Sexual dimorphism in cranial shape and size in geomyoid rodents: multivariate and evolutionary perspectives

Abstract

Geomyoid rodents provide a great study system for the analysis of sexual dimorphism. They are polygynic and many inhabit harsh arid environments thought to promote sexual dimorphism. In fact, there has been extensive work published on the sexual size dimorphism of individual populations and species within this rodent clade. However, little work has been undertaken to assess the evolutionary patterns and processes associated with this sexual dimorphism. We use multivariate analyses of cranial measurements in a phylogenetic framework to determine the distribution of size and shape dimorphism among geomyoids and test for Rensch’s rule. Our results suggest that sexual dimorphism is more common in geomyids than heteromyids, but it is not in fact universal. There is evidence for variation in sexual dimorphism across populations. Additionally, in many taxa, geographic variation appears to overwhelm existing sexual dimorphism. We find support for the repeated independent evolution of shape and size dimorphism across geomyoid taxa, but we do not find support for an association between size and shape dimorphism. There is no evidence for Rensch’s rule in geomyoids, whether at the superfamily or family level. Together, our findings suggest that there is no single explanation for the evolution of sexual dimorphism in geomyoids and that, instead, it is the product of numerous evolutionary events. Future studies incorporating phylogenetic relationships will be necessary to paint a more complete picture of the evolution of sexual dimorphism in geomyoids.

Evaluation of pocket gopher diet in a perennial productive area

“…The present study reports the measurements of a larger number of specimens of G. arenarius. Males showed a larger body size than females, consistent with several studies (Hendricksen 1972;Daly and Patton 1986;Mauk et al 1999;Connior 2011;Calede and Brown 2021).…”

Multivariate analyses of skull morphology inform the taxonomy and evolution of geomyoid rodents

“…Our sample is built upon that of Calede and Brown (2021) , which analyzed sexual dimorphism in skull size and shape in geomyoids. It contains 886 specimens ( Table 1 ).…”

“…We included data from 396 geomyid specimens representing all 7 genera and 17 of 41 species as well as 490 heteromyid specimens representing all 5 genera and 22 of 68 species (mean 22.7 per species, median 18). Based on prior results of the sampling necessary to accurately quantify size and shape in geomyoids ( Calede and Brown 2021 ), we included a minimum of 16 specimens per species in our analyses in all but one species. We only analyzed data from adult specimens (based on the fusion of cranial sutures and the presence of fully erupted worn teeth) to avoid ontogenetic effects on morphology.…”

“…Whenever possible, we sampled specimens across a large proportion of the geographic range for the species to cover geographic and environmental variation. The role of geographic variation in geomyoid morphology is discussed in part in Calede and Brown (2021) . We also included, when possible, a range of sampling expedition dates, in part by selecting specimens across museums.…”

“…Our goal is to determine the potential of morphology to inform taxonomy, quantify morphological disparity, and determine morphospace overlap across a broad sample of geomyoid species. We build upon Calede and Brown (2021) , which quantified sexual dimorphism in skull shape and size in geomyoids and explore morphological variation in skull shape and size across taxa. Combined with phylogenetics, our morphological data enable an initial study of the pattern of skull shape evolution within Geomyoidea.…”