Mechanisms of sperm competition in insects

Sperm competition has been demonstrated in a variety of insects and is, in addition to ecological resource distribution and sex ratios, generally beli eved to play a major role in the evolution of insect reproductive strategie s and mating systems. In this paper, I review the main theories and some of the empirical evidence regarding sperm competition in insects. Sperm utili zation is shaped by selection on both males and females, sometimes in oppos ite directions. Here I focus mainly on adaptive mechanisms for sperm priori ty and paternity assurance, and consequences of such adaptations for female s. I also evaluate the importance of the conflicts between the sexes for th e evolution of mating behaviour from existing theory and available empirica l evidence. Some urgent research areas for future workers are suggested. An explanation for the large intraspecific variation in last male sperm prior ity is still lacking. To this end, we need detailed studies of the mechanis ms of sperm usage within the female, and to what extent females influence p ostcopulatory fertilization processes.