POLLEN COMPETITION IN TURNERA-ULMIFOLIA (TURNERACEAE)

We performed mixed pollinations, involving self vs. within- or between -population pollen, and used starch gel electrophoresis to assay 2,210 progeny to detect pollen competition in Turnera ulmifolia. Within pop ulations there was no evidence for a competitive advantage to outcross pollen. Between populations a marked advantage to self pollen occurre d for most populations, and the extent of this competitive advantage w as correlated with increasing morphological divergence of the outcross pollen donor population. A comparison of rates of ovule abortion reve aled that the biased paternity ratios cannot be the result of ovule ab ortion alone, and that pollen competition must be the major contributi ng factor. We suggest that reproductive divergence among the populatio ns, perhaps through adaptation to different pollinators or through the evolution of increased selfing, has resulted in the evolution of repr oductive isolation through pollen competition.