Desenvolvimento intrauterino da paca (cuniculus paca), um roedor histricomorfo precocial.

Abstract

The intrauterine development consists of a preparation of the neonates for the aerial life. Beyond the phylogenetic relationships, this phase reflects the strategies adopted by mammals to maximize the maternal and neonatal survival, which strongly influences the dynamics of their wild populations and their resilience to disturbances. Here, we used samples of 137 pregnant pacas (Cuniculus paca), obtained along 15 years through collaborative methods with local hunters in the Amazon, to describe the development of the external and internal morphology of the species during the intrauterine phase, discussing the newborn survival strategy adopted in comparison to other rodents. In the embryos/fetuses acquired, we performed (i) an assessment of the presence probability of external features along the gestation; (ii) an estimation of fetal age and an external biometry; and (iii) a measurement of the volume of thoracic and abdominal organs, comparing their relative volumes with those of adults. The crown-rump length (CRL) ranged from 0.6 cm to 24.6 cm. The fetal features appeared in the following chronological order: limbs, eyelid buds, fusioned eyelids, genitalia, outer ear, tactile pelage, claws, skin, skin spots, covering pelage, teeth and open eyelids. Fetuses with CRL > 19.5 cm presented all features assessed. The growth formula of fetal age was ∛W = 0.082 (t - 37.25), and the age was accurately associated with CRL. The liver showed a decreasing trend in its proportion in the internal cavity, while the relative volume of tubular gastrointestinal organs increased significantly. All organs but the heart and the thymus presented similar relative volumes between advanced fetuses and adults. This study reveals that pacas produce precocial neonates with appropriate structures for survival with low dependence on the mother’s care. In addition, the species’ neonates are more developed than other studied rodents. Although the paca is currently the most hunted species in the Amazon, its reproductive strategy is compatible to a low prey condition, suggesting that the species is not reproductively prepared to respond to high hunting pressures. Therefore, our results have a critical importance for clinical diagnosis and in situ and ex situ reproductive management of the species.