Phylogeography of Daphnia magna Straus (Crustacea: Cladocera) in Northern Eurasia: Evidence for a deep longitudinal split between mitochondrial lineages.

Eugeniya I Bekker,Alexey A Kotov,Christoph R Haag,Yan R Galimov,Dmitry P Karabanov,Tatiana V Neretina,Tzen-Yuh Chiang

doi:10.1371/journal.pone.0194045

Abstract

Species with a large geographic distributions present a challenge for phylogeographic studies due to logistic difficulties of obtaining adequate sampling. For instance, in most species with a Holarctic distribution, the majority of studies has concentrated on the European or North American part of the distribution, with the Eastern Palearctic region being notably understudied. Here, we study the phylogeography of the freshwater cladoceran Daphnia magna Straus, 1820 (Crustacea: Cladocera), based on partial mitochondrial COI sequences and using specimens from populations spread longitudinally from westernmost Europe to easternmost Asia, with many samples from previously strongly understudied regions in Siberia and Eastern Asia. The results confirm the previously suspected deep split between Eastern and Western mitochondrial haplotype super-clades. We find a narrow contact zone between these two super-clades in the eastern part of Western Siberia, with proven co-occurrence in a single lake in the Novosibirsk region. However, at present there is no evidence suggesting that the two mitochondrial super-clades represent cryptic species. Rather, they may be explained by secondary contact after expansion from different refugia. Interestingly, Central Siberia has previously been found to be an important contact zone also in other cladoceran species, and may thus be a crucial area for understanding the Eurasian phylogeography of freshwater invertebrates. Together, our study provides an unprecedented complete, while still not global, picture of the phylogeography of this important model species.

Highlights

Planktonic water fleas (Crustacea: Cladocera) are attractive models for phylogeographic investigations [1,2,3,4]
As we found that these haplotypes belong to two strongly divergent clades (“super- clades” A and B, see below), we analyzed genetic diversity in the whole sample as well as within each of the two super-clades (S3 Table) and carried out neutrality tests and assessed mismatch distributions for each super-clade separately (S4 Table)
The genetic diversity at c oxidase subunit I (COI) was high in the entire sample as well as in super-clades A and B

Summary

Introduction

Planktonic water fleas (Crustacea: Cladocera) are attractive models for phylogeographic investigations [1,2,3,4]. Planktonic samples usually contain many (tens, hundreds or even thousands) of specimen of several cladoceran taxa. Freshwater animals are highly suitable for phylogeographic studies because they have well-defined populations in water bodies separated by unsuitable habitat [5]. Many cladocerans are thought to be distributed across the entire Holarctic region, with populations being common throughout the range, which would potentially make them excellent models for Pan-Holarctic phylogeographic studies. One major difficulty for phylogeographic studies of potentially Pan-Holarctic species is the need to cover large territories by adequate sampling. Clustered sampling of species with uniform isolation by distance may lead to erroneous identification of genetic clusters, which may falsely be interpreted as cryptic species [13]

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