Comparative morphology of the gastrointestinal tract in the feeding specialist Sciurus aberti and several generalist congeners

Abstract

Abert's squirrel (Sciurus aberti) is a highly specialized mammal dependent upon ponderosa pine (Pinus ponderosa) for a significant part of its yearly diet. For up to six months of the year, these squirrels only eat ponderosa pine phloem, which is a high-fiber, low-quality diet. We compared gross morphologies of the gastrointestinal tract in specialized Abert's squirrels to those of generalist fox squirrels (S. niger) and found that Abert's squirrels have significantly longer gastrointestinal tracts with greater tissue surface area and weight than do fox squirrels. Published data describing the eastern gray squirrel (S. carolinensis) and the western gray squirrel (S. griseus) indicate that these generalist species have body weights and a gut morphology very similar to that of the fox squirrel. We conclude that the morphology of the digestive tract of Abert's squirrel has become adapted to its low-quality diet.