Phenotypic clines in herbivore resistance and reproductive traits in wild plants along an agricultural gradient

Abstract

The conversion of natural landscapes to agriculture is a leading cause of biodiversity loss worldwide. While many studies examine how landscape modification affects species diversity, a trait-based approach can provide new insights into species responses to environmental change. Wild plants persisting in heavily modified landscapes provide a unique opportunity to examine species’ responses to land use change. Trait expression within a community plays an important role in structuring species interactions, highlighting the potential implications of landscape mediated trait changes on ecosystem functioning. Here we test the effect of increasing agricultural landscape modification on defensive and reproductive traits in three commonly occurring Brassicaceae species to evaluate plant responses to landscape change. We collected seeds from populations at spatially separated sites with variation in surrounding agricultural land cover and grew them in a greenhouse common garden, measuring defensive traits through an herbivore no-choice bioassay as well as reproductive traits such as flower size and seed set. In two of the three species, plants originating from agriculturally dominant landscapes expressed a consistent reduction in flower size and herbivore leaf consumption. One species also showed reduced fitness associated with increasingly agricultural landscapes. These findings demonstrate that wild plants are responding to landscape modification, suggesting that the conversion of natural landscapes to agriculture has consequences for wild plant evolution.

Agricultural landscape simplification affects wild plant reproduction indirectly through herbivore-mediated changes in floral display

“…Previous work on B. vulgaris documented lower leaf consumption in herbivore bioassays (suggesting higher resistance) and smaller flower size (suggesting reduced pollinator visitation) for plants originating from simplified landscapes 56 . Therefore, we expect that for phytometer plants landscape simplification will increase herbivore damage (Fig.…”

“…Barbarea vulgaris , known commonly as yellow rocket, was selected as a model species because it can be found growing in high abundance in a diversity of landscapes from predominantly natural to those dominated primarily by agriculture 56 . Although B. vulgaris is not native, it has been naturalized in North America for more than 200 years and has a rich community of pollinators and herbivores.…”

“…Within a 500, 1000, and 1500 m radius of each experimental plot, we calculated the proportion of land cover categorized as agriculture, pasture, urban development, natural open, and natural forested land area. Given the high number of landscape variables and scales, we retained three land cover classifications found in previous work to be most predictive of Brassicaceae trait variation (agriculture, non-forest natural land cover, and pasture) 56 and then conducted a principal component analysis to produce PC1 and PC2 values that summarized the relative landscape composition of each source site (Fig. 3 ).…”

“…B. vulgaris has been present in North America for over 200 years and documented in the Finger Lakes region for over 50 years 60 , and therefore has been established long enough for local adaptation to occur. Further, the landscape composition has been stable in this region for at least the last decade, potentially allowing for adaptation to the gradient of landscape simplification 56 . If the resident plants are locally adapted, we do not expect that the landscape will affect herbivory (Fig.…”

Harnessing Computational Methods to Characterize Chemical Impacts on Biodiversity

“…In the lab, different bioassays can be used to monitor functional traits to inform ecosystem function. For example, the relationship between insect herbivores and plants can be tested through choice and no choice assays to monitor changes in both herbivore feeding behavior and plant defenses following ecosystem disturbance. , The Gammarus feeding assay can be used to monitor the behavioral response of gammarids to environmental contaminants, which is crucial as macroinvertebrate feeding is a rate-limiting step in organic matter decomposition in streams . However, as with assays for other levels of biological organization, the utility of short-term bioassays to predict long-term effects from chemical pollution is limited.…”