The theory of evolution” by Zilber-Rosenburg and

The articles we read and discussed last week were “We Get By with a Little Help from Our (Little) Friends” by Ruby et al. and “Role of microorganisms in the evolution of animals and plants: the hologenome theory of evolution” by Zilber-Rosenburg and Rosenberg. The former article’s main idea is that “we are not alone”, which essentially means that our bodies and those of other complex organisms are home to a diverse ecosystem of microbes, which greatly influence our behavior. The article offers several examples of interactions between microbes and hosts which all serve to emphasize the point that we would not be what we are today without our microbes. The article also discusses the modern view of microbial symbioses with regard to new research in the growing field. Today, scientists realize that there are both pathogenic and mutualistic microbes which play important roles in the evolution and behavior of complex organisms. Researchers are continuing to develop new approaches and better technology to understand these reactions between microbes and their hosts. Although researchers are hard at work trying to improve research in this field, there are still many challenges ahead. For example, some microbes can’t be cultured in a lab, which makes studying those specific microbes much more difficult. Another challenge lies within the fact that several different disciplines are involved in microbial research, so it can be difficult to exchange information across so many fields of study. To improve research in the future, we need to work on integrating all of the different ideas and types of data coming from different disciplines in order to advance the host-microbe interaction field as a whole.

The second article that we read and discussed focuses on the hologenome theory of evolution which states that an individual plant or animal is a community consisting of the host and all of its symbiotic microbes and serves as a unit of selection in evolution. This community of microorganisms within the host is referred to as a holobiont, and it is considered a “unit of selection” in evolution because the genetic diversity of microbial symbionts plays an important role in adaptation and evolution of higher organisms. The hologenome can vary based on changes within the genome of the host or the microbes, which can be brought on by rapid changes in the environment. During periods of environmental stress, the diversity of the microbial population may help the host survive, giving them sufficient time to adapt and evolve to meet the demands of the changing environment. This is a potential benefit of a symbiotic relationship, but there could be drawbacks as well. For example, in some cases the host and the microbe can’t survive without each other, so if an external factor damages either the host or the microbe, the entire holobiont could suffer. Also, pathogenic microorganisms can cause infectious disease which directly harm the host. Due to the vast diversity of both pathogenic and mutualistic microbes within a holobiont, we can’t accurately describe the microbiome of an animal. The microbiome is constantly changing in response to environmental factors and genetic mutation and variation, which makes it impossible to tell exactly what microbes are interacting with a host at any given time. Even though the microbial community is always fluctuating, genomes are still passed on through generations. Therefore, any organism in close contact with offspring can transfer symbionts, influencing the next generation. Although the microbes and host consistently interact with each other, the microbial community can be regulated by the host. For example, bacteriophages and other opposing forces can limit and regulate which strains can survive and form meaningful interactions in the holobiont. The ultimate effect of being free of symbionts is that the organism without symbionts would be left to evolve based on selection by random variants, while the holobiont has the ability to evolve by adaptation to changing environments.  

            I enjoyed reading both of the articles because I thought that although the concepts seemed difficult at first, the numerous examples given increased not only my understanding of the main ideas but also my overall interest in the topics. For example, the second article states how termites feed their feces to their offspring to transfer symbionts. The many examples given are both intriguing and demonstrate concepts described in the text. The first article also seemed very relevant in today’s society. For example, it gave the example of microbes within coral reefs protecting them from damage, which is extremely important now as the coral reefs are beginning to die. Finally, both articles discussed how the field will continue to adapt and improve in the future, which is something I’m very interested as a future researcher.