Sex differences and seasonal trade-offs in response to injured and non-injured conspecifics in red-spotted newts, Notophthalmus viridescens

Abstract

Injured prey often release alarm chemicals that induce antipredator behaviors in conspecifics. Injured or killed prey most likely release a wide array of chemicals in addition to alarm substances, such as sexual pheromones, which could enhance or compromise antipredator responses. Thus, damage-release cues provide an excellent opportunity to examine the influence of seasonally fluctuating sexual pheromones on antipredator behaviors. We used a series of laboratory and field experiments and meta-analysis to examine seasonal changes and sex differences in the response of red-spotted newts, Notophthalmus viridescens, to the odor of non-injured conspecifics and conspecific tissue extracts, the latter of which presumably contain pheromones of non-injured conspecifics combined with alarm chemicals signaling predation. During the peak of the breeding season, males were attracted to females and multiple males, but did not avoid tissue extracts from either sex. As the breeding season waned, male attraction to females and males decreased, while avoidance of alarm extracts from both sexes concurrently increased. In contrast to male behavior, females were indifferent to both sexes during the breeding season, and showed significant avoidance only of female extract. As the breeding season progressed, females displayed no change in response to treatments. Male and female responses to female rinse and extract differed significantly, but their response to male treatments did not. During the non-breeding season, both males and females were indifferent to the odor of conspecifics and avoided conspecific tissue extracts, with the magnitude of male avoidance greater than that of female avoidance, suggesting sex differences in response to alarm cues in both the breeding and non-breeding seasons. In general, both male and female response to conspecific odor and tissue extracts covaried positively, suggesting that social pheromones can be detected within conspecific macerates and compromise alarm-chemical avoidance. Many of the sex differences in both seasons are likely explained by selection pressures imposed on males to intensely mate search during the breeding season, suggesting that the mating system of newts directly influences predation threat during reproductive activity and may have significant indirect consequences on risk during the non-breeding season.