SHORT-TERM AND LONG-TERM SPERM PRECEDENCE IN THE BEETLE TENEBRIO-MOLITOR - A TEST OF THE ADAPTIVE SPERM REMOVAL HYPOTHESIS

Sperm removal in Tenebrio molitor L. (Coleoptera: Tenebrionidae) has b een proposed as an adaptation to sperm competition and has been docume nted when the remating interval between successive copulations is shor t, but not when it is long (Gage, 1992). If sperm removal is adaptive, it follows that there should be different fertilization outcomes from double matings with different remating intervals. Sperm precedence pa tterns were assessed using reciprocal double matings of normal and gam ma-irradiated (sterile) virgin males of controlled size and age with v irgin females of controlled size and age. Immediate last male sperm pr ecedence was high whether the remating interval was short (<10 min) (P -2 = 0.89) or long (24 h) (P-2 = 0.92). Sperm precedence in eggs laid in a 16-day period after the last copulation showed no difference in t he pattern of change between females with short and long remating inte rvals. By examining the aedeagus of males we show that sperm are remov ed at the end of copulation by the first and the second male to mate w ith a virgin female regardless of whether the remating interval is sho rt or long. We conclude that sperm removal is unlikely to be the prima ry mechanism by which males gain such high levels of last male sperm p recedence.