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Hybridisation and diversification in the adaptive radiation of clownfishes.

Litsios G, Salamin N - BMC Evol. Biol. (2014)

Bottom Line: While two species of clownfish are likely to have been described from hybrid specimens, the occurrence and effect of hybridisation on the clade diversification is yet unknown.Our results show that consistently with the syngameon hypothesis, hybridisation events are linked with a burst of diversification in the clownfishes.Moreover, several recently diverged clownfish lineages likely originated through hybridisation, which indicates that diversification, catalysed by hybridisation events, may still be happening.

View Article: PubMed Central - PubMed

Affiliation: Department of Ecology and Evolution, Biophore, University of Lausanne, 1015, Lausanne, Switzerland. glenn.litsios@unil.ch.

ABSTRACT

Background: The importance of hybridisation during species diversification has long been debated among evolutionary biologists. It is increasingly recognised that hybridisation events occurred during the evolutionary history of numerous species, especially during the early stages of adaptive radiation. We study the effect of hybridisation on diversification in the clownfishes, a clade of coral reef fish that diversified through an adaptive radiation process. While two species of clownfish are likely to have been described from hybrid specimens, the occurrence and effect of hybridisation on the clade diversification is yet unknown.

Results: We generate sequences of three mitochondrial genes to complete an existing dataset of nuclear sequences and document cytonuclear discordance at a node, which shows a drastic increase of diversification rate. Then, using a tree-based jack-knife method, we identify clownfish species likely stemming from hybridisation events. Finally, we use molecular cloning and identify the putative parental species of four clownfish specimens that display the morphological characteristics of hybrids.

Conclusions: Our results show that consistently with the syngameon hypothesis, hybridisation events are linked with a burst of diversification in the clownfishes. Moreover, several recently diverged clownfish lineages likely originated through hybridisation, which indicates that diversification, catalysed by hybridisation events, may still be happening.

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Related in: MedlinePlus

Homoplasy excess test. Panel (a) shows the distribution of the bootstrap support for each node which showed a homoplasy excess during the removal analysis. Each boxplot shows the  distribution of bootstrap values for the node and the red dot shows the bootstrap value of the node when the taxon of interest (name on the right) has been removed. Nodes names as given on the left correspond to that of panel (b) which shows the consensus tree of the nuclear phylogeny. There, nodes and taxa which showed up as outliers in the analysis have been coloured in orange. Species used as outgroup are shown in grey. The size of node labels has been altered to facilitate reading.
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Fig2: Homoplasy excess test. Panel (a) shows the distribution of the bootstrap support for each node which showed a homoplasy excess during the removal analysis. Each boxplot shows the distribution of bootstrap values for the node and the red dot shows the bootstrap value of the node when the taxon of interest (name on the right) has been removed. Nodes names as given on the left correspond to that of panel (b) which shows the consensus tree of the nuclear phylogeny. There, nodes and taxa which showed up as outliers in the analysis have been coloured in orange. Species used as outgroup are shown in grey. The size of node labels has been altered to facilitate reading.

Mentions: The two consensus phylogenetic trees that we obtain show an overall good support with only several recent splits showing low posterior probabilities (Figure 1). Major clades appear in both mitochondrial and nuclear phylogenetic trees. Despite the fact that the two datasets show well resolved topologies, the relative position of the main clades is different between the two analyses (Figure 1, see Additional files 1 and 2 for a complete illustration of node support). The organisation of the percula clade at the base of the clownfish tree and the position of A. latezonatus is congruent between the two datasets. However, the Australian group and A. chrysopterus intercalate between the polymnus and Indian groups in the nuclear dataset. We identify two mitochondrial lineages in A. sandaracinos with a posterior probability of 1, but both samples are clustered in the nuclear phylogenetic tree. The ephippium clade, which is the sister group of the clarkii clade in the nuclear phylogenetic tree, becomes sister to the Australian clade with the mitochondrial dataset. This suggest the existence of a hybridisation event at the time of node 8 (Figure 2). Other studies showed that a main upward shift in speciation rate occurred at this specific node [22,23].Figure 1


Hybridisation and diversification in the adaptive radiation of clownfishes.

Litsios G, Salamin N - BMC Evol. Biol. (2014)

Homoplasy excess test. Panel (a) shows the distribution of the bootstrap support for each node which showed a homoplasy excess during the removal analysis. Each boxplot shows the  distribution of bootstrap values for the node and the red dot shows the bootstrap value of the node when the taxon of interest (name on the right) has been removed. Nodes names as given on the left correspond to that of panel (b) which shows the consensus tree of the nuclear phylogeny. There, nodes and taxa which showed up as outliers in the analysis have been coloured in orange. Species used as outgroup are shown in grey. The size of node labels has been altered to facilitate reading.
© Copyright Policy - open-access
Related In: Results  -  Collection

License 1 - License 2
Show All Figures
getmorefigures.php?uid=PMC4264551&req=5

Fig2: Homoplasy excess test. Panel (a) shows the distribution of the bootstrap support for each node which showed a homoplasy excess during the removal analysis. Each boxplot shows the distribution of bootstrap values for the node and the red dot shows the bootstrap value of the node when the taxon of interest (name on the right) has been removed. Nodes names as given on the left correspond to that of panel (b) which shows the consensus tree of the nuclear phylogeny. There, nodes and taxa which showed up as outliers in the analysis have been coloured in orange. Species used as outgroup are shown in grey. The size of node labels has been altered to facilitate reading.
Mentions: The two consensus phylogenetic trees that we obtain show an overall good support with only several recent splits showing low posterior probabilities (Figure 1). Major clades appear in both mitochondrial and nuclear phylogenetic trees. Despite the fact that the two datasets show well resolved topologies, the relative position of the main clades is different between the two analyses (Figure 1, see Additional files 1 and 2 for a complete illustration of node support). The organisation of the percula clade at the base of the clownfish tree and the position of A. latezonatus is congruent between the two datasets. However, the Australian group and A. chrysopterus intercalate between the polymnus and Indian groups in the nuclear dataset. We identify two mitochondrial lineages in A. sandaracinos with a posterior probability of 1, but both samples are clustered in the nuclear phylogenetic tree. The ephippium clade, which is the sister group of the clarkii clade in the nuclear phylogenetic tree, becomes sister to the Australian clade with the mitochondrial dataset. This suggest the existence of a hybridisation event at the time of node 8 (Figure 2). Other studies showed that a main upward shift in speciation rate occurred at this specific node [22,23].Figure 1

Bottom Line: While two species of clownfish are likely to have been described from hybrid specimens, the occurrence and effect of hybridisation on the clade diversification is yet unknown.Our results show that consistently with the syngameon hypothesis, hybridisation events are linked with a burst of diversification in the clownfishes.Moreover, several recently diverged clownfish lineages likely originated through hybridisation, which indicates that diversification, catalysed by hybridisation events, may still be happening.

View Article: PubMed Central - PubMed

Affiliation: Department of Ecology and Evolution, Biophore, University of Lausanne, 1015, Lausanne, Switzerland. glenn.litsios@unil.ch.

ABSTRACT

Background: The importance of hybridisation during species diversification has long been debated among evolutionary biologists. It is increasingly recognised that hybridisation events occurred during the evolutionary history of numerous species, especially during the early stages of adaptive radiation. We study the effect of hybridisation on diversification in the clownfishes, a clade of coral reef fish that diversified through an adaptive radiation process. While two species of clownfish are likely to have been described from hybrid specimens, the occurrence and effect of hybridisation on the clade diversification is yet unknown.

Results: We generate sequences of three mitochondrial genes to complete an existing dataset of nuclear sequences and document cytonuclear discordance at a node, which shows a drastic increase of diversification rate. Then, using a tree-based jack-knife method, we identify clownfish species likely stemming from hybridisation events. Finally, we use molecular cloning and identify the putative parental species of four clownfish specimens that display the morphological characteristics of hybrids.

Conclusions: Our results show that consistently with the syngameon hypothesis, hybridisation events are linked with a burst of diversification in the clownfishes. Moreover, several recently diverged clownfish lineages likely originated through hybridisation, which indicates that diversification, catalysed by hybridisation events, may still be happening.

Show MeSH
Related in: MedlinePlus