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Abstract
BackgroundMammals show a predictable scaling relationship between limb bone size and body mass. This relationship has a genetic basis which likely evolved via natural selection, but it is unclear how much the genetic correlation between these traits in turn impacts their capacity to evolve independently. We selectively bred laboratory mice for increases in tibia length independent of body mass, to test the hypothesis that a genetic correlation with body mass constrains evolutionary change in tibia length.ResultsOver 14 generations, we produced mean tibia length increases of 9-13%, while mean body mass was unchanged, in selectively bred mice and random-bred controls. Using evolutionary scenarios with different selection and quantitative genetic parameters, we also found that this genetic correlation impedes the rate of evolutionary change in both traits, slowing increases in tibia length while preventing decreases in body mass, despite the latter’s negative effect on fitness.ConclusionsOverall, results from this ongoing selection experiment suggest that parallel evolution of relatively longer hind limbs among rodents, for example in the context of strong competition for resources and niche partitioning in heterogeneous environments, may have occurred very rapidly on geological timescales, in spite of a moderately strong genetic correlation between tibia length and body mass.Electronic supplementary materialThe online version of this article (doi:10.1186/s12862-014-0258-0) contains supplementary material, which is available to authorized users.
Highlights
Mammals show a predictable scaling relationship between limb bone size and body mass
Tibia length increased by 0.67-0.94% per generation of selective breeding in males and females for both lines (Figure 2, Table 1)
Tibia lengths in males and females are approximately equal, but females are substantially lighter than males, and have relatively longer tibiae (Table 1, Additional file 1: Table S1 and Additional file 2: Table S2)
Summary
Mammals show a predictable scaling relationship between limb bone size and body mass This relationship has a genetic basis which likely evolved via natural selection, but it is unclear how much the genetic correlation between these traits in turn impacts their capacity to evolve independently. Limb bone size and shape among terrestrial mammals scale allometrically with body mass, both within populations [1], and across species with a wide range of body masses [2,3,4,5,6] (Figure 1). The links between limb bone dimensions and body mass indicates that they are functionally, developmentally and genetically integrated [17], to the extent that selection on body mass causes correlated changes in the size and shape.
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