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Time and time again: unisexual salamanders (genus Ambystoma) are the oldest unisexual vertebrates.

Bi K, Bogart JP - BMC Evol. Biol. (2010)

Bottom Line: Our results support a monophyletic lineage for unisexual Ambystoma that shares its most recent common ancestor with an A. barbouri lineage from western Kentucky.We reject a recent origin of unisexual Ambystoma and provide strong evidence that unisexual Ambystoma are the most ancient unisexual vertebrates known to exist.The likely presence of an ancient cytochrome b numt in some Kentucky A. barbouri represents a molecular "fossil" reinforcing the hypothesis that these individuals are some of the closest extant relatives to unisexual Ambystoma.

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Integrative Biology, University of Guelph, Guelph, Ontario, Canada.

ABSTRACT

Background: The age of unisexual salamanders of the genus Ambystoma is contentious. Recent and ancient evolutionary histories of unisexual Ambystoma were proposed by a few separate studies that constructed phylogenies using mitochondrial DNA markers (cytochrome b gene vs. non-coding region). In contrast to other studies showing that unisexual Ambystoma represent the most ancient unisexual vertebrates, a recent study by Robertson et al. suggests that this lineage has a very recent origin of less than 25,000 years ago.

Results: We re-examined the phylogenetic relationship of the unisexuals to A. barbouri from various populations using both mitochondrial markers as well as the complete mitochondrial genomes of A. barbouri and a unisexual individual from Kentucky. Lineage dating was conducted using BEAST and MultiDivTime on a complete mitochondrial genome phylogeny. Our results support a monophyletic lineage for unisexual Ambystoma that shares its most recent common ancestor with an A. barbouri lineage from western Kentucky. In contrast to the Robertson et al.'s study, no A. barbouri individual shared an identical or almost identical cytochrome b haplotype with any unisexual. Molecular dating supports an early Pliocene origin for the unisexual linage (approximately 5 million years ago). We propose that a unisexual-like cytochrome b numt (or pseudogene) exists in the controversial A. barbouri individuals from Kentucky, which was likely the cause of an erroneous phylogeny and time estimate in Robertson et al.'s study.

Conclusion: We reject a recent origin of unisexual Ambystoma and provide strong evidence that unisexual Ambystoma are the most ancient unisexual vertebrates known to exist. The likely presence of an ancient cytochrome b numt in some Kentucky A. barbouri represents a molecular "fossil" reinforcing the hypothesis that these individuals are some of the closest extant relatives to unisexual Ambystoma.

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A close phylogenetic relationship of unisexual Ambystoma (JPB39932) and Kentucky A. barbouri (JPB34342) inferred from mtgenome phylogeny. Other species are incorporated to introduce calibration points for molecular dating analyses, and to serve as outgroups. Left numbers along branches represent the Bayesian posterior probabilities (BPP) and right numbers represent bootstrap proportions (BSP) derived from the parsimony analysis. BPP and BSP below 50 are not shown. Branch lengths are estimated by the Bayesian inference.
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Figure 3: A close phylogenetic relationship of unisexual Ambystoma (JPB39932) and Kentucky A. barbouri (JPB34342) inferred from mtgenome phylogeny. Other species are incorporated to introduce calibration points for molecular dating analyses, and to serve as outgroups. Left numbers along branches represent the Bayesian posterior probabilities (BPP) and right numbers represent bootstrap proportions (BSP) derived from the parsimony analysis. BPP and BSP below 50 are not shown. Branch lengths are estimated by the Bayesian inference.

Mentions: A total of 17 mtgenome sequences, including 13 downloaded from GenBank, were used for phylogenetic construction (Table 2). The combined DNA dataset contained 9647 bp with 3464 variable sites and 2361 were phylogenetically informative. Parsimony analysis generated a single tree 8803 steps in length (CI = 0.569, RI = 0.614). For Bayesian analysis, a GTR+I+G model was selected as the best-fit model. The tree topologies derived from parsimony and Bayesian analyses were similar, with slight differences in the relationships of some outgroup species, and we present the Bayesian tree in Figure 3. The monophyly of Kentucky A. barbouri JPB34342 and unisexual JPB39932 was strongly supported by both analyses (BSP = 100; BPP = 100).


Time and time again: unisexual salamanders (genus Ambystoma) are the oldest unisexual vertebrates.

Bi K, Bogart JP - BMC Evol. Biol. (2010)

A close phylogenetic relationship of unisexual Ambystoma (JPB39932) and Kentucky A. barbouri (JPB34342) inferred from mtgenome phylogeny. Other species are incorporated to introduce calibration points for molecular dating analyses, and to serve as outgroups. Left numbers along branches represent the Bayesian posterior probabilities (BPP) and right numbers represent bootstrap proportions (BSP) derived from the parsimony analysis. BPP and BSP below 50 are not shown. Branch lengths are estimated by the Bayesian inference.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3020632&req=5

Figure 3: A close phylogenetic relationship of unisexual Ambystoma (JPB39932) and Kentucky A. barbouri (JPB34342) inferred from mtgenome phylogeny. Other species are incorporated to introduce calibration points for molecular dating analyses, and to serve as outgroups. Left numbers along branches represent the Bayesian posterior probabilities (BPP) and right numbers represent bootstrap proportions (BSP) derived from the parsimony analysis. BPP and BSP below 50 are not shown. Branch lengths are estimated by the Bayesian inference.
Mentions: A total of 17 mtgenome sequences, including 13 downloaded from GenBank, were used for phylogenetic construction (Table 2). The combined DNA dataset contained 9647 bp with 3464 variable sites and 2361 were phylogenetically informative. Parsimony analysis generated a single tree 8803 steps in length (CI = 0.569, RI = 0.614). For Bayesian analysis, a GTR+I+G model was selected as the best-fit model. The tree topologies derived from parsimony and Bayesian analyses were similar, with slight differences in the relationships of some outgroup species, and we present the Bayesian tree in Figure 3. The monophyly of Kentucky A. barbouri JPB34342 and unisexual JPB39932 was strongly supported by both analyses (BSP = 100; BPP = 100).

Bottom Line: Our results support a monophyletic lineage for unisexual Ambystoma that shares its most recent common ancestor with an A. barbouri lineage from western Kentucky.We reject a recent origin of unisexual Ambystoma and provide strong evidence that unisexual Ambystoma are the most ancient unisexual vertebrates known to exist.The likely presence of an ancient cytochrome b numt in some Kentucky A. barbouri represents a molecular "fossil" reinforcing the hypothesis that these individuals are some of the closest extant relatives to unisexual Ambystoma.

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Integrative Biology, University of Guelph, Guelph, Ontario, Canada.

ABSTRACT

Background: The age of unisexual salamanders of the genus Ambystoma is contentious. Recent and ancient evolutionary histories of unisexual Ambystoma were proposed by a few separate studies that constructed phylogenies using mitochondrial DNA markers (cytochrome b gene vs. non-coding region). In contrast to other studies showing that unisexual Ambystoma represent the most ancient unisexual vertebrates, a recent study by Robertson et al. suggests that this lineage has a very recent origin of less than 25,000 years ago.

Results: We re-examined the phylogenetic relationship of the unisexuals to A. barbouri from various populations using both mitochondrial markers as well as the complete mitochondrial genomes of A. barbouri and a unisexual individual from Kentucky. Lineage dating was conducted using BEAST and MultiDivTime on a complete mitochondrial genome phylogeny. Our results support a monophyletic lineage for unisexual Ambystoma that shares its most recent common ancestor with an A. barbouri lineage from western Kentucky. In contrast to the Robertson et al.'s study, no A. barbouri individual shared an identical or almost identical cytochrome b haplotype with any unisexual. Molecular dating supports an early Pliocene origin for the unisexual linage (approximately 5 million years ago). We propose that a unisexual-like cytochrome b numt (or pseudogene) exists in the controversial A. barbouri individuals from Kentucky, which was likely the cause of an erroneous phylogeny and time estimate in Robertson et al.'s study.

Conclusion: We reject a recent origin of unisexual Ambystoma and provide strong evidence that unisexual Ambystoma are the most ancient unisexual vertebrates known to exist. The likely presence of an ancient cytochrome b numt in some Kentucky A. barbouri represents a molecular "fossil" reinforcing the hypothesis that these individuals are some of the closest extant relatives to unisexual Ambystoma.

Show MeSH