Global Drivers of Morphological Variation in Grey Wolves

Aim To investigate the ecological and evolutionary drivers of morphological variation in grey wolves (Canis lupus) across their global range: Location The entire Holarctic distribution of grey wolves, from Greenland to New Mexico in North America, from Norway to Israel in Eurasia, including several samples from Russia and India. Methods We analysed 227 wolf skulls using high-resolution 3D geometric morphometrics (585 cranial and 96 mandibular landmarks) to assess the influence of continental separation, latitude, prey mass and population history on skull (cranium and mandible) size and shape. Results Skull size was primarily influenced by population identity, increasing with average prey mass and latitude up to roughly 65°, with minimal differences between continents. Skull shape was mainly determined by population identity, with minor contributions from skull size, continent, and latitude; prey mass had no detectable effect. Average crania differed in the length-to-width ratio, shape and relative position of the frontal bones and zygomatic arches. Populations with the most distinct skull shapes included Modern Scandinavian wolves, Arctic wolves (East Greenland and Ellesmere Island), Italy and Coastal Alaska. These disparities are consistent with expected changes associated with long-term isolation, demographic events (e.g., bottlenecks, founder effects), human-driven fragmentation and extirpation of wolves, shifts in prey availability, and possible hybridization. Main Conclusions Morphological variation in wolves is shaped by a combination of ecological pressures, geography and human impacts. Past isolation and human-induced declines have increased divergence, emphasizing the importance of considering ecomorphological patterns when assessing evolutionary resilience and informing conservation planning for large carnivores.