Extreme sexual size dimorphism correlates with proxies of postcopulatory sexual selection across selected <em>Dolomedes</em> fishing spiders

Sexual size dimorphism (SSD) and mating system diversity are key factors shaping reproductive evolution, yet their relationships with post-mating sexual selection remain incompletely understood. Here, we use a comparative framework across multiple species of Dolomedes fishing spiders to examine how mating systems, sperm production strategies, and proxies of postcopulatory selection relate to SSD. We quantified testes size and spermatogenesis in three closely related species— D. tenebrosus, D. okefinokensis, and D. scriptus —that differ in mating system and SSD. Dolomedes tenebrosus, a monogynous species with extreme female-biased SSD (eSSD) and male self-sacrifice, showed evidence of termination of spermatogenesis at maturity, indicating a terminal investment strategy. Dolomedes okefinokensis exhibited a similar pattern, suggesting convergent evolution toward monogyny. In contrast, D. scriptus, with moderate SSD and a polygynous system, maintained continuous spermatogenesis, consistent ..., , # Data from: Extreme sexual size dimorphism correlates with proxies of postcopulatory sexual selection across selected *Dolomedes* fishing spiders Dataset DOI: [10.5061/dryad.cfxpnvxn8](https://doi.org/10.5061/dryad.cfxpnvxn8) ## Description of the data and file structure Data of histological (TableS2_testis_volume.pdf, TableS3_histology_specimen.pdf) and microCT analysis (TableS1_spermophor_volume.pdf) as well as the results (TableS4_MCMCglmm_analysis_results.pdf, TableS5_GLMM_analysis_results.pdf) and R scripts for the trait analysis (GLMM_spermatogensis.R, mcmcGLMM.R) based on the ultrametric phylogenetic tree topology (MCMCtree.tre). **Variables:** * CL: carapace length measured from the most anterior to posterior point of the prosoma * CW: carapace width measured in the widest part of the prosoma * extrapolated weight: estimated weight from prosoma width using a regression model for Lycosidae (see Methods section for more detail) * rel. spermophor volume: the relative volume o..., ,