Embryonic and fetal morphology in the lowland paca (Cuniculus paca): A precocial hystricomorph rodent

Abstract

In mammals, the embryonic and fetal development of a species has evolved to maximize neonatal survival. In this study, we use a sample of 132 embryos/fetuses of wild lowland paca (Cuniculus paca), obtained over a period of 15 years through collaborative methods with local hunters in the Amazon to describe the intrauterine development of external and internal morphology of this Neotropical rodent. We also compare the newborn survival strategy in this species with other rodents. The crown-rump length (CRL) ranged between 0.6 and 24.6 cm. External 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 external features fully developed. The growth formula of fetal age was calculated as ∛W = 0.082 (t - 37.25), and age was accurately associated with CRL. We described the relationship between CRL and external and internal biometry. The liver declined in proportion within the internal cavity, while the relative volume of tubular gastrointestinal organs increased significantly along the embryo/fetal development. All organs, except the heart and the thymus, had similar relative volumes in advanced fetuses and adults. Our comparison of the intrauterine development in several rodent species indicates that the paca's reproductive strategy is comparable to species that are subject to low natural predation. Given that C. paca is perhaps the most hunted animal in Latin America, sustainable hunting throughout its range must take into account its relative reproductive performance.

Involving local communities for effective citizen science: Determining game species' reproductive status to assess hunting effects in tropical forests

“…Using the formula obtained from the first round of interviews, we estimated that hunters would start diagnosing pregnancies with ≥90% accuracy for conceptuses larger than 12.6 cm in length. This length corresponds to around 100 days gestational age (El Bizri et al., 2017). Thus, by including a retroactive 3‐month time‐lag (~90 days) to the percentage of conceptions provided by El Bizri et al.…”

“…first round of interviews, we estimated that hunters would start diagnosing pregnancies with ≥90% accuracy for conceptuses larger than 12.6 cm in length. This length corresponds to around 100 days gestational age (El Bizri et al, 2017). Thus, by including a retroactive 3-month time-lag (~90 days) to the percentage of conceptions provided by El Bizri et al (2018), the average monthly pregnancy rate increased by 19.3%, reaching 42.0% with the inclusion of 108 females that were in fact pregnant but incorrectly diagnosed as non-pregnant (Table 2).…”

Temperament, Plasticity, and Emotions in Defensive Behaviour of Paca (Mammalia, Hystricognatha)

“…The pacas could face high levels of hunting deaths and could be easily caught. This may occur in situations of high hunting pressure, reported by several authors [12][13][14][15][16], or when other targeted species are reduced in numbers and pacas may then become selected prey. In turn, behavioural plasticity may favour the species' survival: by not avoiding foraging, even in supposedly dangerous situations, pacas can increase their energy intake, therefore having better fitness, and reproducing more efficiently.…”

“…The paca (Cuniculus paca), a Neotropical caviomorph rodent, provides the most soughtafter game meat in all its range [8], and therefore faces high hunting pressure [9][10][11]. The unsustainable hunting of the paca has led to local depletion of the species in several locations, especially due to its relatively low reproductive rate [12][13][14][15][16]. However, due to its wide distribution, occurrence in a number of protected areas, and presumed large population, the paca is unlikely to be declining and, consequently, it is categorized as being of least concern on the IUCN Red List [17].…”

Age at sexual maturity, first parturition and reproductive senescence in wild lowland pacas (Cuniculus paca): Implications for harvest sustainability

“…rodent species. This results in pacas giving birth to well-developed neonates that are relatively independent in their extra-uterine life and with a lesser need for parental care (El Bizri et al, 2017). In precocial species, there is a relatively greater metabolic energy utilization during pregnancy with compensation occurring as a result of less time devoted to lactation and offspring care, leading to earlier maturity of the offspring (Derrickson, 1992;Martin et al, 2005).…”