BREEDING STRUCTURE OF A YUCCA FILAMENTOSA (AGAVACEAE) POPULATION

Yucca filamentosa and its species-specific pollinator, the yucca moth, Tegeticula yuccasella (Lepidoptera: Prodoxidae), form a relationship that is often cited as a classic example of a coevolved plant-pollinator mutualism. Observations of the moth's behavior have led to predictions that moth dispersal is relatively limited and that, as a consequence, the self-compatible Y. filamentosa should experience relatively high rates of self-fertilization. In contrast, analyses of its mating system indicated that Y. filamentosa was predominantly outcrossed. To better understand effective breeding patterns in Y. filamentosa populations, 10 polymorphic allozyme loci were investigated to analyze the breeding structure of a natural Y. filamentosa population. Analyses revealed that Y. filamentosa is predominantly outcrossed, has multiply sired fruits, and that each fruit was sired by a different set of pollen donors. The effective number of pollen donors per fruit ranged from 1.56 to 3.13, indicating that some correlated mating exists within fruits. Paternity analyses revealed that pollen moved from 6 m to 293 m (mean = 118 m) within the study population and that a minimum of 10% of the progeny were sired by pollen originating outside of the population. These results are discussed in the context of the yucca-yucca moth mutualism.