The Effects of Testosterone on Calling Behavior in Green Treefrogs, Hyla cinerea

摘要

Circulating androgen levels can have a profound effect on the expression of elaborate male traits and courtship behaviors that are important in attracting females. For example, elevated androgens are necessary for the expression of vocal displays used by male anurans (frogs and toads) to attract mates. However, the nature of the relationship between androgen levels and the extent, or magnitude, of vocalization in male anurans is unclear. For example, androgens may have a threshold effect on vocalization wherein elevation in androgens is required for vocal expression, but elevations above threshold do not mediate an increase in the magnitude or extent of vocalization. Alternatively, androgens may have graded effects on vocalization, wherein elevations above threshold levels required for vocal expression correspond to an increase in the extent or magnitude of vocalization. Numerous androgen-based models of sexual selection propose that as testosterone levels increase, the extent and/or magnitude of elaborate male traits increases in a graded, dose-dependent (linear) manner. This relationship provides the basis for ‘honest signals’ (e.g., signals that confer ‘good genes’). I examined how circulating androgen levels relate to vocal parameters known to be important in mate selection in male green treefrogs, Hyla cinerea. Results provided no evidence of a graded effect of testosterone on vocalization. Hence, circulating androgens do not appear to mediate changes in vocalization important in mate selection in a graded manner, contrary to the predictions of theoretical models.ud