Economics of mate choice at leks: do female waxmoths pay costs for indirect genetic benefits?

摘要

Sexual selection theory predicts low costs of choice when females choose among males for genetic (indirect) benefits, as occurs at leks. However, few empirical studies have investigated the actual costs incurred during the process of pair formation, and we generally do not know whether and to what extent females incur energetic expenditure, exposure to predation, or simple allocation of time by virtue of their choosiness. Do females that choose mates at larger aggregations of males necessarily pay these costs? Moreover, what costs are they willing to pay to obtain potential benefits? We addressed these questions in an acoustic pyralid moth, Achroia grisella, in which males aggregate and attract females with an advertisement song. Female choice is based on acoustic characters of displaying males, and only genetic benefits appear to be available. We measured the movement and time that females spent in mate sampling when presented with varying numbers of males in a laboratory arena. We found that female choice for specific males was retained as male number increased, although their sampling effort increased: female trajectories lengthened and reversed direction more often. The repeatability of female choice at larger leks and the basic precision of female phonotaxis indicated that the lengthened trajectories reflected sampling and choosiness as opposed to confusion. We propose that the cost of such choosiness in natural populations may be an increased exposure to predation and that females pay this cost because of the opportunity to mate with a specific male with certain song characteristics.