Graduate Thesis Or Dissertation
 

A comparative study of prenatal behavior ontogeny in altricial and precocial murid rodents

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  • Using techniques that permit the direct observation of fetuses in vivo, prenatal behavioral development was compared among four species in the rodent family Muridae: the Norway rat (Rattus norvegicus), Mongolian gerbil (Meriones unguiculatus), cotton rat (Sigmodon hispidus), and spiny mouse (Acomys cahirinus). Rattus and Meriones bear altricial offspring, as do nearly all other Murid rodents. But Sigmodon and Acomys have independently evolved the reproduction of precocial young. The behavioral maturity of precocial neonates implies significant differences from altricial rodents in patterns of prenatal development. Specifically, fetal behavioral patterns that are antecedent to postnatal behavior should be accelerated relative to birth in precocial species, while patterns that promote the survival of the fetus in utero (ontogenetic adaptations) should be retained through gestation and therefore appear retarded relative to antecedent behavior. Numerous quantitative measures were used to characterize the development of fetal behavior. These included: (a) the incidence of movement in discrete body regions of the fetus and overall fetal activity, (b) the tendency for fetal movements to be temporally clustered in bouts, (c) the emergence of synchronous movement, (d) the sequential patterning of fetal behavior, (e) the response to intraoral chemosensory stimulation, (f) the expression of species-typical behavioral patterns, such as facial wiping and contact-righting, and (g) the behavioral response to experimental occlusion of the umbilical cord. In precocial species, most patterns of fetal behavior emerged relatively earlier in gestation than in altricial species. However, a few patterns, such as the fetal response to umbilical cord occlusion, were accelerated in altricial species. This developmental pattern was consistent with the predicted shift in the timing of events during prenatal behavioral ontogeny. Consistent patterns of behavioral development observed in all four species further suggested the existence of transient motor patterns that may serve as a developmental bridge between randomly produced movements and coordinated behavioral patterns. The existence of prenatal behavioral heterochrony and behavioral scaffolding imply that early behavioral development is not a unitary process, but involves multiple, independent ontogenetic trajectories.
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