Abai, MR

6th International Congress of DipterologyThe reluctant fly: What makes Sepsis cynipsea femaleswilling to copulate?Blanckenhorn, W.U. & Y. TeuschlZoologisches Museum, Universität Zürich-Irchel, Winterthurerstrasse 190, Ch-8057Zürich, SwitzerlandA female’s willingness to copulate (i.e. her receptivity) can depend onseveral endogenous, environmental and social factors. The black scavengeror dung fly Sepsis cynipsea (Diptera: Sepsidae) is a classic example forstrong female reluctance to mate and sexual conflict over mating. Previouslaboratory studies found high variability in female receptivity and evenvirgins unwilling to mate. The aim of this study was to determine theproximate factors influencing female receptivity. Females need to ingestfresh dung to produce eggs. Female receptivity strongly depended on afemale’s egg laying cycle rather than age: receptivity was highest whenfemales had no ripe eggs. This is probably required for spermatophoretransfer, leading to the unusual pre-copulatory guarding and postovipositionmating of Sepsids. Non-virgins were less receptive than virginsexcept when they were in need of sperm. Non-virgins were more receptivewhen they were larger and had previously laid more eggs. Only when notin need of sperm did females copulate with males larger than their previousmate. This suggests sequential female choice, but females typicallycopulated with the first of up to ten presented males or not at all, providedthey were at the appropriate stage of their laying cycle. Femaleunwillingness to mate in this and probably other species therefore hasvarious, sometimes physiological (intrinsic) reasons. These must becontrolled in experiments assessing mate choice, costs and benefits ofmating, or sexual conflict. Not taking into account female egg laying statecan mask female choice, bias data and suggest wrong associations.Key Words: female mate choice, mating behavior, reproduction, sexualconflict, sexual selection26