Abstract
Pond-dwelling cyclic parthenogens are often proposed to be highly vagile. However, the Holarctic biogeography of parthenogens has been hampered by very limited sampling in the eastern Palearctic. Here we examine the geographic boundaries, diversity, and connectivity across the Palearctic for the Daphnia curvirostris complex (Cladocera: Daphniidae). Nuclear (HSP90) and mitochondrial (ND2) sequence data supported the existence of five main clades (most of which corresponded to presumptive species) with one eastern Palearctic clade being novel to this study (the average mitochondrial genetic divergence from known species was 19.2%). D. curvirostris s.s. was geographically widespread in the Palearctic, with a population genetic signature consistent with postglacial expansion. The Eastern Palearctic had local nine endemic species and/or subclades (other Holarctic regions lacked more than one endemic subclade). Even though several endemic species appeared to have survived Pleistocene glaciation in the eastern Palearctic, much of the Palearctic has been recolonized by D. curvirostris s.str. from a Western Palearctic refugium. A disjunct population in Mexico also shared its haplotypes with D. curvirostris s.str., consistent with a recent introduction. The only apparently endemic North American lineage was detected in a thermally disturbed pond system in northwestern Alaska. Our results for pond-dwelling cyclic parthenogens further support the hypothesis that the Eastern Palearctic is a diversity hotspot for freshwater invertebrates.
Highlights
The “ejected relict” scheme initially proposed by Wallace[1], and later adapted for the freshwater Cladocera (Crustacea) by Korovchinsky[10] has been used to explain latitudinal diversity centers
Even less is known of the interactions of ecological and evolutionary processes that contributed to the biogeography of Eastern Palearctic cladocerans[29,30,31,32]
All but one of our analyses found the same root for the D. curvirostris complex (Figs 2 and 3; Supplementary Figs S1–S3)
Summary
The “ejected relict” scheme initially proposed by Wallace[1] (see review by Eskov11), and later adapted for the freshwater Cladocera (Crustacea) by Korovchinsky[10] has been used to explain latitudinal diversity centers. According to this hypothesis, a step-by-step mass extinction from the middle Caenozoic to recent times resulted from climate aridization. Evidence has emerged that the temperate Eastern Palearctic represents a zone of cladoceran endemism[33]. We know little of the geographic boundaries of these species because there has been very limited geographic sampling
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