Reproductive isolation and life-history divergence between outcrossing and recently evolved selfing populations of Arabidopsis lyrata

Abstract

Mating system transitions from self-incompatibility to self-compatibility (i.e. being able to self-fertilize), represent a common evolutionary shift in plants and clearly play a role in speciation. Self-compatibility is also associated with an annual habit. However, many questions remain about the initial mechanistic basis of pre- and post-pollination reproductive isolation and life history divergence during the evolution of self-compatibility. I used Arabidopsis lyrata, a normally self-incompatible perennial that has recently experienced a shift to self-compatibility in several populations, to test whether the transition to self-compatibility has led to reproductive isolation and/or life history divergence. To test whether there was pre-pollination isolation between self-compatible (SC) and self-incompatible (SI) plants, I conducted a common garden experiment with plants from SC and SI populations and their between-population hybrids. First, I investigated whether there were differences in flowering phenology and/or pollinator visitation. Flowering largely overlapped between plants from SC and SI populations and I recovered no differences in pollinator visitation related to mating system. To test for post-pollination isolation between SC and SI populations, I compared seed sets resulting from crosses within populations, between populations of the same mating system, and between populations with different mating systems. Plants from SC and SI populations were not reproductively isolated via the investigated post-pollination mechanisms. Finally, I monitored survival of plants in the common garden over two years to test if the evolution of self-compatibility was accompanied by a shift towards the annual habit. Self-compatible plants exhibited a 39% decrease in survival after the first year compared to SI plants. While I found no strong evidence of pre- or post-pollination reproductive isolation between SC and SI populations, I did find unambiguous evidence for divergence in life history. Examinations of the dynamics of self-compatibility, reproductive isolation, and life history will continue to contribute to a more comprehensive understanding of mating system evolution.