Mating System and the Evolution of Quantitative Traits: An Experimental Study of Mimulus Guttatus

Abstract

Abstract. The mating system of a population profoundly influences its evolution. Inbreeding alters the balance of evolutionary forces that determine the amount of genetic variation within a population. It redistributes that variation among individuals, altering heritabilities and genetic correlations. Inbreeding even changes the basic relationships between these genetic statistics and response to selection. If populations differing only in mating system are exposed to the same selection pressures, will they respond in qualitatively different ways? Here, we address this question by imposing selection on an index of two negatively correlated traits (flower size and development rate) within experimental populations that reproduce entirely by outcrossing, entirely by self-fertilizing, or by a mixture of outcrossing and selfing. Entirely selfing populations responded mainly by evolving larger flowers whereas outcrossing populations also evolved more rapid development. Divergence occurred despite an equivalent selection regime and no direct effect of mating system on fitness. The study provides an experimental demonstration of how the interaction of selection, genetic drift, and mating system can produce dramatic short-term changes in trait means, variances, and covariances.

Does inbreeding promote evolutionary reduction of flower size? Experimental evidence from Crepis tectorum (Asteraceae)

“…Thus, it is possible that most interactions arose because of some genotype × environment effect, caused by uncontrolled year‐to‐year variation in the greenhouse environment. The unusually small flowers of F2 plants from the IS treatment could also be an outcome of genetic drift (see below) or reflect a synergistic effect between inbreeding and selection, as previously observed for a floral size character in a selection experiment with outcrossing and selfing populations of Mimulus guttatus (Phrymaceae) (Holeski and Kelly, 2006). Whatever the explanation, the relationship between flower size and the level of inbreeding does not seem to be a consistently linear in this study system.…”

“…Thus, the potential for inbreeding‐mediated evolution should be greatest, and easiest to detect, in historically outcrossing populations that are in the process of undergoing an evolutionary shift toward selfing, rather than in populations with a fully evolved selfing syndrome. So far, only a few studies have experimentally manipulated the mating regime of initially outcrossing populations to assess whether short‐term responses to inbreeding (based on standing genetic variation) can be sufficiently strong to influence large‐scale patterns of variation (Lynch et al, 1999; Rao et al, 2002) and, more specifically, how inbreeding interacts with selection to produce evolutionary change in floral characters (Holeski and Kelly, 2006). Since the response to inbreeding may be environment‐dependent (Dudash, 1990; Cheptou and Donohue, 2011) and involve suites of characters related by development, for example, flower and fruit size (Primack 1987), it is informative to perform such studies using progeny grown in multiple environments and to include a variety of potentially correlated characters in the analyses.…”

Genomic Signature of Adaptation to Climate in Medicago truncatula

“…In this study we used whole-genome data, so the lack of evidence for strong balancing selection on genes responsible for adaptation along environmental clines, a form of local adaptation, is unlikely to be the result of failing to examine phenotypically important loci. It is possible that we fail to find evidence for balancing selection because balancing selection is very difficult to detect for genes underlying polygenic traits, and adaptive traits are often polygenic (Holeski and Kelly 2006;Chevin and Hospital 2008;Messer and Petrov 2013). However, if this were the reason, we would not expect to find that diversity in the genomic regions flanking candidate SNPs differ from the rest of the genome.…”

Contribution of chromosomal polymorphisms to the G‐matrix ofMimulus guttatus

“…Genetic correlations with the phenological traits were generally nonsignificant (except for corolla length with days to bud), but this is likely caused by a lack of power. Artificial selection on corolla size induces a correlated response in days to flower (Holeski & Kelly, 2006; Kelly, 2008). When QTLs are included in the model (Table 3b), genetic correlations involving the phenological traits are clearly identified.…”