Meeting Abstract

P1.60  Friday, Jan. 4  Through thick and thin: the adaptive significance of leaf trait variation in wild tomatoes MUIR, CD*; DAVIS, PA; CONESA, MÀ; ROLDÁN, E; GALMÉS, J; MOYLE, LC; Indiana University; Indiana University; University of the Balearic Island’s; University of the Balearic Island’s; University of the Balearic Island’s; Indiana University cdmuir@indiana.edu

Trait-environment correlations are frequently used to infer adaptation if confounding factors, such as shared ancestry, can be ruled out.  It is generally observed that thicker and/or denser leaves, indicated by high leaf mass per area (LMA), are more common in dry habitats because they confer greater tolerance to drought.  I tested this hypothesis using a common garden study of 16 wild relatives of cultivated tomato.  Contrary to my a priori prediction, I found that LMA was lower in species from drier habitats. Since species were measured in a common garden, this variation is genetic rather than a plastic response to the environment. I took an ecophysiological, mechanistic approach to understanding what could explain this pattern.  One consequence of high LMA is that it hinders CO₂ diffusion from the substomatal cavities to the chloroplasts.  Using standard ecophysiological methods, I found that lower internal CO₂ diffusion, commonly measured as mesophyll conductance (g_m), reduces photosynthetic rates and intrinsic water-use efficiency (WUE) in these species.  Low LMA may therefore allow plants from dry habitats to balance the competing demands of rapid growth and high WUE.  My working hypothesis is that in this system, low LMA enables plants in dry habitats to avoid drought by growing rapidly, yet efficiently, to use a limiting resource wisely. Since wild tomatoes are a genetically tractable, emerging model system for ecological and evolutionary genomics, future work will examine the genetic basis of traits associated with increased CO₂ diffusion that were identified in this common garden study. I have begun by locating QTL for LMA and stomatal distribution, another trait affecting CO₂ diffusion, in interspecific crosses.