Masters Thesis

Differential Mate Choice Responses to Chemical Cues in Male and Female Rough-skinned Newts (Taricha granulosa)

Purpose of the Study: To understand male and female mate choice patterns affecting species and gender recognition via long distance chemical cues, this study examined the rough skin newt, Taricha granulosa, in both pond and creek habitats. Response to chemical cues of males vs. females was examined for T. granulosa, whereas the California newt (Taricha torosa), and the red-bellied newt (Taricha rivularis) were used to examine how T. granulosa would respond to heterospecific chemical cues as compared to conspecific cues in a region of the species’ ranges where all three species occur in sympatry. Methods: To simulate mate choice decisions in nature as closely as possible, we conducted behavioral experiments in the field using a Y-maze apparatus (olfactometer). All trials were run in the field using unique individuals. Data were combined across multiple years. Mate choice was analyzed using a nominal logistic regression model accounting for variation among year, researcher, Y-maze apparatus, sex, and species. Findings: T. granulosa females chose chemical cues of conspecific males significantly more than heterospecific males, whereas males showed no preference between chemical cues of conspecific and heterospecific females. In addition, T. granulosa males chose chemical cues of conspecific males over conspcific females, whereas females showed no preference between chemical cues of conspecific males and females. Conclusions: The results of this study support long-standing theoretical paradigms that males, who have less parental investment in offspring will adopt a strategy of seeking matings with females regardless of quality, whereas females, with greater levels of parental investment, will engage in a more discriminating mate choice strategy. In this case, females use chemical cues to avoid heterospecific males during breeding season encounters and reduce wasting her singular mating event on an act of hybridization. A result of this mating strategy is that reinforcement of reproductive isolation is maintained in this region of sympatric range overlap. In contrast, will mate with any female across multiple mating events, and use chemical cues to either locate females or to avoid other males (or both).

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