Journal Article

The importance of autonomous selfing in preventing hybridization in three closely related plant species

Brys, Rein, van Cauwenberghe, Jannick, Jacquemyn, Hans

2016

Overview

1. In plants that are able to self-fertilize, autonomous selfing has been hypothesized to function as an effective mechanism that prevents heterospecific mating. However, there have only been few studies that have assessed the relative and absolute contribution of different modes of selfing to total reproductive isolation acting between species. Because selfing can be expected to increase fitness costs when offspring are sired from more outcrossing sister taxa, it can be hypothesized that the contribution of post-zygotic barriers to total reproductive isolation becomes stronger in selfing than in more outcrossing relatives. 2. To assess the efficiency of different modes of selfing against heterospecific mating, we conducted mixed-pollination experiments in three Centaurium species showing strong differences in mating system (i.e. delayed selfing in Centaurium erythraea, competing selfing in C. littorale and prior selfing in C. pulchellum). The contribution of selfing to total reproductive isolation was further examined by quantifying the strength of three pre-zygotic (flowering phenology, pollinator fidelity and pollen production) and four intrinsic post-zygotic (seed set and germination, survival and flowering capacity) barriers for each of the six species pair combinations. 3. Although autonomous selfing as a reproductive barrier was unable to completely impede gene flow, its efficiency as a mechanism to prevents heterospecific pollination strongly depended on the mode of selfing, with prior selfing being by far the most efficient mechanism and delayed selfing only offering a limited protection against hybrid fertilization at the end of a flower's lifetime. Apart from the prevention effect of selfing, differences in pollinator fidelity and pollen production also contributed substantially to total reproductive isolation. 4. Post-zygotic hybrid costs were high and most prevalent for seed production and germination success. Reductions in hybrid vigour were significantly associated with the mating system of the maternal species, with the highest reductions in the most selfing C. pulchellum and the lowest reductions in predominant outcrossing C. erythraea. 5. Synthesis. Our findings indicate that selfing may prevent species from interspecific gene flow and hybridization. The association between the capacity to self-autonomously and hybrid vigour further suggests that selfing may foster post-zygotic costs following hybridization.

• Publisher: John Wiley & Sons Ltd,Blackwell Publishing Ltd
• Subject: autonomous selfing / Centaurium / Centaurium erythraea / flowering / flowers / Flowers & plants / Gene flow / Gentianaceae / germination / heterosis / hybrid costs / Hybridization / hybrids / mating systems / Offspring / outcrossing / phenology / Plant species / Plant–plant interactions / Pollen / Pollination / Pollinators / post‐zygotic isolation / pre‐zygotic isolation / progeny / reproductive isolation / seed set / selfing / speciation