Despite decades of research, the evolution of sex remains an enigma in evolutionary biology. Typically, research addresses the costs of sex and asexuality to characterize the circumstances favoring one reproductive mode. Surprisingly few studies address the influence of common traits that are, in many organisms, obligately correlated with asexuality, including hybridization and polyploidy. These traits have substantial impacts on traits under selection. In particular, the fitness consequences of hybridization (that is, reduced fitness due to interspecific reproductive isolation) will influence the evolution of sex. This may comprise a cost of either sex or asexuality, due to the link between hybridity and asexuality. We examined reproductive isolation in the formation of de novo hybrid lineages between two widespread species in the ecological model system Boechera. 17% of 664 crosses produced F1 fruits, and only 10% of these were viable, suggesting that postmating prezygotic and postzygotic barriers inhibit hybrid success in this system. The postmating prezygotic barrier was asymmetrical, with 110 of 115 total F1 fruits produced when B. stricta acted as maternal parent. This asymmetry was confirmed in wild-collected lineages, using a chloroplast phylogeny of wild-collected B. stricta, B. retrofracta, and hybrids. We next compared fitness of F2 hybrids and selfed parental B. stricta lines, finding that F2 fitness was reduced by substantial hybrid sterility. Multiple reproductively isolating barriers likely influence the formation and fitness of hybrid lineages in the wild, and the costs of hybridization likely have profound impacts on the evolution of sex in the natural environment.

Three datasets are included in this submission, and each was collected in the greenhouse. The first ("F1success_data.csv") is a dataset collected in the greenhouse that contains information on the identity of a given cross and whether or not crossed flowers developed into fruits and successfully set seed. The second ("F1germination_data.csv") is another greenhouse-collected dataset that contains information on each individual fruit produced, and germination rate, viability, and sterility for each. Columns in both datasets that start with the prefix "Prop" are proportions that were calculated according to the README document. The third dataset ("Greenhouseexpt_data.csv") was collected during a greenhouse experiment on F2 plants. Average seed set for a given genotype was calculated as in Rushworth et al. 2019 (https://doi.org/10.1101/719252). No processing was conducted.

One final file provided is a Nexus file used to create the chloroplast tree. New sequences generated in this publication have been submitted in Genbank (Genbank #s MW052148 - MW052220).

Missing values are indicated by X, NA, or blank spaces. All headers from datasets are explained in the README file. Analyses for all three datasets are in the R script. Please feel free to address any questions to the corresponding author.