Rapid morpho-functional changes among insular populations of the greater white-toothed shrew

Abstract

Islands are often considered to be natural laboratories where repeated ‘evolutionary experiments’ have taken place. Consequently, islands have been key model systems in our understanding of evolutionary theory. The greater white‐toothed shrew (Crocidura russula) is of interest as it has invaded French Atlantic islands within the last few thousand years and is considered to be morphologically and genetically stable in this area. In this article, we study the shape of the mandible of the greater white‐toothed shrew on four islands and compare it with that of individuals from populations on the mainland to quantify the effects of insularity. The degree of insularity (i.e. island size and distance to the continent) is thought to be linked to differences in ecological characteristics of islands compared with the mainland. We used geometric morphometric analyses to quantify differences in size and shape between populations and employed a simple biomechanical model to evaluate the potential effects of shape differences on bite force. Specimens from island populations are different from continental populations in shape and mechanical potential of the mandible. Among islands, the mandible shows various shapes that are correlated with both the distance from the coast and island area. The shape differences are located on different parts of the mandible, suggesting different ecological constraints on each island. Moreover, these shapes are linked to the ‘mechanical potential’, which is markedly different between islands. Mechanical potential has been suggested to evolve in response to prey size and or mechanical properties. In conclusion, our results show that, in spite of the relatively recent colonization of the Atlantic Islands, the mandible of C. russula possesses a distinct shape. Moreover, the shape differs among islands and is probably linked to the consumption of different prey. © 2012 The Linnean Society of London, Biological Journal of the Linnean Society, 2012, ••, ••–••.

The shrew tamed by Wolff's law: Do functional constraints shape the skull through muscle and bone covariation?

“…Conversely, the mean shape of our island individuals is more similar to the shapes associated with low bite forces and low muscular cross sectional areas. This confirms earlier results suggesting that lower bite forces are present in insular populations of both C. russula and the closely related C. suaveolens on the French Atlantic islands (Cornette et al, ). These differences are possibly related to differences in prey availability on islands (Young et al, ).…”

“…Moreover, muscle cross sectional area data and in vivo bite forces are collected for these same individuals. We predict that the animals from the island will be characterized by a cranial shape that is similar to that observed in individuals with low bite forces given previous suggestions of low bite force in insular shrew populations (Cornette et al, ). Moreover, we specifically predict that specimens with high bite force and those with large temporalis muscles will show an enlarged parietal area of the skull, the insertion site for the temporalis muscle.…”

The jaw is a second-class lever inPedetes capensis(Rodentia: Pedetidae)

“…The mammalian jaw is frequently treated as a lever for the purposes of biomechanical analysis (e.g., Crompton, 1963; Bramble, 1978; Greaves, 1978; Greaves, 1982; Greaves, 2000; Gingerich, 1979; Thomason, 1991; Satoh, 1998; Satoh, 1999; Spencer, 1998; Spencer, 1999; Satoh & Iwaku, 2006; Satoh & Iwaku, 2009; Davis et al, 2010; Druzinsky, 2010; Cornette et al, 2012; Becerra, Casinos & Vassallo, 2013; Santana, 2015). More specifically, it is frequently considered to be a third-class lever i.e., one in which the input force sits between the fulcrum and the output force (Kerr, 2010).…”

Description of a new endemic species of shrew (Mammalia, Soricomorpha) from PrÍncipe Island (Gulf of Guinea)

“…Although there are some doubts regarding the anthropogenic introduction and the ensuing colonization of shrews of some Mediterranean and Philippine islands ( Cosson et al 2005 , Esselstyn andOliveros 2010 ), there is evidence of humans introducing shrews to other islands ( Mascheretti et al 2003, Tosh et al 2008, McDevitt et al 2011, Bover et al 2012. Recent studies show that fast (100-year time-scale) morpho-functional changes can affect human-mediated shrew populations on islands ( Cornette et al 2012 ). Anthropogenic introduction seems unlikely as the first known human arrival to the island was by Portuguese colonists in the late fifteenth century, long after the estimated split of Crocidura fingui from its sister taxon.…”