Integrative and Comparative Biology Advance Access published online on May 5, 2006
Integrative and Comparative Biology, doi:10.1093/icb/icj048
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Stephen C. Weeks 1 *,
Chiara Benvenuto 1,
and
Sadie K. Reed 1
* To whom correspondence should be addressed. Synopsis Androdioecy (populations consisting of males and hermaphrodites) is a rare mating system in plants and animals: up to 50 plants and only 36 animals have been described as being androdioecious, with most of the latter being crustaceans. To date, a thorough comparative analysis of androdioecy in animals has not been undertaken. Herein we present such an analysis. Androdioecy has only been extensively surveyed in 2 animal taxa: the nematode Caenorhabditis and the clam shrimp Eulimnadia. The other major taxon having androdioecious species is the Cirripedia (barnacles), but there are only limited studies on androdioecy in this group. In animals, androdioecy is found either in species that have morphologically and ecologically distinct sexes (that is, hermaphrodites and small, "complemental" males) that are derived from hermaphroditic ancestors (that is, the barnacles) or in species that have similarly-sized males and hermaphrodites that have been derived from dioecious ancestors (the remaining androdioecious species). We suggest that the barnacles have evolved a sexual specialization in the form of these complemental males that can more efficiently use the constrained habitats that these barnacles often experience. For the remaining species, we suggest that androdioecy has evolved as a response to reproductive assurance in species that experience episodic low densities. Additionally, we hypothesize that the development of mechanisms allowing reproductive assurance in species with a number of sexually differentiated traits is most likely to result in androdioecy rather than gynodioecy (mixtures of females and hermaphrodites), and that these species may be developmentally constrained to stay androdioecious rather than being capable of evolving into populations solely consisting of efficient, self-compatible hermaphrodites. We conclude by suggesting several areas in need of further study to understand more completely the evolution and distribution of this interesting mating system in animals.
Sexual Selection and Mating Systems in Hermaphrodites
When males and hermaphrodites coexist: a review of androdioecy in animals
1 Program in Evolution, Ecology, and Organismal Biology, Department of Biology, The University of Akron, Akron, OH 44325-3908, USA
Stephen C. Weeks, E-mail: scw{at}uakron.edu
Abstract
From the symposium "Sexual Selection and Mating Systems in Hermaphrodites" presented at the annual meeting of the Society for Integrative and Comparative Biology, January 4-8, 2005, at San Diego, California.
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