Dual function of seminal substances for mate guarding in a ground beetle

Abstract

Males of internally fertilizing animals often produce ejaculates consisting of various substances in addition to sperm. Seminal substances can inhibit female remating through physical blocking of the female genitalia or by physiological induction of the female refractory period. We demonstrated that the seminal substances of the ground beetle Leptocarabus procerulus serve as both physical (i.e., mating plugs) and physiological (i.e., substances inducing female refractory behavior) devices for mate guarding. Although females counteract these functions via expulsion of the plug and the delay of the occurrence of refractory behavior, the interplay of these 2 functions can be compensatory and consistently lowers the female remating rate during a postmating period that is important for male fertilization success. Such interplay of 2 defensive strategies may be a male adaptation against female resistance, as predicted by the hypothesis that multiple functions in seminal substances are a historical outcome of an arms race between males and females. Our findings highlight the importance of sexual conflict in the evolution of complex seminal substances.