Data from: Daphnia invest in sexual reproduction when its relative costs are reduced

The timing of sex in facultatively sexual organisms is critical to fitness, due to the differing demographic consequences of sexual vs. asexual reproduction. In addition to the costs of sex itself, an association of sex with the production of dormant life stages also influences the optimal use of sex, especially in environments where resting eggs are essential to survive unfavourable conditions. Here we document population dynamics and the occurrence of sexual reproduction in natural populations of Daphnia magna across their growing season. The frequency of sexually reproducing females and males increased with population density and with decreasing asexual clutch sizes. The frequency of sexually reproducing females additionally increased as population growth rates decreased. Consistent with population dynamic models showing that the opportunity cost of sexual reproduction (foregoing contribution to current population growth) diminishes as populations approach carrying capacity, we found that investment in sexual reproduction was highest when asexual population growth was low or negative. Our results support the idea that the timing of sex is linked with periods when the relative cost of sex is reduced due to low potential asexual growth at high population densities. Thus, a combination of ecological and demographic factors select on the optimal timing of sexual reproduction, allowing D. magna to balance the necessity of sex against its costs.Data for clutchsize and sex ratioThis data contains the information of the females carrying asexual eggs from each pond and information on the asexual clutch size as well as the sex of the offspring. Each sample number contains up to 10 entries for individual females from the same sampling event and pond. Additionally, we recorded whether the females next clutch contained an ephippium.ClutchsizeData.txtData for Cost of sex lab experimentThis is the data for the analysis of the lab experiment in the Reproductive life-history trade-offs. The data contains the ID, the treatment (light or dark) the birth and death date (where the death date is censored), C1, C2, C3 etc is the date of the first, second, third etc. clutch and the number of males and females or ephippia in the respective clutch.ReproductiveLHTO.txtPopulationSamplingDataThis file contains the data from the population sampling containing the counts of the different categories(females with eggs, females with ephippium, males, etc) for every sampling event and pond. The dataset also contains density information as well as growth rates, birth rates and death rates (calculated for a 3-day interval)