Data and code from: Group size dependent selection for cooperation versus freeloading in collective chemical defence

Cooperation in public goods is expected to evolve more rapidly in smaller groups than in larger groups because individuals receive a larger share of the benefits, reducing the benefits of freeloading. However, experimental evidence for this hypothesis remains limited to microorganisms, restricting our understanding of the evolution of cooperative traits. Here, we show that in the collectively defending larvae of Neodiprion sertifer, survival against predation is higher in cooperative groups, with the benefits of cooperation more pronounced in small groups (5 larvae) than in large groups (20 larvae). Individuals also participate less in collective defence in larger groups, not because of higher life-history costs resulting from increased resource competition, but because they adjust their contribution according to group size. These results provide novel empirical evidence that selection for cooperation in collective goods is group size-dependent, promoting cooperation in smaller groups, ..., , # Data and code from: Group size dependent selection for cooperation versus freeloading in collective chemical defence

Dataset DOI: [10.5061/dryad.jq2bvq8pc](https://doi.org/10.5061/dryad.jq2bvq8pc)

## Description of the data and file structure

This dataset contains the experimental data required to replicate statistical analyses from Van Meyel et al. (submitted). The data were collected during two experiments testing how group size influences the selection for cooperation in collective chemical defence in the gregarious pine sawfly (Neodiprion sertifer). The first experiment used larvae of N.sertifer  collected in Puumala, Finland in June 2023. Experimental treatments manipulated group size (5 or 20 larvae) and group level of cooperation (control vs. low level of defence) and the larval survival was measured against predation by wood ants. The second experiment conducted in 2017 used F1 generation of N.sertifer from Puumala and Pieksämäki, Finland. Experimental treatments manipulate..., ,