Convergence, constraint and the potential for mutualism between ants and gut microbes

Abstract

Ants are a hugely diverse family of eusocial insects that dominate terrestrial ecosystems all over the planet. Did mutualistic gut microbes help ants to achieve their diversity and ecological dominance? Initial studies suggested the potential for widespread convergence in ant gut bacterial communities based on dietary niche, but it now seems possible that dedicated bacterial symbionts are restricted to a minority of ant lineages (Russell et al., 2017). Nevertheless, as most ants are omnivores, the evidence so far has suggested a broad, positive correlation between the evolution of dietary specialization and ant investment in nutrient‐provisioning gut bacteria. In this issue of Molecular Ecology, Sapountzis et al. (2019) and Rubin et al. (2019) examine the evolution of gut bacterial communities in two iconic ant taxa—the attine fungus farmers and the Pseudomyrmex plant bodyguards, respectively—in a comparative context. By comparing gut bacteria between ant species of differing dietary specialization within each taxon, these studies demonstrate a hint of convergence in the midst of widespread apparent constraints. These results raise numerous interesting questions about the nature of these apparent constraints and whether they are causes or consequences of varying investment by ants to mutualism with their gut microbes.

Diet and phylogeny shape the composition, diversity, and structure of the ant-gut bacterial community

“…It was understandable for our herbivorous ants feed on plants (seeds), which contain large amounts of starch. This showed that there is a positive correlation between dietary specialization and the abundance of nutrient-providing bacteria in the ant gut [25]. Similarly, there were signi cant differences in the abundance of dominant gut bacteria among ants with different phylogenies (Fig.…”

“…From the two ternary phase diagrams (Fig. S6), we found herbivorous ants, carnivorous ants, and omnivorous ants developed unique gut bacterial communities [25,42]. In the same way, Ponerinae ants, Formicinae ants, and Myrmicinae ants developed unique gut bacterial communities although the relative abundance of "speci c bacteria" was low.…”

“…The guts of herbivorous ants may symbiose with groups of bacteria unique to herbivores [28]. Moreover, diet specialization decreases the diversity of the gut microbial community [25]. In addition, the high diversity of the gut bacterial communities of herbivorous ants may be caused by three reasons.…”

“…The ant-gut microbiota is complex, and some studies have investigated the effects of different diets on the ant-gut microbiota [22][23][24]. Dietary specialization increases the abundance of nutrient-provisioning bacteria in the ant gut [25]. Moreover, different dietary patterns of different ant species cause differences in the function of the ant-gut microbiota.…”

Bacterial communities associated with arboreal and ground-dwelling Odontomachus ants (Formicidae: Ponerinae) from the Cerrado savanna and the Atlantic Rain Forest

“…The last decade has seen a great increase in the number of studies on microbial communities associated with ants Pringle, 2019). The 'omics' revolution allowed myrmecologists to deepen their view of ants' eco-evolutionary relationship with plants, herbivores, and fungi.…”