Award: OCE-1608709

Microbial symbionts can be important for the survival of their animal hosts by contributing to host nutrition of defense. The marine invertebrate, Bugula neritina, possesses a bacterial symbiont that produces bioactive compounds that are distasteful to animals that prey on the host; interestingly, these compounds have been studied for their anticancer, anti-Alzheimer’s disease, and anti-HIV properties. While the B. neritina is found in coastal environments around the world, not all of the colonies possess the microbial symbiont. In this project, we investigated the role of environmental factors, such as temperature, salinity, and predation pressure, on the distribution of the symbiotic bacterium and its animal host along the East Coast of the United States. We found that factors like latitude, and average temperature were important in the distribution of the symbiont in colonies, with more colonies that live at lower latitudes and higher temperatures possessing the symbiont. Conversely, we also found that populations in close proximity can be significantly different from one another, suggesting that local pressures also impact these populations. It is unclear how the symbiont is lost in individual B. neritina colonies, so we measured relative symbiont levels in colonies grown at different temperatures and in the presence of predators. We showed that colonies grown in these different conditions had symbiont levels close to that of their parents while they are younger, but as they get older, the symbiont levels change in an unpredictable way. All in all, neither temperature nor predation pressure seem to be the cause of these changes, and these data show a high level of plasticity in the symbiotic state of the offspring. In addition, while symbiont titers are highly variable in B. neritina colonies, the presence of the symbiont impacts the other microbes that associate with B. neritina. Taken together, it appears that the interaction between B. neritina and its symbiont is highly variable. Last Modified: 11/24/2020 Submitted by: Nicole B Lopanik