Abstract Detail

Hybrids and Hybridization

Mitchell, Nora [1], Rieseberg, Loren [2], Owens, Gregory [3], Whitney, Kenneth [1].

Hybridization speeds adaptation in Texas sunflowers: insights from field experimental evolution.

Natural hybridization has been associated with speciation, adaptive diversification, and range expansion in plants, but its effect on the speed at which microevolution occurs largely remains to be determined. Using a multi-generation field experiment, we experimentally test whether hybridization can speed adaptive evolution.       There are numerous instances where hybridization has resulted in adaption in North American sunflowers (Helianthus, Asteraceae). Contact between the widespread annual species Helianthus annuus and more geographically restricted Helianthus species has produced the hybrid subspecies H. annuus ssp. texanus, which has expanded the range of the former parental species.       Here, we use artificially created backcross (BC1) lines and parental controls to compare rates of evolution between hybrid and non-hybrid lineages. Populations of experimental hybrids and parental controls were established in the field and allowed to naturally grow and reproduce for eight generations. We grew seeds collected from each generation in a common-garden setting, estimated whole-plant fitness, and measured traits associated with ecophysiology, herbivore damage, phenology, floral morphology, and growth architecture. We use Bayesian models to assess changes in fitness and trait values through time and compare hybrid and non-hybrid lineages with parental species.       Despite low initial hybrid fitness, hybrid fitness increased to exceed that of controls in just eight generations. Specific traits tended to evolve more rapidly in hybrids than in controls, and the speed of evolution of these traits is positively related to previous estimates of selection differentials in early-generation BC1 hybrids. To our knowledge, this is the first field experiment to demonstrate that hybridization speeds adaptive evolution in a wild setting.

1 - University of New Mexico, Department of Biology, MSC03-2020, 219 Yale Blvd NE, 1 University of New Mexico, Albuquerque, NM, 87131
2 - University Of British Columbia, Department Of Botany, 6270 University Blvd, Vancouver, BC, V6T 1Z4, Canada
3 - University of California, Berkeley, Department of Integrative Biology, 3040 Valley Life Sciences Bldg #3140, Berkeley, CA, 94720, USA

Experimental evolution

Presentation Type: Oral Paper
Abstract ID:229
Candidate for Awards:Margaret Menzel Award

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