Reproductive isolation and drift load in selfing populations of an otherwise obligately outcrossing species
Final Report Abstract
Breeding system and mating system transitions from predominant outcrossing to selfing are frequent in plant evolution. This is usually associated with dramatic changes in floral morphology and life history, and often leads to speciation. However, how reproductive isolation builds up after transitions to selfing was largely unknown. To address this, this project used North American Arabidopsis lyrata, a normally self-incompatible perennial that has recently experienced a shift to self-compatibility in several populations. To test for pre-pollination isolation mechanisms isolating outcrossing and selfing populations, we conducted a common garden experiment which simulated secondary contact between plants from SC and SI populations and their cross-progeny. To study post-pollination isolation mechanisms, we assessed the success of controlled crosses in an insect-free growth chamber in terms of seed set. The common-garden experiment revealed no differences in flowering phenology, pollinator visitation and pollinator behaviour, but identified a pronounced reduction in winter survival for plants from selfing populations. The crossing experiment revealed that seed set was not reduced when crossing plants from populations with different mating system. Taken together, our experiments thus showed a lack of reproductive isolation between outcrossing and selfing populations through pre- and post-pollination mechanisms, although the propensity of pollinators to move between flowers on the same plant could still promote reproductive isolation indirectly. However, the increased opportunities for self-fertilization due to pollinator behaviour only led to marginally lower outcrossing rates for plants from selfing populations. These results mean that secondary contact between selfing (SC) and outcrossing (SI) lineages might re-establish gene flow between these lineages, and could result in (local) maintenance of a mixed-mating system.
Publications
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(2020) A shift towards the annual habit in selfing Arabidopsis lyrata. Biology Letters 16: 20200402
Gorman, Courtney E.; Steinecke, Christina; van Kleunen, Mark; Dorken, Marcel E. & Stift, Marc
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(2020) Limited phenological and pollinatormediated isolation among selfing and outcrossing Arabidopsis lyrata populations. Proceedings of the Royal Society B 287: 20202323
Gorman, Courtney E.; Bond, Lindsay; van Kleunen, Mark; Dorken, Marcel E. & Stift, Marc
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(2021). No evidence for incipient speciation by selfing in North American Arabidopsis lyrata. Journal of Evolutionary Biology 34: 1397-1405
Gorman, Courtney E.; Li, Yan; Dorken, Marcel E. & Stift, Marc
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(2022). Outcrossing rates in an experimentally admixed population of self-compatible and self-incompatible Arabidopsis lyrata. Heredity 128: 56-62
Steinecke, Christina; Gorman, Courtney E.; Stift, Marc & Dorken, Marcel E.
