ibclogo XVI International Botanical Congess


Abstract Number: 5176
Session = 13.1.2


EXPERIMENTAL AND HISTORICAL INVESTIGATIONS OF HYBRID SPECIATION


L. H. Rieseberg, Department of Biology, Indiana University, Bloomington, IN 47405, USA


The origin of new homoploid species via hybridization is theoretically difficult because it requires the development of reproductive isolation in sympatry. Nonetheless, considerable evidence for this mode of speciation has been compiled in several organismal groups, including wild sunflower species of the genus Helianthus. Here, I present data from genetic mapping studies of both experimental and natural hybrid sunflower species to evaluate the genetic processes that accompany or facilitate this mode of speciation. As predicted by theory, hybrid speciation appears to be promoted by rapid chromosomal evolution. Likewise, congruence observed between the genomes of experimentally synthesized hybrid lineages and an ancient hybrid species, H. anomalus, suggest that deterministic forces (i.e., selection) rather than chance largely govern hybrid genomic composition. Finally, as predicted by simulation studies and crossing experiments, this mode of speciation appears to be extremely rapid. In fact, comparison of the distribution of observed block sizes with theoretical expectations derived from R. A. FisherĘs theory of junctions suggest that H. anomalus arose in less than 60 generations.


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