Physiological Variability In Juvenile Nine Banded Armadillos

Physiological development is a function of an organism's genotype, its environment, and the interaction between these two factors. Assessing the relative influence of these factors on an animal's physiology has occupied researchers for decades. Clonal offspring, such as those in the nine-banded armadillo (Dasypus novemcinctus) provide a unique opportunity to essentially eliminate genotypic variation and focus on environmental causes of physiological variation. Typically, variation in offspring physiology is significantly less within litters than between litters, a phenomenon known as the "sibling effect". Ten D. novemcinctus neonates were removed from their mother following birth and hand-reared in identical environments. As juveniles, the armadillos, comprised of four litters, were exposed to acute hypoxia/hypercapnia, mimicking severe burrow conditions, and O2 consumption and CO2 production were measured via flow through respirometry. The physiological challenge of burrow conditions provides a view of sibling variation under stress. Although, the gas stressor in this study was acute, the burrow conditions in the wild are chronic for neonates. Resting O2 consumption and CO2 excretion were also measured to determine mass-specific basal metabolic rate (BMR). D. novemcinctus is known for having a lower mass-specific BMR and lower body temperature in comparison to other mammals. Although adult armadillos have been reported as a unique mammal in regards to energetics, the armadillo juveniles follow the same trends as other mammalian neonates and juveniles. Armadillo juveniles, similar to other mammalian juveniles, follow a trend toward decreased mass-specific BMR over time. When exposed to acute hypoxia/hypercapnia, an increase in mass-specific O2 consumption and mass-specific CO2 production was seen in all armadillo juveniles, consistent with previous research of neonatal mammals exposed to hypoxia and hypercapnia. By controlling the neonatal environment (i.e. feeding and temperature regime), it can be stated that the physiological variation found is due primarily to genetics. Within-litter variation was a significant source of the variation for mass-specific basal metabolic rate in both normoxia and hypoxia/hypercapnia, while between-litter variation was not. Although this does not conclusively indicate the presence of a sibling effect, the litter-treatment interaction and the age-litter interaction found within the data provide evidence for its presence.

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The word armadillo is Spanish for “little armored one.” This midsize mammal that looks like a walking tank is a source of fascination for many people but a mystery to almost all. Dating back at least eleven million years, the nocturnal, burrowing insectivore was for centuries mistaken for a cross between a hedgehog and a turtle, but it actually belongs to the mammalian superorder Xenarthra that includes sloths and anteaters. Biologists W. J. Loughry and Colleen M. McDonough have studied the nine-banded armadillo (Dasypus novemcinctus) for more than twenty years. Their richly illustrated book offers the first comprehensive review of everything scientists know about this unique animal. Engaging both scientists and a broader public, Loughry and McDonough describe the armadillo’s anatomy and physiology and all aspects of its ecology, behavior, and evolution. They also compare the nine-banded armadillo with twenty or so other, related species. The authors pay special attention to three key features of armadillo biology—reproduction, disease, and habitat expansion—and why they matter. Armadillos reproduce in a unique and puzzling manner: females always give birth to litters of genetically identical quadruplets, a strategy not found in any other vertebrates. Nine-banded armadillos are also the only vertebrates except for humans known to contract leprosy naturally. And what about habitat expansion? The authors suggest that the armadillo’s remarkable spread across the southeastern United States may be the consequence of its most notable feature: a tough, protective carapace. Biologists, evolutionists, students, and all those interested in this curious creature will find The Nine-Banded Armadillo rich in information and insight. This comprehensive analysis will stand as the definitive scientific reference for years to come and a source of pleasure for the general public.