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Abstract
After birth, mammals acquire a community of bacteria in their gastro-intestinal tract, which harvests energy and provides nutrients for the host. Comparative studies of numerous terrestrial mammal hosts have identified host phylogeny, diet and gut morphology as primary drivers of the gut bacterial community composition. To date, marine mammals have been excluded from these comparative studies, yet they represent distinct examples of evolutionary history, diet and lifestyle traits. To provide an updated understanding of the gut bacterial community of mammals, we compared bacterial 16S rRNA gene sequence data generated from faecal material of 151 marine and terrestrial mammal hosts. This included 42 hosts from a marine habitat. When compared to terrestrial mammals, marine mammals clustered separately and displayed a significantly greater average relative abundance of the phylum Fusobacteria. The marine carnivores (Antarctic and Arctic seals) and the marine herbivore (dugong) possessed significantly richer gut bacterial community than terrestrial carnivores and terrestrial herbivores, respectively. This suggests that evolutionary history and dietary items specific to the marine environment may have resulted in a gut bacterial community distinct to that identified in terrestrial mammals. Finally we hypothesize that reduced marine trophic webs, whereby marine carnivores (and herbivores) feed directly on lower trophic levels, may expose this group to high levels of secondary metabolites and influence gut microbial community richness.
Highlights
Bacteria inhabiting the gastro-intestinal tract of mammals expand their host’s metabolic potential by harvesting energy that would otherwise be inaccessible [1,2,3]
The gut morphology of hosts did not contribute to significant differences in the gut bacterial community (Table 1)
The influence of captivity in leopard seals was identified as a strong driver of the gut bacterial community [17]
Summary
Bacteria inhabiting the gastro-intestinal tract of mammals expand their host’s metabolic potential by harvesting energy that would otherwise be inaccessible [1,2,3]. This symbiosis between mammals and bacteria has contributed, in part, to the success of the class Mammalia, allowing them to radiate in large numbers to occupy a variety of environmental niches [3,4]. Genetic factors within the host shape the gut bacterial community, a result of their long history of co-evolution [9,10,11]. This is evident in the strong physiological effects which the gut bacterial community can exert on the host mammal, such as modulating the immune response system or affecting brain development [12,13]
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