Pyganodon grandis and P. lacustris, widespread and common species in North America, are known to co-occur across parts of their distributions. These mussels are genetically distinguishable with a sequence divergence between 9% and 13% for the mitochondrial (mt) DNA barcoding region, cytochrome c oxidase subunit I (COI), which is well beyond thresholds for distinct species. The objectives of this study were to (1) confirm the presence of two genetically distinct species (P. grandis and P. lacustris) in Font Lake and Lake Geneserath on Beaver Island in northern Lake Michigan, (2) identify hybrids using mitogenotype mismatch and (3) compare species and populations morphometrically. Of the 212 specimens sequenced, 146 (68.9%) were found to be heteroplasmic, with successful amplifications of both maternally (F-type, from mantle tissue) and paternally (M-type, from gonad tissue) inherited mt DNA sequences. Mismatches in species identity of the F- and M-type COI sequences were found in 22 specimens (15.1% of heteroplasmic specimens), with these being considered putative hybrids. Geometric morphometric analyses of shell shape reliably differentiated specimens by species (identified using COI sequences) and between lakes, correctly assigning 97.4% of homoplasmic and heteroplasmic specimens with matching mitogenomes to both species and lake of origin. The shape of putative hybrids generally resembled those of the F-type mt DNA sequence that was recovered. This study confirms that hybridization does occur between sympatric Pyganodon species. Additionally, our results reemphasize the value of modern morphometric techniques for distinguishing among species and populations with overlapping morphological variability.

中文翻译：

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使用F型和M型线粒体DNA序列和几何形态计量学检测杂种霸王和湖生毕赤酵母（Bivalvia：Unionidae）

在北美分布广泛且常见的美洲霸王龙和P. lacustris，在它们的分布的不同部分共同存在。这些贻贝在遗传上是可区分的，线粒体（mt）DNA条形码区域（细胞色素C氧化酶亚基I（COI））的序列差异在9％和13％之间，该差异远远超出了不同物种的阈值。这项研究的目的是（1）确认存在两种遗传上不同的物种（P. grandis和P. lacustris）在密歇根湖北部海狸岛的Font Lake和Geneserath湖中，（2）使用有丝分裂基因型不匹配识别杂种，以及（3）在形态上比较物种和种群。在测序的212个样本中，发现146个（68.9％）是异质的，成功扩增了母体（F型，来自地幔组织）和父系（M型，来自性腺组织）遗传的mt DNA序列。在22个样本（占异质样本的15.1％）中发现了F型和M型COI序列的物种同一性不匹配，这些被认为是杂种。壳形的几何形态分析可靠地区分了不同物种的标本（使用COI序列识别）以及各湖之间，正确分配了97。4％的同质和异质标本具有与物种和起源湖泊相匹配的有丝分裂基因组。推定的杂种的形状通常类似于回收的F型mt DNA序列的形状。这项研究证实同胞之间确实发生了杂交侏儒物种。此外，我们的结果再次强调了现代形态计量技术在区分形态变异重叠的物种和种群中的价值。