Category: Science

An ecosystem is a complex web of interactions between different organisms and their environment. The interactions between species have often been tuned by years of co-evolution, resulting in specialized defense mechanisms and adaptations to their specific environment. When a non-native species is introduced, it has the potential to become very disruptive.

How are exotic species introduced?

The introduction of non-native species is often an unwanted result of human activity. Ever since humans started exploring and colonizing new lands, hitchhiking organisms have accompanied them. Perhaps the most famous example of this has been the spread of the common house rat Rattus rattus, native to Asia and now a worldwide pest. Alien species are still spread today through human transportation systems, like when fish and marine invertebrates are carried in the ballast water of ships.

Other times, nonnative species are deliberately introduced. For example, rabbits were released in Australia in the 1800s for sport and have since become widespread, to the detriment of Australian ecology. In other cases, animals are liberated into the wild by well-meaning pet owners who no longer wish for or are able to care for their exotic pets.

To be sure, not every alien species turns into a threat, or even manages to survive. Introduced organisms have not adapted to cope with the new site’s climate, predators and competitors. Moreover, if they were previously kept in captivity they might be ill-suited to survive on their own, and are likely to die from starvation, depredation or exposure. However, some species manage to survive and even thrive, often at the expense of native organisms. Whether an alien species becomes invasive or not depends on several factors, including lack of natural predators or diseases, flexibility to adapt to different environmental conditions, dispersion and reproduction rates, and diet diversity.

An invasive species, then, is any non-indigenous animal, plant, fungus, or bacteria, that becomes established in a new environment, and threatens or damages resident species. In fact, invasive species are considered one of the top causes for loss of biodiversity worldwide, and can lead to the extinction of native species.

Why are invasive species harmful?

Invasive species may outcompete native organisms for food or shelter. Native species often don’t have defense mechanisms against introduced species, and so can easily become prey. Invasive species can also modify the environment in a way that is detrimental for indigenous organisms. For example, the common carp, native to Eurasia but introduced in America, increases the turbidity of water and uproots vegetation due to its eating habits, affecting native fish that need clear water to survive. Other times, invasive species may harbor pathogens for which the native organisms have no adequate defenses. A concerning example of this is the case of the European salamanders, which are rapidly disappearing as a result of the fungus Batrachochytrium salamandrivorans, likely introduced through the pet trade.

Read on to learn about some of the most important invasive species affecting our ecosystems today:

1. Lionfish

Lionfish are fish with showy fins and venomous spikes, popular among aquarists. They are native to the Indo-Pacific Ocean, but two species, Pterois volitans and Pterois miles, have become very successful invasive species in the Eastern Atlantic Ocean and the Caribbean Sea. They were first observed off the coast of Florida in the 1980s, and have since spread along the East coast of the US and throughout the Caribbean, with some specimens found as far south as Brazil. There have even been some sightings as far north as Rhode Island, although they are not suited for cold temperatures. It is generally accepted that the lionfish invasion was a result of several introductions, including specimens released by aquarists. Several lionfish were also reportedly released into the wild from a flooded aquarium after Hurricane Andrew in 1992.

There are several reasons why the lionfish invasion has been so successful. They are aggressive fish with a voracious appetite and a very diverse diet. They are also able to spread widely using ocean currents for the dispersion of their larvae. Lionfish have few natural predators thanks to the protection of their venomous spikes. As a result, they have become an important threat to the health of the native coral-reefs and fish communities. In a study on lionfish eating habits off of the Bahamas, scientists found that during the period from 2004 to 2010, lionfish numbers increased considerably, to the point of constituting 40% of predator biomass in the area. Meanwhile the biomass of the 42 species of fish identified as prey for the lionfish decreased by 65%. Current control efforts include spearfishing, and promoting lionfish meat as a delicacy.

2. Cane Toad

The cane toad, Rhinella marina, is a species of toad native to Central and South America. It is a large toad with a blotched, warty skin that produces a toxic secretion. In the early 20th century, cane toads were introduced in Australia and several islands of the Caribbean and Oceania as biological control for pests plaguing sugarcane plantations. However, the toads soon became pests themselves.

Cane toads breed prolifically and have a long lifespan, living up to 15 years in the wild. They have a voracious appetite and a broad diet, which includes rodents, reptiles and other amphibians, birds, invertebrates, plants, dog food, and even hosehold waste. In addition, they have a powerful protection against predators. Adult toads have glands that release potent toxins, and tadpoles are toxic if ingested.  The toads are detrimental to many native species of reptiles, with which they compete for food, as well as for frog-eating predators, which can become intoxicated.

3. American Mink

American mink, Neovison vison, were brought into Scotland in the 1950s to be farmed for their fur. It is not clear whether some individuals escaped the farms, or if they were intentionally released, but the minks found their way out into Scottish wilderness and proliferated, causing great damage to native species. The American mink is a very adept hunter, and eats fish, small mammals, birds, and amphibians. Particularly vulnerable are species of ground-nesting birds such as moorhens and arctic tern, and small mammals like the water vole. The American mink also causes significant losses for farmers by taking domestic chickens and ducks. Fortunately, aggressive campaigns to eradicate this furry fiend from key locations have been put in place successfully, and many of the local species are making a comeback.

4. Burmese Python

The Burmese python, Python bivittatus, is one of the large constrictor snake species, measuring on average 3.7 m. It is often found on land near bodies of water, but can also climb trees, especially as a juvenile. Their native range is South and Southeast Asia, but they are an invasive species in the Everglades National Park, in South Florida. The introduction of pythons is thought to have occurred when specimens escaped python farms as a result of Hurricane Andrew in 1992, as well as through the release of python pets.

In the Everglades, they hunt and eat birds, mammals, and alligators. Their diet is varied and has been known to include endangered native species. In fact, the spread of pythons in the Everglades has been associated with the decline in several species of mammals, including raccoons, opossums, bobcats and rabbits. Efforts to control the python population include annual capturing competitions, and the use of trained dogs to spot and capture the snakes.

5. Walking Catfish

Walking catfish is the common name of Clarias batrachus, a species of freshwater catfish native to Southeast Asia. It is an air-breathing fish, and gets its name from its ability to “walk” on its pectoral fins while wiggling its tail (see video below). The fish uses this ability to look for food and new bodies of water. It was introduced in Florida in the 1960s, and has since become an invasive species.

The walking catfish has a voracious appetite and a diverse diet, which includes other fish, invertebrates and plants. They sometimes enter aquaculture farms, going from pool to pool preying on the captive fish. They are also known to harbor the bacteria for enteric septicemia, which can infect farmed fish. These catfish are able to thrive even in small, stagnant pools that are often low in oxygen. They become most aggressive in small pools during the dry season, and can easily become dominant. During cold months or periods of drought, they burrow in the mud and become dormant, emerging when the weather turns more favorable.

6. Water Hyacinth

The water hyacinth, Eichhornia crassipes, is an aquatic plant native to the Amazon. It is characterized by floating leaves and pretty flowers that range in color from lavender to pink. The water hyacinth reproduces very rapidly. New plants can be formed by runners from parent plants, or through seeds. Because of their prolific growth, the water hyacinth tends to cover entire bodies of water when not controlled. This is a problem, because it blocks sunlight from reaching other native plants, and removes oxygen from the water, killing the fish. Furthermore, they create a favorable environment for mosquito and snail reproduction, which are known vectors for diseases, including malaria. Water hyacinth populations are known to double their biomass in as little as 12 days. Their uncontrolled growth also clogs waterways and reduces access for boats, fishing, and other human activities.

Their pretty flowers make them popular ornamental plants, which is probably the pathway that has lead to the introduction of this species in foreign ecosystems. The seeds of the water hyacinth can survive for a long time which, along with its rapid growth rate, makes it very difficult to completely exterminate this plant. The water hyacinth is a pernicious species in Lake Victoria, the largest African lake and one of the largest lakes worldwide. Eradication efforts began in the 1990s, but a recent resurgence is causing important economic losses, making fishing and water access difficult.

 

What can we do to help?

The Nature Conservancy lists some simple actions to help combat and prevent the spread of invasive species:

• Avoid keeping exotic plant species in your garden
• Report sightings of non-native species or, even better, volunteer to help remove invasive species in your area.
• Never release unwanted pets into the wild. Not only is it inhumane for the pet, it can be devastating for the ecosystem. Do extensive research if you plan on keeping exotic pets.
• Avoid transporting hitchhikers. Check your boots and clothes after a hike to avoid transporting invasive weeds, seeds, or parasites. Check your boat thoroughly before moving it to a different body of water.

To learn more, check out the following resources:

Global Invasive Species Database. 2017. 100 of the World’s Worst Invasive Alien Species.

Green, S.J., et al. 2012. Invasive Lionfish Drive Atlantic Coral Reef Fish Declines. PLoS ONE, 7(3): e32595.

Dorcas, M.E., et al. 2012. Severe mammal declines coincide with proliferation of invasive Burmese pythons in Everglades National Park. Proceedings of the National Academy of Sciences, 109(7): 2418-2422.

 

 

Check out some of the most interesting science news published this week:

1. Plastic-Eating Caterpillar

It’s one of those scientific discoveries that happened entirely by accident. Federica Bertocchini was busy removing waxworms from her honey beehives when she noticed that the plastic bag where she was collecting the caterpillars had become riddled with holes. The caterpillars were the larvae of the moth Galleria mellonella. These moths lay their eggs in beehives, and when they hatch, the caterpillars feed on the wax.

Back at the lab, Bertocchini and her team confirmed that these caterpillars can indeed digest polyethylene, the most common plastic. Their ability to digest polyethylene could be related to their consumption of wax, since the chemical structure of both compounds is similar. Although polyethylene is a very useful material—its main application is in packaging, including shopping bags—it is creating important ecologic problems. Plastic bags are known to clog landfills and become troublesome in the ecosystems that they enter. Animals often eat them by mistake, or become entangled in them and die. Although these waxworms are not the first organisms discovered to degrade plastic, the rate at which they do it is very surprising. Experiments with plastic shopping bags revealed that 100 worms could consume 92 mg of plastic in 12 hours, which is a rate more than 1000 times higher than that of other previously reported plastic-consuming organisms.

Bombelli, P., et al. Current Biology. DOI: http://dx.doi.org/10.1016/j.cub.2017.02.060

2. Gut Bacteria Can Influence What Animals Eat

Several recent studies have linked the bacteria present in the body, the microbiome, with changes in the brain and behavior. Now a group of researchers has found evidence suggesting that gut bacteria can influence animal appetite. Scientists working with the fruit fly, Drosophila melanogaster, recently observed how the presence of certain bacteria species in their gut affects their food preference. When fruit flies are fed a diet deficient in essential amino acids, their reproduction rate markedly decreases and their preference for protein-rich yeast increases significantly. The mechanism through which an amino acid deficiency leads the flies to change their food choices is not entirely understood. In this study, scientists found that bacteria commonly found in the gut of wild fruit flies managed to override the flies’ need to consume protein when fed food that lacked essential amino acids. Even more, the flies that were colonized by these bacteria also didn’t experience a decline in reproduction rate. Surprisingly, the researchers didn’t find evidence that the bacteria provided the lacking essential amino acids to the flies. Furthermore, the flies tended to eat more from food that contained the bacteria than food that didn’t, suggesting that they can alter their feeding patterns to obtain the protective action of the bacteria.

Leitao-Goncalves, R., et al. PLOS Biology. DOI https://doi.org/10.1371/journal.pbio.2000862

3. Synthetic Adhesive Inspired by Gecko Feet

Nature has always been an important source of inspiration for researchers and innovators. This time, scientists developed a new adhesive inspired by the feet of geckos. Geckos, a diverse group of lizards native to warmer climates, are remarkable for their ability to climb up vertical walls and even across ceilings. They can do this thanks to their adhesive toe pads, which are covered in setae, very fine hair-like structures. Different adhesives have been developed mimicking the gecko’s feet, but working on wet conditions has remained a challenge. A potential solution to this problem is the use of hydrogels, which change their stickiness properties by swelling or shrinking depending on the pH. Now, a group of researchers has developed a double-sided adhesive that consists of a membrane covered by hydrogel on both sides. Their experiments showed that the material was capable of switching from high friction and adhesion at a low pH, to low friction and adhesion at high pH, even when wet. A synthetic adhesive capable of working in wet environments opens up a whole range of underwater applications, including underwater robotics and sensors.

Ma, S., et al. The Journal of Physical Chemistry C. DOI: 10.1021/acs.jpcc.7b01305

4. Baby Humpback Whales Whisper to Avoid Predators

For newborn baby whales, the ocean can be a dangerous place. Humpback whales migrate from their feeding grounds near the north and south poles to warmer tropical waters every year to breed and mate. Afterwards, they return to their higher latitude range with their calves in tow. For a newborn calf, the journey is long and fraught with perils. Exmouth Gulf in Western Australia is a known spot where humpback whale cows and calves rest on their journey south. The researchers tagged mothers and calves to study their behavior without disrupting them. They found that whale calves communicated with their mothers using low volume sounds, much lower than adult humpback whale vocalizations. These sounds, the equivalent of whale whispers, probably to avoid drawing unwanted attention both from male whales who would turn the mother’s attention away from the calf, and from eavesdropping predators. Killer whales are known to hunt humpback calves in the area. Unfortunately, their low-level communications could mean that they are more easily disturbed by encroaching human activities, such as the use of powerboats.

Videsen, K., et al. Functional Biology. doi: 10.1111/1365-2435.12871

5. Medical Rulebook for Astronauts Coming Soon

Long-term outer space travel has always been an exciting topic, and now it seems more possible than ever, with plans of manned missions to Mars and even colonizing the moon. In anticipation of this, scientists are working on the publication of a set of medical guidelines for astronauts and all those traveling outside of our planet for extended periods of time.

Researchers from the University of Plymouth and Northumbria University, the Aerospace Medical Association (AsMA), the European Space Agency (ESA), the Royal Air Force (RAF), the International Space University, and Blue Abyss are putting together a Review Group to be launched in May of this year that will systematically analyze all the publications in aerospace medicine. They aim to understand the challenges that astronauts’ bodies will face, such as the effects of microgravity, and will also advice on how to deal with problems the astronauts might face when coming back to Earth. Their conclusions will result in a rulebook intended to help keep all those travelling in space in good health during long trips.

Click here to learn more about this.

“The enemy of my enemy is my friend,” reads an ancient proverb, and in the fight against antibiotic-resistant bacteria affecting human lives, it is proving true. Earlier this month, researchers from Baylor College of Medicine in Houston published a paper in the journal Scientific Reports, in which they described the use of bacteriophages to combat antibiotic-resistant bacteria. Read on to find out more about what phages are, and why we need them.

The Rise of the Superbugs

Resistance to antibiotics has existed since the development and widespread use of the first antibiotic, penicillin, in the 1940s. In fact Sir Alexander Fleming, the discoverer of penicillin, warned in his Nobel Lecture against the development of resistance that could result from easy access and subsequent incorrect usage of the antibiotic.

As resistance to penicillin inevitably spread, new generations of antibiotics were developed. Bacterial resistance eventually became problematic again, and in the decades that followed, many new antibiotics emerged. However, bacteria are becoming resistant to those as well. We call them “superbugs”, because not even the best weapons in our arsenal of drugs can kill them. Together with a lack of new antibiotic development, this has plunged us into what people have begun calling the “post-antibiotic era,” in which common injuries and infections can once again be life-threatening.

 

Examples of these superbugs include methicillin-resistant Staphylococcus aureus (MRSA), multi-drug-resistant Mycobacterium tuberculosis (MDR-TB), and carbapanem-resistant Enterobacteriaceae (CRE), like E. coli and Salmonella. CREs, in particular, are resistant to all or nearly all antibiotics available, and around 50% of hospital patients who suffer a blood infection caused by CREs die.

A dramatic example of a superbug infection was reported earlier this year. An elderly woman died of an infection caused by a CRE. She had been in a long-term trip to India, where she broke her femur some years back. She later developed a bone infection, and was hospitalized in India several times. After returning to the US, the woman sought medical care. She was hospitalized in Reno, where it was discovered that she had a CRE infection, in this case by Klebsiella pneumoniae. The bacteria was resistant to 26 different antibiotics, all of the ones that are available in the US. The woman went into septic shock and died shortly after. Even though infections like this one are not common, it is certainly an alarming reminder of what is already starting to happen.

Deaths attributable to antimicrobial resistance (from The Review on Antimicrobial Resistance) / CC BY 4.0

According to the Centers for Disease Control and Prevention, every year at least 2 million people in the United States are infected with antibiotic-resistant bacteria, and at least 23,000 people die from those infections every year. In The Review on Antimicrobial Resistance published in 2014, it is estimated that by 2050 the number of human deaths due to antibiotic-resistant bacteria will be 10 million.

 

How does resistance develop?

Some bacteria can be naturally resistant to antibiotics. Others may become resistant as a result of random mutations to their DNA. These bacteria then pass their resistance to their offspring. But, even more critically, they can pass their resistance genes horizontally to other bacteria through the exchange of plasmids, or mobile DNA elements. The horizontal spread of resistance can also happen from one species of bacteria to another.

When a bacterial population is exposed to an antibiotic, the susceptible bacteria die. However, if some of them have developed or acquired resistance, they will survive. The continued presence of the antibiotic acts as a selection pressure, killing all susceptible bacteria and allowing the resistant ones to thrive. Overusing antibiotics, as well as using them at a sublethal dose, promotes the development of resistance.

Factors contributing to the crisis

Overprescription of antibiotics, and the widespread lack of regulations regarding their use lead to excessive or unjustified human consumption. As we have seen, such abuse of antibiotics is an important cause of resistance development, but perhaps an even bigger threat is their agricultural use.

Although the practice has become increasingly controversial, antibiotics are still commonly used on farm animals, like pigs and chickens, to keep them healthy in crowded environments. They are also used to help the animals grow faster while consuming less food. This allows farmers to increase their yield substantially, but the great amount of antibiotics used, in total greater than that for human consumption, also means these farms are a prime source of resistant bacteria.

Antibiotic-resistant bacteria are present in the feces of these animals, and can become airborne and contaminate the environment. The presence of antibiotic-resistant bacteria has been confirmed in the gut of farm workers, and is also present in slaughterhouses, where the meat of these animals is processed for human consumption. This means that the bacteria can also reach consumers through contaminated meat. Among the resistant bacteria that have been linked to farm animals is Staphylococcus aureus (MRSA).

Adding to this, pharmaceutical companies are less inclined to develop new antibiotics than before. Developing these drugs has become a very expensive and lengthy process for companies, who must comply with very meticulous regulatory standards before being able to market a new drug. The speed with which resistance is developed in bacteria means that some antibiotics are soon obsolete, and many companies have turned their resources to the production of more profitable drugs.

Measures to restrict the use of antibiotics, both for human and animal use, have been established in some places. But as resistance continues to develop faster than new drugs can be created, scientists are beginning to look beyond antibiotics for potential solutions to this looming health crisis.

Bacterio…what?

Bacteriophages are viruses that infect bacterial cells and can destroy whole bacteria populations. They are widespread in nature wherever bacteria are present in high concentrations, like in the intestines of animals and sewages.

The first reports of bacteriophage activity date from the end of the 19th century. In 1896, Ernest Hankin wrote about the healing properties of the Ganges River in India, particularly against cholera. He attributed this property to an unidentified agent, which was small enough to pass through filters and could be inactivated by heat. Later on, in 1915, Frederick Twort described similar findings and suggested several agents that could be responsible, including a virus. However, Twort did not further pursue this line of research, and it was not until a few years later that Félix d’Hérelle, a French-Canadian microbiologist, began to study them seriously. He established that these agents were in fact viruses that could infect and kill bacteria. He named them “bacteriophages,” which means “bacteria eaters.”  D’H’erelle also introduced the term page-therapy, or the treatment of bacterial infections with the use of bacteriophages.

Soon, phages started being used on patients, and were even commercially produced in Paris by what is now L’Oreal, and in the US by Eli Lilly. However, the studies analyzing the efficacy of phage therapy were controversial, and this, together with the discovery of antibiotics, led to a decline in interest in Western countries. Phages continued to be used in Eastern countries, particularly in Georgia and Poland, but most of the research was published in non-English languages and was largely unavailable to Western scientists.

With the rise superbugs now considered one of the greatest threats to public health, and the lack of new antibiotics, interest in bacteriophages is again rising in the West. Bacteriophages have several advantages over antibiotics. Since superbugs and phages are both present in the environment, phages can evolve and adapt to their hosts in real-time, something antibiotics can’t do. They are also very specific for the type of bacteria they infect, which means that they won’t attack other beneficial bacteria, like our gut bacteria, the way antibiotics do. Furthermore, phages replicate inside their bacterial hosts, which means their dosage will increase inside the body as necessary. 

The Research Findings

In the study published by the team from Baylor College of Medicine, the researchers sought to identify a phage for the extraintestinal pathogenic E. coli ST131 (ExPEC ST131). These bacteria are known to colonize the intestinal tract of people without producing symptoms, but can branch out and infect other organs, eventually leading to sepsis and even death. Strains of the type ST131 are resistant to multiple drugs, and are also very virulent. These bacteria are one of the main causes behind antibiotic-resistant E. coli infections in the United States.

The phages were obtained from goose, duck, and canine feces collected from local parks, and chicken feces from a farm. The researchers isolated the phages and tested them against several ExPEC ST131 strains taken from patients. Although no single phage was active against all bacterial strains, the combination of all the phages was. 

The researchers then selected one of the promising phages and carried out experiments in mice to evaluate its performance in vivo. After injecting the mice with a virulent strain of ExPEC ST131, followed by a dose of the bacteriophage, they observed that phage-treated mice appeared healthier and had significantly lower bacterial counts than in those that didn’t receive phages. 

Human patients with a compromised immune system, such as can be developed as a side effect of chemotherapy, are among the most susceptible to infection by superbugs. Antibiotics are routinely used on these patients, which in addition to promoting bacterial resistance, also eliminate useful gut bacteria , and are not useful with drug-resistant strains.

In this research paper, the this scenario was recreated by allowing a strain of ExPEC ST131 to colonize the intestines of two groups of mice. The researchers then gave the mice alternating daily doses of chemotherapy or phage for six days. Control mice received a placebo instead of the phages. After six days, they counted the bacterial load in several organs and found that it was significantly lower in all organs of phage-treated mice compared to those without phage therapy. The phages were able to lower the bacterial load to levels below what is considered fatal.

Conclusions

As the authors note, the most noteworthy aspect of this study is that they were able to demonstrate that phages against clinically-relevant strains of superbugs can be easily obtained from the environment, and applied in a short time. The fact that at least one of the phages obtained in this way was effective in a mouse model of bacterial infection with a compromised immune system was also encouraging.

Although no single phage was able to kill all the bacterial strains used, the combination of phages from all the sources resulted in killing all the strains. Therefore a cocktail of phages could be relevant in the clinic. The authors also propose the use of phages in combination with antibiotics. Although bacteria can develop resistance to phages, this might cause them to lose their resistance to antibiotics.

Phage therapy, although promising, has some challenges. As mentioned above, it is possible for bacteria to develop resistance to the phages, although phages can also change to adapt to their hosts. However, it has also been observed that the human immune system sometimes develops antibodies to fight the phages, making the therapy ineffective. Notwithstanding, phage therapy certainly seems like an interesting and so-far viable new weapon in our line of defense against bacterial pathogens.

 

Useful resources to learn more:

Loc-Carrillo, C. and Abendon, S.T. 2011. Pros and cons of phage therapy. Bacteriophage, 1(2), 111-114.

Review on Antimicrobial Resistance. Antimicrobial Resistance: Tackling a Crisis for the Health and Wealth of Nations. 2014.

Sulakvelidze, A., et al. 2001. Bacteriophage Therapy. Antimicrobial Agents and Chemotherapy,  45(3), 649-659.

Ventola, C.L. 2015. The Antibiotic Resistance Crisis. Pharmacy and therapeutics, 40(4), 277-283.

 

Hi! Here is a brief roundup of some of the week’s most interesting science news. Enjoy!

1. Giant Worm-like Organism Discovered

A giant, worm-like mollusk has been described for the first time, and it is the weirdest thing you have seen. The organism, Kuphus polythalamia, is a member of the shipworm family, long bivalved marine mollusks that burrow in wood. It forms a calcareous shell as it burrows into marine sediment. These shells had been observed for years, but the live organism had never been fully described before. The specimens were found in the Philippines, in a muddy marine lagoon full of wood debris. They can grow up to 1.5 meters long, and reach a diameter of 6 cm.

Shipworms normally ingest wood, digesting the cellulose with the help of bacterial symbionts. However, Kuphus polythalamia relies on an inorganic chemical for food. It bores into mud, which it sifts through its gills. Bacteria in the gills transform hydrogen sulfide into carbon compounds that the shipworm uses for survival. In fact, the digestive tract of this worm is much shrunken from disuse. The researchers are now studying how the transition from wood-consuming shipworms to giant shipworms that thrive on noxious gas happened.

Video credit: Marvin Altamia

Distel, D., et al. Proceedings of the National Academy of Sciences. DOI10.1073/pnas.1620470114

2. Nanoparticles to cure cancer

Researchers at the Fred Hutchinson Cancer Research Center have developed nanoparticles to be used in the fight against cancer. These tiny particles, which are made of a biodegradable material and carry DNA, can penetrate white blood cells and program them to fight cancer cells. A cell-based therapy that has shown promising results in clinical trials involves removing T-cells from the body and manipulating them in the laboratory before implanting them back into the patient. In contrast, the nanoparticles are injected into the patient and used to program the cells inside the body. The DNA-carrying particles attach to the T cells, which ingest them, and deliver their DNA into the cell nucleus. It is like inserting a set of instructions into the cell, which direct it to produce receptors that can identify leukemia cells. The use of these nanoparticles improved animal survival when used in a mouse model for leukemia, from a median survival of 2 weeks to an average survival of 58 days. 

Smith, T.T., et al. Nature Nanotechnology. doi:10.1038/nnano.2017.57 

3. Got the Flu? Try Some Frog Slime

Scientists are continually finding potential drugs in the unlikeliest of places. This time, a group of researchers looking into frog slime for compounds exhibiting antimicrobial properties discovered a molecule with anti-flu virus activity. The compound, a peptide they called “urumin” was found in the mucus of the frog Hydrophylax bahuvistara, a species native to Kerala, India. It probably works by binding to hemagluttinin, a protein on the surface of many strains of virus, that the virus needs to in order to infect human cells. Antimicrobial compounds are found in the secretions of many animals, as a form of defense. Frogs are a particularly interesting source because it is relatively easy to obtain the mucus that contains these compounds.

Holthausen, D.J., et al. Immunity. DOI:http://dx.doi.org/10.1016/j.immuni.2017.03.018

4. Viruses vs superbugs

In the fight against antibiotic-resistant bacteria that seem to be becoming more common than ever, scientists are looking beyond antibiotics to combat them. Earlier this week, researchers from the Baylor College of Medicine described in Scientific Reports, how they used bacteriophages, or bacteria-killing viruses, to combat antibiotic-resistant bacteria in mice. They isolated phages from dog and bird feces found at local parks, and selected one with potential for drug development. They tested the phage in mice infected with clinically relevant strains of resistant bacteria, and found that it greatly improved the health outcome of the mice.

Although the use of phages for therapy is not new, it was largely forgotten in the Western world after the advent of antibiotics. Now that antibiotic-resistant “superbugs” are on the rise, interest in phage therapy has been renewed. Among the benefits of phage therapy is that protective gut bacteria in the patient are not destroyed. Also, their renowned capacity to adapt and evolve means they could change in response to bacterial mutation, something antibiotics cannot do.

Green, S.I., et al. Scientific Reports. doi:10.1038/srep46151

5. European Salamanders in Danger

A fungus that has been imported into Europe, probably through the pet trade, is decimating European salamander populations at an alarming rate. The fungus, Batrachochytrium salamandrivorans, is native to Asia, and has affected populations of fire salamanders in Belgium, the Netherlands, and Germany. It infects the skin of the salamanders, leading to necrosis and death. The infection and mortality rate is extremely high, with only 13% of infected salamanders surviving over a 10-day period. The immune system of the salamanders cannot effectively fight off the infection, and the fungus is very resistant to environmental conditions. Making matters worse, amphibians that share the habitat of the fire salamander may become reservoirs for the fungus. This means that the fungus will remain in the environment even after the salamanders die off, making re-introduction efforts ineffective. Research efforts are in place to combat the spread of the fungus, as well as a ban on imported salamanders and newts. The fungus is carried by the fire belly newt, popular among hobbyists.

Stegen, G., et al. Nature. doi:10.1038/nature22059

Resting on the sandy bottom, digging my hands into it to anchor myself against the current, I could see them slowly circling around us. I was trying to make out the silhouette of one cut against the deep blue of the sea, the only sound that of the bubbles coming from our regulators. A fellow diver pointed to my right, and I turned. Swimming straight towards me, was a massive bull shark.

It was the stuff of nightmares, only this was, in fact, the purpose of our dive. Staring at the shark as it swam smoothly in my direction, totally undisturbed by the current, I couldn’t help but think what an easy meal I would make, if the shark meant to eat me. It came so close, I could see every detail of its muscular body, it’s small dark eyes, down to the pores around its snout with which it can sense electric fields. Then, before it reached me, it effortlessly modified its course, gracefully gliding by me instead.

It was December 2016 and we were diving off the coast of Playa del Carmen, in the southern tip of Mexico. Every year, between the months of November and March, bull sharks congregate in these waters. They are a magnet for shark divers, and a source of fear for many people who go in the water. It is a season of struggle between those who would like to see them protected and those who would like to see them gone. But what are the characteristics that set these sharks apart from others?

Characteristics of Bull Sharks

Bull sharks, Carcharhinus leucas, are strong, stocky sharks with a gray coloration on top that turns to white underneath. They have a characteristic blunt snout, and a long caudal fin. Bull sharks usually grow to be 2.1-3.4 meters long and 90-230 kg, with females being larger and heavier than males. They have an impressive bite force, which has been estimated to be higher than that of the great white shark (1).

Widely described as having an aggressive temperament, bull sharks are one of the shark species that are considered most dangerous to humans. This is due to several factors, including their size, habitat and preferred hunting grounds. These sharks inhabit the warm coastal waters of all the world’s oceans. They swim in shallow water near the coast and at the mouth of estuaries, which humans also frequent. They like to hunt in murky water with low visibility, which could lead to mistaking humans for their natural prey. 

Distribution map for Carcharhinus leucas. By Chris_huh/ CC BY-SA 3.0

Additionally, unlike other shark species, bulls have adapted to thrive in a variety of water salinities. Their presence has been well documented in rivers throughout their range, like the Zambezi River in Africa, the Brisbane River in Australia, and the Mississippi in the United States. Bull sharks have even been found in lakes. In Central America, their presence in lake Nicaragua has earned them the name of Nicaragua shark. They were originally thought to be a distinct shark species from the Pacific Ocean that became trapped there when the lake was formed. However, it was later discovered that the sharks travel to the lake from the Atlantic Ocean, swimming up the San Juan River, and navigating the rapids (2).

Bull sharks are able to survive in fresh water thanks to their kidneys, liver, gills and rectal glands, which work together to balance the salt and water concentration in their bodies. They use fresh water bodies as nursery grounds, and it is thought that this gives the young sharks a safe space to grow without the threat of bigger sharks preying on them.

Most of the sharks that gather in Playa are female sharks, and many of them are pregnant. It is thought that they come to these shores to give birth in the nearby mangroves, but there is still much to learn about them. In 2010, an association called Saving our Sharks (SOS) was founded, with the purpose of leading conservation and research efforts. Studying sharks in their natural environment is a complicated endeavor, but research efforts are slowly beginning to yield answers. How are they doing this?

Research Efforts

One way to study the movement of animals in nature is through the use of tags. At Playa del Carmen, researchers are using both external and internal tags. External tags are placed on the base of the dorsal fin using a fishing harpoon and dart. Internal tags, on the other hand, are placed in the peritoneal cavity. To place them, the shark must first be caught with line and hook, and stabilized alongside the boat. The tag is then surgically implanted. Both kinds of tags carry a code that is specific for that shark, and is passed to receivers placed along the coast every time the shark comes near.

Scientists can also obtain information about animal populations by analyzing small tissue samples, or biopsies. At Playa, small cylindrical probes are used to take tissue samples from the sharks, from the area at the base of the dorsal fin. The tissue samples are then used for different analyses. For example, DNA extracted from the skin has been used to determine the relationship between these sharks and other bull shark populations in the Gulf of Mexico.

The analysis of biopsies can also reveal information about the sharks’ diet. Traditionally, diet has been researched by looking at the stomach content of different specimens. This, however, has several disadvantages, including the need to dissect a large number of sharks, and the possibility of finding empty stomachs. An alternative way to do it is through stable isotope analysis.

Isotopes are atoms of the same element that have different number of neutrons. Most elements found in nature exist as stable isotopes. The specific ratio of isotopes found in the tissues of an organism reflects the isotope composition of its diet. By measuring the isotope composition of animal tissues, scientists are able to study food webs and predator-prey relationships within an ecosystem.

Need for Shark Conservation Efforts

The first shark I ever saw underwater was a bull shark. Contrary to what I had anticipated, it was a peaceful experience. The shark was even a bit shy, barely noticing us before disappearing into the blue. Ever since then, I’ve come to realize all the misconceptions and misinformation that abound about sharks, even among otherwise educated people. “Why didn’t they bite you?” and similar questions are often brought up, even though you have a far greater chance of drowning at the beach, than being bitten by a shark.

Sharks play a vital role in maintaining the balance in their ecosystems. They eat the weak and the sick, keeping fish populations healthy and under control. The elimination of sharks can destabilize entire food chains, and bring about the degradation of the ecosystem. Sadly, millions of sharks are killed each year for their fins and meat. In particular, the conservation status of the bull sharks is NT, Near Threatened.

Fortunately, studies are showing that sharks are worth more alive than dead. In a study published in Oryx: The International Journal of Conservation in 2013 it was estimated that shark fisheries generate around $630 million dollars per year globally, but this amount has been declining over the past decade. On the contrary, the shark tourism industry generates around $314 million dollars per year, and is expected to grow to over $700 million dollars within 20 years. In Palau, a study by the Australian Institute of Marine Science and the University of Western Australia showed that a single reef shark can generate $1.9 million dollars over the course of its lifetime, compared to $108 if it were fished and sold. In Playa del Carmen, SOS estimates a single live shark contributes $220 thousand dollars per season. On the other hand, a dead shark can make the fisherman $300 to $400 dollars, but only once.

The more we learn about the sharks and their behavior, the better we can understand how to protect them. Clearly, however, changing the public’s opinion is key to their survival. After all, a feared shark is most probably a dead shark. This is best done through education and outreach efforts to dispel the myths surrounding sharks and change the negative public portrayal of these animals.

As for me, after having spent countless hours researching sharks and shark attacks, when I finally saw that first shark underwater…a sense of wonder filled me. I marveled at this powerful creature that was for sure capable of inflicting serious harm on me, and yet did not. Time seemed to stand still as I stared at it, mesmerized by its beauty. I already loved sharks but, after this experience, my perspective on them and their relationship with humans changed even more.

Bull shark dive from M Granados on Vimeo.

References:

(1) Habegger, M.L., et al. Feeding biomechanics and theoretical calculations of bite force in bull sharks (Carcharhinus leucas) during ontogeny. 2012. Zoology, 115(6): 354-364.

(2) Thorson, T.B. Movement of Bull Sharks, Carcharhinus Leucas, Between Caribbean Sea and Lake Nicaragua Demonstrated by Tagging. 1976. Investigations of the Ichthyofauna of Nicaraguan Lakes. Paper 38.