Meeting Abstract

P2.92  Monday, Jan. 5  Sexual dimorphism in skeletal proportions of California voles ROGERS, Nala/L*; CARRIER, David/R; Univ. of Utah, Salt Lake City; Univ. of Utah, Salt Lake City mostlyapples@gmail.com

The genus Microtus (voles) is ideal for studying sexual selection because it contains several closely-related species with diverse mating strategies. We hypothesized that polygynous species will show sexual dimorphism in body proportions due to functional tradeoffs for aggressive male-male competition versus locomotion. For example, we expected polygynous males to have more robust skulls, thicker limb bones, and greater mechanical advantage at their limb joints. To test this hypothesis, we measured skeletal metrics on male and female California voles (Microtus californicus) and looked for differences in proportions while controlling for body size. The males of this polygynous species are approximately ten percent heavier than the females. Contrary to our expectations, we found no sexual dimorphism in the postcranial skeletal proportions. There was dimorphism in the skull, but the direction was opposite to our predictions; for their size, females had larger skulls. There are several possible explanations for this result. First, proportions that are advantageous for fighting may be so maladaptive for other purposes that they are not selected for even among polygynous males. Second, the same body proportions could be advantageous for both fighting and locomotion, so that specialization for fighting does not lead to a difference in shape. Finally, females might need to fight in order to guard against infanticide. In this case, both sexes would be specialized for fighting.