Cooperation in Context: Biotic and abiotic drivers of interaction outcome in cleaner shrimp-client fish mutualisms

Brown University, Providence RI

Investigators

Abstract

Determining when, and with whom, to cooperate, is a central challenge for many organisms. Even when cooperation seems the obvious outcome—as in mutualisms, interactions between species where cooperation results in benefits to each party—huge variation is seen in the outcome of an interaction. However, there are major knowledge gaps in our understanding of why this variation exists. This project explores these knowledge gaps in cleaning mutualisms in which cleaner shrimp, which live in groups at “cleaning stations,” remove and eat parasites from their reef fish “clients.” Specifically, Biological Market Theory (BMT) is used as a framework for understanding variation in cleaning mutualisms based on economic principles from human marketplaces. In both mutualisms and marketplaces, individuals exchange goods or services (in an economic marketplace, goods are exchanged for cash; in a mutualistic marketplace, parasite removal services are exchanged for food), and interactions can be positive, neutral, or negative for either party depending on supply and demand, and the costs and benefits of cooperating. This project combines field and lab experiments, behavioral observations, and mathematical modeling to explore several factors related to supply, demand, and the costs and benefits of interacting, and how they affect the decisions of cleaners and clients to interact cooperatively with one another. This project will provide research experiences to a postdoctoral researcher, scientific dive certifications and fieldwork experience to two undergraduates from underrepresented backgrounds in marine science, and outreach to the public through community events and a podcast series. This project enhances our understanding of context-dependency in mutualism by focusing on how three aspects of the context in which a cleaning interaction occurs—the “intragroup context,” the composition of the cleaner group, the “interspecific context,” the presence or behaviors of third-party species not directly involved in the mutualism, and the “spatial context,” the density and distribution of cleaning stations—link to extensive observed variation in interaction outcome, cleaning service quality, and decisions by cleaners and clients. Specifically, BMT predicts that (1) service quality should vary depending on contextual factors that affect supply and demand, and (2) individuals in mutualisms should assess potential partners and choose to interact only with those that provide the highest service quality. This work will combine non-invasive camera-based observations and experimental manipulations in nature with behavioral experiments in the lab and a spatially-explicit mathematical model of cleaning station distribution. Understanding how does the broader biotic (e.g., group or interspecific) or abiotic (e.g. spatial) context affect these crucial interactions, and what ecological and behavioral factors correlate with variation in mutualistic interaction outcome is important, since variation in the outcome of species interactions affects both the ecology of communities (e.g., variation in population growth and stability), and the evolution of species (e.g., the strength of selection on certain traits). Answers to these questions are currently lacking, especially in nature, but promise to significantly deepen our understanding of how mutualisms evolve, persist, and function. 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.