Accumulation of hybrid incompatibilities within two plant species (Arabis alpina and Cardamine hirsuta)

Abstract

Accumulation of reproductive isolation (RI) is the central process leading to formation of new biological species. However, little is known about how fast postzygotic RI accumulates between diverging populations, and whether factors such as mating system influence the rate of postzygotic RI accumulation. Flowering plants show a variety of mating systems ranging from strict outcrossing to predominant selfing. Selfing may increase genetic divergence between populations, as restricted pollen dispersal limits the amount of gene flow between populations. It can also potentially promote local adaptation and accumulation of RI between populations. In this project, I aimed to estimate the accumulation of postzygotic RI in terms of hybrid seed failure and hybrid sterility within the two species Arabis alpina and Cardamine hirsuta (Brassicaceae), by performing experimental crosses between parental populations separated by various geographic distances. The results showed that hybrid seed failure has evolved only between some populations in one of the species, A. alpina. However, significant reduction in hybrid pollen fertility was detected within both species, indicating that this postzygotic mechanism provides an important barrier facilitating population divergence. A genomic study based on Genotyping-by-Sequencing (GBS) of two of the parental populations of each species was performed to do a preliminar test of the hypothesis that a selfing mating system influences the rate at which postzygotic RI accumulates between populations. This preliminar test did not show evidence of a relationship between the rate of RI accumulation and selfing, but a final test must await genomic analyses of the remaining parental populations