DOI: 10.5061/dryad.811h1
title: Data from: Within-population covariation between sexual reproduction and susceptibility to local parasites

description: Evolutionary biology has yet to reconcile the ubiquity of sex with its
 costs relative to asexual reproduction. Here, we test the hypothesis that
 coevolving parasites maintain sex in their hosts. Specifically, we
 examined the distributions of sexual reproduction and susceptibility to
 local parasites within a single population of freshwater snails
 (Potamopyrgus antipodarum). Susceptibility to local trematode parasites
 (Microphallus sp.) is a relative measure of the strength of coevolutionary
 selection in this system. Thus, if coevolving parasites maintain sex,
 sexual snails should be common where susceptibility is high. We tested
 this prediction in a mixed population of sexual and asexual snails by
 measuring the susceptibility of snails from multiple sites in a lake.
 Consistent with the prediction, the frequency of sexual snails was tightly
 and positively correlated with susceptibility to local parasites.
 Strikingly, in just two years, asexual females increased in frequency at
 sites where susceptibility declined. We also found that the frequency of
 sexual females covaries more strongly with susceptibility than with the
 prevalence of Microphallus infection in the field. In linking
 susceptibility to the frequency of sexual hosts, our results directly
 implicate spatial variation in coevolutionary selection in driving the
 geographic mosaic of sex.
description: coordinatesThis file contains the latitude and longitude for each of the 13 sites sampled in this study. Coordinates were obtained from Google Earth. Data columns are as follows: (1) site (n=13); (2) latitude; (3) longitude.experimental dataThis file contains the full results of the inoculation experiment from which susceptibility and the proportion of sexual females were determined for 13 sites in each of three years. Juvenile snails from each were exposed to high doses of parasites from Lake Alexandrina. Following parasite development, snails were evaluated for sex, infection and reproductive mode. Data columns are as follows: (1) year (n=3; 2013, 2014, and 2015); (2) site (n=13); (3) replicate (n=3-6 depending on year); (4) sexual: number of sexual females in the replicate; (5) asexual: the number of asexual females; (6) healthy: the total number of healthy females; (7) infected: the total number of females infected with Microphallus; (8) healthy_sexual: the number of healthy, sexual females; (9) infected_sexual: the number of sexual females infected with Microphallus. Columns 4 and 5 give the proportion of sexual females at a site. Columns 6 and 7 give overall susceptibility, while 8 and 9 give susceptibility of sexual females only. In 2014, the proportion of sexual females was obtained from 6 experimental replicates, and susceptibility from 3.experimental+data.csvtemporal changeThis file contains the change in susceptibility and proportion sexual females at each site through time. The change is calculated as the value in 2015 minus the value in 2013. Data columns are as follows: (1) site (n=13); (2) sex: change in the proportion of sexual females; (3) susceptibility: change in overall susceptibility; (4) sexual_susceptibility: change in susceptibility of sexual females.change.csvprevalenceThis file contains the length-corrected estimates of infection prevalence for each site in 2013 through 2015. Length-corrected estimates are given for all females and for sexual females only. The length-corrected estimates of infection prevalence for all females were obtained from Gibson et al. (2016, Am Nat). The raw data for those estimates are associated with that publication – Dryad Digital Repository: http://dx.doi.org/10.5061/dryad.t89hc. The length-corrected estimates of infection prevalence for sexual females only were obtained in the same manner as described in Gibson et al. (2016, Am Nat): they are the estimated marginal means for infection prevalence obtained from a generalized linear model with site, year, their interaction and shell length (mm, covariate) as predictors of the probability of infection of an individual, sexual female. The raw data for those estimates are included in this Dryad data package, with field_data.csv. Infection prevalence of sexual females was only available for 2014-2015. Data columns are as follows: (1) year (n=3); (2) site (n=13); (3) prevalence_lc: length-corrected prevalence for all females; (4) prevalence_sexual_lc: length-corrected prevalence for sexual females.field dataThis file contains data for individual female snails collected from our 13 field sites in 2014 and 2015. These data were used in validating our results for variation in the proportion of sexual females between sites and for estimating the infection prevalence of sexual females. Data columns are as follows: (1) year (n=2); site (n=13); (3) length: shell length in millimeters; (4) infected: 0 for healthy, 1 for castrated with Microphallus; (5) ploidy: 2 for diploid sexual and 3 for triploid asexual.field_data.csv