Sperm-expenditure strategies: the role of mating order, sperm precedence, and non-optimal behavior

We developed a model to examine the amount of sperm that males should trans fer to females under different conditions of sperm precedence. Following a previous model (Parker's), we assume the existence of nonrandom mating role s in which there are males that always mate first and others that always ma te second. However, we alter Parker's model by introducing the possibility that males are non-optimal in their sperm allocation (because males make mi stakes or are interrupted, or because of phenotypic variation among males). We predicted that when males behave optimally, their sperm expenditures wi ll be equal for most levels of sperm precedence, regardless of whether they mate first or second. However, when the possibility that males behave non- optimally is included, we predicted (i) a positive correlation between the allocations of first and second males when there is second-male precedence, (ii) a negative correlation when there is first-male precedence, and (iii) no correlation when there is no precedence. We discuss these and other pre dictions and provide supporting evidence from the literature.