Abstract
The Hydroporus memnonius 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, Hydroporus necopinatus is distributed in the far west of Europe, from central Spain to southern Britain, and has been split into three subspecies, occurring in Iberia (necopinatus sst.), France (robertorum) and England (roni) 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 H. necopinatus and related members of the Hydroporus melanarius subgroup, using mitochondrial COI sequence data. We reveal widespread discordance between mitochondrial DNA sequence variation and morphology in areas where H. necopinatus and H. melanarius come into contact, consistent with historical introgressive hybridization between these taxa. In light of this discordance, the lack of clear genetic divergence between H. necopinatus subspecies, and the fact that both robertorum and roni are morphologically intermediate between H. necopinatus sstr. and H. melanarius, we suggest that these taxa may be of hybridogenic origin, rather than representing discrete evolutionary lineages.
Highlights
Hydroporus Clairville, 1806, with 188 described species (Nilsson, 2016), is one of the largest genera of diving beetles, most species occurring in the Holarctic realm
Beetles from individual localities were either entirely inside or outside this clade; only those from the Lizard Peninsula, in the far southwest of England, grouping in both parts of the trees. Both analyses revealed a second clade (b in Figs. 2A–2B), well-supported in Bayesian inference (BI), and a bootstrap of 65 in maximum likelihood (ML), dominated by the remaining H. melanarius, as well as H. necopinatus robertorum from northern France and Jersey, and H. hebaeuri, which was nested within the second clade, a position well supported in BI analyses
Whilst H. hebaeuri is morphologically similar to H. necopinatus, being distinguished primarily on the detailed structure of the male median lobe, H. melanarius differs from these two taxa on a suite of external and genitalic characters, including habitus and the setation of the metacoxal process (Fery, 1999)
Summary
Hydroporus Clairville, 1806, with 188 described species (Nilsson, 2016), is one of the largest genera of diving beetles, most species occurring in the Holarctic realm. The genus is currently arranged into a number of ‘species groups’ (sensu Nilsson, 2001), these initially being defined on external morphology alone. Most Hydroporus are relatively small dytiscids, with total body lengths in the order of 2–5 mm (Nilsson & Holmen, 1995), and the genus includes a number of taxonomically challenging species groups and complexes, in the southern and eastern Palaearctic. How to cite this article Bilton et al (2017), Frequent discordance between morphology and mitochondrial DNA in a species group of European water beetles (Coleoptera: Dytiscidae).
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