ABSTRACT
Motivation for seeking copulatory interactions is a proxy for reproductive success. Males and females exhibit different patterns of reproductive success in mate-defense polygyny. Reproductive success peaks at a particular age for males, whereas it is relatively constant for females. The sex displaying the greatest amount of parental investment is usually the one with the least variability in reproductive success-Bateman's principle. In polyandrous species, in which several males mate with a single female, females (rather than males) tend to compete for mates, to show more conspicuous secondary sexual characters, and to exhibit greater variation in reproductive success. In monogamy, mates bond for long periods, intrasexual competition (male-male or female-female) can be drastically reduced, variation in reproductive success across sexes tends to be similar, and sexual dimorphism is limited. Female parental care allows the males to leave the pair after copulation and invest little in the progeny without risking their own reproductive success.
