The consistency of individual differences in behaviour: temperature effects on antipredator behaviour in garter snakes.

Differences among individuals are necessary for natural selection to occur. The extent and expression of these differences can limit the power of selection to cause evolutionary change. When individuals inconsistently express a trait, selection is less powerful. Labile traits such as behaviour are most likely to be inconsistent in their expression, because of the substantial role of environmental factors in their immediate expression. Previous work has focused on the consistency, or repeatability, of individual behaviour across different environments or within a single environment; little is known about how repeatability within an environment changes across environments. To address this issue, we examined the consistency of antipredator behaviour in juvenile garter snakes in different thermal environments. A group of 59 laboratory-born garter snakes Thamnophis ordinoides, was repeatedly assayed for sprint speed, distance crawled, and number of reversals performed during flight and antipredator display. Antipredator display showed very little variation and could not be analysed. Each individual was tested three times at each of three temperatures chosen to span the range of temperatures that snakes encounter in the field (15, 22.5, 30 degrees C). Temperature had substantial effects on the average expression of each behaviour; snakes crawled more slowly, for shorter distances, and performed fewer reversals at cooler temperatures. Individuals showed significant consistency in their behaviour, and this consistency of expression was not affected by temperature. Copyright 1999 The Association for the Study of Animal Behaviour.