Divergence Time Estimation of Aloes and Allies (Xanthorrhoeaceae) Based on Three Marker Genes

Zeinab Khodaei,Ben-Erik Van Wyk,Michael Wink

doi:10.3390/d10030060

Zeinab Khodaei, Ben-Erik Van Wyk + Show 1 more

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https://doi.org/10.3390/d10030060

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Journal: Diversity	Publication Date: Jul 10, 2018
Citations: 2	License type: CC BY 4.0

Affiliation: Heidelberg University, University of Johannesburg

Abstract

Aloes and allies are prominent members of African succulent vegetation and especially of the highly diverse Cape Flora. The main goal of this study was to obtain age estimates for alooids by calibrating a Bayesian phylogenetic analysis based on two chloroplast markers (the trnL-trnF spacer region and rbcL gene) and one gene marker (ITS) using a relaxed molecular clock. Seventy four species from all succulent genera of alooids were analysed with MrBayes to infer species relationships. We discuss the age estimates to address the question whether vicariance or dispersal could account for the diversification of Madagascan alooids. In the combined maximum clade credibility tree obtained from BEAST the succulent alooids have split from asphodeloids around 51.8 Mya in Early Miocene. Divergence time age estimation for succulent drought resistant alooids (late Oligocene to early Miocene) correspond well with dates identified for several other plant lineages in southern Africa and does match with the start of dry period in Miocene which triggered speciation and evolutionary radiation of these genera and families. All climbing aloes and some tree aloes which were recently split into new genera are amongst the early diverged group in alooids and the crown node of this group diverged around 16.82 (15.5–22.4) Mya. The oldest node age estimation for aloes from Madagascar (5.1 Mya) is in early Pliocene and our findings support the hypothesis that the Africa-Madagascan divergence is best explained by oceanic long-distance dispersal rather than vicariance. This study is one of the first to give age estimates for clades of alooids in Xanthorrhoeaceae as a starting point for future studies on the historical biogeography of this family of succulent plants which are important for ethnomedicine, and as ornamental and horticultural plants.

Highlights

Alooids or the subfamily Alooideae sensu )Dahlgren, et al 1985
Phylogenetic trees reconstructed from plastid and nuclear data showed almost identical topologies; the cpDNA and ncDNA datasets were combined
A maximum likelihood (ML) phylogram is shown in Figure 1 and posterior probability values from MrBayes analysis and ML bootstrap numbers are provided at the nodes in this tree

Summary

Introduction

Alooids or the subfamily Alooideae sensu )Dahlgren, et al 1985 ([1] are a well-known group of southern African and Cape rosette leaf succulents (ca. 530 species) adapted to life in dry areas; some members of Aloe occur on the Arabian Peninsula, Madagascar and the Mascarene Islands. Alooids or the subfamily Alooideae sensu )Dahlgren, et al 1985 530 species) adapted to life in dry areas; some members of Aloe occur on the Arabian Peninsula, Madagascar and the Mascarene Islands. Aloe ferox is the source of anthraquinones, which are used in medicine as a laxative. Aloe vera is used as a laxative and as a gel used for wound-healing, and skin care (van Wyk and Wink, 2017) [3]. In Africa, harvested species of Aloe come from east and southern Africa. During the 1990s, exports of wild-harvested exudate (Aloe) from Kenya sometimes exceeded 80 tons per annum (Oldfield, 2004) [4]

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