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Discrimination of Variation in a Male Signaling Trait Affects Detection Time in Visual Predators

Authors


J. Andrew Roberts, Department of Evolution, Ecology, and Organismal Biology, The Ohio State University at Newark, Newark, OH, 43055, USA.
E-mail: roberts.762@osu.edu

Abstract

In many species, expression of elaborate male characteristics likely represents a balance between sexual selection and natural selection via predation, as male traits selected to elicit rapid detection or response on the part of females also increase detection by predators. Predation costs are frequently inferred, but the underlying mechanisms associated with specific traits have rarely been directly explored. Males of the wolf spider Schizocosa ocreata (Araneae: Lycosidae) exhibit a sexually selected signaling trait (dark tufts of bristles) on their forelegs, and are sympatric with a number of visually hunting generalist predators, including cannibalistic conspecifics, that may impact spider survival. Here we use latency of orientation response of the American toad, Bufo americanus (Anura: Bufonidae), to video, ‘virtual’ courting S. ocreata male stimuli as an index of predator detection, and latency of orientation response of female S. ocreata to the same stimuli as an index of conspecific detection. When compared with stimuli representing the population average, elimination of the signal trait had no significant effect on predator detection but did increase latency to orient in conspecifics. Increasing the size of the signal trait had no effect on conspecific detection but did significantly reduce latency to orient for predatory toads. Results clearly indicate that for a courting male spider of a given size and vigor level, variation in the expression of a secondary sexual characteristic alone can incur differential direct costs and benefits by influencing latency of orientation to visual signals by predators and conspecifics.

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