Abstract Detail

Phylogenomics

Pokorny, Lisa [1], Johnson, Matthew [2], Gardner, Elliot [3], Olsson, Sanna [4], Riina, Ricarda [4], Wickett, Norm [3], Sanmartí­n, Isabel [4].

The evolutionary origins of the Rand Flora pattern in the Sweet Tabaiba (Euphorbia balsamifera): Hyb-Seq helps bridge the micro-macroevolutionary gap.

The Rand Flora is an enigmatic biogeographic pattern in which plant lineages from different families share a similar disjunct distribution across the continental margins of Africa and adjacent islands: Macaronesia-northwest Africa, Western African mountains, Horn of Africa-South Arabia, East Africa, and Southern Africa. First described in the XIX century by Swiss Botanist H. Christ, the pattern takes its name from the Germanic word “Rand”, aka “rim”, since Rand Flora lineages are confined to the margins of the continent by seemingly inhospitable areas (ecological barriers) such as the northern Sahara Desert and the tropical lowlands of Central Africa. One paradigmatic example of this disjunction is the Sweet Tabaiba, Euphorbia balsamifera (subgen. Athymalus sect. Balsamis) with three subspecies: balsamifera —found in NW Africa and the Canaries—, adenensis —from the Horn of Africa and Southern Arabia—, and sepium —from western Sahel. Several explanations have been proposed for this disjunction, ranging from vicariance of an Early Cenozoic macroflora by climate-driven extinction to long-distance dispersal events in more recent times, or other ecological factors. New molecular estimates of phylogenetic relationships and lineage divergence times have placed the origin of the disjunction around the Miocene-Pliocene coincident with periods of global drought. However, the traditional Sanger approach of sequencing a few selected plastid and nuclear markers failed to provide enough resolution at shallow phylogenetic levels, whereas the low number of taxa hampered the application of macroevolutionary models for testing the climate extinction vs. recent dispersal hypothesis. Here we explore the potential of Hyb-Seq to provide data for improved resolution at different phylogenetic scales, from species to populations and individuals. Hyb-Seq allows simultaneous collection of single-to-low-copy nuclear coding regions together with high copy un-enriched regions that can be used to address questions at both macro and microevolutionary levels. Using two Euphorbia transcriptomes (E. mesembryanthemifolia and E. pekinensis), and the Ricinus communis genome, we designed a 20K-probes kit targeting 431 exons. These were used to sequence Euphorbia sect. Balsamis and close relatives, with a focus on population-level sampling of all currently recognized subspecies of E. balsamifera. In addition to nuclear exons, the approach proved successful to recover introns and chloroplast sequences; the latter retrieved mapping off-target reads to an existing E. virgata (subgen. Esula) chloroplast. Bayesian and likelihood-based gene-species tree methods and statistical phylogeographic approaches were used to reconstruct phylogenetic relationships and explore hypotheses on the spatial and temporal origins of the disjunction.

Related Links:
Living on the edge: timing of Rand Flora disjunctions congruent with ongoing aridification in Africa

1 - Royal Botanic Gardens, Kew, Comparative Plant and Fungal Biology, Jodrell Laboratory, Richmond upon Thames, Surrey, TW9 3DS, UK
2 - Chicago Botanic Garden, Plant Sciences, 1000 Lake Cook Road, Glencoe, IL, 60626, United States
3 - Chicago Botanic Garden, Plant Science and Conservation, 1000 Lake Cook Road, Glencoe, IL, 60022, USA
4 - Real Jardí­n Botánico-CSIC, Biodiversity and Conservation Department, Plaza de Murillo 2, Madrid, 28014, Spain

Keywords:
Biogeography
Africa
phylogenomics
macroevolution
population genetics
hyb-seq
Euphorbia.

Presentation Type: Oral Paper
Session: 16, Phylogenomics II
Location: 202/Savannah International Trade and Convention Center
Date: Tuesday, August 2nd, 2016
Time: 10:00 AM
Number: 16008
Abstract ID:599
Candidate for Awards:Margaret Menzel Award