Multiple colonist pools shape fiddler crab-associated bacterial communities

Abstract

Colonization is a key component of community assembly because it continuously contributes new species that can potentially establish and adds individuals to established populations in local communities. Colonization is determined by the regional species pool, which is typically viewed as stable at ecological time scales. Yet, many natural communities including plants, birds and microbes, are exposed to several distinct and dynamic sources of colonists and how multiple colonist pools interact to shape local communities remains unclear. Using a 16S rRNA amplicon survey, we profiled bacteria within surface, subsurface and burrow sediments and assessed their role as colonist pools for fiddler crab-associated bacteria. We found significant differences in composition among sediment types, driven by halophilic taxa in the surface, and different Desulfobacteraceae taxa in the subsurface and burrow. Bacteria from burrow sediment colonized the crab carapace whereas gut bacterial communities were colonized by burrow and surface sediment bacteria. Despite distinct colonist pools influencing gut bacteria, variation in composition across gut samples did not lead to significant clusters. In contrast, carapace bacterial communities clustered in six distinct groups loosely associated with crab species. Our findings suggest that multiple colonist pools can influence local communities but factors explaining variation in community composition depend on local habitats. Recognizing multiple colonist pools expands our understanding of the interaction between regional and local processes driving community structure and diversity.

Key colonist pools and habitat filters mediate the composition of fiddler crab–associated bacterial communities

“…High similarity in species composition between a local community and a colonist pool reflects strong influence of immigration from that specific source, and thus reveals the main colonist pool. In a previous study, comparing bacterial communities from fiddler crabs and sediment revealed that surface and burrow sediment bacteria colonize fiddler crab carapaces and guts (Cuellar‐Gempeler and Leibold ). These results coincide with the fiddler crab natural history because these crabs feed on organic matter, microalgae, and bacteria by scraping the surface sediment (Dye and Lasiak ), and build J‐shaped burrows to escape from predation and extreme temperatures (Kristensen ).…”

“…We expect burrow sediment to represent the main colonist pool for carapace bacterial communities, whereas surface sediment might contribute fewer, but possibly important key colonists. Based on previous findings (Cuellar‐Gempeler and Leibold ), we expect the gut to receive a mix of colonists from the surface and burrow sediments. However, we expect that strong habitat filters imposed by oral apparatus and hepatopancreas secretions (Vogt et al.…”

“…, salamanders: Loudon et al. , crabs: Cuellar‐Gempeler and Leibold ), this is the first study that quantifies the specific contribution of different colonist pools and their influence on host‐associated microbial communities. Particularly, colonist pool manipulation can reveal contributions from colonist pools that are not similar to local communities, such as key colonist pools.…”

“…). Thus colonist pools can be thought of as subsets of the regional species pool shaped by large‐scale prefiltering and dispersal limitation (Cuellar‐Gempeler and Leibold ). For example, many plant communities receive colonists from the seed rain and seed bank, and which colonist pool is better represented within local a community depends on the soil properties of local habitats (Kalamees and Zobel , Willems and Bik , Wolters and Bakker ).…”

“…For example, many plant communities receive colonists from the seed rain and seed bank, and which colonist pool is better represented within local a community depends on the soil properties of local habitats (Kalamees and Zobel , Willems and Bik , Wolters and Bakker ). Although multiple coexisting sources of colonists are not uncommon (birds: Graves and Gotelli ; plants: Willems and Bik ; bacteria: Cuellar‐Gempeler and Leibold ), the influence of multiple colonist pools on local diversity and composition is still poorly understood.…”