Phenotypic consequences of nest-site selection in black rat snakes (Elaphe obsoleta)

Nest-site selection is the only behaviour that can be considered parental care in most oviparous reptiles because eggs are abandoned after laying and because incubation conditions resulting from nest-site selection can have profound effects on offspring. During a 7-year study of black rat snakes, Elaphe obsoleta (Say in James, 1823), we investigated phenotypic effects of incubation temperature on hatchlings, monitored temperatures in nests, and determined the preferred nesting temperature. Temperatures of communal nests were higher than those of single-female nests. In the laboratory, females preferred to nest at temperatures most similar to those of communal nests. Hatchlings from eggs incubated at temperatures similar to those in the warmer communal nests hatched faster, were longer, swam faster, were less aggressive, and had fewer scale anomalies than hatchlings from eggs incubated at temperatures similar to those in single nests. A possible disadvantage of communal nests is that eggs in communal nests may be at greater risk to parasitism by Nicrophorus pustulatus (Herschel, 1807). The incubation experiment allowed a test of a key assumption of a model proposed to explain environmental sex determination. Contrary to that assumption, we found no evidence that incubation temperature affected males and females differently. Our results might explain why temperature-dependent sex determination appears not to occur in snakes.