A La Carte Seed Harvesting: <i>Messor barbarus</i> Ants Select Durum Wheat Genotypes

Biotic interactions between plants and insects can drive key evolutionary processes. In Mediterranean agroecosystems, the harvester ants <i>Messor barbarus</i> (Hymenoptera: Formicidae) frequently collect seeds, including those of cultivated cereals. Yet their potential role in shaping crop traits remains poorly understood. This study investigates whether harvester ant seed predation is driven by genetic and phenotypic variation in durum wheat (<i>Triticum turgidum</i> ssp. <i>durum</i>), a major Mediterranean crop derived from wild emmer (<i>T. turgidum</i> ssp. <i>dicoccoides</i>). Using a panel of 180 genetically diverse durum wheat inbred lines grown in a field experiment, we visually recorded spike predation and performed a genome-wide association study (GWAS) using SNP markers to assess the genetic architecture of susceptibility to seed predation by <i>M. barbarus</i>. We identified a significant quantitative trait loci (QTL) on chromosome 2A explaining 21% of the variation in predation rate. This region contains a 3.6 Mb chromosomal inversion and 46 candidate genes, including a MYB transcription factor potentially involved in regulating cuticle and chemical traits. To validate these genetic findings, we conducted a cafeteria experiment with 208 spikes from 26 genotypes, placed at the entrances of eight ant nests. Ants preferentially removed spikes from genotypes carrying the allele identified in the GWAS. Additionally, shorter spikes were more likely to be harvested. However, unlike previous studies on wild plants, seed morphology and protein content did not significantly affect ant preference. <i>Synthesis</i>. Our results demonstrate that <i>M. barbarus</i> exhibits genotype-specific preferences in durum wheat, associated with a major QTL, and is influenced by spike traits. This study provides the first evidence of ant-mediated selective pressure in a cereal crop and opens new perspectives on plant-insect dynamics in agroecosystems and the role of plant-insect interactions in the evolutionary history of crop species.