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Early-life social isolation has profound effects on adult social competence. This is often expressed as increased aggression or inappropriate displays of courtship-related behaviors. The social incompetence exhibited by isolated animals could be in part due to an altered ability to participate in communicatory exchanges. House mice (Mus musculus) present an excellent model for exploring this idea, because social isolation has a well-established influence on their social behavior, and mice engage in communication via multiple sensory modalities. Here, we tested the prediction that social isolation during early life would influence ultrasonic vocalizations (USVs) emitted by adult male mice during same-sex social encounters. Starting at three weeks of age, male mice were housed individually or in social groups of four males for five weeks, after which they were placed in one of three types of paired social encounters. Pair types consisted of: two individually housed males, two socially housed males, or an individually housed and a socially housed male (“mixed” pairs). Vocal behavior (USVs) and non-vocal behaviors were recorded from these 15-minute social interactions. Pairs of mice consisting of at least one individually housed male emitted more and longer USVs, with a greater proportional use of USVs containing frequency jumps and 50-kHz components. Individually housed males in the mixed social pairs exhibited increased levels of mounting behavior towards the socially housed males. Mounting in these pairs was positively correlated with increased number and duration of USVs as well as increased proportional use of spectrally more complex USVs. These findings demonstrate that USVs are part of the suite of social behaviors influenced by early-life social isolation, and suggest that altered vocal communication following isolation reflects reduced social competence.

In biparental species, each parent represents a semi-independent source of variable caregiving. The nature of care may differ between parents, and the type of care offspring seek is likely to change across development. We asked if caregiving differed between prairie vole (Microtus ochrogaster) mothers and fathers, and which parent pups prefer over development. We categorized parents as high-or low-contact based on daily recordings of grooming and brooding behavior. Pups were tested for their preferences between parents on postnatal days 10, 14, 18, 22, and 26. We expected individual parents would vary in the amount of care they gave, with pups preferring the parent that gives the most care and/or that most meets their needs at each developmental timepoint. Mothers spent more time in contact with pups than fathers. Mothers were consistent in the amount of care they gave, whereas fathers were variable caregivers. Pups never preferred fathers over mothers, but only demonstrated a preference for mothers before weaning. Lastly, the amount of contact did not influence pup preferences. Our data indicate that mothers are consistent sources of caregiving relative to fathers, and pups show little evidence of attachment to a specific parent beyond meeting its own immediate needs.

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