Microbial Evolution Research Group, Department of Biology, University of Oslo, PO Box 1066 Blindern, N-0316 Oslo, Norway.
BMC Genet. 2010 Jul 12;11:64. doi: 10.1186/1471-2156-11-64.
The mating type loci that govern the mating process in fungi are thought to be influenced by negative frequency-dependent selection due to rare allele advantage. In this study we used a mating type linked DNA marker as a proxy to indirectly study the allelic richness and geographic distribution of mating types of one mating type locus (MAT A) in worldwide populations of the dry rot fungus Serpula lacrymans. This fungus, which causes serious destruction to wooden constructions in temperate regions worldwide, has recently expanded its geographic range with a concomitant genetic bottleneck.
High allelic richness and molecular variation was detected in the mating type linked marker as compared to other presumably neutral markers. Comparable amounts of genetic variation appeared in the mating type linked marker in populations from nature and buildings, which contrast the pattern observed with neutral genetic markers where natural populations were far more variable. Some geographic structuring of the allelic variation in the mating type linked marker appeared, but far less than that observed with neutral markers. In founder populations of S. lacrymans, alleles co-occurring in heterokaryotic individuals were more divergent than expected by chance, which agrees with the expectation for populations where few mating alleles exists. The analyzed DNA marker displays trans-species polymorphism wherein some alleles from the closely related species S. himantoides are more similar to those of S. lacrymans than other alleles from S. himantoides.
Our results support the idea that strong negative frequency-dependent selection maintains high levels of genetic variation in MAT-linked genomic regions, even in recently bottlenecked populations of S. lacrymans.
在真菌的交配过程中，控制交配类型的交配类型基因座被认为受到稀有等位基因优势的负频率依赖选择的影响。在这项研究中，我们使用与交配类型连锁的 DNA 标记作为替代物，间接研究了全球范围内干腐菌蛇形卷枝霉一个交配类型基因座（MAT A）的交配类型等位基因丰富度和地理分布。这种真菌在世界范围内的温带地区对木质结构造成严重破坏，最近随着遗传瓶颈的出现，其地理分布范围也有所扩大。
与其他假定的中性标记相比，在与交配类型连锁的标记中检测到了较高的等位基因丰富度和分子变异。在自然和建筑物中的群体中，与中性遗传标记观察到的模式相反，在与交配类型连锁的标记中观察到了相当数量的遗传变异，而自然群体的遗传变异更大。在与交配类型连锁的标记中出现了一些等位基因变异的地理结构，但远小于中性标记观察到的情况。在蛇形卷枝霉的创始群体中，在异核个体中共存的等位基因比随机预期的更为分化，这与存在少数交配等位基因的种群的预期一致。分析的 DNA 标记显示出跨物种多态性，其中来自密切相关的蛇形卷枝霉菌种的一些等位基因与蛇形卷枝霉菌种的等位基因比来自蛇形卷枝霉菌种的其他等位基因更为相似。
我们的结果支持这样的观点，即在蛇形卷枝霉菌种最近出现遗传瓶颈的情况下，强烈的负频率依赖选择维持了与交配相关的基因组区域中高水平的遗传变异。
