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Douglas C. Currie - One of the best experts on this subject based on the ideXlab platform.
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the speciation continuum ecological and chromosomal divergence in the simulium arcticum complex diptera simuliidae
Biological Journal of The Linnean Society, 2015Co-Authors: Ida M. Conflitti, Gerald F. Shields, Douglas C. Currie, Robert W MurphyAbstract:Chromosome inversions may be involved in adaptation and speciation. We investigate ecological diversification among members of the Simulium arcticum species complex at different stages of chromosome divergence. Our analyses focus on two geographical scales. First, we assess ecological divergence of sibling species throughout North America using niche modelling methods. Then, using canonical correspondence analysis, we investigate habitat associations of sibling species and cytotypes in the northern Rocky Mountains ecoregion, where cytotypes tend to occur. Despite significant overlap in predicted distributions, all sibling species are ecologically unique. On the other hand, we discover various degrees of ecological divergence for cytotypes. Some cytotypes are ecologically distinct and perhaps are in their initial stages of incipient speciation. Other cytotypes are ecologically associated with one another or with particular sibling species. Thus, for members of the S. arcticum complex, ecological and chromosomal differences tend to develop early in lineage formation. Ecological distinctiveness of sibling species and cytotypes suggests that local adaptation may be involved in diversification of these chromosomal forms. © 2015 The Linnean Society of London, Biological Journal of the Linnean Society, 2015, 115, 13‐27.
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the speciation continuum population structure gene flow and maternal ancestry in the simulium arcticum complex diptera simuliidae
Molecular Phylogenetics and Evolution, 2014Co-Authors: Ida M. Conflitti, Gerald F. Shields, Douglas C. Currie, Robert W MurphyAbstract:Comparative analyses of populations at different stages of divergence can yield insights into the process of speciation. We assess population structure, gene flow, and maternal ancestry at five locations containing sympatric members of the Simulium arcticum complex at different stages of chromosome divergence. We analyze both nuclear and mitochondrial DNA markers, including 11 microsatellite loci, as well as COI, COII, cytb, and ND4 gene sequences. Simulium negativum, representing the later stages of divergence, shows both nuclear and mitochondrial differentiation when compared with allopatric and sympatric chromosomal forms, as well as both low contemporary and historical gene flow in sympatry. At intermediate stages of chromosome divergence, populations differ at nuclear, but not mitochondrial, loci in allopatry and sympatry. In one comparison of intermediate stage chromosomal forms (S. arcticum sensu stricto and S. apricarium), populations demonstrate low contemporary, but higher historical, gene flow in sympatry. In a second sympatric comparison (S. arcticum s. s. and S. brevicercum), both contemporary and historical gene flow are high. All analyses of sympatric populations at the earliest stages of chromosome divergence demonstrate panmixia; yet, some nuclear differentiation in allopatry is apparent. These findings suggest that molecular divergence is tracking chromosome divergence along a chromosomally-defined continuum of speciation in black flies.
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molecular phylogeny of the north american simulium malyschevi group species diptera simuliidae
Systematic Entomology, 2012Co-Authors: Ida M. Conflitti, Michael Spironello, Douglas C. CurrieAbstract:We investigated species limits and phylogenetic relationships among chromosomally distinct North American members of the Simulium malyschevi species-group. Maximum parsimony and Bayesian analyses were conducted based on 12S, COII, cyt b and ITS-1 gene sequences. In terms of species limits, monophyly was highly supported for each chromosomally and morphologically distinct taxon analysed (S. decimatum, S. defoliarti, S. malyschevi, and S. murmanum). In contrast, support for monophyly of morphologically homogeneous S. arcticum complex members was significant only in one case (S. saxosum) and not the other (S. negativum). Considering the overall topology, three principal conclusions were drawn: (i) the status of S. subvariegatum as a member of the S. malyschevi species-group remains uncertain. This species either was excluded from the malyschevi-group or formed a sister group with S. malyschevi at the base of the tree; (ii) although S. murmanum and S. decimatum branch after S. malyschevi, the position of the two species relative to each other remains unresolved; and (iii) the structurally homogeneous S. arcticum species complex was not monophyletic due to the inclusion of S. defoliarti. Further investigation may warrant changes to current malyschevi-group classification. Molecular datasets alone may be insufficient for resolving relationships among particular lineages of black flies.
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a complex problem delimiting sibling species boundaries in black flies diptera simuliidae
Canadian Entomologist, 2012Co-Authors: Ida M. Conflitti, Gerald F. Shields, Douglas C. CurrieAbstract:Rapid and recent lineage radiations pose challenges to systematists. Using members of the highly diverse Simulium arcticum Malloch complex, we tested whether the cytochrome c oxidase subunit I (COI) barcoding gene can differentiate black fly sibling species. Members of the S. arcticum complex were monophyletic in relation to two morphospecies and two cryptic species of the Simulium malyschevi Dorogostaisky et al. and Simulium noelleri Friederichs species-groups, respectively. Of five S. arcticum sibling species analysed, only Simulium negativum Adler et al. was monophyletic. No other members of the complex could be distinguished using COI barcodes. The inability to resolve S. arcticum sibling species resulted because (1) haplotypes were shared between species and (2) the distribution of interspecific genetic distances completely overlapped the range of variation within species. Potential sources of incongruence between barcode data and species boundaries include imperfect taxonomy, inadequate genetic information, incomplete lineage sorting, and/or introgressive hybridization. We ruled out imperfect taxonomy because chromosomal, ecological, and distributional evidence support the validity of S. arcticum sibling species. Therefore, current nomenclature should be maintained pending further study. We conclude that one or more of the latter three sources of incongruence could be responsible for the lack of reciprocal monophyly among species of the S. arcticum complex.
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Good species behaving badly: Non-monophyly of black fly sibling species in the Simulium arcticum complex (Diptera: Simuliidae)
Molecular Phylogenetics and Evolution, 2010Co-Authors: Ida M. Conflitti, Michael J. Kratochvil, Michael Spironello, Gerald F. Shields, Douglas C. CurrieAbstract:Abstract Mitochondrial based phylogenetic reconstructions often show deviations from species-level monophyly. We used the Simulium arcticum species complex (Diptera: Simuliidae) as a model system for interpreting non-monophyly in light of chromosomal data supporting species status of siblings. For cytogenetic identification of morphologically indistinguishable black fly sibling species, larvae must be preserved in Carnoy’s solution, a fixative known to degrade DNA. Consequently, we reconstructed phylogenetic relationships based on 12S, COII, cyt b, and ITS-1 gene sequences obtained from larvae sampled from presumed taxon-pure localities. As species composition at ‘taxon-pure’ sites may have changed at the time of sampling, we performed a second study that aimed to: (1) assess phylogenetic relationships among cytologically verified members of the S. arcticum species complex using COI and COII gene sequences; (2) determine whether useable genetic information could be gleaned from Carnoy’s fixed specimens; and (3) determine the extent to which Carnoy’s fixative degrades DNA over time. We consistently obtained genetic data from material stored in Carnoy’s solution for two to three months. Genetic analysis of samples fixed in Carnoy’s solution for up to six years indicates that larvae preserved for a maximum of five years can provide useable information for molecular analysis. Our preliminary and cytologically confirmed phylogenetic analyses demonstrate that mitochondrial DNA fails to resolve species-level monophyly of chromosomally distinct S. arcticum taxa. As results of analyses based on cytologically verified larvae mirror those of our preliminary study, we rule out imperfect taxonomy as the reason for species-level non-monophyly. Although we cannot confidently reject either inadequate phylogenetic information or incomplete lineage sorting as the cause of non-monophyly, the sharing of alleles between sympatric siblings suggests introgressive hybridization between taxa. We conclude that the patterns present in the S. arcticum phylogeny likely represent the initial stages of chromosome based sibling speciation.
Ida M. Conflitti - One of the best experts on this subject based on the ideXlab platform.
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the speciation continuum ecological and chromosomal divergence in the simulium arcticum complex diptera simuliidae
Biological Journal of The Linnean Society, 2015Co-Authors: Ida M. Conflitti, Gerald F. Shields, Douglas C. Currie, Robert W MurphyAbstract:Chromosome inversions may be involved in adaptation and speciation. We investigate ecological diversification among members of the Simulium arcticum species complex at different stages of chromosome divergence. Our analyses focus on two geographical scales. First, we assess ecological divergence of sibling species throughout North America using niche modelling methods. Then, using canonical correspondence analysis, we investigate habitat associations of sibling species and cytotypes in the northern Rocky Mountains ecoregion, where cytotypes tend to occur. Despite significant overlap in predicted distributions, all sibling species are ecologically unique. On the other hand, we discover various degrees of ecological divergence for cytotypes. Some cytotypes are ecologically distinct and perhaps are in their initial stages of incipient speciation. Other cytotypes are ecologically associated with one another or with particular sibling species. Thus, for members of the S. arcticum complex, ecological and chromosomal differences tend to develop early in lineage formation. Ecological distinctiveness of sibling species and cytotypes suggests that local adaptation may be involved in diversification of these chromosomal forms. © 2015 The Linnean Society of London, Biological Journal of the Linnean Society, 2015, 115, 13‐27.
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Genetic panmixia within a narrow contact zone between chromosomally and ecologically distinct black fly sibling species (Diptera: Simuliidae)
Journal of Evolutionary Biology, 2015Co-Authors: Ida M. Conflitti, G. F. Shields, R. W. Murphy, D. C. CurrieAbstract:Hybrid zones are windows into the speciation process, and their study can give clues into the maintenance and breakdown of species boundaries. Using both genetic and ecological tools, we investigate lineage diversification across a contact zone characterized by chromosome rearrangements. We show that black fly sibling species, Simulium arcticum sensu stricto (s.s.) and Simulium saxosum, lack genetic differentiation at both microsatellite and mtDNA loci in allopatry and sympatry, as well as exhibit high levels of gene flow and continuous chromosome variation in sympatry. Furthermore, hybrid frequencies at the contact zone are similar to those seen between races, rather than species. In contrast, S. arcticum s.s. and S. saxosum main-tain ecological differences and distinct habitat associations -the contact zone situated at the margin of suitable habitat for each sibling species. Moreover, gene flow occurs only in a narrow band along an ecological transition. Except for the contact zone, S. arcticum s.s. and S. saxosum hybrids do not occur elsewhere within the sibling species' ranges. Although S. arcticum s.s. and S. saxosum maintain the potential to interbreed freely, we conclude that habitat associations and, perhaps, chromosome systems prevent expansion of ranges and assimilation of lineages.
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the speciation continuum population structure gene flow and maternal ancestry in the simulium arcticum complex diptera simuliidae
Molecular Phylogenetics and Evolution, 2014Co-Authors: Ida M. Conflitti, Gerald F. Shields, Douglas C. Currie, Robert W MurphyAbstract:Comparative analyses of populations at different stages of divergence can yield insights into the process of speciation. We assess population structure, gene flow, and maternal ancestry at five locations containing sympatric members of the Simulium arcticum complex at different stages of chromosome divergence. We analyze both nuclear and mitochondrial DNA markers, including 11 microsatellite loci, as well as COI, COII, cytb, and ND4 gene sequences. Simulium negativum, representing the later stages of divergence, shows both nuclear and mitochondrial differentiation when compared with allopatric and sympatric chromosomal forms, as well as both low contemporary and historical gene flow in sympatry. At intermediate stages of chromosome divergence, populations differ at nuclear, but not mitochondrial, loci in allopatry and sympatry. In one comparison of intermediate stage chromosomal forms (S. arcticum sensu stricto and S. apricarium), populations demonstrate low contemporary, but higher historical, gene flow in sympatry. In a second sympatric comparison (S. arcticum s. s. and S. brevicercum), both contemporary and historical gene flow are high. All analyses of sympatric populations at the earliest stages of chromosome divergence demonstrate panmixia; yet, some nuclear differentiation in allopatry is apparent. These findings suggest that molecular divergence is tracking chromosome divergence along a chromosomally-defined continuum of speciation in black flies.
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molecular phylogeny of the north american simulium malyschevi group species diptera simuliidae
Systematic Entomology, 2012Co-Authors: Ida M. Conflitti, Michael Spironello, Douglas C. CurrieAbstract:We investigated species limits and phylogenetic relationships among chromosomally distinct North American members of the Simulium malyschevi species-group. Maximum parsimony and Bayesian analyses were conducted based on 12S, COII, cyt b and ITS-1 gene sequences. In terms of species limits, monophyly was highly supported for each chromosomally and morphologically distinct taxon analysed (S. decimatum, S. defoliarti, S. malyschevi, and S. murmanum). In contrast, support for monophyly of morphologically homogeneous S. arcticum complex members was significant only in one case (S. saxosum) and not the other (S. negativum). Considering the overall topology, three principal conclusions were drawn: (i) the status of S. subvariegatum as a member of the S. malyschevi species-group remains uncertain. This species either was excluded from the malyschevi-group or formed a sister group with S. malyschevi at the base of the tree; (ii) although S. murmanum and S. decimatum branch after S. malyschevi, the position of the two species relative to each other remains unresolved; and (iii) the structurally homogeneous S. arcticum species complex was not monophyletic due to the inclusion of S. defoliarti. Further investigation may warrant changes to current malyschevi-group classification. Molecular datasets alone may be insufficient for resolving relationships among particular lineages of black flies.
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a complex problem delimiting sibling species boundaries in black flies diptera simuliidae
Canadian Entomologist, 2012Co-Authors: Ida M. Conflitti, Gerald F. Shields, Douglas C. CurrieAbstract:Rapid and recent lineage radiations pose challenges to systematists. Using members of the highly diverse Simulium arcticum Malloch complex, we tested whether the cytochrome c oxidase subunit I (COI) barcoding gene can differentiate black fly sibling species. Members of the S. arcticum complex were monophyletic in relation to two morphospecies and two cryptic species of the Simulium malyschevi Dorogostaisky et al. and Simulium noelleri Friederichs species-groups, respectively. Of five S. arcticum sibling species analysed, only Simulium negativum Adler et al. was monophyletic. No other members of the complex could be distinguished using COI barcodes. The inability to resolve S. arcticum sibling species resulted because (1) haplotypes were shared between species and (2) the distribution of interspecific genetic distances completely overlapped the range of variation within species. Potential sources of incongruence between barcode data and species boundaries include imperfect taxonomy, inadequate genetic information, incomplete lineage sorting, and/or introgressive hybridization. We ruled out imperfect taxonomy because chromosomal, ecological, and distributional evidence support the validity of S. arcticum sibling species. Therefore, current nomenclature should be maintained pending further study. We conclude that one or more of the latter three sources of incongruence could be responsible for the lack of reciprocal monophyly among species of the S. arcticum complex.
Gerald F. Shields - One of the best experts on this subject based on the ideXlab platform.
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the speciation continuum ecological and chromosomal divergence in the simulium arcticum complex diptera simuliidae
Biological Journal of The Linnean Society, 2015Co-Authors: Ida M. Conflitti, Gerald F. Shields, Douglas C. Currie, Robert W MurphyAbstract:Chromosome inversions may be involved in adaptation and speciation. We investigate ecological diversification among members of the Simulium arcticum species complex at different stages of chromosome divergence. Our analyses focus on two geographical scales. First, we assess ecological divergence of sibling species throughout North America using niche modelling methods. Then, using canonical correspondence analysis, we investigate habitat associations of sibling species and cytotypes in the northern Rocky Mountains ecoregion, where cytotypes tend to occur. Despite significant overlap in predicted distributions, all sibling species are ecologically unique. On the other hand, we discover various degrees of ecological divergence for cytotypes. Some cytotypes are ecologically distinct and perhaps are in their initial stages of incipient speciation. Other cytotypes are ecologically associated with one another or with particular sibling species. Thus, for members of the S. arcticum complex, ecological and chromosomal differences tend to develop early in lineage formation. Ecological distinctiveness of sibling species and cytotypes suggests that local adaptation may be involved in diversification of these chromosomal forms. © 2015 The Linnean Society of London, Biological Journal of the Linnean Society, 2015, 115, 13‐27.
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the speciation continuum population structure gene flow and maternal ancestry in the simulium arcticum complex diptera simuliidae
Molecular Phylogenetics and Evolution, 2014Co-Authors: Ida M. Conflitti, Gerald F. Shields, Douglas C. Currie, Robert W MurphyAbstract:Comparative analyses of populations at different stages of divergence can yield insights into the process of speciation. We assess population structure, gene flow, and maternal ancestry at five locations containing sympatric members of the Simulium arcticum complex at different stages of chromosome divergence. We analyze both nuclear and mitochondrial DNA markers, including 11 microsatellite loci, as well as COI, COII, cytb, and ND4 gene sequences. Simulium negativum, representing the later stages of divergence, shows both nuclear and mitochondrial differentiation when compared with allopatric and sympatric chromosomal forms, as well as both low contemporary and historical gene flow in sympatry. At intermediate stages of chromosome divergence, populations differ at nuclear, but not mitochondrial, loci in allopatry and sympatry. In one comparison of intermediate stage chromosomal forms (S. arcticum sensu stricto and S. apricarium), populations demonstrate low contemporary, but higher historical, gene flow in sympatry. In a second sympatric comparison (S. arcticum s. s. and S. brevicercum), both contemporary and historical gene flow are high. All analyses of sympatric populations at the earliest stages of chromosome divergence demonstrate panmixia; yet, some nuclear differentiation in allopatry is apparent. These findings suggest that molecular divergence is tracking chromosome divergence along a chromosomally-defined continuum of speciation in black flies.
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incipient speciation and additional diversity within the simulium arcticum complex of black flies diptera simuliidae
American Midland Naturalist, 2014Co-Authors: Gerald F. ShieldsAbstract:Abstract I analyzed larval polytene chromosomes to determine if the hypothesized remnants of an incipient speciation event in the Simulium arcticum complex of black flies previously discovered at the Coeur d'Alene River, Idaho existed elsewhere. This population not only had Y chromosomes that defined two members of the S. arcticum complex: S. arcticum sensu stricto and S. saxosum, but also possessed combinations of sex chromosomes of the two that were in genetic equilibrium with respect to all sex chromosome types. The geographic overlap between S. saxosum to the west and S. arcticum s. s. to the east generally runs north and south of the Coeur d'Alene River. Accordingly, I made 37 additional collections in a north-south orientation during 2011–2013. Larvae from 10 of the 37 collections had sex chromosome types identical to those of the previously studied site at the Coeur d'Alene River, thus expanding the area of putative remnant populations. The St. Joe River not only had Y chromosome combinations ident...
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a complex problem delimiting sibling species boundaries in black flies diptera simuliidae
Canadian Entomologist, 2012Co-Authors: Ida M. Conflitti, Gerald F. Shields, Douglas C. CurrieAbstract:Rapid and recent lineage radiations pose challenges to systematists. Using members of the highly diverse Simulium arcticum Malloch complex, we tested whether the cytochrome c oxidase subunit I (COI) barcoding gene can differentiate black fly sibling species. Members of the S. arcticum complex were monophyletic in relation to two morphospecies and two cryptic species of the Simulium malyschevi Dorogostaisky et al. and Simulium noelleri Friederichs species-groups, respectively. Of five S. arcticum sibling species analysed, only Simulium negativum Adler et al. was monophyletic. No other members of the complex could be distinguished using COI barcodes. The inability to resolve S. arcticum sibling species resulted because (1) haplotypes were shared between species and (2) the distribution of interspecific genetic distances completely overlapped the range of variation within species. Potential sources of incongruence between barcode data and species boundaries include imperfect taxonomy, inadequate genetic information, incomplete lineage sorting, and/or introgressive hybridization. We ruled out imperfect taxonomy because chromosomal, ecological, and distributional evidence support the validity of S. arcticum sibling species. Therefore, current nomenclature should be maintained pending further study. We conclude that one or more of the latter three sources of incongruence could be responsible for the lack of reciprocal monophyly among species of the S. arcticum complex.
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a remnant of an incipient speciation event in the simulium arcticum complex diptera simuliidae
American Midland Naturalist, 2011Co-Authors: Gerald F. Shields, Michael J. KratochvilAbstract:Abstract By using cytogenetic analysis of larval polytene chromosomes from small samples of the Simulium arcticum complex of black flies (Diptera: Simuliidae) at the Coeur d'Alene River in northern Idaho in 2004 and 2005 we discovered a population that consisted of individuals having sex chromosomes characteristic of S. saxosum, S. arcticum s. s. and combinations of the two. Most taxa of the S. arcticum complex can be identified only on the basis of their well differentiated sex chromosomes, and the presence of larvae having species specific and combinational sex chromosome types presented us with a unique opportunity to further investigate this rare event. This variety of sex chromosome types could be explained if (1) sex-chromosomes in S. saxosum were operating autosomally in S. arcticum s. s. and vice-versa, (2) the combinational types were formed as a result of hybridization or (3) the population was in genetic equilibrium suggesting a unique entity. The latter possibility could be the remnant of an i...
Ho Sub Lee - One of the best experts on this subject based on the ideXlab platform.
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Arctium lappa ameliorates endothelial dysfunction in rats fed with high fat cholesterol diets
BMC Complementary and Alternative Medicine, 2012Co-Authors: Yun Jung Lee, Deok Ho Choi, Guk Hyun Cho, Jin Sook Kim, Dae Gill Kang, Ho Sub LeeAbstract:Background Arctium lappa L. (Asteraceae), burdock, is a medicinal plant that is popularly used for treating hypertension, gout, hepatitis, and other inflammatory disorders. This study was performed to test the effect of ethanol extract of Arctium lappa L. (EAL) seeds on vascular reactivity and inflammatory factors in rats fed a high fat/cholesterol diet (HFCD).
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Arctium lappa ameliorates endothelial dysfunction in rats fed with high fat cholesterol diets
BMC Complementary and Alternative Medicine, 2012Co-Authors: Yun Jung Lee, Deok Ho Choi, Guk Hyun Cho, Jin Sook Kim, Dae Gill Kang, Ho Sub LeeAbstract:Arctium lappa L. (Asteraceae), burdock, is a medicinal plant that is popularly used for treating hypertension, gout, hepatitis, and other inflammatory disorders. This study was performed to test the effect of ethanol extract of Arctium lappa L. (EAL) seeds on vascular reactivity and inflammatory factors in rats fed a high fat/cholesterol diet (HFCD). EAL-I (100 mg·kg−1/day), EAL-II (200 mg·kg−1/day), and fluvastatin (3 mg·kg−1/day) groups initially received HFCD alone for 8 weeks, with EAL supplementation provided during the final 6 weeks. Treatment with low or high doses of EAL markedly attenuated plasma levels of triglycerides and augmented plasma levels of high-density lipoprotein (HDL) in HFCD-fed rats. Chronic treatment with EAL markedly reduced impairments of acetylcholine (ACh)-induced relaxation of aortic rings. Furthermore, chronic treatment with EAL significantly lowered systolic blood pressure (SBP) and maintained smooth and flexible intimal endothelial layers in HFCD-fed rats. Chronic treatment with EAL suppressed upregulation of intercellular adhesion molecule (ICAM)-1, vascular cell adhesion molecule (VCAM)-1, and E-selectin in the aorta. Chronic treatment with EAL also suppressed increases in matrix metalloproteinase (MMP)-2 expression. These results suggested that EAL can inhibit HFCD-induced vascular inflammation in the rat model. The present study provides evidence that EAL ameliorates HFCD-induced vascular dysfunction through protection of vascular relaxation and suppression of vascular inflammation.
Robert W Murphy - One of the best experts on this subject based on the ideXlab platform.
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the speciation continuum ecological and chromosomal divergence in the simulium arcticum complex diptera simuliidae
Biological Journal of The Linnean Society, 2015Co-Authors: Ida M. Conflitti, Gerald F. Shields, Douglas C. Currie, Robert W MurphyAbstract:Chromosome inversions may be involved in adaptation and speciation. We investigate ecological diversification among members of the Simulium arcticum species complex at different stages of chromosome divergence. Our analyses focus on two geographical scales. First, we assess ecological divergence of sibling species throughout North America using niche modelling methods. Then, using canonical correspondence analysis, we investigate habitat associations of sibling species and cytotypes in the northern Rocky Mountains ecoregion, where cytotypes tend to occur. Despite significant overlap in predicted distributions, all sibling species are ecologically unique. On the other hand, we discover various degrees of ecological divergence for cytotypes. Some cytotypes are ecologically distinct and perhaps are in their initial stages of incipient speciation. Other cytotypes are ecologically associated with one another or with particular sibling species. Thus, for members of the S. arcticum complex, ecological and chromosomal differences tend to develop early in lineage formation. Ecological distinctiveness of sibling species and cytotypes suggests that local adaptation may be involved in diversification of these chromosomal forms. © 2015 The Linnean Society of London, Biological Journal of the Linnean Society, 2015, 115, 13‐27.
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the speciation continuum population structure gene flow and maternal ancestry in the simulium arcticum complex diptera simuliidae
Molecular Phylogenetics and Evolution, 2014Co-Authors: Ida M. Conflitti, Gerald F. Shields, Douglas C. Currie, Robert W MurphyAbstract:Comparative analyses of populations at different stages of divergence can yield insights into the process of speciation. We assess population structure, gene flow, and maternal ancestry at five locations containing sympatric members of the Simulium arcticum complex at different stages of chromosome divergence. We analyze both nuclear and mitochondrial DNA markers, including 11 microsatellite loci, as well as COI, COII, cytb, and ND4 gene sequences. Simulium negativum, representing the later stages of divergence, shows both nuclear and mitochondrial differentiation when compared with allopatric and sympatric chromosomal forms, as well as both low contemporary and historical gene flow in sympatry. At intermediate stages of chromosome divergence, populations differ at nuclear, but not mitochondrial, loci in allopatry and sympatry. In one comparison of intermediate stage chromosomal forms (S. arcticum sensu stricto and S. apricarium), populations demonstrate low contemporary, but higher historical, gene flow in sympatry. In a second sympatric comparison (S. arcticum s. s. and S. brevicercum), both contemporary and historical gene flow are high. All analyses of sympatric populations at the earliest stages of chromosome divergence demonstrate panmixia; yet, some nuclear differentiation in allopatry is apparent. These findings suggest that molecular divergence is tracking chromosome divergence along a chromosomally-defined continuum of speciation in black flies.