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      Mesozoic fossils (>145 Mya) suggest the antiquity of the subgenera of Daphnia and their coevolution with chaoborid predators


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      BMC Evolutionary Biology

      BioMed Central

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          The timescale of the origins of Daphnia O. F. Mueller (Crustacea: Cladocera) remains controversial. The origin of the two main subgenera has been associated with the breakup of the supercontinent Pangaea. This vicariance hypothesis is supported by reciprocal monophyly, present day associations with the former Gondwanaland and Laurasia regions, and mitochondrial DNA divergence estimates. However, previous multilocus nuclear DNA sequence divergence estimates at < 10 Million years are inconsistent with the breakup of Pangaea. We examined new and existing cladoceran fossils from a Mesozoic Mongolian site, in hopes of gaining insights into the timescale of the evolution of Daphnia.


          We describe new fossils of ephippia from the Khotont site in Mongolia associated with the Jurassic-Cretaceous boundary (about 145 MYA) that are morphologically similar to several modern genera of the family Daphniidae, including the two major subgenera of Daphnia, i.e., Daphnia s. str. and Ctenodaphnia. The daphniid fossils co-occurred with fossils of the predaceous phantom midge (Chaoboridae).


          Our findings indicate that the main subgenera of Daphnia are likely much older than previously known from fossils (at least 100 MY older) or from nuclear DNA estimates of divergence. The results showing co-occurrence of the main subgenera far from the presumed Laurasia/Gondwanaland dispersal barrier shortly after formation suggests that vicariance from the breakup of Pangaea is an unlikely explanation for the origin of the main subgenera. The fossil impressions also reveal that the coevolution of a dipteran predator (Chaoboridae) with the subgenus Daphnia is much older than previously known -- since the Mesozoic.

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          Most cited references 22

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           Paul Hebert (1978)
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            The scale of divergence: a phylogenetic appraisal of intercontinental allopatric speciation in a passively dispersed freshwater zooplankton genus.

            Molecular studies have enlightened our understanding of freshwater zooplankton biogeography, yet questions remain regarding the scale and commonality of geographic speciation. Here, we present a mtDNA-based phylogenetic hypothesis for 92 Daphnia species from all seven continents, with a focus on North and South America, Europe, and Australia, and use it to explore the frequency, scale, and geographical orientation of allopatric divergence events. Allopatric speciation can conservatively account for at least 42% of cladogenetic events among the species included in our study; most of these involve intercontinental splits. Closely related species pairs are concentrated in the circumarctic region and between northern and southern continents, aligned with bird migration routes, suggesting recent dispersal. By contrast, deeper phylogenetic patterns are consistent with vicariance scenarios linked to continental fragmentation. The possible reasons for the puzzling persistence of these ancient patterns in light of the eroding force of dispersal are considered. Our results demonstrate the high frequency and complex pattern of allopatric speciation in this ancient, passively dispersed genus.
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              Phylogenetics and evolution of the Daphnia longispina group (Crustacea) based on 12S rDNA sequence and allozyme variation.

              Although members of the crustacean genus Daphnia have been the target of much research, there is little understanding of the group's evolutionary history. We addressed this gap by inferring a phylogeny for one of the major species groups (longispina) using nucleotide sequence variation of a 525-bp segment of the mitochondrial 12S rDNA and allozyme variation at 21 loci. We identified the major lineages and their relationships, assessed the phylogenetic utility of the few morphological characters in the group, and examined Daphnia phylogeography. Nuclear and mtDNA phylogenies were generally concordant in recognizing the same four species complexes. An exception was the position of Daphnia galeata mendotae. The allozyme tree paired this species with the Daphnia rosea lineage, whereas the mtDNA trees grouped D. g. mendotae with Daphnia galeata galeata. This discordance was consistent with the reticulate evolution of nuclear genes supporting the hypothesis that D. g. mendotae represents a case of homoploid hybrid speciation. Striking morphological stasis in the longispina group was evidenced by its very limited morphological divergence over an estimated 100 MY, and by the unusual transitional saturation of the conservative 12S rRNA gene within a species group. Phylogenetic inference also provided evidence that similarities in cephalic crest shape likely resulted from convergent or parallel evolution among species. Endemism at the continental level was indicated for previously cosmopolitan species, but the estimated times of these divisions were inconsistent with vicariance events suggesting recent dispersal among continents. A significant role for divergent selection in new habitats during speciation was suggested by the neighboringly sympatric distributions of four sister species pairs over broad geographic areas.

                Author and article information

                BMC Evol Biol
                BMC Evolutionary Biology
                BioMed Central
                19 May 2011
                : 11
                : 129
                [1 ]AN Severtsov Institute of Ecology and Evolution, Leninsky Prospect 33, Moscow 119071, Russia
                [2 ]Department of Biological Sciences, The State University of New York at Buffalo, Buffalo, NY 14260, USA
                Copyright ©2011 Kotov and Taylor; licensee BioMed Central Ltd.

                This is an Open Access article distributed under the terms of the Creative Commons Attribution License ( http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

                Research Article

                Evolutionary Biology


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