Monday, October 22, 2012

Western diamondback rattlesnake females not anorexic during pregnancy

A southern Arizona Crotalus atrox at its den. JCM

Anorexia (cessation of feeding) is frequently associated with gestation in snakes. Several hypotheses have been proposed to explain this, most often it is obstruction of the digestive tract due to the presence of fetuses or eggs, i.e. the increase in eggs and embryos take up so much room that the female cannot get food through her gut. Using radiotelemetry, Schuett et al. (2012)  investigated the feeding and spatial ecology of a live-bearing viperid snake, the western diamond-backed rattlesnakes (Crotalus atrox). From 2001 to 2010, we determined the feeding frequency and home range size of 27 adult females during their active season (March–October) in the Sonoran Desert of Arizona. The authors addressed a central hypothesis: do
hunting and feeding occur throughout pregnancy? They also tested a corollary hypothesis: does pregnancy influence home range size? Other viperid snakes (including some rattlesnakes) have been show to greatly reduce their home range during pregnancy.

Hunting and feeding were documented from March to October and during pregnancy (June to mid-September). They found feeding frequency was significantly greater in late pregnancy, a result that is in sharp contrast to most other large-bodied vipers. Furthermore, home range sizes in gestating subjects did not differ from those in non-reproductive years. Births occurred from mid-August to mid-September and mean litter size was 3.4. Frequent feeding in C. atrox during gestation unquestionably provides energy and nutrients to the mother, which is likely important for survival, but such food consumption does not imply that nutrients are used by the fetuses. There is, however, recent evidence in other snakes, including a pitviper, that amino acids are transferred to fetuses. Feeding during pregnancy in C. atrox may be important for both income and capital mode reproduction. Hunting and feeding throughout gestation might be accomplished by having relatively small litters not burdened by a body cavity filled with fetuses. Thus, reduction in litter size may thus be a life-history (fecundity) trade-off that permits females to survive and maintain pregnancy in regions where drought and high temperatures are often extreme and chronic.

This paper is available in an early on-line view before publication.

Schuett, G. W., Repp, R. A., Amarello, M., Smith, C. F. (2012), Unlike most vipers, female rattlesnakes (Crotalus atrox) continue to hunt and feed throughout pregnancy. Journal of Zoology. doi: 10.1111/j.1469-7998.2012.00969.x

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