The water metabolism and temperature regulation of the primitive Heteromyids, Liomys irroratus and Liomys salvani
Rummel, John Austin
Hudson, Jack W.
Master of Arts
The Heteromyidae are a family of rodents which arose in the middle Oligocene. Some present day members of this family inhabit the deserts of southwestern North America. Studies on the water metabolism of these animas have shown that they are able to survive under desert conditions by possessing a highly efficient kidney, a low evaporative water loss, and nocturnal and burrowing habits. However, there has been a lack of studies on the other members of this family in relation to water metabolism and therefore, the homeostatic range of water metabolism in the Heteromyids is unknown. Another question that arises in relation to those forms presently inhabiting the deserts is that the deserts are of a fairly recent origin being formed in the Pliocene to Pleistocene epoch and the specialized physiological adaptations found in the desert inhabiting forms may have been found to some extent in an ancestorial form which preadapted the present day desert inhabitants for this type of environment. This study proposes some answers to the questions of homeostatic range of water metabolism in the Heteromyids and in their preadaptation to desert life. This is done by studying members of the subfamily Heteromyinae. From their present day range (Central America and northern South America) and from the fossil record it is unlikely that this subfamily ever came into contact with the selection pressures present in the deserts. The fact that physiological adaptations similar to those found in the desert inhabiting forms are found in this subfamily gives strong support to the hypothesis that the Heteromyids were preadapted for life in the desert. Also, members of this subfamily appear to be the most primitive living members of the family and therefore, may reflect the physiology of the stem line of Heteromyids. This study shows that these animals do have an efficient water metabolism and is suggestive that the family Heteromyidae has possessed an unusual water metabolism early in their evolution.