Molecular Ecology and Evolution
Laport, Robert , Minckley, Robert , Ramsey, Justin .
The Biology of Speciation in the North American Polyploid Complex, Larrea tridentata (Zygophyllaceae).
The relative importance of ecological and non-ecological reproductive barriers is widely disputed, even for taxa classically identified as examples of non-ecological speciation. Genome duplication (polyploidy) is a common form of chromosome evolution that causes hybrid inviability (triploid block) and strong reproductive isolation in plants. However, because polyploids are often geographically, morphologically,and physiologically, divergent from diploids, some evolutionists have argued that speciation in polyploids depends upon ecological adaptation. One widely cited example of polyploid speciation is the creosote bush (Larrea tridentata, Zygophyllaceae), a dominant species of the North American desert flora comprised of three geographically isolated chromosome races (diploids (2n=2x=26) occur in the Chihuahuan Desert, tetraploids (2n=4x=52) occur in the Sonoran Desert, and hexaploids (2n=6x=78) occur in the Mojave Desert). Yet, it remains unclear if the chromosome races of L. tridentata represent distinct taxonomic units, not only because of uncertainty over the strength of reproductive isolation, but also due to uncertainty over the degree to which they have diverged ecologically, morphologically, and physiologically. Here, we use a combination of DNA molecular analyses and field observations to estimate the strength of pre- and post-zygotic reproductive isolation within the L. tridentata polyploid complex; determine morphological and physiological divergence among the cytotypes; and test the hypothesis that gene flow is reduced between the cytotypes. We find that the three cytotypes of North American creosote bush exhibit strong intercytotype reproductive isolation mediated by largely allopatric distributions, divergent flowering phenology, and hybrid inviability/sterility. Furthermore, the allopatric ranges are distinct in climatic and edaphic features, as well as floristic elements. The cytotypes differ slightly in morphological features and display differences in water use efficiency as measured by carbon isotope analyses. Finally, DNA molecular data indicates little evidence for intercytotype gene flow. Taken together, these results suggest ecological isolation may play a significant role in establishing reproductive isolation between the cytotypes.
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1 - University Of Rochester, Department Of Biology, RIVER CAMPUS BOX 270211, HUTCHISON HALL, ROCHESTER, NY, 14627, USA
water use efficiency
Presentation Type: Oral Paper:Papers for Topics
Location: Westminster Room/Chase Park Plaza
Date: Monday, July 11th, 2011
Time: 2:30 PM