Costs of macrogamete production
If we ignore the rather atypical and apparently derivative situation in species in which microgametes are transferred en block, for example, in the form of pollinia (some orchids) or spermatophora (some insects, salamanders), then we find that males tend to be r-strategists when compared to females. They produce the greatest possible number of gametes and try to ensure the formation of the greatest possible number of zygotes. In the typical case, they do not try to influence the further fate of these zygotes. In contrast, even through the formation of macrogametes alone, females must always invest a substantial effort into the future zygote, so they are mostly forced to adopt the role of K-strategists. They produce fewer gametes and try to care for their further fate so the greatest numbers of progeny live to reproductive age.
This different starting position of the two sexes generally means both a greater share of females in care for the progeny and also greater efforts that the females exert in selection of a sexual partner. While the optimum reproduction strategy of a male is unselective mating with the greatest possible number of females, females can affect their reproductive success primarily through selection of an optimum mating partner, a male with whom they will combine their genes in a coalition through production of common progeny.