Diversification into novel habitats in the Africa clade of Dioscorea (Dioscoreaceae): erect habit and elephant’s foot tubers
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2016-11-08
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BMC Evolutionary Biology
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BioMed Central
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University of Cape Town
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Abstract
Background: Dioscorea is a widely distributed and highly diversified genus in tropical regions where it is represented
by ten main clades, one of which diversified exclusively in Africa. In southern Africa it is characterised by a distinct
group of species with a pachycaul or “elephant’s foot” structure that is partially to fully exposed above the substrate.
In contrast to African representatives of the genus from other clades, occurring mainly in forest or woodland, the
pachycaul taxa and their southern African relatives occur in diverse habitats ranging from woodland to open
vegetation. Here we investigate patterns of diversification in the African clade, time of transition from forest to
more open habitat, and morphological traits associated with each habitat and evaluate if such transitions have
led to modification of reproductive organs and mode of dispersal.
Results: The Africa clade originated in the Oligocene and comprises four subclades. The Dioscorea buchananii
subclade (southeastern tropical Africa and South Africa) is sister to the East African subclade, which is respectively
sister to the recently evolved sister South African (e. g., Cape and Pachycaul) subclades. The Cape and Pachycaul
subclades diversified in the east of the Cape Peninsula in the mid Miocene, in an area with complex geomorphology
and climate, where the fynbos, thicket, succulent karoo and forest biomes meet.
Conclusions: Diversification out of forest is associated with major shifts in morphology of the perennial tuber
(specifically an increase in size and orientation which presumably led them to become pachycaul) and rotation of
stem (from twining to non-twining). The iconic elephant's foot morphology, observed in grasslands and thicket
biomes, where its corky bark may offer protection against fire and herbivory, evolved since mid Miocene. A shift
in pollination trait is observed within the forest, but entry into open habitat does not show association with
reproductive morphology, except in the seed wing, which has switched from winged all round the seed margin
to just at the base or at the apex of it, or has been even replaced by an elaiosome.
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Reference:
Maurin, O., Muasya, A. M. Catalan, P., Shongwe, E. Z., Viruel, J., Wilkin, P., & van der Bank, M. (2016). Diversification into novel habitats in the Africa clade of Dioscorea (Dioscoreaceae): erect habit and elephant's foot tubers. BMC Evolutionary Biology. 2016 Nov 08;16(1), 238.