Morphometrics as an Insight Into Processes Beyond Tooth Shape Variation in a Bank Vole Population

Abstract

Phenotype variation is a key feature in evolution, being produced by development and the target of the screening by selection. We focus here on a variable morphological feature: the third upper molar (UM3) of the bank vole, aiming at identifying the sources of this variation. Size and shape of the UM3 occlusal surface was quantified in successive samples of a bank vole population. The first source of variation was the season of trapping, due to differences in the age structure of the population in turn affecting the wear of the teeth. The second direction of variation corresponded to the occurrence, or not, of an additional triangle on the tooth. This intra-specific variation was attributed to the space available at the posterior end of the UM3, allowing or not the addition of a further triangle.This size variation triggering the shape polymorphism is not controlled by the developmental cascade along the molar row. This suggests that other sources of size variation, possibly epigenetic, might be involved. They would trigger an important shape variation as side-effect by affecting the termination of the sequential addition of triangles on the tooth.

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

“…Both species are difficult to recognise based on external phenotypic characters, and impossible to identify based on common mitochondrial markers because of the introgression of M. rutilus mtDNA into the northern fringe of M. glareolus distribu-tion. The northern cluster detected by our method corresponds most probably to the occurrence of the northern red-backed vole M. rutilus, that tends to differ in molar shape from its relative M. glareolus(Ledevin et al, 2010b).…”

“…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.…”

Silicon-based plant defences, tooth wear and voles

“…All these individuals were adults, or sub-adults feeding on the same resources as adults. While subtle age-related changes in the morphology of voles due to wear have been measured (Ledevin et al, 2010), DMTA should be insensitive to these inter-age changes and reflect only the mechanical properties of the food ingested. One dataset was composed of 34 individuals from the Biebrza Marshes to test for differences between seasons (spring and summer, in Olszowa Droga) and localities (Olszowa Droga and Barwik, in spring).…”

Developmental integration in a functional unit: deciphering processes from adult dental morphology

“…After birth, tooth shape does not change except from wear (Ledevin et al 2010), but this phenotype is highly derived, with the addition of several cusps posterior to bud subdivisions (Salazar-Ciudad and Jernvall 2002), and continuously growing molars. After birth, tooth shape does not change except from wear (Ledevin et al 2010), but this phenotype is highly derived, with the addition of several cusps posterior to bud subdivisions (Salazar-Ciudad and Jernvall 2002), and continuously growing molars.…”

“…The adult phenotype presents very specific patterns of integration in comparison with the expected model of early integration. After birth, tooth shape does not change except from wear (Ledevin et al 2010), but this phenotype is highly derived, with the addition of several cusps posterior to bud subdivisions (Salazar-Ciudad and Jernvall 2002), and continuously growing molars. Integration produced by late developmental mechanisms may hide this early integration with regard to the relative size, position, and orientation of buds.…”