Variability in Genetic Architecture of the Cryptic Species Complex of Acanthocyclops Vernalis (Copepoda). I. Evidence from Karyotypes, Genome Size, and Ribosomal DNA Sequences

Grishanin, A. K.; Rasch, Ellen M.; Dodson, Stanley I.; Wyngaard, Grace A.

doi:10.1651/c-2558

Cited by 18 publications

(42 citation statements)

References 37 publications

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“…Cultures of isofemale lines and hybrid lines generated from experimental crosses were maintained at 22 Ϯ 0.5ЊC in a Conviron CMP 3244 environmental chamber (Controlled Environments Inc., Winnepeg, Canada) with a photoperiod of 14:10 L:D, reared in Provosoli medium, and fed algal suspension of Cryptomonas ozolini (Skü jja UTEX-LB2194), protozoans, and brine shrimp nauplii as described in Wyngaard and Chinnappa (1982) and Grishanin et al (2005).…”

Section: Culture Methodsmentioning

confidence: 99%

“…We then chose nine lines to represent the maximum range of variability in haploid chromosomal number, while including lines from each of the four sites. Morphologies of these nine lines are described in Dodson et al (2003), and the karyotypes, genome sizes, and 18S RNA sequences are given in Grishanin et al (2005). Voucher specimens of the nine isofemale lines (USNM 1071886-107894) and their 18S molecular sequences (AY643521-AY643529) are deposited in the Smithsonian Institution and GenBank, respectively.…”

Section: Collecting Sites and Populationsmentioning

confidence: 99%

“…Classical morphological characters once used to distinguish populations and species of A. vernalis and A. robustus (Dodson 1994) were revealed to be phenotypically plastic and useless for discrimination (Dodson et al 2003). Similarly, the nuclear DNA content shows little variation among populations in these forms (Grishanin et al 2005;Rasch and Wyngaard 2006). Species boundaries appear less clear with each new investigation.…”

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confidence: 94%

“…In contrast to the constancy of morphology and DNA content, multiple studies reveal marked differences in chromosome number among populations (reviewed by Wyngaard and Chinnappa 1982;Grishanin et al 2005). Wisconsin populations occasionally have aneuploidy, with diploid complements of six, seven, eight, nine, or 10 chromosomes, as well as pairwise differences in 18S rDNA sequences that are equal to or greater than those found among congeners of morphologically well defined freshwater cyclopoids (Grishanin et al FIG. 1.…”

mentioning

confidence: 99%

“…data). The extraordinary variability in chromosome number reported in multiple studies and populations (reviewed by Wyngaard and Chinnappa 1982;Grishanin et al 2005) suggests that variation in chromosomal number is a common feature and the natural hybridizations that may have produced this variation are similarly common-or at least not rare. The potential for some hybrids to have higher fitness relative to their parental lineages in their natural environments has been reported (Harrison 1990;Arnold 1997).…”

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Genetic Architecture of the Cryptic Species Complex of Acanthocyclops Vernalis (Crustacea: Copepoda). Ii. Crossbreeding Experiments, Cytogenetics, and a Model of Chromosomal Evoloution

et al. 2006

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Abstract. Collectively, populations of Acanthocyclops vernalis, a species complex of freshwater copepods, are remarkably similar as to morphology and DNA content, despite variability in chromosome number. Reproductive isolation had been reported among some populations, but with each new investigation the species boundaries and factors that may influence them appeared less clear. To clarify the pattern of biological species within this group of populations, we adopted a comprehensive approach and examined patterns of reproductive isolation in populations for which morphology, chromosome number, DNA content, and 18S rDNA sequences are known. In this study we established nine isofemale lines from four sites in Wisconsin and performed 266 crosses. Crosses within and among these lines were used to relate the degree of reproductive isolation to chromosome differences and to construct a model to explain the origin and maintenance of chromosome number variability. Different gametic and somatic chromosome numbers were observed among specimens within some isofemale lines. In a few cases, gametes with different haploid numbers were produced by a single female. Matings within isofemale lines always produced at least some reproductively successful replicate crosses (produced viable, fertile offspring). Crosses between lines from the same site showed reduced success relative to within-line crosses. Crosses between populations from distant sites showed limited genetic compatibility, producing viable, fertile F 1 offspring but infertile F 2 adults. One cross between lines with different chromosome numbers (one with 2n ϭ 8 and one with 2n ϭ 10) produced fertile viable offspring, which reproduced for at least 60 generations. These hybrids had either eight or nine chromosomes in the third generation of inbreeding, and eight chromosomes after 20 generations. These hybrids also had reduced nuclear DNA contents at the third generation, a level that persisted through the 20th generation. Successful backcrosses between some hybrids and their parental lines further demonstrated the potential for genetic compatibility among forms with different chromosome numbers. We propose a model in which alterations due to Robertsonian fusions, translocations, and/or loss of chromosomal fragments generate heritable variation, only some of which leads to reproductive isolation. Hence, some of the criteria traditionally used to recognize species boundaries in animals (morphology, DNA content, chromosome number) may not apply to this species complex.

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Section: Culture Methodsmentioning

confidence: 99%

Section: Collecting Sites and Populationsmentioning

confidence: 99%

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confidence: 94%

mentioning

confidence: 99%

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confidence: 99%

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Genetic Architecture of the Cryptic Species Complex of Acanthocyclops Vernalis (Crustacea: Copepoda). Ii. Crossbreeding Experiments, Cytogenetics, and a Model of Chromosomal Evoloution

et al. 2006

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A NewAcanthocyclopsKiefer, 1927 (Copepoda: Cyclopoida) from Central Mexico with Comments on the Distributionof the Genus in Middle America

Mercado

Suárez‐Morales

Silva-Briano

2006

Internat. Rev. Hydrobiol.

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A new species of Acanthocyclops KIEFER is described from central Mexico. It differs from its congeners by a combination of characters including mainly: 11-13 antennular segments, a spine formula of 3444 and modified setae on legs 2-4. The presence of a compound distal antennular segment is aberrant within the Cyclopoida. The new species seems to be related to Nearctic forms of the vernalis-robustus clade. Ancestors of this lineage probably reached central Mexico as a result of glaciation events and the new species is a remain of stranded postglacial populations; some of these forms were succesful in colonizing tropical lands. A key for the identification of the species of Acanthocyclops recorded in Mexico is included.

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Taxonomic implications for diaptomid copepods based on contrasting patterns of mitochondrial DNA sequence divergences in four morphospecies

Thum

Derry

2008

Hydrobiologia

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Morphological identification methods do not provide reliable and meaningful species identifications for taxa where morphological differences among distinct species are either absent or overlooked (i.e., cryptic species). For example, due to the minute nature of the morphological characters used to delineate diaptomid copepod species and the apparent potential for copepod speciation to occur with little or no morphological change (i.e., morphological stasis), morphological identifications of diaptomid species may not adequately capture their true species diversity. Here, we present results from a geographic survey of mtDNA sequences from populations across the geographic ranges of four North American diaptomid speciesLeptodiaptomus minutus, Skistodiaptomus pallidus, Skistodiaptomus reighardi, and Onychodiaptomus sanguineus. Shallow mitochondrial DNA sequence divergences (maximum of 1.1%) among haplotypes of L. minutus from across its geographic range suggest that current morphological identification techniques reliably identify this species. In contrast, we found large mitochondrial DNA sequence divergences (14-22%) among populations within the currently recognized morphospecies of S. pallidus, S. reighardi, and O. sanguineus. However, pairwise sequence divergences within four distinct S. pallidus clades and within populations of S. reighardi and O. sanguineus were similarly low (maximum of 1.5%) as found within L. minutus as a whole. Thus, the S. pallidus, S. reighardi, and O. sanguineus morphospecies may be considered best as cryptic species complexes. Our study therefore indicates that morphological identifications, while sufficient for some species, likely underestimate the true species diversity of diaptomid copepods. As such, we stress the need for extensive taxonomic revision that integrates genetic, morphological, reproductive, and ecological analyses of this diverse and important group of freshwater zooplankton. Furthermore, we believe an extensive taxonomic revision will shed important insight into major questions regarding the roles of geography, phylogeny, and habitat on the frequency of cryptic species on earth.

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Variability in Genetic Architecture of the Cryptic Species Complex of Acanthocyclops Vernalis (Copepoda). I. Evidence from Karyotypes, Genome Size, and Ribosomal DNA Sequences

Cited by 18 publications

References 37 publications

Genetic Architecture of the Cryptic Species Complex of Acanthocyclops Vernalis (Crustacea: Copepoda). Ii. Crossbreeding Experiments, Cytogenetics, and a Model of Chromosomal Evoloution

Genetic Architecture of the Cryptic Species Complex of Acanthocyclops Vernalis (Crustacea: Copepoda). Ii. Crossbreeding Experiments, Cytogenetics, and a Model of Chromosomal Evoloution

A NewAcanthocyclopsKiefer, 1927 (Copepoda: Cyclopoida) from Central Mexico with Comments on the Distributionof the Genus in Middle America

Taxonomic implications for diaptomid copepods based on contrasting patterns of mitochondrial DNA sequence divergences in four morphospecies

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