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Mixed mating in androdioecious Mercurialis annua inferred using progeny arrays and diploid-acting microsatellite loci in a hexaploid background

Korbecka, Grażyna, Hamilton, Alastair, Pannell, John R.
Annals of botany 2011 v.107 no.6 pp. 1057-1061
Mercurialis annua, diploidy, genes, genetic variation, genotype, hermaphroditism, hexaploidy, inbreeding, males, microsatellite repeats, outcrossing, paternity, plant density, progeny, selfing, space and time, stochastic processes, systems analysis
BACKGROUND AND AIMS: The frequency at which males can be maintained with hermaphrodites in androdioecious populations is predicted to depend on the selfing rate, because self-fertilization by hermaphrodites reduces prospective siring opportunities for males. In particular, high selfing rates by hermaphrodites are expected to exclude males from a population. Here, the first estimates are provided of the mating system from two wild hexaploid populations of the androdioecious European wind-pollinated plant M. annua with contrasting male frequencies. METHODS: Four diploid microsatellite loci were used to genotype 19-20 progeny arrays from two populations of M. annua, one with males and one without. Mating-system parameters were estimated using the program MLTR. KEY RESULTS: Both populations had similar, intermediate outcrossing rates (tm = 0·64 and 0·52 for the population with and without males, respectively). The population without males showed a lower level of correlated paternity and biparental inbreeding and higher allelic richness and gene diversity than the population with males. CONCLUSIONS: The results demonstrate the utility of new diploid microsatellite loci for mating system analysis in a hexaploid plant. It would appear that androdioecious M. annua has a mixed-mating system in the wild, an uncommon finding for wind-pollinated species. This study sets a foundation for future research to assess the relative importance of the sexual system, plant-density variation and stochastic processes for the regulation of male frequencies in M. annua over space and time.