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Division of labour allows group-living species to efficiently complete tasks while minimizing resource expenditure. This generally involves task allocation between individuals. In territorial defence and parental care specifically, division of labour can be completed using different strategies, often involving one or more individuals defending the territory while others care for offspring. Little is known, however, about division of labour by monogamous and biparental mammals. We investigated labour division strategies across territorial defence and pup retrievals by monogamous, biparental, territorial California mice along with the role of vocal communication in coordinating these behaviours. Male and female pair-bonded California mice display aggression towards same-sex intruders and retrieve pups while alone, but how pairs complete these tasks while together remains unknown. We found that California mouse pairs used one of two strategies during territorial defence: (1) joint defence or (2) divided defence. Overall, these strategies were not altered by the intruder sex or the birth of pups. However, postpartum individuals spent more time alone in the nest and pairs spent less time together investigating intruders. Pup retrievals, conversely, followed a sex-specific strategy where mothers retrieved pups in 89% of pairs while males retrieved pups in 11% of pairs. This study shows for the first time that a monogamous and biparental rodent uses different strategies to divide labour during vital tasks of territorial defence and pup retrieval. Moreover, we found that vocal communication via sustained vocalizations were predictive of aggressive behaviour but not retrieval behaviour, indicating that vocalizations may only play a role in coordinating specific behaviours. Importantly, these strategies were task dependent and robust across intruder sex and parental status, providing a framework for better understanding division of labour in mammals. • Pairs defended territories across contexts using a joint or divided defence strategy. • There was a sex difference in pup retrievals such that females predominantly retrieved. • Male sustained vocalizations predicted defence behaviour but not retrieval behaviour. [ABSTRACT FROM AUTHOR]

The steroid hormone testosterone (T) is a well-known mediator of male sexual behavior in vertebrates. However, less is known about T's rapid effects on sexual behavior, particularly those involving ultrasonic vocalizations (USVs), a mode of communication that can influence mate acquisition in rodents. Using the monogamous California mouse, Peromyscus californicus , we tested whether T rapidly alters male USV production by giving T or saline injections to non-paired (sexually naïve) males and paired (paternally experienced and pair-bonded) males immediately prior to a brief exposure to an unrelated, novel female. Among non-paired males, no differences in the total number of USVs were observed; however, T increased the proportion of simple sweeps produced. Among paired males, T decreased the number of USVs produced, and this change was driven by a reduction in simple sweeps. These results suggest a differential rapid effect of T pulses between non-paired and paired males upon exposure to a novel female. Additionally, we observed a positive correlation in the production of USVs made between males and novel females, and this relationship was altered by T. Given the importance of USVs in sexual communication, our study supports an essential concept of monogamy in that mate fidelity is reinforced by decreased responsiveness to prospective mates outside of the pair bond. The central mechanism in pair bonded males that decreases their responsiveness to novel females appears to be one that T can trigger. This is among the first studies to demonstrate that T can inhibit sexually related behaviors and do so rapidly. [ABSTRACT FROM AUTHOR]

Geyer [Am. Zool. 21 (1981) 117] hypothesized that infant rodents increased the number of ultrasonic vocalizations when they moved in and out of the nest in order to elicit extended care from parents. We tested these hypotheses by recording ultrasonic vocalizations (USVs) and coordinated movements (locomotion and grooming) in California mouse and by recording USVs from pups before and after their parents retrieved them. In Experiment 1, USVs and coordinated movements were recorded from 2 to 30 days of age, in female and male Peromyscus californicus pups. USVs at 37, 42, 47, and 52 kHz were digitized and recorded by computer and an event recorder program which was simultaneously used to record coordinated movement. Vocalizations persisted to 30 days of age. Vocalizations increased for both males and females after they spent more than 180 s in coordinated movement and females vocalized more than males. Females also displayed more coordinated movement and earlier development of coordinated movement than males. There was no effect of litter size on USVs. In Experiment 2, the number of USVs emitted by pups and the latency of dams and sires to contact their pups and retrieve them was measured. There was no significant correlation between the number of USVs emitted by pups and the latency for a parent to contact or retrieve a pup. Results from Experiment 1 provided some support for Geyer’s (1981) hypothesis and results from Experiment 2 did not support the hypothesis that the main function of USVs in California mouse pups was to elicit parental care. [Copyright &y& Elsevier]