Salivary Water Loss to Seeds In Yellow Pine Chipmunks and Merriam's Kangaroo Rats

Abstract

Seeds are known to serve as sources of preformed and metabolic water for desert rodents, but water loss to hygroscopic seeds has received little attention. Salivary water loss by yellow pine chipmunks (Tamias amoenus) and Merriam's kangaroo rats (Dipodomys merriami) to Jeffrey pine (Pinus jeffreyi) and antelope bitterbrush (Purshia tridentata) seeds was measured to determine its magnitude and potential importance. Chipmunks rapidly lost salivary water to individual seeds inserted into their cheek pouches. Jeffrey pine seeds (129 mg) absorbed 9.8 mg of water and bitterbrush seeds (36 mg) absorbed 4.6 mg of water when held in the cheek pouches for 15 min. Only 3—5% of this water can be reclaimed if the chipmunk eats the seed because most of the absorbed water resides in the inedible seed coat, which the animal discards. The kangaroo rats, which possess external, fur—lined cheek pouches, lost no water to seeds held in their cheek pouches for 15 min. Chipmunk salivary water loss to Jeffrey pine and bitterbrush seeds was equivalent to 19 and 59%, respectively, of the water (performed plus metabolic water) contained in those seeds. Salivary water loss is a major and previously overlooked component of the water budgets of granivorous rodents with internal cheek pouches. The presence of fur—lined cheek pouches in heteromyid rodents (Kangaroo rats, pocket mice, and kangaroo mice) may have contributed to the great success of these rodents in the deserts of North America by solving the problem of salivary water loss to the seeds they handle and store.