BAUMBERGER, ROLF1* and KEVIN CUMMINS2. 1Department of Biological Sciences, University of Zurich, Zollikerstrasse 107, CH-8008 Zurich, Switzerland; 2Department of Biology, San Diego State University, 5500 Campanile Drive, San Diego. - Phenotypic transition in the bush monkeyflower Mimulus aurantiacus.
The Mimulus aurantiacus complex, comprising endemic shrubs in
Southern California, shows a high degree of phenotypic plasticity. It
is currently thought that this high degree of plasticity is due to
natural hybridization at the subspecies level. However, our studies of
Mimulus aurantiacus plants over the last six years suggest that
individuals of ssp. australis producing large, yellow,
insect-pollinated flowers can undergo a dramatic phenotypic transition
to produce small, red, bird-pollinated flowers. The entire transition
takes several years until completion. To our knowledge this is the
first case demonstrating morphological and biochemical (pigment)
alterations over a considerable time span, which finally lead to a
new, discrete and stable form. The transitional zone (what is
«classically» termed the hybrid zone) migrates towards the East in the
most southern part of California. Intrinsic and extrinsic factors are
suggested as forcing this rapid transition process resulting in
phenotypic evolution. (Mimulus aurantiacus transition
http://217.162.182.115 )
Key words: hybrid zone, Mimulus aurantiacus, phenotypic evolution, phenotypic plasticity, pigment, transition zone