Journal
JOURNAL OF EVOLUTIONARY BIOLOGY
Volume 23, Issue 3, Pages 539-556Publisher
WILEY
DOI: 10.1111/j.1420-9101.2009.01919.x
Keywords
conflicts; population genetics; sexual selection; theory
Categories
Funding
- Research Grants Council, Hong Kong [600406]
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The nematode worm Caenorhabditis elegans and the clam shrimp Eulimnadia texana are two well-studied androdioecious species consisting mostly of self-fertilizing hermaphrodites and few males. To understand how androdioecy can evolve, a simple two-step mathematical model of the evolutionary pathway from a male-female species to a selfing-hermaphrodite species is constructed. First, the frequency of mutant females capable of facultative self-fertilization increases if the benefits of reproductive assurance exceed the cost. Second, hermaphrodites become obligate self-fertilizers if the fitness of selfed offspring exceeds one-half the fitness of outcrossed offspring. Genetic considerations specific to C. elegans and E. texana show that males may endure as descendants of the ancestral male-female species. These models combined with an extensive literature review suggest a sexual conflict over mating in these androdioecious species: selection favours hermaphrodites that self and males that outcross. The strength of selection on hermaphrodites and males differs, however. Males that fail to outcross suffer a genetic death. Hermaphrodites may never encounter a rare male, and those that do and outcross only bear less fecund offspring. This asymmetric sexual conflict results in an evolutionary stand-off: rare, but persistent males occasionally fertilize common, but reluctant hermaphrodites. A consequence of this stand-off may be an increase in the longevity of the androdioecious mating system.
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