Integration of Spatial and Ecological Data in Evolutionary Studies
Edwards, Erika , Still, Chris J. .
Phylogeny and the ecological distribution of C4 grasses.
C4 photosynthesis refers to a suite of biochemical and anatomical traits that reduce photorespiration in plants and promote photosynthetic efficiency in high light, high temperature environments. While the C4 pathway has evolved in numerous angiosperm lineages, it is most common in the grasses. Globally, C4 grasses are dominant members of tropical grassland/savanna communities and are conspicuously absent from cooler climates. There are well-understood physiological mechanisms that have been invoked to explain this pattern; however, C4 photosynthesis evolved exclusively in grass lineages of tropical origin, so an alternative and untested hypothesis is that C4 grasses were pre-adapted to warm climates and that photosynthetic pathway variation is not the primary driver of perceived C3/C4 sorting along temperature gradients. We tease this problem apart by analyzing the climate niches of 156 species of the Hawaiian grass flora within a phylogenetic framework. Using climate data from location points for over 3500 georeferenced herbarium specimens and current knowledge of evolutionary relationships within Poaceae, we find strong phylogenetic conservatism for all climate parameters. Most cool climate grasses belong to the “BEP” grass clade, while most warm climate grasses belong to the “PACCAD” clade, which contains a mix of both C3 and C4 species. Within the PACCAD clade, shifts to C4 photosynthesis are more tightly correlated with lower precipitation than with higher temperatures. Additionally, divergences in temperature profiles between C4 sister taxa are significantly smaller than those between C3 sister taxa or C3/C4 splits. These results suggest that the relationship between C4 grass distribution and climate is complex, and that the broad global patterns correlating C4 abundance with high temperatures may be mostly due to historical effects. Furthermore, C4 photosynthesis may in part be limiting ecological diversification by restricting the realized temperature ranges of C4 species.
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1 - Brown University, Ecology and Evolutionary Biology, 80 Waterman Street, Providence, Rhode Island, 02912, U.S.A.
2 - University of California at Santa Barbara, Geography, Santa Barbara, CA, 93106, USA
Presentation Type: Symposium or Colloquium Presentation
Location: Stevens 2/Hilton
Date: Wednesday, July 11th, 2007
Time: 10:30 AM