Melania Cristescu - Academia.edu (original) (raw)

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Papers by Melania Cristescu

Limnology and Oceanography, 2001

Molecular Ecology, 2009

A major question in our understanding of eukaryotic biodiversity is whether small bodied taxa hav... more A major question in our understanding of eukaryotic biodiversity is whether small bodied taxa have cosmopolitan distributions or consist of geographically localized cryptic taxa. Here, we explore the global phylogeography of the freshwater cladoceran Polyphemus pediculus (Linnaeus, 1761) (Crustacea, Onychopoda) using two mitochondrial genes, cytochrome c oxidase subunit I and 16s ribosomal RNA, and one nuclear marker, 18s ribosomal RNA. The results of neighbour-joining and Bayesian phylogenetic analyses reveal an exceptionally pronounced genetic structure at both inter- and intra-continental scales. The presence of well-supported, deeply divergent phylogroups across the Holarctic suggests that P. pediculus represents an assemblage of at least nine, largely allopatric cryptic species. Interestingly, all phylogenetic analyses support the reciprocal paraphyly of Nearctic and Palaearctic clades. Bayesian inference of ancestral distributions suggests that P. pediculus originated in North America or East Asia and that European lineages of Polyphemus were established by subsequent intercontinental dispersal events from North America. Japan and the Russian Far East harbour exceptionally high levels of genetic diversity at both regional and local scales. In contrast, little genetic subdivision is apparent across the formerly glaciated regions of Europe and North America, areas that historical demographic analyses suggest that were recolonized just 5500–24 000 years ago.

Bythotrephes Leydig is a predatory, onychopod cladoceran native to Eurasia that typically inhabit... more Bythotrephes Leydig is a predatory, onychopod cladoceran native to Eurasia that typically inhabits oligo-and mesotrophic water bodies of the Palaearctic region. It recently invaded 66 North American lakes, prompting a re-evaluation of the taxonomic status, global distribution, and determinants of local occurrence and abundance.

Bythotrephes Leydig is a predatory, onychopod cladoceran native to Eurasia that typically inhabit... more Bythotrephes Leydig is a predatory, onychopod cladoceran native to Eurasia that typically inhabits oligo-and mesotrophic water bodies of the Palaearctic region. It recently invaded 66 North American lakes, prompting a re-evaluation of the taxonomic status, global distribution, and determinants of local occurrence and abundance.

Molecular Phylogenetics and Evolution, 2006

The Branchiopoda display extraordinary variation in body form, even within the morphologically di... more The Branchiopoda display extraordinary variation in body form, even within the morphologically diverse crustaceans. To fully understand the origin and evolution of these morphological reconWgurations, a robust phylogeny of the group is essential. To infer the aYnities among branchiopods, we employed two approaches to taxon and gene sampling, presented new sequence data from three genes, incorporated previously published sequence data from three additional genes, and utilized comprehensive techniques of phylogeny reconstruction. The results provided support for a number of longstanding hypotheses concerning the relationships among the orders. For example, we obtained support for the Cladoceromorpha and Gymnomera, and favoured a unique arrangement of the cladoceran orders. A few aYnities remain to be resolved, particularly at the base of the Phyllopoda and within the Anomopoda. However, the results suggest that increased gene sampling is recommended for future investigations of branchiopod systematics.

Molecular Ecology, 2003

The Black, Azov, Caspian and Aral Seas, remnants of the intracontinental Paratethys basin, are ho... more The Black, Azov, Caspian and Aral Seas, remnants of the intracontinental Paratethys basin, are home to a spectacular diversity of crustaceans. This study examines the past history of the Ponto-Caspian fauna through comparative phylogeographical studies on both benthic and planktonic taxa, based on an examination of nucleotide diversity in the mitochondrial, cytochrome c oxidase subunit 1 (COI) gene. The COI data reveal a striking example of phylogeographical concordance. All species analysed, three amphipods and three cladocerans, are characterized by two monophyletic clades corresponding to the Black and Caspian regions. However, this phylogeographical partition is, on average, four times deeper for the benthic amphipods than for the planktonic cladocerans. Based on standard molecular clocks, the Black and Caspian lineages of benthic crustaceans diverged at varied intervals from 1 to 8 million years ago. By contrast, planktonic lineages are more recent with their divergence occurring in the last million years. Levels of intraspecific polymorphisms are variable and generally lower in planktonic than benthic taxa. The mechanisms responsible for the high diversity of crustaceans in the Ponto-Caspian region are discussed on the basis of these results.

Limnology and Oceanography, 2001

Molecular Ecology, 2009

A major question in our understanding of eukaryotic biodiversity is whether small bodied taxa hav... more A major question in our understanding of eukaryotic biodiversity is whether small bodied taxa have cosmopolitan distributions or consist of geographically localized cryptic taxa. Here, we explore the global phylogeography of the freshwater cladoceran Polyphemus pediculus (Linnaeus, 1761) (Crustacea, Onychopoda) using two mitochondrial genes, cytochrome c oxidase subunit I and 16s ribosomal RNA, and one nuclear marker, 18s ribosomal RNA. The results of neighbour-joining and Bayesian phylogenetic analyses reveal an exceptionally pronounced genetic structure at both inter- and intra-continental scales. The presence of well-supported, deeply divergent phylogroups across the Holarctic suggests that P. pediculus represents an assemblage of at least nine, largely allopatric cryptic species. Interestingly, all phylogenetic analyses support the reciprocal paraphyly of Nearctic and Palaearctic clades. Bayesian inference of ancestral distributions suggests that P. pediculus originated in North America or East Asia and that European lineages of Polyphemus were established by subsequent intercontinental dispersal events from North America. Japan and the Russian Far East harbour exceptionally high levels of genetic diversity at both regional and local scales. In contrast, little genetic subdivision is apparent across the formerly glaciated regions of Europe and North America, areas that historical demographic analyses suggest that were recolonized just 5500–24 000 years ago.

Bythotrephes Leydig is a predatory, onychopod cladoceran native to Eurasia that typically inhabit... more Bythotrephes Leydig is a predatory, onychopod cladoceran native to Eurasia that typically inhabits oligo-and mesotrophic water bodies of the Palaearctic region. It recently invaded 66 North American lakes, prompting a re-evaluation of the taxonomic status, global distribution, and determinants of local occurrence and abundance.

Bythotrephes Leydig is a predatory, onychopod cladoceran native to Eurasia that typically inhabit... more Bythotrephes Leydig is a predatory, onychopod cladoceran native to Eurasia that typically inhabits oligo-and mesotrophic water bodies of the Palaearctic region. It recently invaded 66 North American lakes, prompting a re-evaluation of the taxonomic status, global distribution, and determinants of local occurrence and abundance.

Molecular Phylogenetics and Evolution, 2006

The Branchiopoda display extraordinary variation in body form, even within the morphologically di... more The Branchiopoda display extraordinary variation in body form, even within the morphologically diverse crustaceans. To fully understand the origin and evolution of these morphological reconWgurations, a robust phylogeny of the group is essential. To infer the aYnities among branchiopods, we employed two approaches to taxon and gene sampling, presented new sequence data from three genes, incorporated previously published sequence data from three additional genes, and utilized comprehensive techniques of phylogeny reconstruction. The results provided support for a number of longstanding hypotheses concerning the relationships among the orders. For example, we obtained support for the Cladoceromorpha and Gymnomera, and favoured a unique arrangement of the cladoceran orders. A few aYnities remain to be resolved, particularly at the base of the Phyllopoda and within the Anomopoda. However, the results suggest that increased gene sampling is recommended for future investigations of branchiopod systematics.

Molecular Ecology, 2003

The Black, Azov, Caspian and Aral Seas, remnants of the intracontinental Paratethys basin, are ho... more The Black, Azov, Caspian and Aral Seas, remnants of the intracontinental Paratethys basin, are home to a spectacular diversity of crustaceans. This study examines the past history of the Ponto-Caspian fauna through comparative phylogeographical studies on both benthic and planktonic taxa, based on an examination of nucleotide diversity in the mitochondrial, cytochrome c oxidase subunit 1 (COI) gene. The COI data reveal a striking example of phylogeographical concordance. All species analysed, three amphipods and three cladocerans, are characterized by two monophyletic clades corresponding to the Black and Caspian regions. However, this phylogeographical partition is, on average, four times deeper for the benthic amphipods than for the planktonic cladocerans. Based on standard molecular clocks, the Black and Caspian lineages of benthic crustaceans diverged at varied intervals from 1 to 8 million years ago. By contrast, planktonic lineages are more recent with their divergence occurring in the last million years. Levels of intraspecific polymorphisms are variable and generally lower in planktonic than benthic taxa. The mechanisms responsible for the high diversity of crustaceans in the Ponto-Caspian region are discussed on the basis of these results.