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Neuropeptides and Social Behavior Development 181mals in this study also received a series of other behavioral tests, including a secondalloparental care test, a partner preference test (Williams, Catania, & Carter,1992), plus-maze testing (to index anxiety in a novel environment; Ramos &Mormede, 1998), same-sex aggression tests and, in males, tests of mating behaviorand reproductive fertility.Alloparental behavior is measured as the time spent huddling over pups, retrievingthe pup, licking and grooming, and so forth, whereas ignoring or attackinginfants is considered nonalloparental. In the immediate postweaning period, ahigh percentage of both male and female voles are alloparental. However, whereasmale alloparenting normally stays high throughout life (with 70–80% of animalsresponsive to pups), female alloparenting starts nearly as high, but declines withage (Bales, Pfeifer, & Carter, 2004b; Lonstein & De Vries, 1999; Lonstein andDe Vries, 2000; Roberts et al., 1998). A deficit in parenting or alloparenting couldbe indicative of increasing anxiety or fear of the pups (Bales et al., 2004b; Fleming& Corter, 1995; Fleming & Leubke, 1981). Both OT and AVP are capable of influencinganxiety although as mentioned above, the effects, especially of AVP,may be complex and not necessarily linear. It is possible that sex differences inalloparental behavior during the postweaning period may be related to a sexualdimorphism in the actions of OT or AVP or other neuroendocrine changes thatemerge during this or other periods of rapid maturation.Sex Differences in the DevelopmentalEffects of NeuropeptidesThe developmental manipulations of OT described above tend to produce longlastingeffects that are different in male versus female prairie voles. At the comparativelylow doses used in this initial study, neither neonatal OT nor OTAaffected alloparental behavior in females; however, in male voles, a single exposureto OTA on the first day of life significantly reduced responsivity to an infantand significantly increased attacks in animals tested during the immediate postweaningperiod (Bales et al., 2004b).In addition, males treated with exogenous OT (1 mg/kg) formed pair bonds asadults more quickly than controls (Bales & Carter, 2003b). However, when allowedto mate, males that had been exposed to OT or OTA showed atypical patternsof sexual behavior. Many OT- or OTA-treated males failed to mate. Evenamong those males that showed behavioral ejaculations, OT- and OTA-treatedmales were less likely to leave sperm in the female tract during mating (Bales,Abdelnabi, Cushing, Ottinger, & Carter, 2004). Males treated with OTA tendedto be less aggressive than those treated with OT or controls (Bales & Carter, 2003a),and had higher corticosterone and dysregulated reactions to stress (Carter, 2003).