Limits...
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').

Show MeSH

Related in: MedlinePlus

Combined nuclear (ITS and ETS) and plastid (trnT-trnL and psbA-trnH) 50% majority-rule consensus Bayesian tree from the MrBayes analysis. Nodes supported by either parsimony bootstrap (≥75%) or both Bayesian posterior probability (≥0.95) and BEAST posterior probability (≥0.95) are indicated with * above the relevant node. Note that node G is supported by Bayesian PP but not by BEAST PP). The support values for individual nodes A – G are reported in the text. Multiple accessions of each species are distinguished by lower-case letters after the species name (see Table 1). All species occur in South Africa or Lesotho (see Figure 1) except those with upper-case letters after the species: NAM (Namibia), NA (North Africa and/or Mediterranean and surrounds), EA (East Africa and Yemen). Gnaphalieae outgroup specimens Galeomma and Ifloga have been trimmed from the tree.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
getmorefigures.php?uid=PMC3927823&req=5

Figure 4: Combined nuclear (ITS and ETS) and plastid (trnT-trnL and psbA-trnH) 50% majority-rule consensus Bayesian tree from the MrBayes analysis. Nodes supported by either parsimony bootstrap (≥75%) or both Bayesian posterior probability (≥0.95) and BEAST posterior probability (≥0.95) are indicated with * above the relevant node. Note that node G is supported by Bayesian PP but not by BEAST PP). The support values for individual nodes A – G are reported in the text. Multiple accessions of each species are distinguished by lower-case letters after the species name (see Table 1). All species occur in South Africa or Lesotho (see Figure 1) except those with upper-case letters after the species: NAM (Namibia), NA (North Africa and/or Mediterranean and surrounds), EA (East Africa and Yemen). Gnaphalieae outgroup specimens Galeomma and Ifloga have been trimmed from the tree.

Mentions: The combined plastid and nuclear tree is well-resolved with a topology that closely resembles the individual nuclear topology (Figure 4), with no observed decrease in support values upon the inclusion of taxa sampled for only nuclear or plastid data. While the monophyly of the Relhania clade sensu Bergh & Linder[43] is supported (Node E; MrBayes posterior probability (PP) = 1.0, BS = 100; hereafter referred to as the “Relhania clade sensu lato”), the strength of this result is compromised by the rather limited outgroup sampling. The monophyly of the Relhania clade sensu lato has, however, been verified in other studies with more extensive outgroup sampling[43,44]. There is also support for a clade consisting of Macowania, Arrowsmithia, Relhania, Oedera, Leysera, Rhynchopsidium, Comborhiza and Rosenia (henceforth named “Relhania clade sensu stricto”: Node F; PP = 1.0, BS = 100). Within the Relhania clade sensu stricto, M. pinifolia is placed as sister to a clade also comprising Relhania, Oedera, Leysera and relatives which is resolved as sister to the rest of Macowania. The placement of Macowania pinifolia in this position, however, lacks bootstrap support (Node G; PP = 0.97, BS < 75). Though the position of the East African species within Macowania is unsupported, these are nevertheless confirmed as most closely-related to Macowania than to any other genus (their inclusion in the genus has also been confirmed by bootstrap, Bayesian and BEAST PP support in a subsequent analysis where near-complete sampling with multiple species accessions of the Relhania clade sensu lato and additional outgroups has been carried out by Bentley et al. unpubl. data). The South African members of Macowania are monophyletic (Node C; PP = 1.0, BS = 100) subject to the inclusion of A. styphelioides. Within this ‘core’ Macowania clade, there is good support for two principal subclades, A and B. Clade B, which lacks support in the separate analyses, comprises M. revoluta (the type species), M. hamata, M. corymbosa and A. styphelioides (PP = 1.0, BS = 97), while clade A (PP = 1.0, BS = 90), which was also recovered in the nuclear gene tree, comprises M. tenuifolia, M. glandulosa, M. pulvinaris, M. deflexa, M. sororis and M. conferta. The species relationships within clade A are largely unresolved, but there is good support (PP = 1.0, BS = 99) for a subclade containing M. conferta, M. deflexa and M. sororis. The monophyly of multiple accessions of each species in our tree is well-supported, with the exception of M. pulvinaris whose monophyly is not, however, contradicted.


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)

Combined nuclear (ITS and ETS) and plastid (trnT-trnL and psbA-trnH) 50% majority-rule consensus Bayesian tree from the MrBayes analysis. Nodes supported by either parsimony bootstrap (≥75%) or both Bayesian posterior probability (≥0.95) and BEAST posterior probability (≥0.95) are indicated with * above the relevant node. Note that node G is supported by Bayesian PP but not by BEAST PP). The support values for individual nodes A – G are reported in the text. Multiple accessions of each species are distinguished by lower-case letters after the species name (see Table 1). All species occur in South Africa or Lesotho (see Figure 1) except those with upper-case letters after the species: NAM (Namibia), NA (North Africa and/or Mediterranean and surrounds), EA (East Africa and Yemen). 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 4: Combined nuclear (ITS and ETS) and plastid (trnT-trnL and psbA-trnH) 50% majority-rule consensus Bayesian tree from the MrBayes analysis. Nodes supported by either parsimony bootstrap (≥75%) or both Bayesian posterior probability (≥0.95) and BEAST posterior probability (≥0.95) are indicated with * above the relevant node. Note that node G is supported by Bayesian PP but not by BEAST PP). The support values for individual nodes A – G are reported in the text. Multiple accessions of each species are distinguished by lower-case letters after the species name (see Table 1). All species occur in South Africa or Lesotho (see Figure 1) except those with upper-case letters after the species: NAM (Namibia), NA (North Africa and/or Mediterranean and surrounds), EA (East Africa and Yemen). Gnaphalieae outgroup specimens Galeomma and Ifloga have been trimmed from the tree.
Mentions: The combined plastid and nuclear tree is well-resolved with a topology that closely resembles the individual nuclear topology (Figure 4), with no observed decrease in support values upon the inclusion of taxa sampled for only nuclear or plastid data. While the monophyly of the Relhania clade sensu Bergh & Linder[43] is supported (Node E; MrBayes posterior probability (PP) = 1.0, BS = 100; hereafter referred to as the “Relhania clade sensu lato”), the strength of this result is compromised by the rather limited outgroup sampling. The monophyly of the Relhania clade sensu lato has, however, been verified in other studies with more extensive outgroup sampling[43,44]. There is also support for a clade consisting of Macowania, Arrowsmithia, Relhania, Oedera, Leysera, Rhynchopsidium, Comborhiza and Rosenia (henceforth named “Relhania clade sensu stricto”: Node F; PP = 1.0, BS = 100). Within the Relhania clade sensu stricto, M. pinifolia is placed as sister to a clade also comprising Relhania, Oedera, Leysera and relatives which is resolved as sister to the rest of Macowania. The placement of Macowania pinifolia in this position, however, lacks bootstrap support (Node G; PP = 0.97, BS < 75). Though the position of the East African species within Macowania is unsupported, these are nevertheless confirmed as most closely-related to Macowania than to any other genus (their inclusion in the genus has also been confirmed by bootstrap, Bayesian and BEAST PP support in a subsequent analysis where near-complete sampling with multiple species accessions of the Relhania clade sensu lato and additional outgroups has been carried out by Bentley et al. unpubl. data). The South African members of Macowania are monophyletic (Node C; PP = 1.0, BS = 100) subject to the inclusion of A. styphelioides. Within this ‘core’ Macowania clade, there is good support for two principal subclades, A and B. Clade B, which lacks support in the separate analyses, comprises M. revoluta (the type species), M. hamata, M. corymbosa and A. styphelioides (PP = 1.0, BS = 97), while clade A (PP = 1.0, BS = 90), which was also recovered in the nuclear gene tree, comprises M. tenuifolia, M. glandulosa, M. pulvinaris, M. deflexa, M. sororis and M. conferta. The species relationships within clade A are largely unresolved, but there is good support (PP = 1.0, BS = 99) for a subclade containing M. conferta, M. deflexa and M. sororis. The monophyly of multiple accessions of each species in our tree is well-supported, with the exception of M. pulvinaris whose monophyly is not, however, contradicted.

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