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Global isolation by distance despite strong regional phylogeography in a small metazoan.

Mills S, Lunt DH, Gómez A - BMC Evol. Biol. (2007)

Bottom Line: Surprisingly, given this strong phylogeographic structure, B. plicatilis s. s. shows a significant correlation between geographic and genetic distance on a global scale ('isolation by distance' - IBD).Our data indicates that geographic speciation, contrary to historical views, is likely to be very important in microorganisms.By presenting compelling evidence for geographic speciation in a small eukaryote we add to the growing body of evidence that is forcing us to rethink our views of global biodiversity.

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Biological Sciences, University of Hull, Hull, HU6 7RX, UK. mills@ansp.org

ABSTRACT

Background: Small vagile eukaryotic organisms, which comprise a large proportion of the Earth's biodiversity, have traditionally been thought to lack the extent of population structuring and geographic speciation observed in larger taxa. Here we investigate the patterns of genetic diversity, amongst populations of the salt lake microscopic metazoan Brachionus plicatilis s. s. (sensu stricto) (Rotifera: Monogononta) on a global scale. We examine the phylogenetic relationships of geographic isolates from four continents using a 603 bp fragment of the mitochondrial COI gene to investigate patterns of phylogeographic subdivision in this species. In addition we investigate the relationship between genetic and geographic distances on a global scale to try and reconcile the paradox between the high vagility of this species and the previously reported patterns of restricted gene flow, even over local spatial scales.

Results: Analysis of global sequence diversity of B. plicatilis s. s. reveals the presence of four allopatric genetic lineages: North American-Far East Asian, Western Mediterranean, Australian, and an Eastern Mediterranean lineage represented by a single isolate. Geographically orientated substructure is also apparent within the three best sampled lineages. Surprisingly, given this strong phylogeographic structure, B. plicatilis s. s. shows a significant correlation between geographic and genetic distance on a global scale ('isolation by distance' - IBD).

Conclusion: Despite its cosmopolitan distribution and potential for high gene flow, B. plicatilis s. s. is strongly structured at a global scale. IBD patterns have traditionally been interpreted to indicate migration-drift equilibrium, although in this system equilibrium conditions are incompatible with the observed genetic structure. Instead, we suggest the pattern may have arisen through persistent founder effects, acting in a similar fashion to geographic barriers for larger organisms. Our data indicates that geographic speciation, contrary to historical views, is likely to be very important in microorganisms. By presenting compelling evidence for geographic speciation in a small eukaryote we add to the growing body of evidence that is forcing us to rethink our views of global biodiversity.

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Average sum of residuals by sample site for the RMA regression analysis. Laboratory kept clones are shown in red and error bars indicate the standard error of the mean. Site abbreviations as in Table 1.
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Figure 4: Average sum of residuals by sample site for the RMA regression analysis. Laboratory kept clones are shown in red and error bars indicate the standard error of the mean. Site abbreviations as in Table 1.

Mentions: Consideration of the regression residuals revealed that the largest deviation from the regression model was represented by pairwise comparisons involving two laboratory kept clones (sites ATL and MEA see Figure 4 and Table 1). In the case of ATL, a larger than expected genetic distance was found, in the case of MEA a smaller than expected genetic distance was found. Although natural events could be responsible for this pattern, laboratory clones are exposed to contamination and mislabelling problems. Removal of all laboratory kept clones from the RMA analysis (representing 5 localities) markedly increased the correlation coefficient between geographic and genetic distance (r2 = 0.91, P = < 0.01, y = 1.13 × 10-2 + 4.93 × 10-6x).


Global isolation by distance despite strong regional phylogeography in a small metazoan.

Mills S, Lunt DH, Gómez A - BMC Evol. Biol. (2007)

Average sum of residuals by sample site for the RMA regression analysis. Laboratory kept clones are shown in red and error bars indicate the standard error of the mean. Site abbreviations as in Table 1.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC2254418&req=5

Figure 4: Average sum of residuals by sample site for the RMA regression analysis. Laboratory kept clones are shown in red and error bars indicate the standard error of the mean. Site abbreviations as in Table 1.
Mentions: Consideration of the regression residuals revealed that the largest deviation from the regression model was represented by pairwise comparisons involving two laboratory kept clones (sites ATL and MEA see Figure 4 and Table 1). In the case of ATL, a larger than expected genetic distance was found, in the case of MEA a smaller than expected genetic distance was found. Although natural events could be responsible for this pattern, laboratory clones are exposed to contamination and mislabelling problems. Removal of all laboratory kept clones from the RMA analysis (representing 5 localities) markedly increased the correlation coefficient between geographic and genetic distance (r2 = 0.91, P = < 0.01, y = 1.13 × 10-2 + 4.93 × 10-6x).

Bottom Line: Surprisingly, given this strong phylogeographic structure, B. plicatilis s. s. shows a significant correlation between geographic and genetic distance on a global scale ('isolation by distance' - IBD).Our data indicates that geographic speciation, contrary to historical views, is likely to be very important in microorganisms.By presenting compelling evidence for geographic speciation in a small eukaryote we add to the growing body of evidence that is forcing us to rethink our views of global biodiversity.

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Biological Sciences, University of Hull, Hull, HU6 7RX, UK. mills@ansp.org

ABSTRACT

Background: Small vagile eukaryotic organisms, which comprise a large proportion of the Earth's biodiversity, have traditionally been thought to lack the extent of population structuring and geographic speciation observed in larger taxa. Here we investigate the patterns of genetic diversity, amongst populations of the salt lake microscopic metazoan Brachionus plicatilis s. s. (sensu stricto) (Rotifera: Monogononta) on a global scale. We examine the phylogenetic relationships of geographic isolates from four continents using a 603 bp fragment of the mitochondrial COI gene to investigate patterns of phylogeographic subdivision in this species. In addition we investigate the relationship between genetic and geographic distances on a global scale to try and reconcile the paradox between the high vagility of this species and the previously reported patterns of restricted gene flow, even over local spatial scales.

Results: Analysis of global sequence diversity of B. plicatilis s. s. reveals the presence of four allopatric genetic lineages: North American-Far East Asian, Western Mediterranean, Australian, and an Eastern Mediterranean lineage represented by a single isolate. Geographically orientated substructure is also apparent within the three best sampled lineages. Surprisingly, given this strong phylogeographic structure, B. plicatilis s. s. shows a significant correlation between geographic and genetic distance on a global scale ('isolation by distance' - IBD).

Conclusion: Despite its cosmopolitan distribution and potential for high gene flow, B. plicatilis s. s. is strongly structured at a global scale. IBD patterns have traditionally been interpreted to indicate migration-drift equilibrium, although in this system equilibrium conditions are incompatible with the observed genetic structure. Instead, we suggest the pattern may have arisen through persistent founder effects, acting in a similar fashion to geographic barriers for larger organisms. Our data indicates that geographic speciation, contrary to historical views, is likely to be very important in microorganisms. By presenting compelling evidence for geographic speciation in a small eukaryote we add to the growing body of evidence that is forcing us to rethink our views of global biodiversity.

Show MeSH
Related in: MedlinePlus