Inbreeding depression and low between-population heterosis in recently diverged experimental populations of a selfing species

Abstract

In fragmented populations, genetic drift and selection reduce genetic diversity, which in turn results in a loss of fitness or in a loss of evolvability. Genetic rescue, that is, controlled input of diversity from distant populations, may restore evolutionary potential, whereas outbreeding depression might counteract the positive effect of this strategy. We carried out self-pollination and crosses within and between populations in an experimental subdivided population of a selfing species, Triticum aestivum L., to estimate the magnitude of these two phenomena. Surprisingly, for a self-fertilizing species, we found significant inbreeding depression within each population for four of the six traits studied, indicating that mildly deleterious mutations were still segregating in these populations. The progeny of within-and betweenpopulation crosses was very similar, indicating low betweenpopulation heterosis and little outbreeding depression. We conclude that relatively large population effective sizes prevented fixation of a high genetic load and that local adaptation was limited in these recently diverged populations. The kinship coefficient estimated between the parents using 20 neutral markers was a poor predictor of the progeny phenotypic values, indicating that there was a weak link between neutral diversity and genes controlling fitnessrelated traits. These results show that when assessing the viability of natural populations and the need for genetic rescue, the use of neutral markers should be complemented with information about the presence of local adaptation in the subdivided population.

Response of bi-parental spring barley populations to cultivation in organic and conventional farming systems

“…They had high Nei genetic identity index (>0.95) and each pair clustered together in PCoA. This is in agreement with Rousselle et al (2011) who observed no loss of within population diversity and little genetic divergence of sub-populations in wheat populations cultivated over 12 generations. We found that in bi-parental subpopulations there were more alleles at most loci than in the parental varieties.…”

Population Structure Has Limited Fitness Consequences in the Highly Selfing PlantLeavenworthia uniflora(Brassicaceae)

“…Often, experiments in benign environments may not be as effective as those in natural environments in revealing the expression of dominance in fitness traits, although this is not always the case (Dudash 1990;Keller and Waller 2002;Johansen-Morris and Latta 2006). In addition, it is also possible that the divergence between populations of L. uniflora may truthfully be very shallow, so that there has not been sufficient time for the substitution of deleterious mutations in each lineage (Rouselle et al 2011). It is likely that the divergence between populations east and west of the Mississippi river is indeed very recent, since there is very little segregating variation among populations in the western portion of the species range.…”

“…Line-cross analyses involving closely related populations or ecotypes of highly selfing plants have yielded inconsistent support for the action of mutation accumulation. Crosses among highly selfing populations have sometimes shown little evidence of heterosis (Rouselle et al 2011) yet more frequently document its importance (Weller et al 2005;Johansen-Morris and Latta 2006;Hereford 2009). Observations of heterosis in these highly selfing lineages reinforce the more general finding of heterosis in many plant species with small populations and spatial structure (Ouborg and van Treunen 1994;Richards 2000;Paland and Schmid 2003).…”

Cryptic genetic subdivision in the San Benito evening primrose (Camissonia benitensis)

“…The average inbreeding level of just the field-collected samples, which had larger sample sizes, was very similar to the full dataset (field collected F IS = 0.869, all populations F IS = 0.813). This level of inbreeding in C. benitensis is indicative of predominantly self-pollinating species like Arabidopsis thaliana (F IS = 0.92-1.0; Stenoien et al 2005), Mimulus laciniatus (F IS = 0.80; Awadalla and Ritland 1997), Medicago lupulina (F IS = 0.92; Yan et al 2009), and Triticum aestivum (F IS = 0.84-0.98; Rousselle et al 2011). It is unclear why C. contorta and C. strigulosa would have much lower levels of inbreeding.…”