Geographic variation in skull shape of the water rat Scapteromys tumidus (Cricetidae, Sigmodontinae): isolation-by-distance plus environmental and geographic barrier effects?

Abstract

The geographic variation in skull size and shape of the swamp rat Scapteromys tumidus was examined in samples from eight geographic clusters in almost of its distribution in southern Brazil and Uruguay. For analysis we used two-dimensional geometric morphometric methods for dorsal, ventral and lateral views of the skull. The geometric descriptors showed no signifi cant differences in skull size between geographic clusters, while differences in shape were highly signifi cant. We found a signifi cant and moderate correlation between geographic and morphological distances, corroborating the isolation-by-distance model. Samples from the Rio Grande do Sul central coastal plain were the most differentiated, segregating completely from all other samples in canonical variate analysis for the dorsal view. The most visible variable regions in skull were the zygomatic arch (mainly the squamosal root of zygomatic) and the lateral braincase borders. Once correlation between geographic and morphological distances were not strong, it is possible that other factors (environmental heterogeneity and/or geographic barriers) may are acting in S. tumidus skull differentiation.

Skull variation in populations of the Indian gerbil Tatera indica (Gerbillinae, Rodentia) sampled across its broad geographic range

“…Potentially, this could be explained by the isolation-by-distance model (Wright 1943), whereby the further the populations are from each other, the more limited the dispersal between them will be, and consequently the more differentiation. The association between skull morphometric and geographic distance is not a novel observation, and has been shown to occur in numerous previous rodent studies (Muñoz-Muñoz et al 2011;Cordero and Epps 2012;Quintela et al 2016;Alhajeri 2018;Alhajeri 2019). Other non-climatic spatial factors unexamined in this study could also explain the detected association with skull variation, such as environmental heterogeneity and geographic barriers (Quintela et al 2016).…”

“…The association between skull morphometric and geographic distance is not a novel observation, and has been shown to occur in numerous previous rodent studies (Muñoz-Muñoz et al 2011;Cordero and Epps 2012;Quintela et al 2016;Alhajeri 2018;Alhajeri 2019). Other non-climatic spatial factors unexamined in this study could also explain the detected association with skull variation, such as environmental heterogeneity and geographic barriers (Quintela et al 2016).…”

“…When these conspecific populations occupy widely different habitats, then selective pressures could potentially direct this differentiation (i.e., adaptive), otherwise, morphological differentiation could be neutral (i.e., when spatially separated populations occupy similar habitats). The effect of spatial separation and climate on skull differentiation is a widely studied topic in rodents, both within populations (Monteiro et al 2003;Tabatabaei Yazdi and Adriaens 2011;Cordero and Epps 2012;Renvoisé et al 2012;Tabatabaei Yazdi et al 2012;Nanova 2014;Quintela et al 2016;Alhajeri 2019;Alhajeri 2021a) and between species (Renaud and Millien 2001;Croft et al 2011;Martínez and Di Cola 2011;Alhajeri 2018;Alhajeri 2021c;Tabatabaei Yazdi and Alhajeri 2018;Yağcı and Gurbanov 2019;Álvarez et al 2021).…”

Pleistocene climatic oscillations in Neotropical open areas: Refuge isolation in the rodent Oxymycterus nasutus endemic to grasslands

“…Similarly, studies on haplogroups of sympatric akodonts (e.g., Deltamys kempi [ 63 , 64 ] and Scapteromys spp. [ 65 , 66 ]). were also divergent in the geometric or linear morphometric analysis of the skull.…”