Among-Population Variation of Outcrossing Rate in the Winter Annual Plant Collinsia verna

Abstract

Many plants utilize a mixed mating system whereby reproduction may occur by self-fertilization (selfing) and by cross-pollination (outcrossing). In population genetics, knowledge of the mating system is very important, because mating patterns influence the amount and the distribution of genetic variability of populations (i.e. the mating structure) and consequently evolutionary processes in these populations. The most common descriptor of the mating structure of plant populations is the estimated outcrossing rate (t), the proportion of seeds produced by outcrossing. This study quantifies the outcrossing rates in 11 natural populations of the mixed mating, winter annual plant Collinsia verna from across its entire geographic range, and compares the results to a previous study that quantified outcrossing rates in populations of C. verna from only Michigan and Illinois. It was hypothesized that because more environmental variation exists over a larger geographic range, there would be more variation in outcrossing rates over the larger geographic range. Outcrossing rates were quantified by genotyping at least five offspring from 32 plants in 11 populations spanning the geographic range of C. verna. Outcrossing rates varied markedly from t = 0.59 – 0.86 across the sampled populations, but there was no significant variation between studies. It is thought that this among-population variation in outcrossing rates is due to among-population variation in factors that have been shown to affect outcrossing rates in other species, such as types of pollinators, pollinator availability, population size, plant density, herkogamy, protandry, and floral display size. However, further studies directed toward quantifying these factors at different sites are needed in order to more fully understand the evolutionary processes on the mixed mating system employed by C. verna.