Collaborative Research: RUI: Keystone molecules and estuarine foodwebs: chemical defense and a novel biosynthetic pathway in a common mudflat mollusc

Occidental College, Los Angeles CA

Investigators

Abstract

Estuaries are ecologically sensitive nursery habitat for many economically important coastal species. A potentially important but understudied food resource for migratory waterbirds, juvenile fish, and diverse invertebrate predators are small sea slugs (genus Alderia), which can occur in dense aggregations of over 1,000 slugs per square meter on temperate mudflats throughout the Northern Hemisphere. We hypothesize that Alderia use a recently discovered branch of metabolism to make bad-tasting molecules termed polyketides, a family of compounds that include medically important drugs. We will characterize new polyketides from these abundant slugs, test how they repel predators, and then explore how they may affect many other aspects of the ecosystem. Potential effects of these slug compounds include changing the bacteria in the mud through antibiotic effects; repelling some animal species that live in the mud while attracting others; and causing the evolution of slug mimicry in palatable ‘roly-polies’ that co-occur on the mudflat. These studies will provide new insight into how energy moves through the food-chain in estuaries, and how one species can have unexpected effects on many surrounding species in its ecosystem. We will also study how climate change has altered the distribution of slug species (and hence their compounds) along the U.S. west coast, which may have cascading but previously unrecognized effects on the inhabitants of threatened estuaries. Finally, the project will support the collaboration between two primary undergraduate institutions, one of which is Hispanic serving and a large research institution, via the collaboration between the three school many undergraduate and master’s students will be supported each year by the project. The project will focus on the recruitment of students historically underrepresented in science to the proposed research and outreach activities. We will test whether polyketide (PK) compounds produced by sea slugs function as keystone molecules, altering energy flow and community structure in Northern Hemisphere estuaries. Small sea slugs (Alderia) are exceptionally abundant (>1000/m2) on mudflats, representing a potential resource for diverse fish, bird and invertebrate consumers. We will characterize a biosynthetic pathway and novel PK metabolites produced by slugs, and determine if PKs protect Alderia from wetland predators using a combination of laboratory and field assays with extracts and pure compounds. We will then estimate the net loss of primary production to higher trophic levels due to this chemical defense. The rapid evolution of Batesian mimicry in introduced isopods along the U.S. west coast will be assessed in this system to understand how chemical defense and visual predation affect phenotypic evolution of co-occuring organisms over short timescales. Manipulative experiments will test the effects of PKs on the microbiome and infaunal community of mudflats to determine the impact of shed compounds on diverse ecological processes in this sensitive nursery habitat. These studies will address, from gene to ecosystem, the impacts of potential keystone compounds synthesized as an antipredator defense in a common temperate mollusc. Modeling studies will explore the basis for range limits and the effects of ongoing climate change on shifting range boundaries between two Alderia species. These results will collectively provide new insight into how global change may alter the distribution of keystone molecules and thus have unanticipated effects on communities in already-threatened habitats such as estuaries. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.