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Welwitschia: Phylogeography of a living fossil, diversified within a desert refuge.

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.

SUBMITTER: Jurgens N

PROVIDER: S-EPMC7840819 | biostudies-literature | 2021 Jan

REPOSITORIES: biostudies-literature

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Welwitschia: Phylogeography of a living fossil, diversified within a desert refuge.

Jürgens Norbert N Oncken Imke I Oldeland Jens J Gunter Felicitas F Rudolph Barbara B

Scientific reports 20210127 1

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 g ...[more]

PMID: 33504814

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Project description:Emerging data from the coelacanth genome are beginning to shed light on the origin and evolution of tetrapod genes and noncoding elements. Of particular relevance is the realization that coelacanth retains active copies of transposable elements that once served as raw material for the evolution of new functional sequences in the vertebrate lineage. Recognizing the evolutionary significance of coelacanth genome in this regard, we employed an ab initio search strategy to further classify its repetitive complement. This analysis uncovered a class of interspersed elements (Latimeria Harbinger 1-LatiHarb1) that is a major contributor to coelacanth genome structure and gene content (?1% to 4% or the genome). Sequence analyses indicate that 1) each ?8.7 kb LatiHarb1 element contains two coding regions, a transposase gene and a gene whose function is as yet unknown (MYB-like) and 2) copies of LatiHarb1 retain biological activity in the coelacanth genome. Functional analyses verify transcriptional and enhancer activities of LatiHarb1 in vivo and reveal transcriptional decoupling that could permit MYB-like genes to play functional roles not directly linked to transposition. Thus, LatiHarb1 represents the first known instance of a harbinger-superfamily transposon with contemporary activity in a vertebrate genome. Analyses of LatiHarb1 further corroborate the notion that exaptation of anciently active harbinger elements gave rise to at least two vertebrate genes (harbi1 and naif1) and indicate that the vertebrate gene tsnare1 also traces its ancestry to this transposon superfamily. Based on our analyses of LatiHarb1, we speculate that several functional features of harbinger elements may predispose the transposon superfamily toward recurrent exaptive evolution of cellular coding genes. In addition, these analyses further reinforce the broad utility of the coelacanth genome and other "outgroup" genomes in understanding the ancestry and evolution of vertebrate genes and genomes.

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Welwitschia: Phylogeography of a living fossil, diversified within a desert refuge.

Publications

Welwitschia: Phylogeography of a living fossil, diversified within a desert refuge.

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