Changing Names with Changed Address: Integrated Taxonomy and Species Delimitation in the Holarctic Colymbetes paykulli Group (Coleoptera: Dytiscidae).

Marcus K Drotz,Tomas Brodin,Anders N Nilsson

doi:10.1371/journal.pone.0143577

Abstract

Species delimitation of geographically isolated forms is a long-standing problem in less studied insect groups. Often taxonomic decisions are based directly on morphologic variation, and lack a discussion regarding sample size and the efficiency of migration barriers or dispersal/migration capacity of the studied species. These problems are here exemplified in a water beetle complex from the Bering Sea region that separates North America from Eurasia. Only a few sampled specimens occur from this particular area and they are mostly found in museum and private collections. Here we utilize the theory of integrated taxonomy to discuss the speciation of the Holarctic Colymbetes paykulli water beetle complex, which historically has included up to five species of which today only two are recognized. Three delimitation methods are used; landmark based morphometry of body shape, variation in reticulation patterns of the pronotum exo-skeleton and sequence variation of the partial mitochondrial gene Cyt b. Our conclusion is that the Palearctic and Nearctic populations of C. paykulli are given the status of separate species, based on the fact that all methods showed significant separation between populations. As a consequence the name of the Palearctic species is C. paykulli Erichson and the Nearctic species should be known as C. longulus LeConte. There is no clear support for delineation between Palearctic and Nearctic populations of C. dahuricus based on mtDNA. However, significant difference in size and reticulation patterns from the two regions is shown. The combined conclusion is that the C. dahuricus complex needs a more thorough investigation to fully disentangle its taxonomic status. Therefore it is here still regarded as a Holarctic species. This study highlights the importance to study several diagnosable characters that has the potential to discriminate evolutionary lineage during speciation.

Highlights

The application of the biological species concept [1] to geographically isolated forms is a longstanding problem [2,3,4]
Distribution map of reported observations of the Holarctic (Δ) Colymbetes dahuricus, the Palearctic (●) C. paykulli and the Nearctic (&) C. paykulli. The latter is within this study accepted as a valid species. This means that the name of the Palearctic species is C. paykulli Erichson and the Nearctic species should be known as C. longulus LeConte. doi:10.1371/journal.pone.0143577.g001
We found a small morphological overlap in both sexes of this species-complex (Fig 2), but the difference in morph space was significant in both sexes (t-test of the first component: males (d.f. = 86, t-value = 13.30) P

Summary

Introduction

The application of the biological species concept [1] to geographically isolated forms is a longstanding problem [2,3,4]. As geographical isolation per se is a reproductive barrier, such forms behave as distinct biological species until they at some point meet due to dispersal or geographical events [5]. Species delimitation will as a consequence of this always include some degree of uncertainty, often ending up being qualified guesses at best [2, 15,16] This general problem is apparent in the taxonomy of northern terrestrial and freshwater faunas, in which Holarctic distributions of species are often declared [17]. Such decisions are often made disregarding sample size and the effectiveness of barriers separating North America from Eurasia, and the migratory capacity of the actual species being discussed. Taxonomic decisions, within this group, are still strongly dependent on museum and private collections [7] and morphological analyses are predominantly used due to difficulties/restrictions of extracting DNA from such specimens

Methods

Results

Discussion

Conclusion