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Erosive processes after tectonic uplift stimulate vicariant and adaptive speciation: evolution in an Afrotemperate-endemic paper daisy genus.

Bentley J, Verboom GA, Bergh NG - BMC Evol. Biol. (2014)

Bottom Line: Between sister species pairs we expect high morphological divergence where speciation has happened in sympatry (adaptive) while with geographic (vicariant) speciation we may expect to find less morphological divergence and a greater degree of allopatry.The other subclade occupies a greater variety of habitats and exhibits far greater morphological differentiation, but contains species with overlapping distribution ranges.The greater relative morphological divergence in sympatric species of Macowania indicates that speciation in the non-sympatric taxa may not have required obvious adaptive differences, implying that simple geographic isolation was the driving force for speciation ('neutral speciation').

View Article: PubMed Central - HTML - PubMed

Affiliation: University of Cape Town, Cape Town, South Africa. bntjoa002@myuct.ac.za.

ABSTRACT

Background: The role of tectonic uplift in stimulating speciation in South Africa's only alpine zone, the Drakensberg, has not been explicitly examined. Tectonic processes may influence speciation both through the creation of novel habitats and by physically isolating plant populations. We use the Afrotemperate endemic daisy genus Macowania to explore the timing and mode (geographic versus adaptive) of speciation in this region. Between sister species pairs we expect high morphological divergence where speciation has happened in sympatry (adaptive) while with geographic (vicariant) speciation we may expect to find less morphological divergence and a greater degree of allopatry. A dated molecular phylogenetic hypothesis for Macowania elucidates species' relationships and is used to address the potential impact of uplift on diversification. Morphological divergence of a small sample of reproductive and vegetative characters, used as a proxy for adaptive divergence, is measured against species' range distributions to estimate mode of speciation across two subclades in the genus.

Results: The Macowania crown age is consistent with the hypothesis of post-uplift diversification, and we find evidence for both vicariant and adaptive speciation between the two subclades within Macowania. Both subclades exhibit strong signals of range allopatry, suggesting that geographic isolation was important in speciation. One subclade, associated with dry, rocky environments at high altitudes, shows very little morphological and ecological differentiation but high range allopatry. The other subclade occupies a greater variety of habitats and exhibits far greater morphological differentiation, but contains species with overlapping distribution ranges.

Conclusions: Species in Macowania are likely to have diversified in response to tectonic uplift, and we invoke uplift and uplift-mediated erosion as the main drivers of speciation. The greater relative morphological divergence in sympatric species of Macowania indicates that speciation in the non-sympatric taxa may not have required obvious adaptive differences, implying that simple geographic isolation was the driving force for speciation ('neutral speciation').

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Separate nuclear (combined ITS and ETS) and plastid (combined trnT-trnL and psbA-trnH) 75% majority-rule consensus parsimony topologies from PAUP. Bootstrap values are indicated above the branches. Node ‘X’ and node ‘Y’ in the nuclear tree are referred to in the text. Multiple accessions of each species are distinguished by lower-case letters after the species name (see Table 1). Gnaphalieae outgroup specimens Galeomma and Ifloga have been trimmed from the tree.
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Figure 3: Separate nuclear (combined ITS and ETS) and plastid (combined trnT-trnL and psbA-trnH) 75% majority-rule consensus parsimony topologies from PAUP. Bootstrap values are indicated above the branches. Node ‘X’ and node ‘Y’ in the nuclear tree are referred to in the text. Multiple accessions of each species are distinguished by lower-case letters after the species name (see Table 1). Gnaphalieae outgroup specimens Galeomma and Ifloga have been trimmed from the tree.

Mentions: The two nuclear regions (ETS & ITS) produced completely congruent trees, and so were combined to form a single nuclear matrix consisting of 47 accessions and 1,092 aligned nucleotides, of which 433 (40%) characters were parsimony-informative (Figure 3). Similarly, the two plastid regions (trnT-L and psbA-F) yielded poorly-resolved but congruent trees, and were combined to form a matrix consisting of 1,051 characters, of which 104 (10%) were parsimony-informative (Figure 3). Both the plastid and the nuclear gene trees independently recover Macowania as part of a clade containing the Relhania group of genera (represented here by Relhania, Oedera and Comborhiza). While the plastid topology neither rejects nor confirms the monophyly of Macowania, the nuclear gene tree resolves a clade comprising most species of Macowania (Node X; bootstrap percentage (BS) = 100) and including Arrowsmithia. Within this clade, a group of Macowania species form a strongly supported subclade (Node Y; BS = 99). Multiple accessions of species were always recovered as monophyletic in the nuclear ribosomal tree, while only those from Arrowsmithia and M. pinifolia grouped together at the 75% BS level in the plastid tree. Conflict between nuclear and plastid partitions is observed only with regard to the placement of the outgroup taxa Leysera leyseroides and Rhynchopsidium sessiliflorum. Since relationships amongst the ingroup taxa showed no conflict, all genetic partitions were concatenated into a single matrix and analysed in combination.


Erosive processes after tectonic uplift stimulate vicariant and adaptive speciation: evolution in an Afrotemperate-endemic paper daisy genus.

Bentley J, Verboom GA, Bergh NG - BMC Evol. Biol. (2014)

Separate nuclear (combined ITS and ETS) and plastid (combined trnT-trnL and psbA-trnH) 75% majority-rule consensus parsimony topologies from PAUP. Bootstrap values are indicated above the branches. Node ‘X’ and node ‘Y’ in the nuclear tree are referred to in the text. Multiple accessions of each species are distinguished by lower-case letters after the species name (see Table 1). Gnaphalieae outgroup specimens Galeomma and Ifloga have been trimmed from the tree.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3927823&req=5

Figure 3: Separate nuclear (combined ITS and ETS) and plastid (combined trnT-trnL and psbA-trnH) 75% majority-rule consensus parsimony topologies from PAUP. Bootstrap values are indicated above the branches. Node ‘X’ and node ‘Y’ in the nuclear tree are referred to in the text. Multiple accessions of each species are distinguished by lower-case letters after the species name (see Table 1). Gnaphalieae outgroup specimens Galeomma and Ifloga have been trimmed from the tree.
Mentions: The two nuclear regions (ETS & ITS) produced completely congruent trees, and so were combined to form a single nuclear matrix consisting of 47 accessions and 1,092 aligned nucleotides, of which 433 (40%) characters were parsimony-informative (Figure 3). Similarly, the two plastid regions (trnT-L and psbA-F) yielded poorly-resolved but congruent trees, and were combined to form a matrix consisting of 1,051 characters, of which 104 (10%) were parsimony-informative (Figure 3). Both the plastid and the nuclear gene trees independently recover Macowania as part of a clade containing the Relhania group of genera (represented here by Relhania, Oedera and Comborhiza). While the plastid topology neither rejects nor confirms the monophyly of Macowania, the nuclear gene tree resolves a clade comprising most species of Macowania (Node X; bootstrap percentage (BS) = 100) and including Arrowsmithia. Within this clade, a group of Macowania species form a strongly supported subclade (Node Y; BS = 99). Multiple accessions of species were always recovered as monophyletic in the nuclear ribosomal tree, while only those from Arrowsmithia and M. pinifolia grouped together at the 75% BS level in the plastid tree. Conflict between nuclear and plastid partitions is observed only with regard to the placement of the outgroup taxa Leysera leyseroides and Rhynchopsidium sessiliflorum. Since relationships amongst the ingroup taxa showed no conflict, all genetic partitions were concatenated into a single matrix and analysed in combination.

Bottom Line: Between sister species pairs we expect high morphological divergence where speciation has happened in sympatry (adaptive) while with geographic (vicariant) speciation we may expect to find less morphological divergence and a greater degree of allopatry.The other subclade occupies a greater variety of habitats and exhibits far greater morphological differentiation, but contains species with overlapping distribution ranges.The greater relative morphological divergence in sympatric species of Macowania indicates that speciation in the non-sympatric taxa may not have required obvious adaptive differences, implying that simple geographic isolation was the driving force for speciation ('neutral speciation').

View Article: PubMed Central - HTML - PubMed

Affiliation: University of Cape Town, Cape Town, South Africa. bntjoa002@myuct.ac.za.

ABSTRACT

Background: The role of tectonic uplift in stimulating speciation in South Africa's only alpine zone, the Drakensberg, has not been explicitly examined. Tectonic processes may influence speciation both through the creation of novel habitats and by physically isolating plant populations. We use the Afrotemperate endemic daisy genus Macowania to explore the timing and mode (geographic versus adaptive) of speciation in this region. Between sister species pairs we expect high morphological divergence where speciation has happened in sympatry (adaptive) while with geographic (vicariant) speciation we may expect to find less morphological divergence and a greater degree of allopatry. A dated molecular phylogenetic hypothesis for Macowania elucidates species' relationships and is used to address the potential impact of uplift on diversification. Morphological divergence of a small sample of reproductive and vegetative characters, used as a proxy for adaptive divergence, is measured against species' range distributions to estimate mode of speciation across two subclades in the genus.

Results: The Macowania crown age is consistent with the hypothesis of post-uplift diversification, and we find evidence for both vicariant and adaptive speciation between the two subclades within Macowania. Both subclades exhibit strong signals of range allopatry, suggesting that geographic isolation was important in speciation. One subclade, associated with dry, rocky environments at high altitudes, shows very little morphological and ecological differentiation but high range allopatry. The other subclade occupies a greater variety of habitats and exhibits far greater morphological differentiation, but contains species with overlapping distribution ranges.

Conclusions: Species in Macowania are likely to have diversified in response to tectonic uplift, and we invoke uplift and uplift-mediated erosion as the main drivers of speciation. The greater relative morphological divergence in sympatric species of Macowania indicates that speciation in the non-sympatric taxa may not have required obvious adaptive differences, implying that simple geographic isolation was the driving force for speciation ('neutral speciation').

Show MeSH
Related in: MedlinePlus