Abstract - Evolutionary Ecology, 2001, 15:205-221


Androdioecy (populations comprised of mixtures of males and hermaphrodites) is a rare mating system, found only in a few plants and animals.  The rarity of this system stems from the limited benefits to males in an otherwise all-hermaphroditic population.  One of the potential benefits to males is typified by the nematode Caenorhabditis elegans, wherein hermaphrodites do not produce sufficient sperm to fertilize all of their eggs.  Herein we explore the possibility that males are needed to fully fertilize hermaphrodites’ eggs in a second androdioecious animal, the clam shrimp Eulimnadia texana.  We compare the fertilization rate of outcrossed to selfed eggs to note whether the latter exhibit lower fertilization due to sperm limitation (as in C. elegans).  Because the above comparison confounds differences in egg fertilization due to sperm limitation with the potential for early inbreeding depression, we also used a third mating treatment, a brother/sister cross, to allow separation of sperm limitation from inbreeding depression.  The proportion of eggs that were fertilized linearly decreased when comparing eggs produced by outcrossing, brother/sister, and selfed matings, respectively, in both populations examined.  This pattern suggests that differences in fertilization among these three treatments were caused solely by inbreeding depression, and therefore that hermaphrodites are not sperm limited.   These results are combined with previous data on this reproductive system to note whether the maintenance of males can be explained using a population genetics model specifically designed for this species.



Last Updated : 10/18/04

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