Presentation Detail

Speciation

Twyford, Alex [1], Kidner, Catherine [2], Ennos, Richard [3].

Endless forms most beautiful: population processes and the origin of diversity in Begonia.

The Neotropics is the most species-rich region on Earth, harbouring over 90 000 species of flowering plants. Many Neotropical plant lineages are characterized by recent rapid speciation events,with little known about the processes promoting diversification. Here we use the species-rich Neotropical clade of Begonia (650 species) to study processes affecting diversification acting at the level of individual genes, populations, and species. In particular we assess whether dispersal limitation and strong genetic drift have driven the rapid evolution of reproductive isolation, which may be responsible for the high number of endemic species present in the clade.
Plastid and nuclear microsatellites were developed from next-generation sequencing data to measure levels of intraspecific genetic differentiation. Markers were scored in populations of two widespread Begonia species(B. heracleifolia and B. nelumbiifolia) across Mexico,selected for their contrasting habitat preferences. We combined assessments of genetic structure at neutral loci, fertility of interpopulation crosses, and genome size variation, to test for early evidence of reproductive isolation within species. We then analysed replicate hybrid swarms to test the strength of reproductive isolation between species in the field. Quantitative trait locus (QTL) mapping in a related species pair was used to test the number of genomic regions responsible for trait differences.
Begonia nelumbiifolia showed strong substructure at nuclear loci, with no polymorphisms at plastid loci, suggesting a selective sweep or population bottleneck. We found strong population substructure for both nuclear and plastid loci in B. heracleifolia, and a genetically divergent population from southern Oaxaca possessed a significantly greater genome size than the species mean. Interpopulation crosses with this genotype had a reduced fertility. At the species level, hybrid zones between B. heracleifolia and B. nelumbiifolia include only the F1 generation. In a related species pair, we find single QTL of major effect for some important reproductive traits, such as stamen number.Our results provide evidence that genetic drift acts strongly in isolated Begonia populations,allowing divergence on a trajectory towards speciation. Reproductive barriers appear to evolve rapidly within species, and sister-species comparisons in hybrid swarms confirm the resultant strength of reproductive isolation. The rapid evolution of reproductive isolation may be enabled by key traits having a simple genetic architecture. Overall, these data give a first indication of the mechanisms underlying diversification in a group of Neotropical herbs, and show the importance of population processes on patterns of species diversity.

1 - Syracuse University, Life Sciences, 107 College Place, Room 110, Syracuse, NY, 13224, USA
2 - Royal Botanic Garden Edinburgh, Tropical Diversity, 20A Inverleith Row, Edinburgh, EH35LR, UK
3 - University of Edinburgh, Institute of Evolutionary Biology, Ashworth Building, King's Buildings, Edinburgh, EH9 3JT, UK

Keywords:
Speciation
tropical diversity
Differentiation
population genetics
begonia
reproductive isolation.

Presentation Type: Regular Oral Presentation
Session: 98
Location: Cotton C/Snowbird Center
Date: Monday, June 24th, 2013
Time: 9:00 AM
Number: 98003
Abstract ID:837
Candidate for Awards:W.D. Hamilton Award for Outstanding Student Presentation