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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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Distribution map of Macowania and Arrowsmithia. Clade A species are indicated by black symbols, clade B species by white symbols. The dotted line represents the Escarpment edge. The disjunct distributions of M. abyssinica and M. ericifolia in the East African highlands and Yemen are indicated at the top right of the figure. Insets of selected parts of the distribution in South Africa are provided for small areas that house multiple species.
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Figure 1: Distribution map of Macowania and Arrowsmithia. Clade A species are indicated by black symbols, clade B species by white symbols. The dotted line represents the Escarpment edge. The disjunct distributions of M. abyssinica and M. ericifolia in the East African highlands and Yemen are indicated at the top right of the figure. Insets of selected parts of the distribution in South Africa are provided for small areas that house multiple species.

Mentions: In southern Africa, Pliocene tectonic uplift played a major role in creating the geomorphically diverse Drakensberg (‘Dragon’s Mountain’) range[11-14]. The Drakensberg constitutes the higher, eastern façade of the central plateau (‘the Great Escarpment’) of South Africa (Figure 1). In terms of both height and endemic plant diversity, the Drakensberg is more modest than the Andes, with a maximum altitude of 3,482 m and the core area hosting ca 2,520 species or subspecies of flowering plants, of which 16% are endemic[15]. Nevertheless, the Drakensberg region is one of three centres of Afrotemperate endemism, and appears to have been an important link between the centre in the Ethiopian highlands and that in the highly diverse Cape region with dispersal in both directions resulting from, and possibly facilitating, floristic radiations (e.g. northwards after radiation: Disa, Irideae, Pentachistis, Restionaceae[16]; southwards: Scabiosa[17]; Erica[18]). Within the mega-diverse southern African subregion, the Drakensberg constitutes the highest-lying land and the only true alpine habitat[19,20]. The endemic Drakensberg flora is thus directly or indirectly a product of the tectonic processes that created these high-altitude habitats.


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)

Distribution map of Macowania and Arrowsmithia. Clade A species are indicated by black symbols, clade B species by white symbols. The dotted line represents the Escarpment edge. The disjunct distributions of M. abyssinica and M. ericifolia in the East African highlands and Yemen are indicated at the top right of the figure. Insets of selected parts of the distribution in South Africa are provided for small areas that house multiple species.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

Figure 1: Distribution map of Macowania and Arrowsmithia. Clade A species are indicated by black symbols, clade B species by white symbols. The dotted line represents the Escarpment edge. The disjunct distributions of M. abyssinica and M. ericifolia in the East African highlands and Yemen are indicated at the top right of the figure. Insets of selected parts of the distribution in South Africa are provided for small areas that house multiple species.
Mentions: In southern Africa, Pliocene tectonic uplift played a major role in creating the geomorphically diverse Drakensberg (‘Dragon’s Mountain’) range[11-14]. The Drakensberg constitutes the higher, eastern façade of the central plateau (‘the Great Escarpment’) of South Africa (Figure 1). In terms of both height and endemic plant diversity, the Drakensberg is more modest than the Andes, with a maximum altitude of 3,482 m and the core area hosting ca 2,520 species or subspecies of flowering plants, of which 16% are endemic[15]. Nevertheless, the Drakensberg region is one of three centres of Afrotemperate endemism, and appears to have been an important link between the centre in the Ethiopian highlands and that in the highly diverse Cape region with dispersal in both directions resulting from, and possibly facilitating, floristic radiations (e.g. northwards after radiation: Disa, Irideae, Pentachistis, Restionaceae[16]; southwards: Scabiosa[17]; Erica[18]). Within the mega-diverse southern African subregion, the Drakensberg constitutes the highest-lying land and the only true alpine habitat[19,20]. The endemic Drakensberg flora is thus directly or indirectly a product of the tectonic processes that created these high-altitude habitats.

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