Abstract
Welwitschia mirabilis is one of the most extraordinary plant species on earth. With a fossil record of 112 My and phylogenetically isolated within the order Gnetales, the monotypic genus Welwitschia has survived only in the northern Namib Desert in Angola and Namibia. Despite its iconic role, the biogeography, ecological niche, and evolutionary history of the species remain poorly understood. Here we present the first comprehensive map of the strongly disjunct species range, and we explore the genetic relationships among all range fragments based on six SSR markers. We also assess the variation of the environmental niche and habitat preference. Our results confirm genetic divergence, which is consistent with the hypothetical existence of two subspecies within Welwitschia. We identify an efficient geographical barrier separating two gene pools at 18.7°S in northern Namibia. We also identify further diversification within each of the two subspecies, with several different gene pools in ten isolated range fragments. Given the presence of well-isolated populations with unique gene pools and the association with different bioclimatic variables, rock types, and habitats within arid river catchments, we can hypothesize that the present intraspecific diversity may have evolved at least in part within the present refuge of the northern Namib Desert.
Highlights
Welwitschia mirabilis is one of the most extraordinary plant species on earth
Our objectives are to (1) investigate genetic differentiation among the sample records from all range fragments in Angola and Namibia to determine whether they support the existence of two subspecies; (2) examine environmental differences among the geographic fragments; and (3) discuss the results that most obviously characterize the ecological niche of Welwitschia
We found aggregates of two large range fragments separated by gaps smaller than 30 km; the two in Angola (Tombua–Virei and Iona) are 309 km from the two in Namibia (Etendeka and Messum)
Summary
With a fossil record of 112 My and phylogenetically isolated within the order Gnetales, the monotypic genus Welwitschia has survived only in the northern Namib Desert in Angola and Namibia. Given the presence of well-isolated populations with unique gene pools and the association with different bioclimatic variables, rock types, and habitats within arid river catchments, we can hypothesize that the present intraspecific diversity may have evolved at least in part within the present refuge of the northern Namib Desert. The phylogeny, morphology, and ecology of Welwitschia mirabilis make it one of the most extraordinary plant species on Earth. The minimal gene flow between populations separated by as little as 18 km implies limited transport of the pollen and seeds This view is supported by Wetschnig and Depisch[10], who reported mainly insect pollination and almost no longer-distance transport by wind.
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