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

Abstract

Daphnia galeata Sars, D. longispina O. F. Müller and D. cucullata Sars (Crustacea: Cladocera) are closely related species which often produce interspecific hybrids in natural populations. Several marker systems are available for taxon determination in this hybridizing complex, but their performance and reliability has not been systematically assessed. We compared results from identifications by three molecular methods. More than 1,200 individuals from 10 localities in the Czech Republic were identified as parental species or hybrids by allozyme electrophoresis and the analysis of the restriction fragment length polymorphism of the internal transcribed spacer (ITS-RFLP); over 440 of them were additionally analyzed and identified by 12 microsatellite loci. Identification by microsatellite markers corresponded well with allozyme analyses. However, consistent discrepancies between ITS-RFLP and other markers were observed in two out of 10 studied localities. Although some marker discrepancies may have been caused by occasional recent introgression, consistent deviations between ITS-RFLP and other markers suggest a long-term maintenance of introgressed alleles. These results warn against its use as a sole identification method in field studies. Additionally, we quantitatively evaluated the discriminatory power of geometric morphometric (elliptic Fourier) analysis of body shapes based on photos of over 1,300 individuals pre-classified by allozyme markers. Furthermore, a randomly selected subset of 240 individuals was independently determined from photos by several experts. Despite a tendency for morphological divergence among parental Daphnia species, some taxa (especially D. galeata, D. longispina, and their hybrids) substantially overlapped in their body shapes. This was reflected in different

The stabilizing effect of resting egg banks of the Daphnia longispina species complex for longitudinal taxon heterogeneity in long and narrow reservoirs

“…Evidence of introgression of ITS1 alleles among species of the D. longispina complex was recently reported (Gießler & Englbrecht, 2009). Similarly, Dlouhá et al (2010) observed that substantial deviations in identifications by ITS-RFLP and other methods may occur in some reservoir populations; in particular, D. galeata 9 longispina hybrids were overestimated at some localities. However, the discrepancy between the two molecular methods (ITS-RFLP and allozyme electrophoresis) should not have substantially affected our results.…”

“…However, the discrepancy between the two molecular methods (ITS-RFLP and allozyme electrophoresis) should not have substantially affected our results. Both methods were intercalibrated for populations from all but one (Ž lutice) of the studied reservoirs and showed 89-96% agreement (Dlouhá et al, 2010), and differences between the composition of active Daphnia populations and resting egg banks in Ž lutice did not show any suspiciously deviating patterns.…”

Fine-scale temporal and spatial variation of taxon and clonal structure in the Daphnia longispina hybrid complex in heterogeneous environments

“…As reference parental species, we used 40 well-defined genotypes of D. cucullata , D. galeata and D. longispina , originating from 23 locations in Europe and one location in North America, which were also classified using two allozyme loci, recognised to be diagnostic for species identification [33,43]. For detailed information about those genotypes see [18].…”

Anthropogenic eutrophication shapes the past and present taxonomic composition of hybridizing Daphnia in unproductive lakes

“…Allozyme electrophoresis can be applied to fresh or frozen animals, but not to diapausing eggs. In contrast, microsatellite analysis can be applied to both, but the knowledge about speciesspecific alleles is limited (Brede et al 2006;Dlouhá et al 2010). Allozyme electrophoresis was performed, as described by Keller and Spaak (2004), using the two speciesspecific loci aspartate amino transferase (enzyme commission number [EC] 2.6.1.1) and aldehyde oxidase (EC 1.2.3.1).…”