Linking environmental adaptation and genetic structure to the biogeography of flower colour lineages in Lysimachia monelli (Primulaceae).

Reproductive traits such as flower colour can have a profound influence on the diversification of plant species, making understanding their evolutionary ramifications one of the foremost challenges for evolutionary biologists. Lysimachia monelli is a Mediterranean endemic with two markedly divergent flower colour lineages, blue and orange, which do not coexist within the same populations. We examined the relationship between lineage divergence and environmental niche differentiation for the two lineages. Genetic relationships among individuals from 21 blue and six orange populations were assessed using seven nSSR markers. Environmental niche models were projected for the present and three past periods. Low gene flow between populations and elevated heterozygosity were pervasive across L. monelli populations. Western populations of both orange and blue lineages had higher genetic diversity than their eastern counterparts, with blue lineages displaying higher diversity than orange lineages. There was conspicuous genetic differentiation between colour lineages, and populations were aggregated into five nSSR clusters. Colour lineages occupied distinct environmental niches, with lineage-specific habitat suitability primarily influenced by variations in annual precipitation and solar radiation. Bioclimatic fluctuations in the region appear to have driven the divergence of L. monelli populations along a west-to-east gradient. The findings suggest comprehensive geographic and genetic separation of the two L. monelli colour lineages, suggesting an advanced stage of speciation.