Parental investment

[Extract] Sexually reproducing animals invest in offspring metabolically through the generation of gametes (eggs and sperm). Beyond this initial energetic investment, the majority of animals provide no additional investment in their offspring. However, in species that do provide parental investment following conception, the quantity, quality, form, and duration of investment vary dramatically between species, as well as between the sexes within species (Clutton-Brock 1991). In vertebrates, females often show a disproportionately higher metabolic level of investment than males through the generation of yolk or placenta that provides nourishment for the developing embryo (Clutton-Brock 1991; Trivers 1972)