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Exploring the maintenance of and selection on two distinct male morphs in a Schizocosa wolf spider
The maintenance of variation in sexually-selected traits is of great interest in evolutionary biology. While strong directional selection imposed by female choice should deplete variation in male secondary sexual traits, this variation persists. This dissertation examines the persistence of a male sexual-trait dimorphism. First, I examine if two male morphs are genetically distinct. Then, I test whether the more ornamented morph incurs greater costs associated with predation, and shows greater behavioral plasticity in response to the threat of predation.^ Male sexual-trait dimorphisms may persist in a single population unless drift or selection fixes one male morph in a population. Using mitochondrial sequence data and microsatellite data, I tested whether two male morphs are genetically distinct in a population in Mississippi that exhibits both male morphs, and in localities in the Ohio Valley where only one male morph exists per location. I found for all locations, that despite having distinct secondary sexual traits, the two male forms are genetically indistinguishable.^ The persistence of a male polymorphism requires equal fitness of the morphs, and implies a trade-off within each morph. Natural selection by predation has been proposed as a cost that balances sexual selection. I tested whether brush-legged males, thought to be favored by sexual selection, incur greater costs associated with predation than non-ornamented males. Measuring rates of predation in the field and timing of attacks and captures in the laboratory revealed equal predation on the two male forms.^ I next tested whether the more visually conspicuous brush-legged males alter their behavior in response to predation threat to a greater degree than non-ornamented males, thus decreasing their risk of predation. Both male forms increased the time to initiate courtship when predator cues were present versus absent. However, brush-legged males showed a greater change in their time to initiate courtship than non-ornamented males.^
Biology, Entomology|Biology, Evolution and Development|Psychology, Behavioral Sciences
Fowler-Finn, Kasey D, "Exploring the maintenance of and selection on two distinct male morphs in a Schizocosa wolf spider" (2009). ETD collection for University of Nebraska - Lincoln. AAI3386581.