ON TEMPORAL VARIATION AND CONFLICTING SELECTION PRESSURES: A TEST OF THEORY USING NEWTS

Abstract

Most studies that examine conflicting selection pressures hold resources and risks constant, despite their ubiquitous fluctuation. Since little is known about the consequences of neglecting this variation, we examined the temporal response of male red-spotted newts, Notophthalmus viridescens, to conflicting female pheromones and damage-release alarm chemicals signaling predation. After a single exposure in both the laboratory and field, males were attracted to female odor and avoided conspecific alarm chemicals. Response to these combined cues depended on time after exposure, with males initially avoiding, and then being attracted to, the cue combination. This response shift was due to the resource and risk declining at different rates, and female odor accelerating male recovery from antipredator behavior. In the laboratory, males suppressed activity when exposed to alarm chemicals alone but increased their activity when female odor was added. Iterative exposures through the breeding season revealed that, as male mate search activity declined, male avoidance of alarm chemicals increased, but alarm chemical production appeared unchanged. Thawing dates differed between ponds of the same and different populations, which offset levels of mate search activity and consequently alarm chemical avoidance. As a result, simultaneous pond surveys made it appear as though there was geographic variation in reproductive and predator-avoidance behaviors. However, when thawing dates were aligned, the time courses of reproductive and predator-avoidance behaviors for the ponds coincided, demonstrating that observed site differences were predominantly due to different behavioral onsets, which would have gone overlooked had the larger temporal scale not been considered. These results indicate that temporal variation can be easily mistaken for geographic variation in behavior, increasing the potential for data interpretation errors. These studies underscore the importance of considering temporal variation when examining conflicting selection pressures.