Genetic diversity, outcrossing rate, and demographic history along a climatic gradient in the ruderal plant Ruellia nudiflora (Acanthaceae)

Ruellia nudiflora has shown a high potential to easily invade disturbed areas. Outcrossing rate and genetic structure and diversity in this species were examined along a climatic gradient in the Yucatán Peninsula (Mexico) in order to understand the effects of environmental heterogeneity - isolation by environment (IBE) - as well as correlation in herkogamy on genetic structure, diversity, and demographic history in this species. Nine populations were sampled along a temperature-precipitation gradient with marked differences in vegetation, measuring the degree of herkogamy in each sampled plant. To evaluate genetic diversity and structure, amplified fragment length polymorphism (AFLP) markers from 76 plants in these populations were used, while the outcrossing rate was evaluated in 22 genetic families from six populations. All populations had high levels of within-population genetic diversity and high outcrossing rates. Virtually all populations were also undergoing demographic and spatial expansion. The partial Mantel test found a positive correlation between geographic and genetic distance, but none between mean temperature, precipitation, and herkogamy with genetic distance. In this context, R. nudiflora shows incipient evidence of genetic differentiation on a small geographical scale (isolation by distance, IBD) but not along the environmental gradient (IBE). Results suggest that under conditions of constant disturbance, R. nudiflora is able to continuously colonize new areas.