Environment, but not genetic divergence, influences geographic variation in colour morph frequencies in a lizard.

Adnan Moussalli,Claire A Mclean,Devi Stuart-Fox

doi:10.1186/s12862-015-0442-x

Adnan Moussalli, Claire A Mclean + Show 1 more

Open Access

https://doi.org/10.1186/s12862-015-0442-x

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Abstract

BackgroundIdentifying the causes of intraspecific phenotypic variation is essential for understanding evolutionary processes that maintain diversity and promote speciation. In polymorphic species, the relative frequencies of discrete morphs often vary geographically; yet the drivers of spatial variation in morph frequencies are seldom known. Here, we test the relative importance of gene flow and natural selection to identify the causes of geographic variation in colour morph frequencies in the Australian tawny dragon lizard, Ctenophorus decresii.ResultsPopulations of C. decresii are polymorphic for male throat coloration and all populations surveyed shared the same four morphs but differed in the relative frequencies of morphs. Despite genetic structure among populations, there was no relationship between genetic similarity or geographic proximity and similarity in morph frequencies. However, we detected remarkably strong associations between morph frequencies and two environmental variables (mean annual aridity index and vegetation cover), which together explained approximately 45 % of the total variance in morph frequencies.ConclusionsSpatial variation in selection appears to play an important role in shaping morph frequency patterns in C. decresii. Selection associated with differences in local environmental conditions, combined with relatively low levels of gene flow, is expected to favour population divergence in morph composition, but may be counteracted by negative frequency-dependent selection favouring rare morphs.Electronic supplementary materialThe online version of this article (doi:10.1186/s12862-015-0442-x) contains supplementary material, which is available to authorized users.

Highlights

Identifying the causes of intraspecific phenotypic variation is essential for understanding evolutionary processes that maintain diversity and promote speciation
Such geographic variation in polymorphism may act as a precursor to speciation if the processes generating geographic variation in morph frequencies promote phenotypic and genetic differentiation leading to reproductive isolation
Spatial variation in polymorphism cannot be explained by selection alone [9, 10], and it is likely that genetic drift and gene flow play a role

Summary

Introduction

Identifying the causes of intraspecific phenotypic variation is essential for understanding evolutionary processes that maintain diversity and promote speciation. Polymorphic species, in which multiple, discrete phenotypic variants coexist within a population [1], exhibit extreme, measurable, intraspecific phenotypic variation that often varies geographically in the composition and frequency of morphs. Such geographic variation in polymorphism may act as a precursor to speciation if the processes generating geographic variation in morph frequencies promote phenotypic and genetic differentiation leading to reproductive isolation. One of the most important processes generating morph frequency variation is spatial variation in selection and local adaptation [5] This has been shown to influence population morph frequencies in multiple species Despite a rich history of research on polymorphic species, the relative importance of selection, genetic drift and gene flow for explaining geographic variation in polymorphism remains poorly understood (reviewed in [4])

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