Abstract Detail

Molecular Ecology and Evolution

Hawkins, Angela K. [1], Garza, Elyssa [1], Hawkins, W. Daryl [2], Pepper, Alan E. [1].

Transcriptome comparisons reveal signatures of selection, small population size, and reticulate evolution in the evolutionary history of Caulanthus amplexicaulis var. barbarae.

Serpentine outcrops are derived from ultramafic rock and usually have extremely low levels of essential plant nutrients (e.g. N, P, Ca), very high to toxic levels of heavy metals (e.g. Ni), and very poor water availability and retention. These outcrops provide habitat to many endemic plant species. Serpentine soils have long been considered an ideal model system for plant molecular ecology as they offer an extreme example of adaptation to environment. Caulanthus amplexicaulis var. barbarae (J. Howell) Munz (CAB) is a wild relative of Arabidopsis thaliana (L.) Heynh, and is endemic to serpentine outcrops. Its sister species, C. amplexicaulis var. amplexicaulis S. Watson (CAA), is more wide-spread, found predominately found on granite soils and, in reciprocal growth experiments, has shown 100% mortality when grown in serpentine-like conditions. As a rare endemic species, CAB population clusters are very small, several with fewer than ten reproductive individuals have been observed over multiple years. Therefore, all evolutionary studies must consider both selective and non-selective processes such as genetic drift. Normalized transcriptome libraries of both taxa were sequenced, assembled, and rigorously annotated. PAML was used to calculate dN, dS, and dN/dS ratios between CAA and CAB tentative ortholog pairs (TOPs) to assign categories (purifying, stabilizing, or neutral) of selection. Blast2Go was implemented to assign GO terms for TOPs and enrichment analyses were performed to identify terms found more frequently than expected among high dN/dS loci. The relative timing of divergence between CAA and CAB was estimated for all genomic compartments using BEAST. Finally, gene duplication history was assessed using a Blastall approach to detect paralogs. Together with data obtained from the draft genome assemblies of both taxa, (see poster by Garza et al.,) we have identified a set of plausible candidate loci that may play roles in serpentine tolerance and endemism.

1 - Texas A&M University, Department of Biology, 100 Butler Hall, 3258 TAMUS, College Station, TX, 77843-3258, USA
2 - Texas A&M University, Department of Nuclear Engineering, AI Engineering Building, 3133 TAMU, College Station, TX, 77843-3133, USA

Keywords:
Brassicaceae
Caulanthus
endemism
selection
Serpentine
Transcriptome.

Presentation Type: Oral Paper
Session: 40, Molecular Ecology and Evolution
Location: 102/Savannah International Trade and Convention Center
Date: Wednesday, August 3rd, 2016
Time: 11:15 AM
Number: 40012
Abstract ID:756
Candidate for Awards:Margaret Menzel Award