Tychoparthenogenesis and mixed mating in natural populations of the mayflyStenonema femoratum

Tychoparthenogenesis is a breeding system characterized by low population m ean hatching success (usually <10%) of unfertilized eggs from females of ty pically sexually reproducing species. I used progeny-array analysis to esti mate outcrossing and parthenogenetic rates for two tychoparthenogenetic pop ulations of the mayfly, Stenonema femoratum. Based on multilocus outcrossin g rate estimates (t(m)), populations exhibited moderate rates of tychoparth enogenetic reproduction (population LD: 1-t(m) = 0.266; population RBG:1-t( m) = 0.495). Differences between multilocus and average single-locus outcro ssing rates indicated some biparental inbreeding in population LD, but not in population RBG. Family outcrossing rates ranged from 0 to 1.0, indicatin g mixed mating in which some females generated a mixture of sexually and pa rthenogenetically produced offspring. Outcrossing rates showed substantial heterogeneity among families. Correlation with paternity was high, indicati ng that outcrossed sibs within families were sired by the same father. Prog eny-array sex ratios were significantly female biased for both populations and did not differ significantly between populations. However, family outcr ossing rate was not significantly correlated with family sex ratio. Results indicate that substantial amounts of parthenogenetic reproduction are occu rring in these natural S. femoratum populations and that some females produ ce mixed broods of sexually and parthenogenetically produced offspring.