The evolution of nuptial gifts has traditionally been considered a harmonious affair, providing benefits to both mating partners. There is growing evidence, however, that receiving a nuptial gift can be actively detrimental to the female. In decorated crickets (Gryllodes sigillatus), males produce a gelatinous spermatophylax that enhances sperm transfer but provides little nutritional benefit and hinders female post-copulatory mate choice. Here, we examine the sexually antagonistic coevolution of the spermatophylax and the female feeding response to this gift in G. sigillatus maintained in experimental populations with either a male-biased or female-biased adult sex ratio. After 25 generations, males evolving in male-biased populations produced heavier spermatophylaxes with a more manipulative combination of free amino acids than those evolving in female-biased populations. Moreover, when the spermatophylax originated from the same selection regime, females evolving in male-biased populations always had shorter feeding durations than those evolving in female-biased populations indicating the evolution of greater resistance. Across populations, female feeding duration increased with the mass and manipulative combination of free amino acids in the spermatophylax suggesting sexually antagonistic coevolution. Collectively, our work demonstrates a key role for interlocus sexual conflict and sexually antagonistic coevolution in the mating system of G. sigillatus. Collapse README README: Sexually antagonistic coevolution of the male nuptial gift and female feeding behaviour in decorated crickets We subjected replicated populations of decorated crickets to different regimes of interlocus sexual conflict by altering the adult sex ratio to be male-biased (increased conflict) or female-biased (reduced conflict). After 25 generations of experimental evolution we measured how manipulative the nuptial gifts produced by males (the spermatophylax) were. Manipulativeness of the gift is measured by dry mass (measured using an electronic balance) and amino acid composition (measured by GC-MS). We also measured female resistance in these populations as the time the female spent feeding on this gift (through behavioural observations). Description of the data and file structure Microsoft Excel is required to open the data files. We have uploaded 3 files: named "Dryad_Spermatophylax data_raw", "Dryad_Feeding data_raw" and "Dryad_mean spermatophylax and feeding data". "Dryad_Spermatophylax data_raw" contains all of the raw data on how manipulative the nuptial gift is from the replicate populations. The first column "Selection regime" describes whether the population had a male-biased or female-biased adult sex ratio, the second column "Replicate" describes the replicate population (one to six) and the third column "Male SPHYLAX" is an ID for the male that the spermatophylax was taken from. The next 19 columns is the log10 amount of free amino acids in the spermatophylax. The naming of these columns used the conventional abbreviation for these free amino acids and is provided in the manuscript text. The columns labelled "DF1" and "DF1" are discriminant functions derived from these amino acids to determine how populations with alternate selection regimes have diverged. The column "SPHYLAX dry weight (mg)" provides the dry weight of spermatophylaxes and the column named " Manipulation score" provides the multivariate score of how manipulative the free amino acids is to the female (full details on how this is calculated is provided in the manuscript text). "Dryad_Feeding data_raw" provides the raw feeding data of females from each population. "Selection regime" and "Replicate" columns are as described for "Dryad_Spermatophylax data_raw". "SPHYLAX origin" describes the population origin of the nuptial gift presented to female - being either from their "own" population or "crossed" from the same replicate population experiencing the opposite selection regime. " ID" provides the unique identity of females and "Feeding duration (secs)" provides the amount of time the female fed on the gift (in seconds). "Dryad_mean spermatophylax and feeding data" provides the mean data for each of the male manipulation measured and female feeding time taken from the above two data sets. "Selection regime" and "Replicate" are the same as the two above files. "Mean SPHYLAX dry weight" and "Mean manipulation score" are the mean of the data for each replicate population provided in "Dryad_Spermatophylax data_raw". "Mean feeding duration_own population (secs)" and "Mean feeding duration_crossed population (secs)" is the mean feeding time of females when recieving a gift from their own population or crossed from the opposite selection regime, respectively. These mean estimates come from "Dryad_Feeding data_raw". Sharing/Access information Links to other publicly accessible locations of the data: The data contained on Dryad will be also be made publically available via the Research Data Management System at Western Sydney University. Data was derived from the following sources: All uploaded data has been collected from experiments conducted by the authors. Code/Software No code is provided. All analyses were conducted using IBM SPSS (version 29.0.0.0). Methods We manipulated the intensity of interlocus sexual conflict in replicate experimental population by manipulating the adult sex ratio to be either male -biased (increased conflict) or female-biased (reduced conflict). This was done for 25 generations of evolution. We then measured the manipulative properties of the male nuptial gift (the spermatophylax) in these populations (spermatophylax dry mass and amino acid composition), as well as female feeding duration on these gifts (as a measure of resistance to manipulation). We present the raw data and population mean data for these traits. Spermatophylax dry mass was measured using an electronic balance. Spermatophylax amino acid composition was measured using GC-MS. Female feeding behaviour was measured in behavioural assays. Usage notes Data is presented in Microsoft Excel.