Abstract
Androdioecy (the coexistence of males and hermaphrodites) is a rare mating system for which the evolutionary dynamics are poorly understood. Here, we investigate the cottony cushion scale, Icerya purchasi, one of only three reported cases of androdioecy in insects. In this species, female-like hermaphrodites have been shown to produce sperm and self-fertilize. However, males are ocassionally observed as well. In a large genetic analysis, we show for the first time that, although self-fertilization appears to be the primary mode of reproduction, rare outbreeding events do occur in natural populations, supporting the hypothesis that hermaphrodites mate with males and hence androdioecy is the mating system of I. purchasi. Thus, this globally invasive pest insect appears to enjoy the colonization advantages of a selfing organism while also benefitting from periodic reintroduction of genetic variation through outbreeding with males.
Highlights
Androdioecy is a rare mating system for which the evolutionary dynamics are poorly understood
In a large genetic analysis, we show for the first time that, self-fertilization appears to be the primary mode of reproduction, rare outbreeding events do occur in natural populations, supporting the hypothesis that hermaphrodites mate with males and androdioecy is the mating system of I. purchasi
We developed a panel of polymorphic microsatellite markers for use in a genetic analysis to estimate outbreeding rates in natural populations of I. purchasi
Summary
Androdioecy (the coexistence of males and hermaphrodites) is a rare mating system for which the evolutionary dynamics are poorly understood. Androdioecy appears to have independently evolved several times in eukaryotes and is often thought of as an advantageous strategy for colonizing new locations: enjoying the benefit of reproductive assurance (i.e., allowing even a single hermaphrodite to found a new population through self-fertilization) without incurring the inbreeding cost of pure selfing as the production of males permits outcrossing (Weeks 2012) This logical hypothesis has not been formally tested and it remains unclear how organisms anatomically and cytologically acquire the capacity to produce both gamete types in one sex morph but not the other. Males in androdiecious species can only pass genes on through mating with hermaphrodites, but if the cost of selfing is lower than 50%, hermaphrodites pass on their genes at a higher rate via selfing (Chasnov 2010)
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