WINN, A. A.* and K.S. MORIUCHI. Department of Biological Science, Florida State University, Tallahassee, FL. - Integration of plastic responses of leaves and flowers to seasonal environmental variation in a perennial violet.
Theoretical treatments of the evolution of adaptive phenotypic
plasticity commonly invoke a cost of plasticity as the force that
limits further evolution of a particular plastic response. To date,
there is little empirical support for the existence of such costs. One
way in which a particular plastic response could be costly is if it
disrupts the expression of another trait or the plasticity of another
trait. We are examining the possibility that compromises between
plasticity in leaf morphology and in flower morphology in a single
species limit the evolution of adaptive plasticity in both traits. The
perennial violet, Viola septemloba exhibits seasonal leaf and
flower dimorphism in response to day length. Individuals produce
primarily entire leaves during the fall and winter and switch to the
production of deeply lobed leaves during the spring and summer. Lobed
leaves are able to maintain average mesophyll temperatures nearly 3
degrees C lower than entire leaves during the hot summer. Thus
heterophylly appears to be adaptive plasticity in response to seasonal
environmental variation. Individuals of this species also exhibit
seasonal variation in flower morphology. The production of open
(chasmogamous) flowers occurs simultaneously with increasing
production of lobed leaves during the late winter, and the production
of closed (cleistogamous), obligately selfed flowers during the
mid-summer and fall corresponds to increasing production of entire
leaves. We have raised replicates of inbred lines of V.
septemloba under long and short days and demonstrated heritable
variation in response of leaf and flower morphology to day length.
Preliminary results also suggest a genetic covariance between the
plastic responses of the two traits, which could underlie a cost of
plasticity. We will illustrate how simultaneous consideration of
adaptive plasticity in multiple traits can contribute to understanding
the existence and mechanistic basis of costs that limit the evolution
of adaptive plasticity.
Key words: cleistogamy, cost of plasticity, heterophylly, phenotypic plasticity, Viola septemloba