Adaptations for leaf eating in the great basin kangaroo rat, Dipodomys microps

Abstract

Dipodomys microps forages in saltbush (Atriplex confertifolia), gathering the leaves into its external check pouches and returning them to the burrow to be cached or eaten. The leaves are available throughout the year and contain 50-80% water. D. microps can survive on these leaves in the laboratory without other food or water, but it is unusual among kangaroo rats in that it quickly succumbs when placed on a diet of air-dried seeds without water or succulent plant material. Its mean urine concentration on the seed diet was 2827 mOsm/l, which is lower than any previously reported for the genus. On the other hand, D. merriami, which occurs with D. microps and is well known as a seed specialist, cannot survive on the saltbush leaves, although it is capable of living on a seed diet without water or green vegetation. D. microps is behaviorally and morphologically specialized for exploiting the unusual leaves of A. confertifolia. The leaves are higher in electrolyte content than the leaves of most plants; but the electrolytes, which are most highly concentrated on the leaf surfaces, apparently serve in the maintenance of water balance in the leaves. D. microps does not usually consume saltbush leaves in toto, but rather uses its unique, chisel-shaped lower incisors to shave off the outer tissue from both sides of the leaf, and then consumes the inner tissue. Sodium concentration with respect to water in the eaten tissue was only 3% that of the discarded shavings, and the specialized photosynthetic parenchyma which is eaten is high in starch content.The highly divergent dietary habits of D. microps should serve to minimize competition with its granivorous congeners. Some of the present limits to the geographic distribution of D. microps are a reflection of its reliance on the leaves of perennial shrubs throughout the year; but where its does occur, D. microps should be independent of the unpredictable availability of ephemeral annuals.