The consortium of microbes that live in and on an organism can strongly influence the host's condition and fitness. Fish are the most diverse vertebrate group, but little is known about their microbial constituents of fish or how they impact their ecology and evolution. To explore factors that shape fish microbial communities, this project investigates the variation in gut bacteria across fish using three major model systems: sticklebacks, guppies and Tanganyikan cichlids. This work aims to determine how fish gut microbial communities have shifted in response to alterations in diet, trophic level, and habitat, and to determine how fish adaptations (i.e., to different feeding ecologies) may feed back and affect the microbial communities within their environment. An experimental approach with sticklebacks and guppies will investigate the variability of gut microbes due to diet and habitat as well as the impact of fish ecology on bacterial communities in the environment. The work on cichlids will investigate broad scale patterns of gut microbial communities across multiple, related species that have diverse diets.
This investigation will address the role of evolutionary history and diet in structuring microbial communities across wild fish populations, laying groundwork for future studies on their functional contributions to fish ecology. By enhancing the understanding of what constitutes a typical gut bacterial community of wild fish, this research will also provide insights into fish health and physiology. The PIs will train undergraduates, use next-generation sequencing technologies, and integrate data generated from this project in undergraduate coursework. They will also disseminate findings to the public through popular and peer-reviewed articles and presentations at scientific meetings.
Through this dissertation research grant, we focused on studying the gut microbial communities of Tanganyikan fish to explore how changes in diet shape gut microbial communities over long, evolutionary timescales, with particular focus on cichlids. Within Lake Tanganyika multiple lineages of cichlids have rapidly diversified to feed on substantially different diets. Through surveying the microbial communities of 32 fish species from the Tanganyikan system, we investigated how gut microbial communities are structured according to diet and fish relatedness. Our results have yielded several significant findings, including that gut microbial community composition varies according to diet. Additionally, we found particularly divergent gut microbial communities in herbivores and zooplanktivores. We also found that the diversity of gut microbial communities of fish decreases with increasing trophic level (i.e. placement on the food chain), so that herbivorous fish have greater microbial diversity than carnivorous fish. We also focused on two herbivorous species to explore how geographic location within the lake affects cichlid gut microbial community structure. By examining the gut microbial communities of these two species, which were collected from 8 different locations, we found clear differences in gut microbial community structure between them. We also saw site differences in microbial diversity, supporting previous findings that gut microbial communities are shaped by both host genetics and environment. This research has enabled a better understanding of how ecology, diet and relatedness influence the bacterial community diversity and structure within fish communities. We have presented our research and findings through various forms of outreach, including presentations at secondary schools, universities and scientific meetings. We are currently preparing our findings for publication in scientific journals.
