Gut Feelings

This boy may be influencing who he will marry when
he grows up. Photo by Orrling at Wikimedia Commons.

Animals (including humans) are swarming with microorganisms both on and in our bodies. Humans harbor so many different microorganisms that we have over 150 times more microbial genes than mammalian genes, and it is reasonable to suspect that this scenario is similar for most animals. But before you run to soak in a tub of hand sanitizer, you should realize that many of these microorganisms are actually beneficial to the health of both your body and your mind. Although this field is still very much in its infancy, we have found that the microbes that live in digestive tracts in particular significantly influence their host animal’s behaviors. This connection between our digestive communities and our behaviors has been termed the microbiota–gut–brain axis.

Much of the early research on the microbiota-gut-brain axis was done using specialized mice that have never been exposed to any bacteria. You may think this sounds like a healthy lifestyle, but these so-called germ-free mice have all kinds of health and behavioral problems. They often have digestive difficulties and high levels of anxiety, symptoms common of people with irritable bowel syndrome (IBS). They also typically have deficits in social behavior and increased repetitive behaviors. Similar to autism-spectrum disorders and obsessive compulsive disorder (OCD), these behavioral problems are more likely to occur in males than in females. When faced with a challenge, many struggle with solving the problem and show a higher tendency to give up, symptoms common in patients with depression. Interestingly, simply feeding germ-free mice some species of Bifidobacteria and Lactobacilli bacteria (similar to bacterial strains found in different brands of yogurt) can reduce symptoms of anxiety, depression, cognitive difficulties, autism, and OCD. This has led to a boom in biomedical research on the benefits of probiotics (that contain microbes that live in our guts) and prebiotics (that contain things that the microbes in our guts eat).


Yogurt bacteria. Photo by Josef Reischig at Wikimedia Commons.

These gut microbes don’t just help animals maintain their physical and mental health, they are also involved in complex social behaviors. For example, fruit flies prefer mates that grew up eating the same diet that they grew up eating. However, if they are treated with antibiotics, which kill the gut bacteria, they lose their mate choice preferences. If they are then treated again with microbes from their initial diet (with one Lactobacillus bacteria in particular), they gain their mate choice preferences back. This all makes me wonder, how important is yogurt to choosing the people we date and marry?

How do microbes in our guts affect our brains anyway? Although the answer to this is still mostly unknown, we know that the gut has the potential to influence the brain through multiple means, including hormone production, immune function, and even directly through specific nerves. The specific mechanisms are still being very actively researched, but it is clear that microscopic critters living in our guts likely influence our brains and behaviors in many different physiological ways.

Microbiota-gut-brain axis research is revolutionizing the way we think about health, medical treatments, behavior and even existential questions like who am I? But one thing is for sure: I’m gonna go have another yogurt.


Want to know more? Check these out:

Cryan, J., & Dinan, T. (2015). More than a Gut Feeling: the Microbiota Regulates Neurodevelopment and Behavior Neuropsychopharmacology, 40 (1), 241-242 DOI: 10.1038/npp.2014.224

Ezenwa, V., Gerardo, N., Inouye, D., Medina, M., & Xavier, J. (2012). Animal Behavior and the Microbiome Science, 338 (6104), 198-199 DOI: 10.1126/science.1227412

Komodo Dragons: Their Bite is Worse than Their Bark (A Guest Post)

By Shelly Sonsalla


Komodo Dragon.
Image by Arturo de Frias Marques on Wikimedia.

Komodo dragons are the world’s largest living lizard and can be found only on select islands in the Indonesian archipelago. These massive lizards can grow to be 10 feet in length and up to 150 pounds! Their natural prey includes wild boars, deer, and water buffalo—animals which may outweigh them by several hundred pounds. So how does a lizard, even such a large one, manage to take down prey so much larger than them? The answer lies in their bite.

Komodo dragons’ mouths are a complex interplay of force, toxins, and bacteria. A study by Brian Fry and his colleagues at the Howard Florey Institute in Australia determined the amount of force that a komodo dragon could generate with its bite. What did they find the answer to be? Not much. They found that a komodo dragon’s bite was 6.5 times less than that of an Australian saltwater crocodile. That’s comparable to a 3.5 pound fennec fox! Obviously, this means that the komodo dragon couldn’t possibly bring down such large prey by strength alone. Luckily for them, there are two more factors at play.


Size comparison between a komodo dragon and a fennec fox.
Computer Rendered by Michelle Sonsalla.

The first is venom secreted by a number of venom glands found on the lower jaw. The amount of venom that can be held in these glands totals less than half a teaspoon! This venom has a number of properties meant to kill its prey, properties which prevent the prey’s blood from coagulating and cause painful cramping in the intestines, paralysis, and loss of consciousness. These effects alone would be enough to bring down most prey, but in case they aren’t, there is a final piece of the puzzle—bacteria.

All living things have a multitude of bacteria and fungi that are naturally present on their skin and in their digestive system, but the bacteria found in the mouths of komodo dragons are specialized. According to Joel Montgomery, a researcher at the University of Texas at Arlington, there are 54 species of bacteria found in the mouths of komodo dragons which cause illness and 1 species which has been found to be lethal to mice. These bacteria enter the prey’s bloodstream through its bite and work to infect the creature slowly, causing severe infection within days or weeks.

All three factors of a komodo dragon’s bite work together to take down its prey efficiently and effectively. The bite, though weak, is enough to open the skin and allow the venom and bacteria into the prey’s bloodstream. Once in the bloodstream, the venom works to weaken the animal, which in turn allows the bacteria to gain a foothold to infect, and eventually kill, the victim. These factors allow this large, magnificent lizard, this dragon among beasts, to take down prey much larger than themselves and have helped them survive the extinction of the past’s other great lizards.


References:

Christiansen P, & Wroe S (2007). Bite forces and evolutionary adaptations to feeding ecology in carnivores. Ecology, 88 (2), 347-58 PMID: 17479753

Fry, B., Wroe, S., Teeuwisse, W., van Osch, M., Moreno, K., Ingle, J., McHenry, C., Ferrara, T., Clausen, P., Scheib, H., Winter, K., Greisman, L., Roelants, K., van der Weerd, L., Clemente, C., Giannakis, E., Hodgson, W., Luz, S., Martelli, P., Krishnasamy, K., Kochva, E., Kwok, H., Scanlon, D., Karas, J., Citron, D., Goldstein, E., Mcnaughtan, J., & Norman, J. (2009). A central role for venom in predation by Varanus komodoensis (Komodo Dragon) and the extinct giant Varanus (Megalania) priscus Proceedings of the National Academy of Sciences, 106 (22), 8969-8974 DOI: 10.1073/pnas.0810883106

Merchant, M., Henry, D., Falconi, R., Muscher, B., & Bryja, J. (2013). Antibacterial activities of serum from the Komodo Dragon (Varanus komodoensis) Microbiology Research, 4 (1) DOI: 10.4081/mr.2013.e4

Montgomery JM, Gillespie D, Sastrawan P, Fredeking TM, & Stewart GL (2002). Aerobic salivary bacteria in wild and captive Komodo dragons. Journal of wildlife diseases, 38 (3), 545-51 PMID: 12238371

Happy St. Patrick's Day!

Vole Pee: An Epiphany (A Guest Post)

By Nate Kueffer

You’re driving down the road, looking out the window, and you see a large raptor hovering above a field. Have you ever wondered what exactly the raptor could see that you couldn’t? Well, it is thought that raptors may be able to sense ultraviolet light and use it to track voles through urine and feces trails.

A hovering kestrel, possibly tracking a vole. Photo by Mark Likner at Flickr.

Ultraviolet light is a non-detectable form of radiation by the human eye and is similar to X-rays and gamma rays. However, with the help of a black light human eyes can see different materials that we couldn’t see in visible light. The objects that humans can typically see under a black light are fluorescent. This means that the object has the ability to soak up ultraviolet light and then emit the light it took in and produce a light frequency that humans are able to detect.

Jussi Viitala from the University of Jyvaskyla in Finland, and Erkki Korpimäki, Päivi Palokangas (now Lundvall) and Minna Koivula from the University of Turku in Finland set out to find more conclusive evidence on raptors using ultraviolet light to hunt. The four researchers tested the hypothesis that in order to find prey patches, Eurasian kestrels, a species of raptor, look for vole scent marks visible in ultraviolet light. The voles’ scent marks are their urine and feces droppings, which show up under ultraviolet light. The researchers set up experiments in the field and in a laboratory setting.

Kestrel with a captured vole after a successful hunt. Photo by Eugene Beckes at Flickr.

In the laboratory setting, wild captured kestrels were released into a large area made up of four different arenas. All arenas were different, but did not allow any external visual cues. One arena had vole trails in ultraviolet light, another was clean with ultraviolet light, a third arena had visible light and vole trails, and the final arena was clean with visible light. The kestrels were then measured by their time spent over each arena. The kestrels in the laboratory seemed to prefer the arena with ultraviolet light and vole trails. The clean, ultraviolet-lit arena had the least amount of scans and time spent over that arena compared to the other three arenas. The kestrels had no preference over either arena with visible light.

The field setting had 3 experimental groups for 45 kestrel nest boxes: the first had artificial vole trails with urine and feces, the second had artificial vole trails, but no urine or feces, and the last was the control with no vole trails, urine, or feces. The 45 boxes were observed over 24 mornings when the researchers recorded the number of kestrels near each nest and their behavior (hunting, paired, or resting). For the field experiment, 27 of the 45 nest boxes attracted kestrels near them. The most commonly used nest boxes were near artificial trails with urine and feces. The kestrels avoided the other two nest box areas: the one with trails, but no urine, and one with no trails and no urine. This showed that the trails weren’t used as hunting cues. Paired or hunting kestrels preferred to spend time hunting near trails with urine or feces, and resting kestrels were seen evenly in all three areas. Also, four rough-legged hawks were seen hunting near the trails with urine and feces.

Both experiments showed kestrels using trails with markings from voles suggesting that the vole markings may be used to select hunting and nest sites. The researchers propose that the kestrels, in fact, use vole scent markings as visual cues. Kestrels and other predatory birds may use the ultraviolet light from vole markings to scan over large areas new to them before deciding to hunt or nest in the area. The next raptor you see out of your car window could be tracking its prey’s markings using ultraviolet light.


References
Olson, V. (n.d.). Raptor Vision. Retrieved December 10, 2014, from http://www.moremesa.org/wordpress/raptor-vision/

Q & A: Why does a black light make objects glow? (2007, October 22). Retrieved January 21, 2015, from https://van.physics.illinois.edu/qa/listing.php?id=1913

Viitala, J., Korplmäki, E., Palokangas, P., & Koivula, M. (1995). Attraction of kestrels to vole scent marks visible in ultraviolet light Nature, 373 (6513), 425-427 DOI: 10.1038/373425a0

Choosing Mates Wisely Is All The More Important When They Try To Eat You

A praying mantid pair.
Photo by Oliver Koemmerling
at Wikimedia Commons.

Choosing our mates is among the most important decisions of our lives. We agonize over finding "the one", and for good reason. If we are going to spend the rest of our lives with one person and depend on that person to help create and raise our children, the stakes of choosing that person well are high. But at least we don't have to worry that if we choose wrong our partner will bite our head off... not literally, anyway.

Today at Accumulating Glitches, I talk about sexual cannibalism in praying mantids and how it has led to males now choosing less aggressive mates. Check out the article here.