Frequent discordance between morphology and mitochondrial DNA in a species group of European water beetles (Coleoptera: Dytiscidae).

Abstract

<jats:p>The<jats:italic>Hydroporus memnonius</jats:italic>species group includes both widespread and range restricted diving beetle taxa in the western Palaearctic, some of which have been divided into a number of geographical subspecies. Of these,<jats:italic>Hydroporus necopinatus</jats:italic>is distributed in the far west of Europe, from central Spain to southern Britain, and has been split into three subspecies, occurring in Iberia (<jats:italic>necopinatus</jats:italic>sst.), France (<jats:italic>robertorum</jats:italic>) and England (<jats:italic>roni</jats:italic>) respectively—the last of these being a rare example of an insect taxon apparently endemic to northern Europe. Here we explore inter-relationships between populations and subspecies of<jats:italic>H. necopinatus</jats:italic>and related members of the<jats:italic>Hydroporus melanarius</jats:italic>subgroup, using mitochondrial COI sequence data. We reveal widespread discordance between mitochondrial DNA sequence variation and morphology in areas where<jats:italic>H. necopinatus</jats:italic>and<jats:italic>H. melanarius</jats:italic>come into contact, consistent with historical introgressive hybridization between these taxa. In light of this discordance, the lack of clear genetic divergence between<jats:italic>H. necopinatus</jats:italic>subspecies, and the fact that both<jats:italic>robertorum</jats:italic>and<jats:italic>roni</jats:italic>are morphologically intermediate between<jats:italic>H. necopinatus</jats:italic>sstr. and<jats:italic>H. melanarius</jats:italic>, we suggest that these taxa may be of hybridogenic origin, rather than representing discrete evolutionary lineages.</jats:p>