Ecology and Evolutionary Biology, University of Tennessee, Knoxville, Tennessee 37996-1100.
Mycologia. 2013 Nov-Dec;105(6):1577-94. doi: 10.3852/13-041. Epub 2013 Aug 8.
Agaric fungi of the southern Appalachian Mountains including Great Smoky Mountains National Park are often heterozygous for the rDNA internal transcribed spacer region (ITS) with >42% of collections showing some heterozygosity for indels and/or base-pair substitutions. For these collections, intra-individual haplotype divergence is typically less than 2%, but for 3% of these collections intra-individual haplotype divergence exceeds that figure. We hypothesize that high intra-individual haplotype divergence is due to hybridization between agaric fungi with divergent haplotypes, possibly migrants from geographically isolated glacial refugia. Four species with relatively high haplotype divergence were examined: Armillaria mellea, Amanita citrina f. lavendula, Gymnopus dichrous and the Hygrocybe flavescens/chlorophana complex. The ITS region was sequenced, haplotypes of heterozygotes were resolved through cloning, and phylogenetic analyses were used to determine the outcome of hybridization events. Within Armillaria mellea and Amanita citrina f. lavendula, we found evidence of interbreeding and recombination. Within G. dichrous and H. flavescens/chlorophana, hybrids were identified but there was no evidence for F2 or higher progeny in natural populations suggesting that the hybrid fruitbodies might be an evolutionary dead end and that the genetically divergent Mendelian populations from which they were derived are, in fact, different species. The association between ITS haplotype divergence of less than 5% (Armillaria mellea = 2.6% excluding gaps; Amanita citrina f. lavendula = 3.3%) with the presence of putative recombinants and greater than 5% (Gymnopus dichrous = 5.7%; Hygrocybe flavescens/chlorophana = 14.1%) with apparent failure of F1 hybrids to produce F2 or higher progeny in populations may suggest a correlation between genetic distance and reproductive isolation.
阿巴拉契亚山脉南部的蘑菇真菌，包括大烟山国家公园，其 rDNA 内部转录间隔区（ITS）通常为杂合子，超过 42%的采集样本显示出插入缺失和/或碱基对替换的某些杂合性。对于这些样本，个体内单倍型分化通常小于 2%，但对于其中 3%的样本，个体内单倍型分化超过了这一数字。我们假设高个体内单倍型分化是由于具有不同单倍型的蘑菇真菌之间的杂交所致，可能是来自地理隔离冰川避难所的移民。我们检查了四个具有相对高单倍型分化的物种：蜜环菌、橘黄鹅膏菌 f. 薰衣草、双色绒瑚菌和黄白乳菇/黄白菇复合体。对 ITS 区域进行了测序，通过克隆解析了杂合子的单倍型，并进行了系统发育分析，以确定杂交事件的结果。在蜜环菌和橘黄鹅膏菌 f. 薰衣草中，我们发现了杂交和重组的证据。在双色绒瑚菌和黄白乳菇/黄白菇复合体中，鉴定出了杂种，但在自然种群中没有发现 F2 或更高代的后代，这表明杂种果实可能是一个进化的死胡同，而它们衍生的遗传上差异很大的孟德尔种群实际上是不同的物种。ITS 单倍型分化小于 5%（蜜环菌=2.6%不包括缺口；橘黄鹅膏菌 f. 薰衣草=3.3%）与存在假定重组体之间，以及大于 5%（双色绒瑚菌=5.7%；黄白乳菇/黄白菇复合体=14.1%）与 F1 杂种在种群中未能产生 F2 或更高代的后代之间存在关联，这可能表明遗传距离和生殖隔离之间存在相关性。
