Se. Sultan et Fa. Bazzaz, PHENOTYPIC PLASTICITY IN POLYGONUM-PERSICARIA .1. DIVERSITY AND UNIFORMITY IN GENOTYPIC NORMS OF REACTION TO LIGHT, Evolution, 47(4), 1993, pp. 1009-1031
Several aspects of genotype-environment interaction may act to modulat
e natural selection in populations that encounter variable environment
s. In this study the norms of reaction (phenotypic responses) of 20 cl
oned genotypes from two natural populations of the annual plant Polygo
num persicaria were determined over a broad range of controlled light
environments (8%- 100% full sun). These data reveal both the extent of
functionally adaptive phenotypic plasticity expressed by individual g
enotypes, and the patterns of diversity among genotypes for characters
relevant to fitness, in response to an environmental factor that is b
oth highly variable within populations and critical to growth and repr
oduction. Each Polygonum genotype expressed a set of physiologically,
allocationally, and morphologically diverse phenotypes in response to
contrasting light conditions. These phenotypic adjustments were consis
tent with ecophysiological expectations for maximizing light intercept
ion under low light intensities, and resulted in the maintenance of re
lative photosynthetic efficiency as well as successful reproduction ev
en under severe light limitation. Within light levels, the different g
enotypes exhibited uniform responses in several characters related to
light capture. Genotypes differed significantly in other traits, but t
he differences were offset by negatively correlated differences in fun
ctionally related characters. As a result of the functional similarity
of genotypes conferred by both phenotypic plasticity and interaction
among characters, morphologically diverse genotypes within each popula
tion shared equivalent reproductive fitnesses across the full range of
flight environments. Enormous fitness differentials did result from l
ight treatment itself, however. Such environmentally evoked fitness di
fferences would act to promote the maintenance of genetic diversity wi
thin Polygonum populations.