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Environmental stressors differentially affect leaf ecophysiological responses in two Ipomopsis species and their hybrids


The recombination that follows natural hybridization may produce hybrid genotypes with traits that are intermediate or extreme relative to the parental species, and these traits may influence the relative fitness of the hybrids. Here we examined leaf ecophysiological traits that may influence fitness patterns in a natural plant hybrid zone. We compared the biochemical photosynthetic capacity of Ipomopsis aggregata, I. tenuituba, and early generation hybrids, as well as their photosynthetic responses to varying light and temperature, two abiotic factors found to differ among sites along the hybrid zone. In general, ecophysiological traits expressed in these plants were consistent with their natural habitat, even when grown under common greenhouse conditions. I. tenuituba reached higher photosynthetic rates (A) at higher light levels than I. aggregata, and also had a higher optimal temperature for photosynthesis (T opt). This suite of traits may reflect adaptations to the more exposed, rocky sites where I. tenuituba is found, compared to the more vegetated, mesic I. aggregata site. Hybrids had characters that were largely intermediate or tenuituba-like, but particular individual hybrids were extreme for some traits, including light saturation level, light-saturated A, and T opt. Many of these traits are consistent with adaptations reported for plants found in warm, dry sites, so they may put certain hybrids at an advantage at the relatively xeric center of the natural hybrid zone.

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This research was supported by funding from the University of California Irvine, the National Science Foundation (DEB-9806547 to D. R. C. and DEB-0308772 to D. R. C. and C. A. W.), a GAANN Fellowship from the US Department of Education, and a Graduate Women in Science Eloise Gerry Fellowship. G. Aldridge, K. Suding, S. Weller, E. Wu, and two anonymous reviewers provided helpful comments on earlier versions of this manuscript. The experiments reported here comply with all current laws of the USA.

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Correspondence to Carrie A. Wu.

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Communicated by Todd Dawson

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Wu, C.A., Campbell, D.R. Environmental stressors differentially affect leaf ecophysiological responses in two Ipomopsis species and their hybrids. Oecologia 148, 202 (2006).

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  • Environment-dependent selection
  • Hybridization
  • Ipomopsis
  • Temperature response
  • Photosynthesis