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Costs of parental care can include increased physical, physiological, and behavioral demands and reduced prospects for future reproduction. Therefore, animals may benefit from recognizing and discriminating their own offspring during the period of infant care to ensure that they provide care only to their own young. Differences in offspring discrimination between mothers and fathers may arise due to differences in the amount of parental care they provide. In mammals, mothers bear the costs of gestation and lactation, while fathers do not; therefore, we might expect that in mammal species in which both parents provide parental care, mothers will show greater levels of offspring discrimination than fathers. In the present study, we examined possible sex differences in offspring discrimination in the biparental, monogamous California mouse (Peromyscus californicus) across the lactational period. On postpartum days (PPD) 3, 7, 16, and 28, parents were housed individually in a test cage and presented simultaneously with two wire mesh balls, one containing their own pup and the other containing an unrelated pup. On individual test days, parents behaved similarly toward the two balls. Fathers, but not mothers, showed significant changes in latencies to approach and interact with the non-kin ball across test days, but no clear pattern was observed. Fathers also approached the non-kin ball more frequently than mothers when pups reached weaning age (PPD 28). Thus, fathers may show increased interest in unrelated young as their offspring become independent. [ABSTRACT FROM AUTHOR]

Maternal-offspring communication and care are essential for offspring survival. Oxytocin (OXT) is known for its role in initiation of maternal care, but whether OXT can rapidly influence maternal behavior or ultrasonic vocalizations (USVs; above 50 kHz) has not been examined. To test for rapid effects of OXT, California mouse mothers were administered an acute intranasal (IN) dose of OXT (0.8 IU/kg) or saline followed by a separation test with three phases: habituation with pups in a new testing chamber, separation via a wire mesh, and finally reunion with pups. We measured maternal care, maternal USVs, and pup USVs. In mothers, we primarily observed simple sweep USVs, a short downward sweeping call around 50 kHz, and in pups we only observed pup whines, a long call with multiple harmonics ranging from 20 kHz to 50 kHz. We found that IN OXT rapidly and selectively enhanced the normal increase in maternal simple sweep USVs when mothers had physical access to pups (habituation and reunion), but not when mothers were physically separated from pups. Frequency of mothers' and pups' USVs were correlated upon reunion, but IN OXT did not influence this correlation. Finally, mothers given IN OXT showed more efficient pup retrieval/carrying and greater total maternal care upon reunion. Behavioral changes were specific to maternal behaviors (e.g. retrievals) as mothers given IN OXT did not differ from controls in stress-related behaviors (e.g. freezing). Overall, these findings highlight the rapid effects and context-dependent effect a single treatment with IN OXT has on both maternal USV production and offspring care. [ABSTRACT FROM AUTHOR]

Social animals must cope with challenges and opportunities by adjusting how they react to a salient stimulus. Here we use California mice (Peromyscus californicus) and investigate the mechanisms underlying social decision-making by studying (i) rapid effects of testosterone (T) pulses on a male's decisions to approach a novel male (challenge) versus a receptive female (opportunity), and (ii) whether social experience shapes how such effects are manifested. In Experiment 1, we found that sexually naïve males administered saline injections preferentially approached unfamiliar females over unfamiliar males, in contrast, 10 min after receiving a single T-injection, males expressed a preference for approaching unfamiliar males. Such an effect of T only occurred in sexually naïve males, but not pair-bonded males, suggesting that the rapid effects of T on approach behavior may rely on the pair-bonding experiences. Experiment 2 investigated social decision-making across three repeated exposures to the challenge/opportunity situations. Only the initial decision, approach to the challenge, predicted future aggressive behaviors, and such an effect relied on the rapid actions of T. We also found that experience with the controlled challenge situation (the male intruder was restrained behind a wire mesh) dampened the approach to the male side (potential threat) when later exposed to the same conditions. This suggests that a resident's motivation to defend against a threatening individual may decrease as the threat posed by the "neighbors" is reduced. Overall rapid effects of post-encounter T pulses may play important roles in influencing behavioral decisions during social interactions. • Unpaired males approach unfamiliar females over unfamiliar males. • Testosterone (T) in unpaired males induces approach towards unfamiliar males over females. • Paired males approach unfamiliar males over females, independently of the T treatment. • Approach behavior can be altered through multiple testing. • Unpaired T-males that approached unfamiliar males displayed high future aggression. [ABSTRACT FROM AUTHOR]