Seasonal variation in molar outline of bank voles: An effect of wear?

Abstract

Morphometric characters can be of use for elucidating the evolutionary history of species by providing an insight into the selective pressure related to the character of interest, and by allowing integration of fossil specimens. This potential interest of phenotypic characters, however, depends on how much other sources of variation, such as the lifehistory of the animal, may blur an evolutionary signal. For instance, age structure varies along the year, causing in turn various assemblages of wear stages in the teeth sampled at a given place and time. In this context, we investigated the season of trapping as potential source of variation in the size and shape of the molar occlusal surface of the bank vole, Clethrionomys glareolus.The size and shape of the occlusal surface of the third upper molar was quantified using outline analysis in 60 bank voles from Finland, trapped at the same study site in successive spring and autumn. The occlusal surface clearly differed in size and shape between the two seasons of trapping. Using 3D imaging as a visual support, we interpret this difference as the result of differential wear. The population in autumn is dominated by young specimens with unworn teeth whereas spring populations are composed of old animals with worn down molars. The range of seasonal variation in tooth size and shape appears to be of the same order of magnitude as biogeographic variation, demonstrating that differential wear may have a strong impact on biogeographic and evolutionary studies. Yet, beyond the effect of trapping season, a biogeographic signal still emerged, related to the genetic lineages evidenced in other studies. In consequence, morphometric characters such as size and shape of molar occlusal surfaces appear as valuable tracers of biogeographic differentiation, but future studies should take seasonal variations into account for more robust interpretation.

The influence of environmental factors on the morphology of red-backed volesMyodes gapperi(Rodentia, Arvicolinae) in Québec and western Labrador

“…We found morphological variation in the first upper molars of southern red‐backed voles to be strongly affected by tooth wear. Previous studies have also identified a major effect of wear on tooth size and shape in the bank vole Myodes glareolus (Fominykh et al ., ; Guérécheau et al ., ; Ledevin et al ., ). According to these authors, voles trapped in different seasons (e.g.…”

“…Tooth wear has been recognized as a major source of morphological variation in arvicoline teeth (Fominykh et al ., ; Guérécheau et al ., ; Ledevin et al ., ), acting as a confounding factor when analysing covariates of tooth morphology. Therefore, we developed a tooth wear classification method based on the number of closed dentinal space isthmuses (Abe, ), continuity of the enamel crest and presence of dentin in the re‐entrant angles (Appendix 1).…”

Evolutionary history of the bank vole Myodes glareolus: a morphometric perspective

“…These teeth were chosen because UM1 and LM1 are the most widely used teeth in paleontological and biogeographic studies (Kitahara, 1995; Chaline et al ., 1999; Luo et al ., 2004; Martin, Crockett & Marcolini, 2006; Tougard et al ., 2008). We added UM3 because a few studies have used it for systematic purposes (Kaneko, 1992) and evolutionary studies (Barnosky, 1993), and because this tooth displays a large intraspecific variation (Bauchau & Chaline, 1987; Guérécheau et al ., 2010).…”

A Unifying Model for the Analysis of Phenotypic, Genetic, and Geographic Data

“…We note however that these maps are congruent concerning the location of the main area of transition between the clusters and that the analysis based on spatial information is graphically more efficient at displaying the location of this transition. The bank vole molar shape has been shown to display a large variation even within populations, due to wear and developmental factors (Guérécheau et al, 2010;Ledevin et al, 2010b). This may render even clear cut inter-specific boundaries difficult to detect.…”