very busy, attentively guarding his female. Before this time, as well as after—that is, when her eggs are not ripe, and again after his genes are safely tucked away inside the shells—he goes seeking extra-pair copulations with the mates of other males…who, of course, are busy with defensive mate-guarding of their own. In various species, males provide parental care and females mate with multiple males. For example, recent studies show that extra-pair copulation frequently occurs in monogamous birds in which a "social" father provides intensive care for its "social" offspring. Fish A University of Florida scientist reports that male sand gobies work harder at building nests and taking care of eggs when females are present – the first time such "courtship parental care" has been documented in any species. In the cichlid species Tropheus moorii, a male and female will form a temporary monogamous pair bond and spawn; after which, the female leaves to mouthbrood the eggs on her own. T. moorii broods exhibit genetic monogamy (all eggs in a brood are fertilized by a single male). Another mouth brooding cichlid – the Lake Tanganyika cichlid (Xenotilapia rotundiventralis) has been shown that mating pairs maintain pair bonds at least until the shift of young from female to male. More recently the Australian Murray cod has been seen maintaining pair bonds over 3 years. Pair bonding may also have non-reproductive benefits, such as assisted resource defense. Recent study comparing two species of butterflyfishes, C. baronessa and C. lunulatus, indicate increase in food and energy reserves compared to individual fish. However, there is limited research on the advantages of long-term pair boding and increased fitness. Mammals Monogamous voles (such as prairie voles) have significantly greater density and distribution of vasopressin receptors in their brain when compared to polygamous voles. These differences are located in the ventral forebrain and the dopamine-mediated reward pathway. Peptide arginine vasopressin (AVP), dopamine, and oxytocin act in this region to coordinate rewarding activities such as mating, and regulate selective affiliation. These species-specific differences have shown to correlate with social behaviors, and in monogamous prairie voles are important for facilitation of pair bonding. When compared to montane voles, which are polygamous, monogamous prairie voles appear to have more of these AVP and oxytocin neurotransmitter receptors. It is important that these receptors are in the reward centers of the brain because that could lead to a conditioned partner preference in