Implications of Gut Microbial Communities on Host Fitness and Conservation

Every animal is a host to a variety of bacteria, archaea, fungi and viral communities. Some are pathogenic, but the vast majority serve to assist us in our survival, whether it be protecting our skin and reproductive organs or assisting in digestion. As sequencing techniques have advanced in the past decade, researchers are able to study in more detail the microbial communities that constitute the gut microbiomes of many species. Initial research has been human-focused, with efforts directed at isolating microbial communities that support digestion of certain enzymes or those that could act as indices for illness. In the conservation biology realm, conservation metagenomics has emerged as a newfound consideration (Wei et al. 2018). The gut microbiome of organisms can indicate diet, fitness and evolutionary history. We have also learned that these microbiota are especially susceptible to environmental changes, especially those caused by anthropogenic activities (Trevelline et. al 2019). This paper will touch on the alteration to gut microbial communities following anthropogenic disturbance. Along with this, the application of community ecology theories, such as island biogeography theory, in relation to the gut microbiome will be discussed.

Urbanisation is one of the most damaging forms of habitat loss in the world, resulting in large areas of land with little to no natural habitat and the destruction of ecosystems due to an increased demand for timber and fossil fuels (McKinney et. al 2002). Conservation biologists acknowledge that habitat loss severely harms local biodiversity, however, only recently were these theories applied to the microbial communities. In a study looking at the variation of gut microbiota of wild passerine, it was determined that birds living in urban areas contained lower diversity and fewer metabolic functions (Teyssier et. al, 2018). Gut microbiota α-diversity, or OTU richness, significantly decreased corresponding to sparrow’s proximity to urbanised locations (Teyssier et. al, 2018). Β-diversity, or gut microbiota community dissimilarity was also found to be significantly different when comparing passerine that resided in urban and rural areas. Although the conductors of this study found no direct correlation between bird fitness and gut microbiome diversity, they suggest that affects may be seen in the future since “… [A lower diversity] entails a loss of essential functions leading to reduced nutrient assimilation or immunodeficiency…” (Teyssier et. al 2018). There is a heavy suggestion that gut microbiome diversity loss as a result of urbanisation can potentially harm host fitness. This is especially important to note in cases where the host species appear to maintain a stable population size post-habitat loss.

Pesticides, herbicides and nitrogen fertilizers are notoriously harmful to the environment when used in large scale. Increasingly, these chemicals have been criticized for their detrimental impact on honey bee populations which are essential pollinators. In an American study, three commonly used in-hive pesticides were tested to determine if pesticide exposure affected honey bee gut microbial communities. Not unlike the study regarding sparrows, it was found that the gut microbiome diversity of honey bees significantly decreases due to anthropogenic causes (Kakumanu et. al 2016). Of note, one of the most effective pesticides tested, chlorothalonil, was banned in March of 2019 by the EU over human and wildlife health concerns (Carrington, 2019). Chlorothalonil was also found to increase oxidative phosphorylation and decrease sugar metabolism and protease activity in honey bees (Kakumanu et. Al 2016). This suggests that the alteration of the gut microbiome as a result of pesticide exposure could seriously harm the vital processes of this organism.

Community theories, such as island biogeography theory, are often discussed on a macro scale. Island biogeography theory covers many topics, including species richness in relation to immigration and extinction rates. One main point made in this theory is that islands that are smaller and more distant to the mainland should have fewer species than larger and closer islands (Kunin, 2019). In an extensive paper analysing 64 species of bilateria, this portion of the theory is paralleled in gut microbiome communities (Sherrill-Mix et. al, 2018). In this study, “The number of bacterial lineages per gut sample was positively associated with animal mass…implicating body size as a determinant of community stability and niche complexity.” (Sherrill-Mix et. al 2018). Since it has been confirmed through this study that microbial communities behave similarly to communities we see on a larger scale, we suggest the application of known successful community conservation practices to the threatened gut microbiome of many species.

Community-wide conservation stresses that biodiversity in and of itself has an intrinsic and functional value that cannot be characterised by a monetary amount. As we have seen, the gut microbiome plays a crucial role in the survival of its host. This is why conservationists need to consider the health of an organism’s gut microbiome as a factor of success. The success of community conservation is often measured by the maintenance of species richness and population numbers. Determining an ideal ratio of bacterial lineages and density will be a challenge in the upcoming years, but is a necessity in order for researchers to create a baseline in their study organism. In conclusion, microbiology needs to be integrated to conservation science to maximise our understanding that anthropogenic disturbances have on community health (Trevelline et al. 2019).

Works Cited

  1. Wei, Fuwen, et al. “Conservation metagenomics: a new branch of conservation biology.” Science China Life Sciences 62.2 (2019): 168–178.
  2. Trevelline, Brian K., et al. “Conservation biology needs a microbial renaissance: a call for the consideration of host-associated microbiota in wildlife management practices.” Proceedings of the Royal Society B 286.1895 (2019): 20182448.
  3. McKinney, Michael L. “Urbanization, Biodiversity, and Conservation. The impacts of urbanization on native species are poorly studied, but educating a highly urbanized human population about these impacts can greatly improve species conservation in all ecosystems.” Bioscience 52.10 (2002): 883–890.
  4. Teyssier, Aimeric, et al. “Inside the guts of the city: urban-induced alterations of the gut microbiota in a wild passerine.” Science of the Total Environment 612 (2018): 1276–1286.
  5. Kakumanu, Madhavi L., et al. “Honey bee gut microbiome is altered by in-hive pesticide exposures.” Frontiers in microbiology 7 (2016): 1255.
  6. Carrington, Damien. “EU bans UK’s most-used pesticide over health and environment fears.” The Guardian (2019)

7. Sherrill-Mix, Scott, et al. “Allometry and ecology of the bilaterian gut microbiome.” MBio 9.2 (2018): e00319–18.

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