Reproductive output, costs of reproduction, and ecology of the smooth snake, Coronella austriaca, in the eastern Italian Alps

Abstract

A 5-year mark-recapture study of smooth snakes (Coronella austriaca) in the Carnic Alps (1100 m above sea level) of north-eastern Italy provided extensive information on the biology and life-history of these small viviparous snakes. Offspring were relatively large (mean=15 cm total length, 2.9 g) when they were born in late summer, and females grew to maturity (44 cm, 50 g) in approximately 4 years. Larger neonates retained their size advantage for at least 12 months, but did not have a higher probability of survival. Although sexual size dimorphism (at birth and at mean adult body sizes) was minor, the sexes differed significantly in several respects. Females grew faster than males during juvenile life, and adult females diverged in dietary habits from the rest of the population. Whereas juveniles (of both sexes) and adult males fed primarily on lizards, larger females shifted to feeding less frequently, but taking larger prey (mammals and snakes). Reproductive output increased strongly with maternal body size: larger females reproduced more frequently, produced larger litters of larger neonates, had higher relative clutch masses (RCMs), and had a lower proportion of stillborn off-spring. Most females produced a litter every 2nd or 3rd year. We did not detect significant year-to-year variation in reproductive traits over the 5 years of our study. Females were consistent from one litter to the next in several traits (e.g., litter sizes, offspring sizes and shapes, proportions of stillborn neonates, RCMs), but this consistency was due to differences in body size among females rather than to size-independent maternal effects. Overall litter sex ratios averaged 50/50, but sex ratios tended to be more male-biased in litters that were unusually large relative to maternal body size, and in litters containing a high proportion of stillborn offspring. "Costs" of reproduction appear to be high in this population, in terms of both energy allocation and risk. Reproduction reduced growth rates, and females that recovered condition more quickly in the year after reproduction were able to reproduce again after a briefer delay. Mortality was highest in reproducing females with high RCMs, and in females that were very emaciated after parturition. The marked increase in reproductive output with increasing maternal body size in C. austriaca may reflect a reduction in "costs" as females grow larger, and the dietary shift to larger prey may enhance the rate that females can accumulate energy for reproduction.

Reproduction and summer mortality of blue mussels Mytilus edulis in the Magdalen Islands, southern Gulf of St. Lawrence

“…The reduction in future reproductive capacity caused by a decrease in survival or growth in exchange for increased current reproductive effort is called 'reproductive cost' (Reznick 1985). Reproductive cost is often measured in terms of lower survival of reproducers (Calow 1973, Tallamy & Denno 1982, Lemckert & Shine 1993, Boyd et al 1995, Jacobsen et al 1995, Luiselli et al 1996 and is called 'survival reproductive cost' (Bell 1980). As indicated by Roff (1992), it is hard to imagine that reproduction does not deplete the resources of an organism, thereby making it more prone to stress-related sources of mortality.…”

Reproductive strategies in snakes

“…Such energy costs may reduce her future growth rate and thus, probable fecundity (Bell 1980;Shine 1980). Mortality costs are so high for females in some snake species that many produce only a single litter in their lifetimes (Madsen & Shine 1992a, 1994Luiselli et al 1996Luiselli et al , 1997Brown & Weatherhead 1997;Bonnet et al 2002). Such costs impose strong selection to adjust reproductive tactics to local conditions of food supply and predator densities, Ford (1996) thus generating interspecific and intraspecific divergence in reproductive tactics.…”

Food habits of the green lizard,Lacerta bilineata, in central Italy and a reliability test of faecal pellet analysis

“…Diaz, 1995), whereas this pattern is frequently found in other squamates, including snakes (cf. Luiselli & Agrimi, 1991;Luiselli et al, 1996). Conversely, separation along trophic dimensions between conspecifics of different ages ( = sizes) or between different species in Mediterranean lacertids is usually based simply on prey size, with smaller predators taking smaller prey (cf.…”