How does genetic diversity change towards the range periphery? An empirical and theoretical test

Question: How does genetic diversity change as one moves along a species' range, towards the periphery? Previous work shows contradictory evidence for an increase, decrease or no clear trend along the range. Hypothesis: A hump-shaped unimodal pattern of within-population genetic diversity will occur along the range with peak diversity in sub-peripheral populations. This hypothesis incorporates and explains some of the apparent contradictions found in the literature. Organism: Thirteen native chukar partridge (Alectoris cltukar) populations. Location: A steep environmental gradient towards the periphery of the species' range in Israel. Methods: Genetic diversity was estimated in 26 allozyme loci. Conclusions: A unimodal pattern of within-species genetic diversity, as expressed by measures of heterozygosity, is found along the range. Diversity peaks at the sub-periphery of the chukar range. These populations are located at the ecotone between the Mediterranean and desert climatic regions. Appendix: A mathematical model that explores possible mechanisms generating the unimodal pattern. The model suggests that a unimodal pattern can appear under a range of parameters.