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

Sexual dimorphism, where males and females of a species differ in physical traits, is a well-documented concept. However, this variation can differ among populations. This research examined sexual dimorphism and geographic variation in the skulls of Washington State bobcats (Lynx rufus). Using digital calipers, measurements were taken from 35 males and 42 females, focusing on 13 craniomandibular traits.

The findings showed no difference in skull dimorphism between bobcats on the eastern and western sides of the Cascade Mountains. Yet, there were notable differences in size and shape related to sex and geographic region. Males consistently surpassed females in most craniomandibular traits, with the exception of postorbital constriction breadth (POC).

After adjusting for expected size differences, males only exhibited a slightly longer condylobasal length (CBL), suggesting a subtle shape dimorphism not fully explained by allometry. Interestingly, mechanical advantage of the temporalis and masseter muscles, crucial for jaw strength, did not vary between sexes at the bite points.

When comparing populations east and west of the Cascade Range, while sex was the main factor determining overall size, there was a minor regional effect, indicating that western bobcats are slightly larger than their eastern counterparts. This regional difference underscores how environmental pressures, such as local prey availability and harsh winter conditions, can influence skull design and functional morphology.

Further ecological and behavioral studies are necessary to better understand how these localized environmental factors shape phenotypic variation among bobcat populations.