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SKELETAL ADAPTATIONS FOR DIGGING IN THE LIMBS OF TWO SPECIES OF SHORT-TAILED SHREWS (BLARINA). Adam Swisher and Russ Benedict. Department of Biology, Central College, 812 University St., Pella, IA.

ABSTRACT- Blarina hylophaga has been recognized as a species distinct from B. brevicauda only since the 1980s. Consequently, few studies have specifically analyzed the biology of B. hylophaga; its natural history has been assumed to be similar to B. brevicauda. As part of a larger study, roughly 20 individuals of each species were caught each month of the year during 1998 in southeastern Nebraska. During this project, we compared skeletal morphology of the limbs of these two species to determine if they are similarly adapted for digging. Relative to non-diggers, limbs of fossorial mammals typically have wide shafts and wide processes for muscle attachment (epicondyles, tuberosities, etc.), and have short out-levers (portion of a bone distal to joint) and long in-levers (portion of a bone proximal to joint) to increase power using lever mechanics. We measured 14 traits using digital calipers. Given that B. brevicauda weighs 1.7 times more than B. hylophaga, it is not surprising that all traits measured were significantly different, with brevicauda being larger. We standardized all traits by dividing bone length measurements (e.g.: humerus length) by body length, and dividing bone width measurements (e.g.: humerus shaft width) by body weight. The relative lengths of the limb bones (humerus, radius/ulna, femur, tibia/fibula) of these two species are similar with the bones of B. hylophaga averaging 1.1 % longer than B. brevicauda relative to body length. The width measurements, however, are surprisingly different, with the bones of B. hylophaga averaging 31.8 % wider than B. brevicauda relative to body weight (range = 21.8 to 40.2 %). Blarina brevicauda averages larger than B. hylophaga for only one trait, power ratio (in-lever divided by out-lever; brevicauda is 8.9 % larger). A possible explanation for these differences is that both species use the forelimbs to dig. But, because B. brevicauda has a larger power ratio, it does not have to exert as much muscular force as does B. hylophaga. The stouter bones and wider processes of B. hylophaga, therefore, are necessary to create and withstand the greater muscular force needed by this species.

KEY WORDS: morphology, Blarina, fossorial