Data related to: "A different perspective on the cost of sex"

Sexual reproduction in most animals and its coexistence with parthenogenetic lineages remains paradoxical. The typical 'all-else-equal' explanatory model assumes that sexual and parthenogenetic females both invest identical amounts of resources in reproduction. This leads to a twofold net reproduction rate R0, and exponential growth in the parthenogenetic lineage since it does not invest in the production of males. A sexual lineage must compensate for the different growth rate by substantial advantages in resource allocation and/or survival rate, commonly referred to as the 'cost of sex'. While sexual lineages need to produce one female and one male offspring in every generation, a balance between the reproductive modes could be reached if parthenogenetic lineages had a 50% lower reproductive investment, towards their theoretical lower limit of one female offspring. This 'resource-reduction' would lead to similar net reproduction rates for both reproductive modes and enable their coexistence. Here, we demonstrate that such a resource-reduction characterizes communities comprising of sexual and parthenogenetic decomposer microarthropods: oribatid mites.
By counting the numbers of eggs carried by gravid females, we aimed to approximate net reproduction rates of oribatid mites, including data from seasonal samplings and various microhabitats from different regions and forest types in Germany over a period of 14 years. We examined 77,868 individuals (44,671 and 33,197 sexual and parthenogenetic, respectively) from 104 species (84 sexual and 20 parthenogenetic). Gravidity did not differ between reproductive modes – 47% of sexual vs 45% of parthenogenetic females carried eggs – nor did the relative egg size. By contrast, the numbers of eggs differed dramatically: parthenogenetic females carried on average 1.4 eggs, while sexuals had 2.7 eggs. The reproductive investment of parthenogens, as compared to sexuals, was very close to the 50% expected under the 'resource-reduction' hypothesis. In consequence, estimated net reproduction rates did not differ between the reproductive modes and we conclude that the stable coexistence of parthenogenetic and sexual species in equilibrium communities could be explained by harmonized population dynamics.