Tuesday, August 29, 2017

The Olympic Athlete of the Animal Kingdom: The Circulatory System of a Horse (A Guest Post)

By Emily Fandrey


How do you judge the abilities of an athlete? Is it all about speed? What about endurance? Strength? How would you judge an animal that can run up to 48 kilometers per hour (30 mph), cover 48 kilometers (30 miles) in a day, or clear a 2.4 meter (8 foot) jump, all while carrying a human on its back? Because of these abilities, the horse (Equus caballus) is often considered to be one of the animal kingdom’s best athletes. The major factor behind horses’ advanced athleticism is their unique circulatory system, specialized for delivering large amounts of oxygen throughout the body.

Image by Paul Kehrer at Wikimedia Commons.

A horse’s circulatory system has three major players: the heart, the spleen, and the frog (and no, this has nothing to do with the animal frog, but rather a specialized unit of a horse’s hoof). Due to these three components, horses have one of the best aerobic capacities in the animal kingdom. Let’s look at a racehorse for example: During a race, a thoroughbred can reach a maximum oxygen capacity (the amount of oxygen the blood can carry) of 200 milliliters per kilogram per minute, meaning 200 milliliters of blood per kilogram of weight (or 3.1 ounces per pound) are transported to the body every minute! This is more than twice the oxygen capacity of the most elite human athlete!

This diagram illustrates the horse’s circulatory system,
including the heart, arteries, veins, and spleen. Diagram by Emily Fandrey.

So let’s break down this superior aerobic system, starting with the horse heart. Typically, a horse’s heart weighs 1% of its total body weight; meaning if a horse weighs 450 kilograms (1000 pounds), its heart will be roughly 4.5 kilograms (10 pounds). If this was true for humans, a 68 kilogram (150 pound) human’s heart would be 0.68 kilograms (1.5 pounds), although the average human heart is only about 0.23 kilograms (half a pound). The horse’s heart functions very similarly to a human heart. It contains four chambers and is responsible for getting oxygen to the body by pumping the oxygen-filled blood. After the body systems have used the oxygen in the blood, this deoxygenated blood enters the heart and is sent to the lungs where the blood is resupplied with oxygen from breathing air. This oxygenated blood reenters the heart and is pumped back out to the body. Because of the size of their hearts, horses are able to supply large amounts of blood with oxygen to the body with each heartbeat, averaging a combined 38 liters (10 gallons) per minute (this is about ten times as much as a human).

Horses also have very different heart rates than humans during rest and exercise. A horse’s resting heart rate is 28-44 beats per minute (bpm), compared to the average human’s, which is 60-80 bpm. During exercise, a human’s heart rate is 90-170 bpm, depending on age. A horse’s heart rate, however, rises to 80 bpm during a walk, 130 bpm during a trot, 180 during a canter, and 240 bpm while galloping. At top speed, the fast beating heart of the horse is what allows the heart to pump much more blood to the body than a human, increasing their athletic abilities.

A diagram of how the horse’s frog sends blood back to heart quickly,
working against gravity. Diagram by Emily Fandrey.

With the long legs of horses, the heart also has to work against gravity to get blood from the limbs back to the heart. To combat this, the horse has its “frog”. For a horse, the frog is a vessel-filled tissue structure on each of its four hooves. When weight is placed on the frog, this structure can help the heart work against gravity. How? When the horse’s hoof meets the ground, the ground will push up on the frog, resulting in the frog being compressed and squeezing blood in the vessels out and rapidly up the leg. The frog helps heart work against gravity by sending the blood up the leg and back to the heart, allowing for faster blood circulation, increasing the athleticism of the horse.

The last key factor to the horse’s circulatory system is the spleen. This organ improves aerobic capabilities and the horse’s athleticism. Now, the primary function of the horse’s spleen is to remove damaged blood cells. However, when a horse is relaxed, their spleen will fill with up to 30 liters (8 gallons) of oxygen-filled blood. And then, once the excitement of activities like running or jumping sparks, the spleen will contract and send up to 25 liters (6.6 gallons) of this stored blood back into circulation in mere seconds! So in seconds, the spleen is capable of almost doubling the maximum amount of oxygen the blood can carry, increasing the athleticism of the horse as well.

So if you ever need an excelling athlete on your team, consider an animal with a superior circulatory system: the horse. With a large and powerful heart capable of pumping large amounts of blood, a spleen to provide an extra burst of blood in seconds, and a “frog” to work against gravity, there is no wonder why horse is considered to be one of the world’s superior athletes.


References

Allen, K.J., Young, L.E., and Franklin, S.H. (2016). Evaluation of heart rate and rhythm during exercise. Equine Veterinary Education 28: 99-112. DOI: 10.1111/eve.12405.

Cardiovascular System (2007). In EQUINAvet.

Circulatory System of the Horse (2010). In Helpful Horse Hints.

Equine Circulatory System Vet, Horse First Aid (2012). In Equestrian and Horse.

Norton, J. (2013). The equine circulatory system. In EquiMed: Horse Health Matters.

Monday, August 21, 2017

Caught in My Web: Animal Reactions to A Solar Eclipse

Animation by Locutus Borg at Wikimedia Commons.
A solar eclipse is a rare event that can have dramatic effects not only on us people, but on animals as well. For this edition of Caught in My Web, we think about how animals may respond to such a rare celestial event.







Image by Luc Viatour at Wikimedia Commons.
1. National Geographic shares many ways animals are known to behave in strange ways in response to a solar eclipse.

2. Much of the effect of an eclipse on animal behavior is utter confusion, but many groups will be watching animals to see how they respond.

3. Researchers at the University of Nebraska will be collecting behavior data on GPS-tagged red-tailed hawks to see how the solar eclipse affects them.

4. Some nature centers are studying animal behavior during the eclipse.

5. If you found any animals that freaked out so badly as to injure themselves, check here for advice.

Monday, August 14, 2017

Striving for a Honeybee Democracy

Democracy is hard. And slow. And complicated. But if it is done well, it can result consistently in the best decisions and courses of action for a group. Just ask honeybees.

When a honeybee hive becomes overcrowded, the colony (which can have membership in the tens of thousands) divides in what will be one of the riskiest and potentially deadliest decisions of their lives. About a third of the worker bees will stay home to rear a new queen while the old queen and the rest of the hive will leave to establish a new hive. The newly homeless colony will coalesce on a nearby branch while they search out and decide among new home options. This process can take anywhere from hours to days, during which the colony is vulnerable and exposed. But they can’t be too hasty: choosing a new home that is too small or too exposed could be equally deadly.

Our homeless honeybee swarm found an unconventional "branch". We'd better
decide on a new home soon! Photo by Nino Barbieri at Wikimedia.

Although each swarm has a queen, she plays no role in making this life-or-death decision. Rather, this decision is made by a consensus among 300-500 scout bees after an intense “dance-debate”. Then, as a single united swarm, they leave their branch and move into their new home. At this point, it’s critical that the swarm is unified in their choice of home site, because a split-decision runs the risk of creating a chaos in which the one and only queen can be lost and the entire hive will perish. This is a high-stakes decision that honeybees make democratically, efficiently, and amazingly, they almost always make the best possible choice! How do they do that? And how can we do that?

The honeybee house-hunting process has several features that allow them, as a group, to hone in on the best possible solution. The process begins when a scout discovers a site that has the potential to be a new home. She returns to her swarm and reports on this site, using a waggle dance that encodes the direction and distance to the site and her estimate of its quality. The longer she dances, the more suitable she perceived the site to be. Other scouts do the same, perhaps visiting the same site or maybe a new one, and they report their findings in dance when they return. (Importantly, scouts only dance for sites that they have seen themselves). As more scouts are recruited, the swarm breaks into a dancing frenzy with many scouts dancing for multiple possible sites. Over time, scouts that are less enthusiastic about their discovered site stop dancing, in part discouraged by dancers for other sites that head-bump them while beeping. Eventually, the remaining dancing scouts are unified in their dance for what is almost always the best site. The swarm warms up their flight muscles and off they go, in unison, to their new home.

Each dot represents where on the body this dancer was head-bumped by a dancer for a
competing site. Each time she's bumped, she's a little less enthusiastic about her own dance.
Figure from Seeley, et al. 2012 paper in Science.

What can we learn from these democratic experts? As much as I would love to see Congress in a vigorous dance-debate head-butting one another, I don't think that is the take-home message of choice. Tom Seeley at Cornell University has gained tremendous insight into effective group decision-making from his years observing honeybees, which he shares with us in his book, Honeybee Democracy. Tom has summarized his wisdom gained from observing honeybees in the following:

Members of Highly Effective Hives:

1. share a goal

2. search broadly to find possible solutions to the problem

3. contribute their information freely and honestly

4. evaluate the options independently and vote independently

5. aggregate their votes fairly

All of these critical guidelines can be encapsulated with a single objective: The decision-making body needs to objectively consider a range of information from individuals with diverse backgrounds, expertise, and knowledge. We can apply this to our own human decision-making: It means that if you don't agree with the decisions of your School Board, Town Board, City Council, County Legislature, State Legislature, or National Legislature, then your background, expertise and knowledge are likely missing from the deciding body. Yes, you can write and call your representatives and provide them with part of your knowledge, or you can run for office yourself and make people with your background truly included in the decision-making process.

Running for a human political office is more complicated and confusing than becoming a honeybee scout. No matter what your background is, you will need to work hard to gain additional expertise in campaigning. But now is the time to get into the game: there is a tremendous upswell of support for people that are new to politics. Many organizations provide free training, connections, even financial support to recruit new people with new perspectives. And these days, there seems to be a supportive group for just about everyone who wants to get involved.

If many of your views align with a political party, you can often turn to the party itself for support. Democrats can turn directly to Democrats.Org or the National Democratic Training Committee. Likewise, Republicans can go to EquipGOP or the Republican Leadership Initiative. Support is also available for Libertarians and members of the Green Party.

Private groups provide additional resources for candidates of particular backgrounds. For example, Camp Wellstone is a training program for any progressive candidate, and Run For Something provides additional support for progressives under 35. Additional groups working to promote more diverse representation are the BRAT-PAC for African American candidates, the Latino Victory Project for Latino candidates, and the Gay and Lesbian Victory Fund for LGBTQ candidates. And, my own personal favorite, 314 Action promotes scientists and other STEM-trained candidates.

Women candidates, in particular, have more resources than ever right now. This is tremendously valuable to increasing our decision-making diversity, since although women make up more than 50% of the US population, women make up less than 20% of the National Legislature, and less than 25% of state legislatures. Women candidates of every party and background can get support from IGNITE, She Should Run, the Center for American Women and Politics, and the Women's Campaign Fund. The National Federation of Republican Women specifically supports republican women candidates. Likewise, EMILY’s List and Emerge America provides training for progressive women candidates. Higher Heights supports black women candidates for any office.

Many feel that our hive has been homelessly clinging to our exposed branch for too long. If we are going to make good, well-informed, effective, and efficient decisions, we need open and respectful communication across diverse backgrounds. Increasing diversity in the decision-making body improves the quality of the decisions that affect us all. If honeybees can do it, so can we.


Want to know more? Check these out:

1. Honeybee Democracy by Thomas Seeley

2. Seeley, T., Visscher, P., Schlegel, T., Hogan, P., Franks, N., & Marshall, J. (2011). Stop Signals Provide Cross Inhibition in Collective Decision-Making by Honeybee Swarms Science, 335 (6064), 108-111 DOI: 10.1126/science.1210361

3. List, C., Elsholtz, C., & Seeley, T. (2009). Independence and interdependence in collective decision making: an agent-based model of nest-site choice by honeybee swarms Philosophical Transactions of the Royal Society B: Biological Sciences, 364 (1518), 755-762 DOI: 10.1098/rstb.2008.0277

Monday, August 7, 2017

Drinking Beer Makes You More Attractive… To Mosquitoes

Summer is a time of backyard bar-b-ques, camping, baseball games, beer, and mosquitoes. Ugh, mosquitoes! Have you ever noticed that when a bunch of us are hanging out together outside, some of us get eaten alive by those pesky buggers while others are hardly touched at all? It turns out, differences in how much alcohol we have imbibed may be a factor.

An Anopheles gambiae mosquito ready for a meal. Photo by James D. Gathany
at the Public Health Image Library at Wikimedia Commons.

“No! Say it ain’t so!”

I hate to be the bearer of bad news, so I’ll let the scientific evidence speak for itself.

A research team from the French Research Institute for Development, including Thierry Lefèvre, Louis-Clément Gouagna, Eric Elguero, Didier Fontenille, François Renaud, Carlo Costantini, and Frédéric Thomas, and Kounbobr Roch Dabiré, from the Institute for Research in Health Sciences in Burkina Faso set out to test whether people were more attractive to female mosquitoes after drinking a beer compared to beforehand. They only tested females because only female mosquitoes bite, requiring extra protein for their eggs.

The researchers put groups of 50 hungry female mosquitoes into the end of a special Y-shaped maze that let them fly in the direction of one of two odors. At the end of one arm of the Y-maze was a fan, simply blowing outdoor air through a tent and into the apparatus. At the other end of the Y-maze was a fan blowing air through a tent past a shirtless man and into the apparatus. This shirtless man had either not had anything to drink recently, or had recently drunk either a liter of beer or a liter of water. Between the starting chamber and both ends of the arms of the Y-maze were traps that would capture mosquitoes that had chosen to head that direction (lucky for the shirtless men). The number of mosquitoes caught in both traps combined (compared to the total of 50 that was initially released) was called mosquito activation, and reflected how many mosquitoes were motivated to take off and fly upwind. The proportion of mosquitoes caught in the volunteer-bated trap compared to those caught in both traps combined was called mosquito orientation, and reflected the attractiveness of the volunteer’s odor compared to the control odor.

Image A shows the two tents: one in which the man-bait sat (having consumed beer or water), and the other with no one in it. Air from each tent blew threw a tube (seen in picture B) and then into the building, past the traps and into the downwind box, where the mosquito starting-line was located (seen in picture C). Photos from Lefèvre et al., 2010.

The mosquitoes significantly increased both activation and orientation in response to the beer-drinking volunteers, but not in response to the water-drinking volunteers. That is to say, that the smell of someone that has had a beer motivates more mosquitoes to actively pursue them, and makes them more of a focused target of the mosquitoes. The researchers believe there is an interaction between how our bodies naturally smell and how our bodies break down beer that increases the attractiveness of our odors to mosquitoes. People that were more attractive to mosquitoes before they drank were also more attractive to mosquitoes after they drank. But interestingly, people that were warmer or gave off more CO2 were not more attractive to mosquitoes.

You should know that this research is much more important than just being a drag on your summer bar-b-que. The particular mosquito species that these researchers studied was Anopheles gambiae, the primary vector for malaria in Africa. They did this study in Burkina Faso, a country in West Africa with a high rate of malaria, using a local beer called dolo. Dolo, a fermented sorghum beer with low (3%) alcohol content, is the most common alcoholic beverage in Burkina Faso. So if you are in a place with a high rate of malaria, knowing that you should take extra precautions against mosquitoes when you drink could be a life-saver.

Want to know more? Check this out:

Lefèvre, T., Gouagna, L.C., Dabiré, K.R., Elguero, E., Fontenille, D., Renaud, F., Costantini, C. and Thomas, F. (2010). Beer consumption increases human attractiveness to malaria mosquitoes. PloS one, 5(3), e9546.