Old museum samples and recent taxonomy: A taxonomic, biogeographic and conservation perspective of the Niphargus tatrensis species complex (Crustacea: Amphipoda)

Abstract

Natural history museum collections harbour valuable information on species. The usefulness of such data critically depends on the accurate identification of species, which has been challenged by introduction of molecular techniques into taxonomy. However, most collections may suffer from DNA degradation, due to age and/or improper preservation; hence the identification of specimens depends solely on morphological features. This study explores how and to what extent morphological data can help to solve ambiguous taxonomic cases based on selected species concepts and with the use of operational criteria in a species-hypothesis testing procedure. The studied taxon, the Niphargus tatrensis species complex, comprises freshwater subterranean amphipods, distributed across Central Europe, the taxonomic status of which was debated extensively between 1930 and 1960. Using the general species concept, character-and tree-based operational criteria reveal northern and southern diagnosable and exclusive lineages identified here as N. tatrensis Wrześniowski, 1888 and N. scopicauda sp. n., respectively. The remaining populations represent the non-exclusive N. aggtelekiensis Dudich, 1932, which occurs from the eastern Alps to Hungary. In the entire complex, altitudinal distribution is largely limited to areas above 400 m, where the mean annual temperature never exceeds 9°C. Seemingly well-defined distributional ranges of N. tatrensis and N. aggtelekiensis are fragmented in an ecological sense, which raises the question whether two of the three species recognised here actually consist of several unidentified taxa. Morphological similarity between the species, numerous polymorphic features, and the association with cool temperatures lead to a hypothesis in which fragmentation of the ancestral range occurred during post-Pleistocene climate warming, reducing gene flow across lowland populations due to niche conservatism of the ancestral species and/or to invasion of competitive species along the Danube and Drava rivers. The results are discussed regarding how old museum samples are conducive to more detailed moleculartaxonomic and conservation studies.

Bayesian phylogeographic inferences reveal contrasting colonization dynamics among European groundwater isopods

“…the hyporheic zone) might have provided suitable pathways for dispersal (Ward & Palmer 1994;Buhay & Crandall 2005;Lef ebure et al 2006a). However, these dispersal pathways probably did not operate for long durations either because surface water was subsequently colonized by better competitors or subsurface interstices became clogged by finer sediments (Busschers et al 2005;Fi ser et al 2010). Our findings of heterogeneous dispersal rates are consistent with results by Buhay & Crandall (2005), suggesting that the genetic structure of groundwater crayfishes in the southeastern United States resulted from a contiguous surface range expansion during short periods of high water levels followed by periods of isolation in caves.…”

“…; Fišer et al . ). Our findings of heterogeneous dispersal rates are consistent with results by Buhay & Crandall (), suggesting that the genetic structure of groundwater crayfishes in the southeastern United States resulted from a contiguous surface range expansion during short periods of high water levels followed by periods of isolation in caves.…”

Cryptic species as a window into the paradigm shift of the species concept

“…These mechanisms can compensate each other across space to produce an even distribution of cryptic species. An untested hypothesis is that selectively neutral mechanisms (e.g., the recent divergence hypothesis) predominate in regions where recent climatic perturbations fragmented ranges of ancestral species (e.g., Pleistocene glaciations, Fišer et al., ), whereas selection‐based mechanisms ( PNC , morphological convergence ) operate more frequently in environments with strong directional selection (Bickford et al., ; Trontelj & Fišer, ).…”

Molecular phylogeny of the subterranean genusNiphargus(Crustacea: Amphipoda) in the Middle East: a comparison with European Niphargids

“…Small sample size is also one of most common problems in Niphargus taxonomy in Europe. To our knowledge, whether diagnostic morphological characters are non‐polymorphic has rarely been questioned (Fišer et al ., ). The same problem applies to this study: the number of individuals is not sufficient to provide evidence as to whether diagnoses are based on non‐polymorphic characters (see Wiens & Servedio, ).…”