The Contagious Cancer (A Guest Post)

By Stephanie Stanton

The Tasmanian devil, perhaps more popularly known by its animated counterpart Taz in Warner Bros.’ “Looney Toons,” is a carnivorous marsupial native to Tasmania, an island off the southern coast of Australia. Similar to Taz, the Tasmanian devil lives a violent lifestyle. While a good portion of fights don’t go beyond screaming matches, sometimes (especially during the mating season) fights escalate to full-on biting matches. Unfortunately, it is this aggressive nature that has been linked to the alarming drop in Tasmanian devils’ numbers over the last decade. However, it is not violent wounds acquired during fights that are causing this rapid decline, but rather the Devil Facial Tumor Disease (DFTD), a contagious cancer.

DFTD is a transmissible cancer that operates as its own living entity- it is genetically distinct from its host and lives on its host’s face. Most of these tumors appear on their faces. Coincidentally, this also happens to be where a majority of open wounds are acquired in this species. Because of this, it is believed that DFTD is transferred through open wounds on the skin.

A healthy Tasmanian devil in all his glory. Photo by Chen Wu at Wikimedia Commons.

This cancer has been so successful in spreading throughout the population because of the devils’ small population size and low genetic diversity. Among the genes with low genetic diversity in the population is the Major Histocompatibility Complex (MHC), a collection of genes responsible for a strong immune response in vertebrates. Without a strong immune response, it is difficult to fight off serious threats such as DFTD. Unfortunately for the devils, the tumors growing on their faces do not even register on their limited immune system’s radar- so their bodies don’t even fight back! Because of this, DFTD is in most cases fatal within six to nine months of showing clinical symptoms.

A Tasmanian devil afflicted with DFTD. Photo courtesy of Menna Jones, available at Wikimedia Commons

Three Australian scientists by the names of Rodrigo Hamede, Hamish McCullum, and Menna Jones from the University of Tasmania and Griffith University recognized the alarming decline in the Tasmanian devil population and sought to find a way to better understand and control the spread of the disease. They looked at two separate populations over four seasons, collecting data once every three months by taking counts of bites on individual devils and tracking who got DFTD, when, and on what part of their bodies. They hypothesized that because the tumor was transmissible through open wounds, then the number of open wounds could be used as an early predictor for the onset of DFTD.

And they were right…although perhaps not in the ways they thought they would be. Contrary to what common sense would have everyone believe, devils with the least amount of facial wounds were the most likely to develop the fatal cancer. How could this be?

Simply put, it appears that the disease is getting transferred from devil to devil not because their bodies are exposed to a bite from an infected individual, but because devils are biting the tumors of infected individuals, thereby creating a direct path for the tumor to enter the new host.

The scientists argued that the devils that have the fewest open wounds were better at fighting and also the most aggressive (A side effect of the cancer? Perhaps.) Tasmanian devils are likely to have cuts or scrapes in their mouths because of their aggressive eating style, providing a port for the cancer cells to invade. It was because they were biting the tumors of the infected devils that they were contracting the disease, which also explains the higher occurrence of tumors in the mouth. Less aggressive devils accumulated more injuries to the face, but as long as the cancer cells did not come into contact with open wounds, their likelihood of contracting the disease was slim.

Rodrigo, Hamish and Menna hope that their results along with further research can help reduce the effects of the disease on the shrinking Tasmanian devil population by offering potential solutions to better control its spread. Exciting research published in 2016 is also already offering hope in keeping Taz and his furry counterparts alive for future generations to enjoy.


Want to know more? Check out the original article below:

Hamede, Rodrigo K., McCullum, H., Jones, M. (2013). “Biting injuries and transmission of Tasmanian Devil facial tumour disease. Journal of Animal Ecology. DOI: 10.1111/j.1365-2656.2012.02025.x.

One of These Sharks is Not Like the Others (A Guest Post)

By Emily Masterton

When you think of a shark, what usually comes to your mind? Big teeth and the beach, right? Well, that’s not how the Greenland shark likes to live at all. Like the name denotes, this shark prefers cold waters and depths that would kill most sharks and people. The Greenland shark is mostly restricted to the waters of the far North Atlantic Ocean and the Arctic Ocean, which range from 34 – 68 degrees Fahrenheit. The Greenland shark has also been recorded diving down to depths ranging from 0 – 4000 feet. To put that in perspective, that’s equal to 3.2 Empire State Buildings stacked on top of each other!

Picture of a Greenland shark in the Admiralty Inlet, Nunavut.
Image by Hemming 1952 at Wikimedia Commons.

The Greenland shark is able to survive in this harsh environment because of the shark's high levels of nitrogenous waste products (any metabolic waste product that contains nitrogen) in their tissues. The nitrogenous waste products that are found in the Greenland shark are urea and trimethylamine N-oxide (TMAO). These chemicals help the shark maintain their osmotic balance (the movement of water across cells) in this very salty environment. This osmotic balance is important for the body to function and keep water and salt in balance in the cells.

TMAO and urea act as a type of anti-freeze that keeps the cells from freezing and developing ice crystals. The TMAO and urea work by preventing ice crystals from forming in the shark’s cells. They work by lowering the freezing point of water in the cells and by binding to ice crystals and preventing them from forming or growing. This protects the cells from denaturing due to the extreme pressure from the depths the shark dives at. If there were no TMAO and urea in the shark, then ice crystals could form and break cell walls, which could result in tissue and organ damage, then death.

This figure shows how TMAO and urea bind to the shark's protein and keep ice crystals from growing and forming. This prevents the protein from denaturing and ultimately killing the shark. Image by Emily Masterton.

While these chemicals are great for the Greenland shark, they are bad news for anyone or thing who decides to eat them. TMAO and urea are very toxic. The Greenland shark has the most toxic skin among all sharks and even made it to the Guinness World Records in 2013 for this level of toxicity. If you were to eat the skin of a Greenland shark without preparing it right, you will have symptoms similar to being extremely drunk.

Greenland shark meat is eaten in Iceland in a dish called Hákarl. The shark’s meat must be prepared a certain way so that the TMAO and urea are no longer present in the meat. This is done by fermenting the meat and then drying it for 4-5 months. Once it has been dried and is ready to eat, it is often served in cubes on toothpicks in small servings.

Although these extreme conditions would kill any human being or another shark, the Greenland shark is able to survive and thrive in these conditions, thanks to the chemicals TMAO and urea. These chemicals keep ice crystals from forming in the cells of the shark and ultimately keep the shark alive. There are 465 species of sharks in the ocean, but only one can call the harsh North Atlantic Ocean and Arctic Ocean its home.


References
• Farrell, Anthony Peter, et al. Physiology of elasmobranch fishes: internal processes. Academic Press/Elsevier, 2016
• Strøksnes, Morten. “My Hunt for the 400-Year-Old Shark Whose Flesh Gets You High.” Vice, 30 June 2017
• O’Connor, M. R. “The Strange and Gruesome Story of the Greenland Shark, the Longest-Living Vertebrate on Earth.” The New Yorker, The New Yorker, 15 Feb. 2018
• “The Greenland Shark: An Icy Mystery.” Greenland Shark | Sharkopedia Sharkopedia
• Polar Seas: Greenland Shark

A Snail’s Dart of Love (A Guest Post)

By Jenna Miskowic

Snails that shoot darts. Who would have thought? Turns out, snails have a lot of competition for mates. Females of some snail species have evolved ways to select which males they want to be the father of their eggs. One of these strategies is a female can mate with multiple males and store their sperm. The female can then “choose” which sperm she wants to fertilize her eggs. This affects how males compete for mates. Males want to make sure they are the father to the offspring because they want their genes to be passed on. So male snails have developed ways to increase their chances of paternity.

Euhadra quaesita gliding through foliage. Image by Angus Davison
and Satoshi Chiba posted at Wikimedia Commons.

Enter the dart-bearing land snail, Euhadra quaesita. Snails of this species are simultaneous hermaphrodites that use cross-fertilization. Simultaneous hermaphrodites are animals that have both female and male reproductive tissues and systems. Cross-fertilization means that the snails require a mate. So, when two dart-bearing land snails cross paths and decide they want to mate, they will take their love-dart and pierce it into their mating partner. Because the snails are simultaneous hermaphrodites, they both perform this behavior before exchanging their sperm.

Love darts are composed of a crystalline form of calcium carbonite, which is what sea shells are made of, called aragonite. They are very sharp and pointed so that they are able to pierce the other snail. The dart is covered with a secretion from its mucous glands. When the dart pierces into the other snail, mucus is transported from the dart’s glands into the pierced snail’s blood. This mucus helps increase the amount of sperm being stored in the recipient snail and increases the likelihood of the donor snail being the father to the offspring of the recipient snail. Researchers Kazuki Kimura, Kaito Shibuya, and Satoshi Chiba from Tohoku University in Japan hypothesized that the dart’s mucus would also reduce future matings and promote laying eggs, also called oviposition.

Drawing of Euhadra quaesita’s love-dart. Cross-section on the left and lateral view on the right.
Image by Joris M. Koene and Hinrich Schulenburg posted at Wikimedia Commons.

To test these hypotheses, the researchers conducted two separate experiments. The first experiment focused on the effects of dart shooting and future matings of the recipient snail. Individually, non-virgin adult snails were presented with a non-virgin or virgin adult for their initial mating. In this species, non-virgin adults shoot their darts and virgin snails do not shoot their darts while performing the mating behavior. Thus, the subjects paired with a non-virgin adult were pierced with their partner’s love-dart, and the subjects paired with a virgin adult were not pierced with their partner’s love-dart. Then the subjects were offered to mate again with an unfamiliar non-virgin snail with a high mating motivation caused by individual rearing. They recorded how long the snail subject went, in days, before mating again with another individual of the same species. The researchers found that the amount of time between matings was longer in pierced snails than in ones not pierced.

The second experiment focused on the effect of injected artificial mucus on future matings and promotion of oviposition behavior. Researchers dissected an extract of the mucous glands out of adult snails and combined it with saline solution to create the artificial mucus. There were two groups used in this experiment: (1) adult snails injected with the artificial mucus, also known as the treatment group and (2) adult snails injected with only the saline solution, also known as the control group. They recorded the number of hatched eggs and their parentage. They found that artificial mucus-injected snail pairs mated less often than the control pairs. Additionally, they found that the amount of the snails that laid eggs was larger in the snails injected with artificial mucus. These findings support the researchers’ hypotheses that dart mucus can subdue future matings in its recipients.

So what are the benefits to stabbing your partner with a love dart? Well, if an animal has multiple partners, then it is quite advantageous for the partner to make sure that they are the parent. Mating suppression after being injected with the love dart is one way to fight off the competition. So, beware to all who search for Cupid’s arrow this Valentine’s Day. There may be more to an arrow of love than you realize.


References

Kimura, Shibuya, & Chiba. (2013). The mucus of a land snail love-dart suppresses subsequent matings in darted individuals. Animal Behaviour, 85(3), 631-635.