Effects of food and thermal regimes on body condition indices and skin colouration in corn snakes

Abstract

One of the open problems in evolutionary ecology is signal reliability. While the view that signals need to be costly to be honest has attracted most attention, this type of signals may apply only to some contexts. Also, different views exist about the nature of costs involved in signal honesty, and the classification and examination of these costs remains controversial. Pigmentary-based colouration of animal integuments has received considerable attention among researchers seeking to explain what maintains the honesty of visual signals, but support for existing hypotheses is far from conclusive. Here we use a whole-animal approach and consider a distinct time scale, the period of juvenile growth, to test the effects of different feeding and thermal regimes on different physical parameters and skin colouration in corn snakes Pantherophis guttatus. Postnatal body length growth rate and body mass index (BMI) were sensitive to the thermal, but not to the food regime. The length of intervals between skin shedding was shorter and the short-wavelength reflectance of dorsal skin was higher for snakes receiving food more frequently and having an uninterrupted possibility to thermoregulate. This work suggests that if juvenile corn snakes are environmentally constrained, their preferred life history strategy is to grow at faster rates. The study adds to the growing body of evidence in that BMI may not accurately reflect individual condition in reptiles. Instead, this study demonstrates that the length of shedding intervals and the short-wavelength component of skin colouration may be used in this animal system as proxies of the individual’s condition or quality, possibly reflecting exposure to environmental stress or an ability to cope with it.