SCHWEITZER, J.A.* AND T.G. WHITHAM. Dept of Biology, Northern Arizona University, Flagstaff, AZ 86011. - The effect of hybridization on physiological responses to herbivores.
Plant hybridization can result in hybrids having similar
characteristics of either pure parental or combinations of both.
Characters such as anatomy and morphology, leaf chemistry,
susceptibility to herbivores etc., may be quite variable relative to
the pure parentals. However one aspect of hybridization less studied
is physiological response to herbivores. This trait could have
important consequences for fitness if the hybrids responded to
herbivory by allocating carbon and water differently than the pure
parentals. A natural hybrid zone of Populus along the Weber River in
northern Utah provides a unique opportunity to examine photosynthetic
rates and water relations in response to herbivores of different
feeding types. We examined water potential, photosynthesis and water
use efficiency of both naturally occurring and common garden trees of
known genotype. These trees consisted of Populus fremontii, Populus
angustifolia, their F1 hybrids and complex backcross hybrids. The
measured variables were quantified from both naturally occurring and
experimental manipulations of a galling aphid, a free feeding aphid
and a free feeding beetle. Leaves with the herbivore, adjacent leaves
without the herbivore and leaves on a herbivore free shoot were
measured to examine how tree type and herbivore affected the
physiological responses that leaves exhibited. The results indicate
that both tree type and herbivore affect leaf level physiological
processes. All three of these herbivores occur most frequently on
hybrid classes than on the pure parentals and have different impacts
on these trees. The galling aphid, as a mobilizing sink, had the
greatest impact on both photosynthesis and water relations compared to
responses to the other herbivores.
Key words: hybridization, photosynthesis, plant-herbivore interactions, Populus, water use efficiency