Olfactory and Thermal Influences on Ultrasonic Vocalization During Development in Rodents

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Abstract
Ultrasounds are emitted by developing rodents, and changes with age in several parameters of vocalization have been reported for numerous myomorphs. In this paper I integrate with ultrasonic vocalization several behaviors which change during development. Included are studies controlling stimulation by olfactory, thermal, and tactile cues as well as detailed studies of specific responses such as movement, suckling, grooming, and huddling. Development is analyzed in well-known species, such as the rat (Rattus norvegicus), and in less familiar species, especially the pine vole (Microtus pinetorum). Lacking the capacity for physiological thermoregulation, altricial rodent pups with their mother use several behavioral strategies which facilitate thermoregulation. Inside the nest, pups adjust the temperature by changing their huddling. The mother regulates the length of suckling bouts according to her body temperature. When a pup is removed from the warm nest, vocalizations of the pup can increase the likelihood of retrieval by the mother and thereby indirectly facilitate thermoregulation. In several species which have been studied, vocalization rates are highest when pups begin to move into and out of nests and exhibit olfactory-directed movement. As olfactory preferences become established and movement is coordinated, a decline in vocalization appears in rat, mouse, hamster, spiny mouse, and pine vole. In the gerbil, however, the decline precedes competence in olfactory-directed movement. In the presence of home shavings, young rats emit low rates of vocalization, while pine vole young emit calls at a high rate. This contrast may relate to the intensive attachment of young pine voles to the mother in early life.

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