WEINIG, CYNTHIA* and JOHANNA SCHMITT. Dept. of Ecology and Evolutionary Biology, Box G-W, Brown University, Providence, RI 02912. - Constraints on the evolution of plasticity: insights from molecular marker-based linkage mapping.
Molecular genetic approaches, such as marker-based linkage mapping,
can help identify whether multiple traits possess common or
independent genetic pathways. Such analyses are important to studies
of plasticity because they can suggest across-environment genetic
correlations that may constrain the evolution of plasticity. In a
recent field experiment, recombinant inbred lines of Arabidopsis
thaliana (Ler x Col) experienced variable herbivory levels.
Herbivorized plants exhibited the classic increase in basal branching
that occurs after removal of the apical meristem. This increase in
basal branches was associated with enhanced fitness in the
herbivorized plants, whereas basal branches had no effect on fitness
of non-herbivorized plants. In contrast, fitness of the
non-herbivorized plants was strongly influenced by the number of
branches on the primary flowering inflorescence. This variable
selection across herbivory environments suggests that the observed
plasticity is adaptive. Preliminary QTL (quantitative trait loci) and
quantitative-genetic analyses show that basal branch number is
determined by a different genetic mechanism in herbivorized and
non-herbivorized plants; the QTLs for branch number were located on
different chromosomes. Although these independent genetic bases are
somewhat surprising, the result indicates that plasticity of branch
number can evolve freely in response to ambient herbivory conditions.
In the non-herbivorized plants, we detected two QTL in common for
inflorescence and basal branch number. Thus, these two traits may have
a common genetic basis such that selection on inflorescence branches
results in a correlated response in basal branch number. These results
taken together illustrate that different traits may or may not be
correlated in a manner that constrains the evolution of adaptive
plasticity.
Key words: adaptive plasticity, Arabidopsis thaliana , evolutionary constraints, herbivory, QTL analyses