Relaxation of putative plant defenses in a tropical agroecosystem

Evidence of the effects of agriculture on natural systems is widespread, but potential evolutionary responses in non-target species are largely uncharacterized. To explore whether exposure to agrochemicals may influence selective pressures and phenotypic expression in non-agricultural plant populations, we characterized the expression of putative anti-herbivore defense phenotypes in three non-agricultural species found upstream and downstream of irrigated rice fields in Guanacaste Province, Costa Rica. We found that plants downstream of chemically intensive agriculture showed shifts toward reduced expression of putative anti-herbivore defenses relative to upstream counterparts. In two of three tested species, leaf extracts from downstream plants were more palatable to a generalist consumer, suggesting a possible reduction of chemical defenses. In one species with multiple modes of putative defenses, we observed parallel reductions of three metrics of putative biotic and physical defense...