THE SEX IN SHORT SUPPLY FOR MATINGS VARIES OVER SMALL SPATIAL SCALES IN A KATYDID (KAWANAPHILA NARTEE, ORTHOPTERA, TETTIGONIIDAE)

In katydids such as Kawanaphila nartee, a female bias in the operation al sex ratio (OSR) results in female competition for mates and male ch oice of mates. Previous work showed that the excess of sexually active females occurs when food availability is low, in part because less fo od increases the propensity of females to mate as they forage for the large edible spermatophores produced by males. In this study with K. n artee, a pollen-feeding species, we estimate natural variation in numb ers of sexually active males and females by assessing male calling act ivity and the propensity of females to respond to experimental calling males. We found an excess of sexually active males at a site with man y flowers and an excess of sexually active females at a site with few flowers about 900 m away. Between-site differences in gut masses of ca lling males were consistent with the hypothesis that pollen availabili ty controls OSR. Finally, at a third site where flowers were at first scarce, we found that the initial excess in sexually active females ch anged to an excess of sexually active males after a clump of grass-tre es flowered. The mean gut mass of all sampled males from this site inc reased after flowering. The large variation in OSR that we document fo r K. nartee highlights the importance of identifying the appropriate s patial and temporal scales over which OSRs are measured in studies of factors controlling sexual selection.