999;Bonnet et al, 2000;Bonnet et al, 2001;Bonnet et al, 2002;Bonnet, 2011;Ladyman et al, 2003;Zuffi et al, 2009;Michel and Bonnet, 2010). Aspic vipers [Vipera aspis (Linnaeus 1758)] feed mainly on rodents and digestion is impeded when body temperature falls below 15°C (Naulleau, 1983).…”

Influence of body reserves and eye opacity on foraging behaviours of tiger snakes

“…As growth can be sustained by body reserves in snakes (Ji et al,'97), we may further expect that individuals in good body condition will take fewer risks than individuals in poor condition (Clark,'94). When using up body reserves for growth, a snake depletes its physiological asset; however, the energy and materials contained within body reserves still represent a resource that individuals might protect as body size correlates positively with reproductive success and reduces predation risk in both sexes (Bonnet et al, 2000). Overall, a snake with large body reserves may not feed whilst sloughing, both to preserve its physiological asset and also because a cessation of growth is unlikely.…”