Tychoparthenogenesis and mixed mating in natural populations of the mayfly Stenonema femoratum

Abstract

Tychoparthenogenesis is a breeding system characterized by low population mean hatching success (usually < 10%) of unfertilized eggs from females of typically sexually reproducing species. I used progeny-array analysis to estimate outcrossing and parthenogenetic rates for two tychoparthenogenetic populations of the mayfly, Stenonema femoratum. Based on multilocus outcrossing rate estimates (t(m)), populations exhibited moderate rates of tychoparthenogenetic reproduction (population LD: 1 - t(m)=0.266; population RBG: 1 - t(m)=0.495). Differences between multilocus and average single-locus outcrossing rates indicated some biparental inbreeding in population LD, but not in population RBG. Family outcrossing rates ranged from 0 to 1.0, indicating mixed mating in which some females generated a mixture of sexually and parthenogenetically produced offspring. Outcrossing rates showed substantial heterogeneity among families. Correlation with paternity was high, indicating that outcrossed sibs within families were sired by the same father. Progeny-array sex ratios were significantly female biased for both populations and did not differ significantly between populations. However, family outcrossing rate was not significantly correlated with family sex ratio. Results indicate that substantial amounts of parthenogenetic reproduction are occurring in these natural S. femoratum populations and that some females produce mixed broods of sexually and parthenogenetically produced offspring.