Oakley C G, Ågren J, Schemske D W
Department of Plant Biology, Michigan State University, East Lansing, MI, USA.
Department of Plant Ecology and Evolution, Evolutionary Biology Centre, Uppsala University, Uppsala, Sweden.
Heredity (Edinb). 2015 Jul;115(1):73-82. doi: 10.1038/hdy.2015.18. Epub 2015 Mar 18.
Understanding the causes and architecture of genetic differentiation between natural populations is of central importance in evolutionary biology. Crosses between natural populations can result in heterosis if recessive or nearly recessive deleterious mutations have become fixed within populations because of genetic drift. Divergence between populations can also result in outbreeding depression because of genetic incompatibilities. The net fitness consequences of between-population crosses will be a balance between heterosis and outbreeding depression. We estimated the magnitude of heterosis and outbreeding depression in the highly selfing model plant Arabidopsis thaliana, by crossing replicate line pairs from two sets of natural populations (C↔R, B↔S) separated by similar geographic distances (Italy↔Sweden). We examined the contribution of different modes of gene action to overall differences in estimates of lifetime fitness and fitness components using joint scaling tests with parental, reciprocal F1 and F2, and backcross lines. One of these population pairs (C↔R) was previously demonstrated to be locally adapted, but locally maladaptive quantitative trait loci were also found, suggesting a role for genetic drift in shaping adaptive variation. We found markedly different genetic architectures for fitness and fitness components in the two sets of populations. In one (C↔R), there were consistently positive effects of dominance, indicating the masking of recessive or nearly recessive deleterious mutations that had become fixed by genetic drift. The other set (B↔S) exhibited outbreeding depression because of negative dominance effects. Additional studies are needed to explore the molecular genetic basis of heterosis and outbreeding depression, and how their magnitudes vary across environments.
了解自然种群间遗传分化的原因和结构是进化生物学的核心要点。如果隐性或近乎隐性的有害突变因遗传漂变而在种群中固定下来，那么自然种群间的杂交可能会产生杂种优势。由于基因不相容性，种群间的分化也可能导致远交衰退。种群间杂交的净适应性后果将是杂种优势和远交衰退之间的平衡。我们通过对来自两组地理距离相近（意大利↔瑞典）的自然种群（C↔R，B↔S）的重复品系对进行杂交，估计了高度自交的模式植物拟南芥中杂种优势和远交衰退的程度。我们使用亲代、正反交F1和F2以及回交品系的联合尺度检验，研究了不同基因作用模式对终生适应性和适应性成分估计值总体差异的贡献。其中一组种群对（C↔R）先前已被证明是局部适应的，但也发现了局部不适应的数量性状位点，这表明遗传漂变在塑造适应性变异中发挥了作用。我们在两组种群中发现了适应性和适应性成分明显不同的遗传结构。在一组（C↔R）中，显性效应始终呈正向，表明隐性或近乎隐性的有害突变因遗传漂变而固定下来后被掩盖。另一组（B↔S）由于负向显性效应而表现出远交衰退。需要进一步的研究来探索杂种优势和远交衰退的分子遗传基础，以及它们的程度如何随环境变化。
