Rare and widespread: Integrating Bayesian MCMC approaches, Sanger sequencing and Hyb-Seq phylogenomics to reconstruct the origin of the enigmatic Rand Flora genus Camptoloma

<p class="MsoCommentText">Premise</p> <p class="MsoCommentText">Genera that are widespread but have a geographically discontinuous distribution and are represented by few species are intriguing. Did they achieve their disjunct distribution recently, or is it ancient in origin? Why are they species-poor? The Rand Flora is a continental-scale floristic pattern in which closely related species appear co-distributed in isolated regions over the edges of Africa and nearby archipelagos. Genus <i>Camptoloma</i> (Scrophulariaceae) is the most notable example, comprising three species isolated from each other at the ends of the African continent: <i>C. canariense </i>in the west, endemic to the Canary Islands; <i>C. lyperiiflorum </i>in the east, endemic to the Horn of Africa - Southern Arabia; and <i>C. rotundifolia</i>, restricted to Southern Africa.</p> <p class="MsoCommentText">Methods</p> <p class="MsoCommentText">Here, we employed Sanger sequencing of nuclear and plastid markers, together with genomic target sequencing of 2190 low-copy nuclear genes, to infer interspecies relationships and the position of <i>Camptoloma</i> within Scrophulariaceae, using supermatrix and multispecies-coalescent approaches. Lineage divergence times and ancestral ranges were inferred with Bayesian MCMC approaches. Population history was estimated with phylogeographic structured coalescent methods.</p> <p class="MsoCommentText">Key Results</p> <p class="MsoCommentText">Our results support <i>C. rotundifolia</i> as sister to the disjunct clade formed by <i>C. canariense</i> and <i>C. lyperiiflorum.</i> Stem divergence was dated in the Late Miocene, while the origin of extant diversification within the genus was inferred as Early Pliocene.</p> <p class="MsoCommentText">Conclusions</p> <p>We show that the current disjunct distribution of <i>Camptoloma </i>across Africa was likely the result of fragmentation and extinction/population bottlenecking events associated to historical aridification cycles, consistent with the "climatic refugia" hypothesis.</p>