Differentiation of craniomandibular morphology in two sympatric Peromyscus mice (Cricetidae: Rodentia)

Abstract

In the Santa Cruz Mountains of California, dietary partitioning is believed to allow Peromyscus californicus (California mouse) and Peromyscus truei (pinyon mouse) to occur sympatrically; P. californicus feeds primarily on arthropods, whereas P. truei feeds primarily on acorns. To better understand how these species partition resources, we examine if these dietary differences extend to differences in craniomandibular morphology. We use a geometric morphometric approach to test the hypothesis that P. californicus and P. truei exhibited size and shape differences in craniomandibular morphology, in particular, regions of the skulls that pertain to biting ability and mechanical advantage of the jaw adductor muscles. We found that P. truei exhibited relatively wider zygomatic arches, relatively broader, more robust masseteric fossa and coronoid process, and a higher mechanical advantage of the masseter jaw muscle. These craniomandibular traits suggested that P. truei exhibits a relatively stronger bite force that is more suitable to access hard-shelled acorns despite its smaller body size.