Sperm precedence, mating interval, and a novel mechanism of paternity biasin a beetle (Tenebrio molitor L.)

When females mate with more than one male, the ensuing sperm competition le ads to the evolution of male mechanisms that skew paternity. Males of the y ellow mealworm beetle (Tenebrio molitor) transfer a spermatophore to female s during copulation, but sperm release and storage occur later. We investig ated how the interval between two matings with different males affects sper m precedence by varying the interval between the copulations so that the se cond mating was either: (1) before sperm release from the first spermatopho re (<5 min); (2) after sperm release but before spermatophore ejection (15- 20 min); (3) after spermatophore ejection but before sperm storage (4 h), o r (4) after complete sperm storage (24 h). We collected offspring over a pe riod of 2 weeks and determined paternity by protein electrophoresis. There was second-male sperm precedence in all treatments, but when the interval w as <5 min, the second male usually (86% of cases) had complete sperm preced ence (i.e., P-2=1). Investigations into the mechanism of second-male sperm precedence during <5-min mating intervals indicate that sperm release from the first spermatophore is inhibited, a phenomenon which has not been previ ously documented.