Variation in estimates of outcrossing in musk thistle populations

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Abstract
Two allozyme loci were used to estimate rates of outcrosslng in two populations of musk thistle located in northeastern Kansas. Outcrossing rates for six semi-isolated plants also were calculated. Estimates of outcrossing for the two populations were approximately equal to one while those from semi-isolated plants were highly variable but averaged less than 50 percent. Significant heterogeneity in outcrossing rates among individual plants within populations also was observed. This result probably arose from the pollination of individual flower heads by one or very few pollinators. New estimation procedures are needed that take the realities of pollinator behavior into consideration.