A taxonomic reappraisal of the European Daphnia longispina complex (Crustacea, Cladocera, Anomopoda)

Abstract

A taxonomic reappraisal of the European Daphnia longispina complex (Crustacea, Cladocera, Anomopoda). -Zoologica Scripta, 37 , 507-519. The Daphnia longispina complex contains some of the most common water flea species in the northern hemisphere, and has been a model organism for many ecological and evolutionary studies. Nevertheless, the systematics and nomenclature of this group, in particular its Palaearctic members, have been in flux for the past 150 years; this hinders the correct interpretation of scientific results and promotes the erroneous use of species names. We revise the systematics of this species complex based on mitochondrial sequence variation (12S rDNA and COI) of representative populations across Europe, with a special focus on samples from type localities of the respective taxa. Combining genetic evidence and morphological assignments of analysed individuals, we propose a comprehensive revision of the European members of the D. longispina complex. We show that D. hyalina and D. rosea morphotypes have evolved several times independently, and we find no evidence to maintain these morphotypes as distinct biological species. Alpine individuals described as D. zschokkei are conspecific with the above-mentioned lineage. We suggest that this morphologically and ecologically plastic but genetically uniform hyalina-rosea-zschokkei clade should be identified as D. longispina (O. F. Müller, 1776). The valid name of Fennoscandian individuals labelled D. longispina sensu stricto in the recent literature is D. lacustris G. O. Sars, 1862. Additionally, we discovered another divergent lineage of this group, likely an undescribed species, in southern Norway. Our results present a solution for several prevailing taxonomic problems in the genus Daphnia , and have broad implications for interpretation of biogeographical patterns, and ecological and evolutionary studies.

Identifying hybridizing taxa within the Daphnia longispina species complex: a comparison of genetic methods and phenotypic approaches

“…While the taxonomy and nomenclature of D. galeata and D. cucullata has been stable in recent decades, the taxonomy of D. longispina has recently undergone a revision (Petrusek et al, 2008a). In most papers on hybridization, the name D. hyalina has been used for this taxon.…”

“…In the literature, one often finds that the status of certain Daphnia taxa changed several times within a short period of time (e.g., Flößner & Kraus, 1986;Petrusek et al, 2008a). Because of the occurrence of numerous morphological forms and the high similarity of certain species, the genus Daphnia has been considered ''… one of the taxonomically most difficult groups of the animal kingdom'' (Flößner & Kraus, 1986), though many of the perceived difficulties are likely due to inadequate past taxonomic research.…”

“…Members of this genus have long been used as model organisms in various fields of basic and applied science, from aquatic ecology and evolutionary biology to ecotoxicology; however, their taxonomy is far from resolved. Many undescribed cryptic species are still being discovered (see, e.g., Adamowicz et al, 2009), and discussions about the status and validity of even very common Daphnia species remain controversial (e.g., Nilssen et al, 2007;Petrusek et al, 2008a).…”

“…However, environmentally induced phenotypic plasticity is only one of the sources of intraspecific morphological variability. Variation among phenotypes is often genetically based (Gießler, 1997(Gießler, , 2001Petrusek et al, 2008a), and substantial morphological changes may be attributed to interspecific hybridization, possibly followed by introgression. Based on morphology, this has long been suspected in the D. longispina species complex (Lieder, 1956(Lieder, , 1983Einsle, 1966), in which morphologically intermediate forms are particularly common.…”

“…Genetic studies confirmed the presence of interspecific hybrids among some taxa of this complex (e.g., Wolf & Mort, 1986;Schwenk & Spaak, 1997;Hobaek et al, 2004) and showed that parthenogenetically reproducing hybrids often occur in syntopy with parental species. The most common hybridizing species in Europe are D. galeata, D. cucullata, and D. longispina (the taxon including both D. hyalina and D. rosea according to Petrusek et al, 2008a; see ''Materials and methods'' section for details on taxonomy). Sexual reproduction of hybrids and backcrossing followed by nuclear introgression also occurs, but seems to be relatively rare (Spaak, 1996;Jankowski & Straile, 2004;Keller et al, 2007).…”