EFFECT OF COLD TEMPERATURES ON THE MORPHOLOGY OF GASTROINTESTINAL TRACTS OF 2 MICROTINE RODENTS

Microtus ochrogaster and Dicrostanyx groenlandicus are closely related species that share many life-history characteristics, but have differ ent food habits; D. groenlandicus primarily eats dicots, such as everg reen and deciduous shrubs, while M. ochregaster primarily eats forbs a nd grasses. We compared the size of gastrointestinal tracts of these t wo species acclimated to either 5 or 23 degrees C. In both species, an imals acclimated to cold ambient temperatures (5 degrees C) had longer gastrointestinal tracts than did those acclimated to warmer temperatu res (23 degrees C). In addition, animals acclimated to colder temperat ures also carried a greater mass of digesta in their gastrointestinal tracts. Only in M. ochrogaster did the wet mass of the tract increase in response to cold-temperature acclimation. In general, D. groenlandi cus had larger and heavier tracts than did M. ochrogaster. The small i ntestine and cecum increased in size at cold temperatures, but this in crease occurred differently in each species. The differences we observ ed can be attributed to differences in the additional food eaten by ea ch species in the cold.