Outcrossing rates and allozyme variation in rayed and rayless morphs of bidens pilosa

Abstract

Thirty-four isozyme loci were assayed in 1048 plants from three Hawaiian populations of the autogamous introduced weed Bidens pilosa. Total isozyme gene diversity was very low, 0·049. One population containing only rayless plants was completely monomorphic at all loci except PGI-3, and this locus was nearly fixed. In a large population polymorphic for rayed, rayless, and intermediate plants, two loci showed rare variants and PGI-3 was polymorphic. Allele frequencies at PGI-3 were not significantly different among the floral morphs, but outcrossing rates, measured by progeny tests using PGI-3 as a genetic marker, were significantly higher in the radiate morph (9 per cent) than in the rayless and intermediate morphs (5 per cent). Presumably radiate plants have higher outcrossing rates because they are more attractive to pollinators. © 1990 The Genetical Society of Great Britain.