A study titled Similarities and Differences in Gastrointestinal Microbiomes Between Wild and Human-Cared Spotted Dolphins (Stenella attenuata) in Natural Waters, published in the journal Water Biology and Security, with Shijie Bai, an associate Prof. from the Institute of Deep-sea Science and Engineering, Chinese Academy of Sciences as the first author, and Peijun Zhang and Songhai Li as corresponding authors, emphasizes that differences in food sources are a significant factor affecting the composition of the gut microbial communities of spotted dolphins living in similar environments. 

Gut microbes play a crucial role in food digestion and act as the host’s second immune system. Despite growing awareness of their importance, researchers’ understanding of the gut microbial communities of marine mammals remains very limited due to sampling difficulties. The phylogenetic status of the animal itself, living environment, and diet are the main factors influencing the composition of gut microbiota. However, the hierarchical relationship among these three factors is currently unclear. A previous study by the research team showed significant differences in the gut microbiome at the family level and above among marine mammals living in similar dietary and aquatic environments. Building on this, the current study controlled for environmental factors by focusing on the same geographic population of spotted dolphins, emphasizing the impact of food changes on their gut microbiome—wild dolphins naturally forage, while human-cared dolphins are fed a limited variety of fishes.

The study used the V4 region of the 16S rRNA gene to classify gut microbes, revealing significant structural differences in the overall and specific sections of the gastrointestinal microbiota between wild and human-cared dolphins. Interestingly, there was little difference in microbial diversity in their gastrointestinal tracts, suggesting that the differences mainly stem from changes in the composition of the microbial communities.

Researchers identified indicator microorganisms in both the wild dolphin group (five indicative ASVs) and the human-cared dolphin group (three indicative ASVs). Additionally, a large number of potential pathogens were found, highlighting the need for comprehensive future research on the gut microbiology of marine mammals.

The findings of this study not only enhance researchers’ understanding of the gut microbiology of spotted dolphins but also clearly elucidate the similarities and differences in the gastrointestinal microbiota within the same marine mammal species, especially when changes in food sources play a significant role in their ecological lives.

Figure 1: Comparison of the microbial community composition in the hindgut of wild (left) and human-cared (right) spotted dolphins at the phylum (a), family (b), and genus (c) levels