The maintenance of obligate sex in animals is a long-standing evolutionary paradox. To solve this puzzle, evolutionary models need to explain why obligately sexual populations consistently resist invasion by facultative strategies that combine the benefits of both sexual and asexual reproduction. Sexual antagonism and mate availability are thought to shape the occurrence of reproductive modes in facultative systems. But it is unclear how such factors interact with each other to influence facultative invasions and transitions to obligate asexuality. Using individual-based models, we clarify how sexually antagonistic coevolution and mate availability affect the likelihood that a mutant allele that gives virgin females the ability to reproduce parthenogenetically will invade an obligately sexual population. We show that male coercion cannot stop the allele from spreading because mutants generally benefit by producing at least some offspring asexually prior to encountering males. We find that effects of sexual conflict can lead to positive frequency-dependent dynamics, where the spread of the allele is promoted by effective (no-cost) resistance when males are common, and by mate limitation when sex-ratios are female-biased. However, once the mutant allele fixes, effective coercion prevents the complete loss of sex unless linkage disequilibrium can build up between the allele and alleles for effective resistance. Our findings clarify how limitations of female resistance imposed by the genetic architecture of sexual antagonism can promote the maintenance of sexual reproduction. At the same time, our finding of widespread obligate sex when costs of parthenogenesis are high suggests that developmental constraints could contribute to the rarity of facultative reproductive strategies in nature.
Reproductive mode outcomes from discrete-trait models
This data was obtained from simulations of the discrete-trait models (25 runs per parameter combination), showing the number of simulation runs ending in different reproductive mode outcomes. These data were used to create Figure 4 and Figure S1
SINGLE_LOCUS_Reproductive_mode_outcomes_JEB.csv
P allele outcomes from discrete-trait models
This data was obtained from simulations of the discrete-trait models (25 runs per parameter combination), showing the number of simulation runs ending in different P allele outcomes. These data were used to create Figure 4 and Figure S1
SINGLE_LOCUS_P_allele_outcomes_JEB.csv
Reproductive mode outcomes from the continuous-trait model
This data was obtained from simulations of the continuous-trait model (25 runs per parameter combination), showing the number of simulation runs ending in different reproductive mode outcomes. These data were used to create Figure S3.
MULTI_LOCUS_Reproductive_mode_outcomes_JEB.csv
P allele outcomes from the continuous-trait model
This data was obtained from simulations of the continuous-trait model (25 runs per parameter combination), showing the number of simulation runs ending in different P allele outcomes. These data were used to create Figure S3.
MULTI_LOCUS_P_allele_outcomes_JEB.csv
Parthenogenetic reproductive output from the discrete-trait resistance model
This data was collected for 25 runs of the discrete-trait 'resistance' model. It shows the cumulative number of offspring produced parthenogenetically at certain timepoints for different female genotypes. This data was used to create Figure 2.
data.collected.every.timestep.mendl.parth.reproductive.output_25_runs.csv
Parthenogenetic reproductive output BEFORE VS AFTER encounters from discrete-trait models
This data was collected for 25 runs for each of the discrete-trait models. It shows the cumulative number of offspring produced parthenogenetically before and after encounters with males at certain timepoints for different female genotypes. This data was used to create Figure 3.
data.collected.every.timestep.mendl.epistasis.experiment_scarcity_VS_resistance_25_runs.csv
NETLOGO code for discrete-trait model (high density setting)
Use NetLogo version 5.2 to open and view this model. NetLogo can be downloaded for free from https://ccl.northwestern.edu/netlogo/oldversions.shtml. The experiment from which data were collected can be found in the Tools/BehaviorSpace drop-down menu once the file is open.
HighENC.NETLOGO.mendl_additional.nlogo
NETLOGO code for discrete-trait model (low density setting)
Use NetLogo version 5.2 to open and view this model. NetLogo can be downloaded for free from https://ccl.northwestern.edu/netlogo/oldversions.shtml. The experiment from which data were collected can be found in the Tools/BehaviorSpace drop-down menu once the file is open.
LowENC.NETLOGO.mendl_additional.nlogo
NETLOGO code for continuous-trait model (low density setting)
Use NetLogo version 5.2 to open and view this model. NetLogo can be downloaded for free from https://ccl.northwestern.edu/netlogo/oldversions.shtml. The experiment from which data were collected can be found in the Tools/BehaviorSpace drop-down menu once the file is open.
LowENC.NETLOGO.infinit_additional.nlogo
NETLOGO code for continuous-trait model (high density setting)
Use NetLogo version 5.2 to open and view this model. NetLogo can be downloaded for free from https://ccl.northwestern.edu/netlogo/oldversions.shtml. The experiment from which data were collected can be found in the Tools/BehaviorSpace drop-down menu once the file is open.
HighENC.NETLOGO.infinit_additional.nlogo