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Posted by snakeymama on February 04, 2003 at 17:45:49:
In Reply to: Growth rates posted by creep77 on February 01, 2003 at 20:28:38:
The topic of Crotalus growth rates is a very interesting one. The truth is that rules governing growth efficiency are not well-known. Current research is hotly pursuing the exact topics that Brendan inquires about, everything from how temperature, frequency and size of meals, and sex hormones affect how well a snake turns food into more snake.
The paper that you cite is interesting because it shows that postpartum female Crotalus fed different diets do not have different growth rates. Research into just this topic by Steve Beaupre and others has highlighted the idea that postpartum females are so energetically drained from reproduction that they funnel all acquired energy into replenishing their fat stores. So, of course there are no differences in growth in postpartum females fed different diets: their growth axis is completely shut down, and all food goes to fat. So, this study does not provide evidence of a lack of food effect on growth in Crotalus, just in post-partum females which are subjected to very different ecological pressures than males and juveniles.
More pertinent to this discussion is the fact that numerous studies have shown clear-cut effects of food on growth. These effects are much more obvious in juveniles and males than they are in female Crotalus, because the high costs of reproduction in females often keeps them from growing as fast as males. This may be why they are smaller than males. A few interesting references are listed below.
In a recent study in my lab, we found a very clear-cut effect of food intake on growth in C. atrox. Neonates were raised on two diets (one mouse every week vs. one mouse every three weeks) for two years. At the end of the study, the high intake snakes had SVLs in excess of 1 m, whereas the low intake snakes were still quite small. There were no sex differences. The most interesting finding in all this is that we were able to produce females in excess of 1 m just by feeding them a lot and keeping them from reproducing. So, male rattlesnakes may be larger than females purely because females put so much energy into reproduction.
Also, the high intake females reached reproductive maturity in their second year. So, power-feeding neonate snakes can give you reproductively active snakes much earlier than what would happen in the wild. This is good info for breeders, although the long-term effects of the high intake feeding schedule are unknown. Snakes may indeed have health problems from this, but this is very poorly studied.
Beaupre, S. J. 2002. Modeling time-energy allocation in vipers: individual responses to environmental variation and implications for populations. In Biology of the Vipers (G. W. Schuett, M. Hoggren, M. E. Douglas, and H. W. Greene, eds), Eagle Mountain, Utah: Eagle Mountain Publishing.
Ford, N. B. and R. A. Siegel. 1994. An experimental study of the trade-offs between age and size at maturity: effects of energy availability. Functional Ecology 8:91-96.
Forsman, A. and L. E. Lindell. 1996. Resource dependent growth and body condition dynamics in juvenile snakes: an experiment. Oecologia 108:669-675.
Scudder-Davis, R.M. and G.M. Burghardt. 1996. Ontogenetic changes in growth efficiency in laboratory-reared water snakes of the genus Nerodia. The Snake 27:75-84.