Do ecogeographical rules explain morphological variation in a diverse, Holarctic genus of small mammals?

Abstract

AbstractAimWe use ecogeographical rules to understand the relationship between biogeography and morphological evolution in Sorex (Linnaeus, 1758) shrews. Specifically, we test for climatic correlations in body size (Bergmann's rule; larger species in colder habitats) and pelage brightness (Gloger's rule; darker species in more humid/warmer habitats).LocationNorth America and Eurasia (Holarctic).TaxonSorex spp. (Mammalia: Soricomorpha: Soricidae).MethodsWe compiled body size data for 51 species of Sorex and measured pelage brightness from museum specimens for 43 species. We sourced bioclimatic data across the geographical range of each species as well as specific to the museum specimen localities. For comparative purposes, we also estimated a Sorex phylogeny using existing sequence data. To test Bergmann's and Gloger's rules, we constructed phylogenetic least squares models considering latitude, altitude, and bioclimatic variables as predictors of interspecific variation in body size and pelage brightness across Sorex. We then performed these tests separately for the Palaearctic and Nearctic lineages.ResultsSorex exhibits wide variation in both body size and pelage brightness. In models of the entire genus and of the Nearctic clade, neither trait is significantly predicted by the variables tested. A decrease in pelage brightness in the Palaearctic clade is significantly predicted by increasing mean annual temperature and annual precipitation, but only when considering climatic data specific to the measured specimen localities.Main conclusionsSorex does not conform to Bergmann's rule. This result aligns with intraspecific studies suggesting Bergmann's rule is less evident in smaller taxa, but it counters others that found support for the rule in North American and European assemblages. Different patterns in pelage evolution across the Nearctic and Palaearctic clades may result from different historical climatic pressures; however, the significance of the relationship between climate and pelage evolution is dependent on the specificity of the climatic data. Sorex may be a useful focal taxon for exploring the relationship between intra‐ and interspecific ecogeographical patterns as well as the relative roles of morphological, behavioural, physiological, and life history characteristics in explaining the ability to persist in climatically challenging environments.