Secondary sexual traits increase male fitness, but may be maladaptive in females, generating intralocus sexual conflict that is ameliorated through sexual dimorphism. Sexual selection on males may also lead some males to avoid expenditure on secondary sexual traits and achieve copulations using alternative reproductive tactics (ARTs). Secondary sexual traits can increase or decrease fitness in males, depending on which ART they employ, generating intralocus tactical conflict that can be ameliorated through male dimorphism. Due to the evolutionary forces acting against intralocus sexual and tactical conflicts, male dimorphism could coevolve with sexual dimorphism, a hypothesis that we tested by investigating these dimorphisms across 48 harvestman species. Using three independently derived phylogenies we consistently found that the evolution of sexual dimorphism was correlated with that of male dimorphism, and suggest that the major force behind this relationship is the similarity between selection against intralocus sexual conflict and selection against intralocus tactical conflict. We also found that transitions in male dimorphism were more likely in the presence of sexual dimorphism, indicating that if a sexually selected trait arises on an autosome and is expressed in both sexes, its suppression in females probably evolves earlier than its suppression in small males that adopt ARTs.

Measurements of all individualsThis file is an excel workbook where each spreadsheet contains all the measurements for the species used in the study. For some species, the inference about sexual and male dimorphism was based on information in the literature, and these species are not in this data-set. For all other species (45 spp), the data-set contains measurements of: (1) length of the dorsal scute (carapace); (2) length of the lateral apophysis on the coxa of the right fourth leg; and (3) length of the femur of the fourth leg. All measurements are in mm. Some species did not present the coxal apophysis, and therefore there is no data for that structure in their spreadsheet.