Correct species identification and delineation are crucial for effective conservation and management. However, species delineation can be problematic in the presence of morphological ambiguities due to phenotypic plasticity, convergence, and/or interspecific hybridization. Here, we investigated the degree of hybridization between two closely related freshwater mussel species [Bivalvia: Unionidae; Lampsilis siliquoidea (Barnes) and L. radiata (Gmelin)] that present intermediate forms in areas of sympatry. Unionids have a distinct form of mitochondrial DNA (mtDNA) inheritance, termed doubly uniparental inheritance (DUI) where female mtDNA (F-type) is transmitted to all progeny but male mtDNA (M-type) is mostly inherited by the males resulting in mostly homoplasmic females and heteroplasmic males. An individual was identified as hybrid when F-type and M-type mtDNA of the two different species were found in the same individual. Twelve out of 116 sequenced males were identified as hybrids indicating that these species hybridize where their geographic range overlaps in the lower Great Lakes and St. Lawrence basins. Microsatellite analyses further support the occurrence of hybridization but at a larger spatial scale than indicated by the mitochondrial analyses. We also found that strong within-species population genetic structure affects the detection of purebred individuals overestimating the number of hybrids. Given the large geographic scale and proportion of hybrids found in this study, natural hybridization and introgression need to be considered when implementing local biodiversity inventories, identifying waterbodies as source of organisms for relocation and restoration projects and when setting appropriate conservation policies.

正确的物种识别和描述对于有效的保护和管理至关重要。然而，由于表型可塑性、趋同性和/或种间杂交，在存在形态模糊的情况下，物种划分可能会出现问题。在这里，我们研究了两种密切相关的淡水贻贝物种之间的杂交程度 [双壳纲：Unionidae；Lampsilis siliquoidea (Barnes) 和L. radiata(Gmelin)] 在同胞区域呈现中间形式。Unionids 具有独特的线粒体 DNA (mtDNA) 遗传形式，称为双重单亲遗传 (DUI)，其中女性 mtDNA（F 型）传递给所有后代，但男性 mtDNA（M 型）主要由男性遗传，导致主要同质雌性和异质雄性。当在同一个体中发现两个不同物种的 F 型和 M 型 mtDNA 时，个体被确定为杂种。116 名测序雄性中有 12 名被确定为杂交种，表明这些物种在五大湖下游和圣劳伦斯盆地的地理范围重叠的地方杂交。微卫星分析进一步支持杂交的发生，但在比线粒体分析表明的更大的空间尺度上。我们还发现，强大的种内种群遗传结构会影响高估杂种数量的纯种个体的检测。鉴于本研究中发现的杂交种的地理规模和比例较大，在实施当地生物多样性清单、将水体确定为搬迁和恢复项目的生物来源以及制定适当的保护政策时，需要考虑自然杂交和基因渗入。