Wolf cranial morphology tracks population replacement in Fennoscandia

Humans have directly or indirectly contributed to the genetic, and thus often phenotypic, changes of many species. Anthropogenic pressures, such as persecution and hunting, have negatively affected wolf populations in Northern Europe. In line with the genetic replacement that occurred during the 20th century following the extirpation of wolves from Scandinavia (Norway and Sweden) and their near-extirpation from Finland, we provide evidence of morphological changes in wolf cranial morphology across these populations. Using 3D landmark-based geometric morphometrics, we show that modern wolves in Scandinavia and Finland have, on average, crania with wider frontal bones, wider and higher positioned zygomatic arches, and more ventral flexion of the rostrum compared to the historical wolf populations. Although both populations differ in the magnitude and direction of shape change over time, the centroid size, or overall size of the cranium, is significantly larger only in the modern Scandinavian wolves. Different genetic origins of the historical and modern populations have likely played a role in the observed morphological variation; however, it is also likely that morphology has been affected by the availability of different prey, which has changed over time.

Methods
Data was collected from CT-scanned wolf skull specimens and then landmarked in Stratovan Checkpoint v.2023 (Stratovan Corporation, Sacramento, USA).