The Cape element in the Afrotemperate flora: from Cape to Cairo?

Abstract

The build-up of biodiversity is the result of immigration and in situ speciation. We investigate these two processes for four lineages (Disa, Irideae p.p., the Pentaschistis clade and Restionaceae) that are widespread in the Afrotemperate flora. These four lineages may be representative of the numerous clades which are species rich in the Cape and also occur in the highlands of tropical Africa. It is as yet unclear in which direction the lineages spread. Three hypotheses have been proposed: (i) a tropical origin with a southward migration towards the Cape, (ii) a Cape origin with a northward migration into tropical Africa, and (iii) vicariance. None of these hypotheses has been thoroughly tested. We reconstruct the historical biogeography of the four lineages using likelihood optimization onto molecular phylogenies. We find that tropical taxa are nested within a predominantly Cape clade. There is unidirectional migration from the Cape into the Drakensberg and from there northwards into tropical Africa. The amount of in situ diversification differs between areas and clades. Dating estimates show that the migration into tropical East Africa has occurred in the last 17 Myr, consistent with the Mio-Pliocene formation of the mountains in this area.

Frequent colonization and little in situ speciation in Senecio in the tropical alpine‐like islands of eastern Africa

“…Th e area of origin of Senecio is WSA ( Kandziora et al, 2016 ), and based on our phylogeny, most colonizations of alpine-like regions of EA by Senecio seem to have occurred from the montane Drakensberg region, either directly or aft er establishment in montane regions of EA ( Table 4 ). Overall, there is increasing support for a substantial contribution of southern Africa, especially the Drakensberg region, to the afroalpine fl ora ( Galley and Linder, 2006 ;Galley et al, 2007 ;Devos et al, 2010 ;Ahmed, 2013 ;Galbany-Casals et al, 2014 ). Although the importance of northern hemispheric relationships of the tropical afroalpine fl ora had been emphasized by Linder (2014) , our results support the Cape to Cairo migration hypothesis of a recent northward migration from SA via the Drakensberg region to the tropical Afroalpine ( Linder, 1994 ;Galley et al, 2007 ).…”

“…One possible scenario is that a Palearctic lineage gave rise to tropical afroalpine species in the doria subclade, a pattern that has been found before for otherwise predominantly northern temperate groups Gehrke et al, 2008 ;Gehrke and Linder, 2009 ;Pimentel et al, 2013 ). Th e other is that there was one colonization from ESA to the Palearctic via EA by a mrca of the doria clade as hypothesized but never unambiguously demonstrated for other disjunct northern temperate/Mediterranean-SA genera ( Galley et al, 2007 ;Devos et al, 2010 ;Galbany-Casals et al, 2014 ;Kandziora et al, 2016 ). In this latter alternative, the tropical Afroalpine would have been source area of a Palearctic lineage.…”

“…and Ranunculus ; Knox and Palmer, 1995 ;Devos et al, 2010 ;Gehrke and Linder, 2011 ;Gehrke et al, 2015 ], but in situ speciation seems to be generally low, especially in genera that colonized the area several times ( Arabis alpina L., Moraea Mill. and Helichrysum ; Assefa et al, 2007 ;Galley et al, 2007 ;Galbany-Casals et al, 2014 ). Altogether, the EA tropical Afroalpine contains about 191 genera and 521 species.…”

“…Th e affi nity of the tropical afroalpine fl ora to other temperate fl oras has been noted ever since research on the region was conducted ( Engler, 1904 ;Hedberg, 1965 ;Goldblatt, 1978 ;Killick, 1978 ;Smith and Cleef, 1988 ;Rundel et al, 1994 ), and such affi nity has been confi rmed by the few phylogenetic analyses available Galley et al, 2007 ;Popp et al, 2008 ;Bergh and Linder, 2009 ;Gehrke and Linder, 2009 ;Galbany-Casals et al, 2014 ). Considering the probable predominance of macroecological niche conservatism ( Wiens, 2004 ;Donoghue, 2008 ), dispersal from temperate regions seems more likely than adaptive evolution of lineages from surrounding tropical regions.…”

Gourds afloat: a dated phylogeny reveals an Asian origin of the gourd family (Cucurbitaceae) and numerous oversea dispersal events

“…Molecular clock analyses suggest that the majority of lineages of legumes that occur on islands are younger than 30 Myr (Lavin & Beyra Matos 2008) and that plant diaspores from source areas hundreds or thousands of kilometres away regularly reach isolated Arctic islands (Alsos et al 2007), island-like mountains in Eastern Africa and mountain ranges in the Northern Cape, South Africa (Galley et al 2007). Striking dispersal events have also been documented for the flora of Hawaii ( Wagner et al 1990), the montane region of New Zealand ( Winkworth et al 2005) and many other island systems.…”