Estimating the impact of divergent mating phenology between residents and migrants on the potential for gene flow

Abstract

Gene flow between populations can allow the spread of beneficial alleles and genetic diversity between populations, with importance to conservation, invasion biology, and agriculture. Levels of gene flow between populations vary not only with distance, but also with divergence in reproductive phenology. Since phenology is often locally adapted, arriving migrants may be reproductively out of synch with residents, which can depress realized gene flow. In flowering plants, the potential impact of phenological divergence on hybridization between populations can be predicted from overlap in flowering schedules—the daily count of flowers capable of pollen exchange—between a resident and migrant population. The accuracy of this prospective hybridization estimate, based on parental phenotypes, rests upon the assumptions of unbiased pollen transfer between resident and migrant active flowers. We tested the impact of phenological divergence on resident–migrant mating frequencies in experiments that mimicked a single large gene flow event. We first prospectively estimated mating frequencies two lines of Brassica rapa selected or early and late flowering. We then estimated realized mating frequencies retrospectively through progeny testing. The two estimates strongly agreed in a greenhouse experiment, where procedures ensured saturating, unbiased pollination. Under natural pollination in the field, the rate of resident–migrant mating, was lower than estimated by phenological divergence alone, although prospective and retrospective estimates were correlated. In both experiments, differences between residents and migrants in flowering schedule shape led to asymmetric hybridization. Results suggest that a prospective estimate of hybridization based on mating schedules can be a useful, although imperfect, tool for evaluating potential gene flow. They also illustrate the impact of mating phenology on the magnitude and symmetry of reproductive isolation.

An exploration into the conversion of dominance to additive genetic variance in contrasting environments

“…We fertilized plants after most plants developed true leaves, and then once more a week later, with a 100 ppm dilution of a soluble fertilizer (Plant-Prod 15-15-30; Master Plant-Prod, Brampton, Ontario, Canada). To assure that every flower had the potential to produce a fruit (in this case, a silique), we hand-pollinated flowers daily throughout the flowering period, using feathers to transfer pollen between adjacent plants (see Bonner et al, 2019). We made efforts to "visit" each open flower twice per day.…”

Defence by duplication: The relation between phenotypic glyphosate resistance and EPSPS gene copy number variation in Amaranthus palmeri

“…However, it is important to note that although herbicide treatment would be expected to promote strong assortative mating (Cordeiro et al, 2017;Doebeli, 1996) between high-resistance individuals, in the absence of glyphosate stress intermating between low-and high-resistance individuals is expected. Therefore, low-resistance individuals would be predicted to decrease in frequency over time, unless differences in phenology (Baucom, 2019;Bonner et al, 2019;Winterer & Weis, 2004) between low-and high-resistance phenotypes existed. Indeed, Teitel and Caruso (2021)…”

Defense by duplication: The relation between phenotypic glyphosate resistance and EPSPS gene copy number variation inAmaranthus palmeri

“…Therefore, low-resistance individuals would be predicted to decrease in frequency over time, unless differences in phenology (Baucom, 2019;Bonner, Sokolov, Westover, Ho, & Weis, 2019;Winterer & Weis, 2004) between low-and high-resistance phenotypes existed. Indeed, Teitel and Caruso (unpublished data) observed variation that earlier emergence was correlated with higher glyphosate resistance.…”