The species delimitation problem applied to the Agabus bipustulatus complex (Coleoptera, Dytiscidae) in north Scandinavia

Abstract

Agabus bipustulatus (Linnaeus) is one of the most common aquatic beetles in Europe. Two species have been traditionally recognized within the Palaearctic Agabus bipustulatus complex (Coleoptera, Dytiscidae) in Scandinavia: a lowland form A. bipustulatus and a high-altitude form A. solieri Aube. The specific status of solieri has been debated for more than a century but no quantitative investigation has been made to evaluate the status of this taxon. In this study we show that there is no clear-cut delimitation between the two forms, either morphological or genetic, across an altitudinal gradient in north Scandinavia. Morphological differences between 22 populations were analysed separately for each sex with both thin-plate splines relative warp analysis and 'classical-length' morphometrics. Genetic variation at five polymorphic enzyme loci was analysed among seven populations. The morphological studies showed gradual variation correlated with altitude, in particular in the character that is traditionally used to separate solieri and bipustulatus, and in both the beetles' morphometric size and the lateral width of the metasternal plate, which is connected to flight capacity. The genetic study indicates that the a-Gpdh enzyme locus, which is involved in the transfer of energy to the flight muscles, i s evidently subject to directional selection. Only minor population differences were observed without this system. Subdivision was found in some populations and was probably caused by migration from outside or within the local population. The overall conclusion is that there is no clear-cut species delimitation between A. bipustulatus and A. solieri in north Scandinavia. This indicates that A. solieri is a cold-adapted altitudinal form of the variable A. bipustulatus; additional support for this is the finding of solieri 'look alikes' in cold springs in areas normally inhabited by bipustulatus.

Male genital variation in a moth Pammene luedersiana (Lepidoptera: Tortricidae)

“…Zucchi, 2002). Some studies have shown that taxonomy based on the presumption of morphologic invariability has led to wrong taxonomic conclusions (Drotz et al, 2001;Mutanen, 2005). In both these cases, shape variation between "species" was shown to vary notably, but continuously in local or geographical scales.…”

Delimitation difficulties in species splits: a morphometric case study on the Euxoa tritici complex (Lepidoptera, Noctuidae)

“…It is very possible that in many such cases, taxonomic conclusions have been unjustified. For example, when studied quantitatively and genetically, it was shown that the debated sibling beetles Agabus bipustulatus (Linnaeus, 1767) and A. solieri Aubé 1837 had no discontinuity in their morphologies or genomes (Drotz et al ., 2001). Due to increased knowledge and advanced preparation methods, particularly for artificial male vesica eversion, systematic papers based partly or predominantly on vesica characteristics are published frequently (e.g.…”

Technological advancements and their importance for nematode identification

“…For example, Sites Jr. and Marshall (2003), in their review of 12 delimitation methods, cautioned against adherence to the use of one method to solely delimit species, since all of the approaches can possibly fail at some point when used in isolation. This integrative approach has been successfully applied in some studies for examining species diversity (Boisselier-Dubayle and Gofas, 1999;Shaw and Allen, 2000;Williams, 2000;Drotz et al, 2001;Marcussen, 2003, De Ley et al, 2005Ferri et al, 2009). …”