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

Abstract

Aim We 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). Location North America and Eurasia (Holarctic). Taxon Sorex spp. (Mammalia: Soricomorpha: Soricidae). Methods We 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. Results Sorex 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 conclusions Sorex 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.

Evolution of Pelage Luminance in Squirrels (Sciuridae)

“…Gloger's rule is an ecogeographic rule describing the tendency of animals living in warm and wet environments to be darker (Gloger, 1833;Rensch, 1929). This rule has been supported by several quantitative tests from a wide variety of taxa including birds, mammals, reptiles, amphibians, and insects (Delhey, 2019;Delhey et al, 2019;Stanchak and Santana, 2019). There are multiple mechanisms that have been proposed to explain the color patterns that conform to Gloger's rule (Delhey, 2019) with the most common being that darker coloration is selected for in environments with lower light conditions to facilitate greater concealment from predators.…”

Rapid size change associated with intra-island evolutionary radiation in extinct Caribbean “island-shrews”

“…Greater interspecific variation in body mass compared to that between Hispaniolan Nesophontes species is seen within several morphologically and ecologically broadly comparable genera of soricids ("true shrews"), such as Sorex (smallest, S. minutissimus, 1.4-4 g; largest, S. bendirii, 10-21 g) and Suncus (smallest, S. malayanus, 1.1-2.4 g; largest, S. murinus, 23.5-147.3 g) [24]. However, small-bodied and large-bodied species are not closely related to each other within these soricid genera, in contrast to representing rapid recent evolutionary divergence of body sizes as seen in Hispaniolan Nesophontes [71,72].…”

Skull shape and Bergmann's rule in mammals: hints from Old World porcupines

“…2). The divergence of Hystrix species from this rule is common to many rodents and small mammals, but the reason behind this pattern is still unclear (Meiri & Dayan, 2003) and may be due to the effect of multiple environmental variables (Sargis et al, 2018;Stanchak & Santana, 2018). Interspecific competition (e.g.…”

“…Among those, the Bergmann's rule is one of the most debated (Blackburn, Gaston & Loder, ; Raia & Meiri, ; Lokatis & Jeschke, ). The Bergmann's rule states that, within closely related endotherm taxa, body size tends to decrease from colder to warmer climates The (Bergmann, ; Salewski & Watt, ; Stanchak & Santana, ). Bergmann's rule has been revised several times (e.g.…”

“…Monteiro-Filho, Monteiro & Reis, 2002;Caumul & Polly, 2005;Cardini, Jansson & Elton, 2007;C aceres et al, 2014;Tomassini et al, 2014). Past climatic and geographic changes, such as, continental drift, climate oscillations and changes in the sea level, have influenced the present geographic distribution of organisms, together with their morphology, for example, shape and body size (Owen-Smith, 1987;Taberlet et al, 1998;Jablonski et al, 2000;Anthony et al, 2007;Schmitt, 2007;Mouline et al, 2008).…”