Genitalia are multitasking structures whose development is mediated by numerous regulatory pathways. This multi-factorial nature provides an avenue for multiple sources of selection. As a result, genitalia tend to evolve as modular systems comprising semi-independent subsets of structures, yet the processes that give rise to those patterns are still poorly understood. Here, we ask what are the relative roles of development and function in shaping modular patterns of genitalia within populations and across species of stink-bugs. We found that male genitalia are less integrated, more modular, and primarily shaped by functional demands. In contrast, females show higher integration, lower modularity, and a predominant role of developmental processes. Further, interactions among parts of each sex are more determinant to modularity than those between the sexes, and patterns of modularity are equivalent between and within species. Our results strongly indicate that genitalia have been subjected to sex-specific selection, although male and female genitalia are homologous and functionally associated. Moreover, modular patterns are seemingly constant in the evolutionary history of stink-bugs, suggesting a scenario of multivariate stabilizing selection within each sex. Our study demonstrates that interactions among genital parts of the same sex may be more fundamental to genital evolution than previously thought.

We collected genital data using geometric morphometrics and converted landmarks to Jacobian matrices, which were used in the tests of modularity and integration. Here we provide the Jacobian data along with R codes, the phylogenetic trees and all other necessary files for analyses of intra- and interspecific levels and for males and females. Please see the "read.me" file for a complete description of the files, and the paper for detailed methodological procedures.