Breaking the Rules: Museum Data Reveal Divergent Support for Classic Ecogeographical Rules in North American Flying Squirrels
Year: 2026
Type: article
Abstract: ABSTRACT Ecogeographic generalizations or “rules”, such as Bergmann's rule and Allen's rule, propose that endotherms in colder climates evolve larger bodies and shorter appendages to minimize heat loss. These patterns are hypothesized to reflect physiological adaptations to thermal stress through reduced surface area‐to‐volume ratios. Although these rules have been extensively evaluated across birds and mammals, their applicability to arboreal gliders remains untested, with little consideration of how alternative ecological and evolutionary drivers may structure morphological variation in flying squirrels across environmental gradients. Using digitized museum specimens of North American flying squirrels ( Glaucomys sabrinus , Glaucomys oregonensis , and Glaucomys volans ), we tested these classic ecogeographic principles by examining how weight, total length, tail length, and ear length vary across a latitudinal gradient. We found significant support for Bergmann's rule, with body mass and total length increasing with latitude. In contrast, patterns in appendage morphology provided limited support for Allen's rule. Ear length exhibited a weak positive relationship with latitude, while tail length strongly increased with latitude, contradicting the prediction that appendages become shorter in colder climates. These findings suggest that thermoregulatory selection alone cannot explain morphological variation in North American flying squirrels and that functional demands, particularly those associated with gliding performance, may play a stronger role in shaping tail morphology. Overall, our results demonstrate that although classic ecogeographic rules provide a useful framework for understanding morphological variation, they do not fully capture the multiple selective pressures acting on Glaucomys species.
Source: Ecology and Evolution
DOI: 10.1002/ece3.74470
Institutions: University of Wisconsin–Green Bay, Duke University
Language: English
Subfield: Ecology
Field: Environmental Science
Domain: Physical Sciences
Open Access status: gold
Estimated APC paid: $2,570
Funders: Smithsonian Institution, Texas Tech University, University of Washington, Emporia State University, Northern Michigan University, Kentucky Science and Technology Corporation, Eastern Michigan University, National Museum of Natural History, Museum of Comparative Zoology, Harvard University, University of North Carolina at Greensboro, Nicholas School of the Environment, Duke University, Burke Museum, University of Washington
OpenAlex ID: W7221606271