MULTIPLE ORIGINS OF SELF-FERTILIZATION IN TRISTYLOUS EICHHORNIA-PANICULATA (PONTEDERIACEAE) - INFERENCES FROM STYLE MORPH AND ISOZYME VARIATION

Populations of Eichhornia paniculata (Pontederiaceae) exhibit a wide r ange of mating systems, from predominant outcrossing to high levels of self-fertilization. The origin of self-fertilization in this tristylo us species is associated with the loss of style-length morphs from pop ulations and the spread of self-pollinating, floral variants. We exami ned geographic variation in style morph and allozyme frequencies to de termine whether the loss of style morphs and transition to selfing cou ld have multiple origins in E. paniculata. Surveys of floral variation in 167 populations from six states in northeastern Brazil revealed th at at least one style morph was absent from 29.3%. Non-trimorphic popu lations occurred in all states and ranged in frequency from 9% in Cear a to 68% in Alagoas. Selfing variants occurred in 8.5% and 55% of trim orphic and non-trimorphic populations, respectively, and were distribu ted among five of six states with primary concentrations in Alagoas an d Pernambuco. A comparison of electrophoretic variation at 24 isozyme loci in 28 trimorphic, 13 dimorphic and 3 monomorphic populations indi cated that non-trimorphic populations contained 84% of the allelic var iation present in trimorphic populations and were markedly differentia ted from one another. Analyses of genetic distance and the distributio n of rare alleles indicated that non-trimorphic populations were often more similar to neighbouring trimorphic populations than to one anoth er. Populations with selfing variants occurred at low frequency in thr ee genetically distinct parts of the range. These results, in combinat ion with genetic and morphological evidence suggest that style morphs are lost repeatedly from populations of E. paniculata and that selfing variants may have originated on at least three separate occasions in northeastern Brazil.