Microbes and Animal Behavior

Bella Microbio 238 2020

Introduction

By [Bella Stevens]
Animal behavior can be influenced by many factors, making it an interesting yet complex field. From environmental interactions to genetics, there are many ways to look at a certain behavior. How do microbes, particularly bacteria, play a role? Can these microscopic organisms that live inside animals affect who these animals mate with or even how they communicate with conspecifics? Experiments have used genetics, such as rRNA analysis, to study the make-up of symbiotic microbial communities to further understand a certain behavior, like finding another piece to the puzzle. Because animal behavior covers a wide range of topics, from mating to communication, there are possibly many ways microbes, especially symbiotic microbes, could affect behavior in a variety of animals from hyenas to squids, and even humans. How microbes affect and interact with animals can give us insight into our own relationship with microbial organisms and help us understand our own behavior.

Section 1

Microbe-animal interactions are often seen in the form of symbiosis, and these relationships impact various animal behaviors from mate choice to interspecies communication. These reactions range widely from parasitic to mutualistic. Marine animals in particular act as hosts for a diverse range of symbiotic microbes, with at least 7 different phyla acting as hosts for chemosynthetic symbionts. In terms of behavior and physiology, there is a diversity of reductants and oxidants that hosts provide for their symbionts. For example, motile animals such as nematode worms migrate between upper oxidized and lower reduced sediment layers to obtain oxidants and reductants. Thyasirid clams even use their feet, which extend up to 30 times the length of their shells,to form burrows, with the length and number of burrows corresponding to the concentration of hydrogen sulfide in the sediment (1).

There are also many examples in the animal kingdom of gut microbiota influencing animal behavior. For instance, research has shown that commensal bacteria can affect mating in flies (2). After one generation, flies preferred to mate with those that were on the same diet, either starch or molasses, and these preferences continued for at least 37 generations. This 2010 study hypothesized that the change in diet, i.e. rearing the first group of flies on either starch or molasses, altered their gut microbiome and influenced their behavior. Aside from the clear correlation between diet and mating choice, this was further confirmed by antibiotic treatment which caused the mating choices to become totally random, indicating that microbiota played a role in the previously seen preferences. Additionally, analysis of fly rRNA found that flies transferred to starch contained a much higher percentage of Lactobacillus plantarum than the flies raised on standard cornmeal-molasses-yeast (CMY), which the paper suggests influences behavior via the influencing the level of sex pheromones. Gut microbiota not only affects behavior in insects but in vertebrate animals such as mammals. A 2010 study looked at gut microbiota in mice and the effect on behavior and even brain development. Previous studies had found that exposure to some microbial pathogens in certain developmental periods resulted in behavioral abnormalities. A 2010 study hypothesized that a normal gut microbiota plays an important role in the environmental factors that modulate brain development and function (3).

Another instance of microbes playing an important role in animal development is seen in marine animals like the squid. Microbial symbionts can either be vertically or horizontally transmitted. Developmental programs must be altered to accommodate the symbiotic relationship, and establish the correct partners and not interlopers. A 2014 review examined what is known about the symbiotic relationship between the bacteria, Vibrio fischeri, and the Hawaiian bobtail squid, Euprymna scolopes (4). Juvenile squids are colonized in the light organ soon after hatching, the symbiont being obligate for the hosts but not dependent on the host themselves. Within hours of hatching, the juvenile squid has a colonized, bioluminescent organ. This symbiotic relationship is initiated by ventilating the surrounding seawater through the squid’s body cavity, harvesting V. fischeri while excluding other bacterial species. The cells aggregate along the ciliated epithelia, then move into the deep tissues. Finally, a few inoculating V. fischeri cells will fill crypts in the light organ. Vibrio fischeri are bioluminescent bacteria that produce light used by squid hosts as camouflage, an antipredator behavior also known as “counterillumination” that mimics moonlight and starlight. Researchers are also looking into the genome of Vibrio fischeri to better understand how these respiring bacteria generate energy, and what possible role they play in the global carbon cycle (5).

Section 2

Include some current research, with at least one figure showing data.

Section 3

Include some current research, with at least one figure showing data.

References

Authored for BIOL 238 Microbiology, taught by Joan Slonczewski, 2018, Kenyon College.