HARDIG, T. M.1*, PAMELA S. SOLTIS2, DOUGLAS E. SOLTIS2, and RYAN B. HUDSON1. 1Department of Biology and Chemistry, University of Montevallo, Montevallo, AL, 35115; 2Department of Biological Sciences, Washington State University, Pullman, WA, 99164. - Diploid hybrid speciation in Ceanothus: morphomolecular analysis of two putative hybrid species adn their proposed parent species.
Several species of the North American shrub genus Ceanothus
have been proposed as exemplars of diploid hybrid species. Based on
observations of natural hybrids, synthesis of garden hybrids,
cytology, distribution, and perceived morphological intermediacy, Nobs
(1963) concluded that C. masonii and C. sonomensis
(among others) are diploid hybrid species, derived from separate
hybridization events between C. cuneatus and C.
gloriosus. We tested Nob's proposal for the origins of C.
masonii and C. sonomensis using molecular (i.e., nuclear
ribosomal and chloroplast DNA sequences and allozyme diversity) and
morphological (i.e., foliar characteristics) data. Results of our
molecular analyses provided no unequivocal support for the proposed
hybrid origin of either C. masonii or C. sonomensis.
Additionally, statistical and multivariate analyses of foliar
characteristics indicated that the proposed hybrid species possess
character states more extreme than either parent. Recent studies of
character inheritance and expression in hybrids suggest that the
assumption of morphological intermediacy in hybrids is unwarranted,
therefore, our morphological results are not inconsistent with
possible hybrid origins. However, our results do call into question at
least one of Nobs' original premises. As an alternative to the hybrid
origin scenario, we propose that C. masonii and C.
sonomensis are the products of divergent speciation, driven by
recent climatic and geological changes effecting the western edge of
the North American continent.
Key words: allozymes, Ceanothus, cpDNA, diploid hybrid speciation, morphometric, rDNA