Sexual Dimorphism and Geographic Variation in Washington Bobcat (Lynx rufus) Skulls

Sexual dimorphism is a well-studied phenomenon in which males and females of a species exhibit different phenotypic characteristics. However, the degree of sexual dimorphism within a species may vary among populations and may be influenced by geographic factors such as seasonality, prey availability, and population density. In this study, we examined the effects of sexual dimorphism and geographic region on the craniomandibular morphology of bobcats (Lynx rufus) in Washington State. Using digital calipers, we measured 13 craniomandibular traits from 35 males and 42 females. We found that the degree of skull dimorphism does not differ between the eastern and western side of the Cascade Mountains. However, we found significant effects of sex and geographic region on craniomandibular morphology. Across the geographic regions, males were significantly larger than females in most craniomandibular traits, excluding postorbital constriction breadth (POC). After correcting for expected size differences, only condylobasal length (CBL) was disproportionately longer in males, indicating subtle shape dimorphism within this trait, that is largely unexplained by allometry. Mechanical advantage (MA) of the temporalis and masseter muscles did not differ between the sexes at the canine or the molar bite points. Comparisons between populations east and west of the Cascade Range revealed that while sex remains the primary indicator of overall size, there is a small regional effect on size as western bobcats are slightly larger than eastern bobcats. These regional differences highlight how environmental pressures including local prey availability and severe winter conditions may influence functional skull design. Future ecological and behavioral studies are needed to further clarify how these localized environmental drivers shape phenotypic variation across populations.