Caught on Camera: Ancient Greenland Sharks
By Brynn Devine and Jonathan A. D. Fisher
The Greenland shark is one of the world's largest marine species, reaching lengths over six meters (approximately 20 feet). And yet these fish, which prefer the deep, cold waters of the Arctic and North Atlantic oceans, have largely eluded scientific study.
Their evasiveness highlights how little we know about Arctic marine ecosystems—and how much we can learn by developing and employing new technologies.
For scientists like us, the observation and monitoring of marine species can be challenging under the best of circumstances. But sampling at extreme depths and in seasonally ice-covered waters is especially difficult.
Researchers Brynn Devine (right) and Laura Wheeland aboard the vessel Kiviuq I off the community of Grise Fiord on southern Ellesmere Island in 2016 Laura Wheeland, author provided
However, we recently captured some of the first underwater video footage of Greenland sharks in the Canadian Arctic. The recordings gave us valuable insight into their abundance, size and behavior, as well as their distribution in the Canadian Arctic.
These findings are the first step towards closing a major knowledge gap on the population status of the Greenland shark.
And we did it without taking any sharks from the water.
Sleeper Sharks Revealed
Until now, most of what we knew about Greenland sharks came from the historical records of commercial landings. They were fished in the North Atlantic for their oily livers until 1960. A limited harvest still occurs in Greenland, and the species is sometimes encountered as bycatch in fisheries that occur within its geographical range.
But in areas of the North Atlantic and Arctic where commercial fishing has not historically occurred—such as the waters of the Canadian Arctic Archipelago—their full geographic range has remained unknown.
Due to their sluggish and seemingly lethargic behavior, the Greenland shark is part of the family of "sleeper sharks." Despite being remarkably slow swimmers and effectively blind, thanks to eye parasites, the Greenland shark is one of the Arctic's top predators.
A small Greenland shark, less than 1.5 meters long, observed inside Scott Inlet on northern Baffin Island Brynn Devine, author provided
Although they feed mostly on a diverse buffet of bottom-dwelling fishes, there is some evidence that they can capture live seals. Just how they catch these fast-swimming marine mammals remains a mystery to researchers.
Greenland sharks are by far the largest fish in the Arctic. They rival the great white shark in length, if not its fear factor.
Scientists have also puzzled over their life span and growth rates. They appear to grow extremely slowly—less than one centimeter per year—and are believed to not reach maturity until females are 4.5 meters (approximately 14.7 feet) long and males are three meters (approximately 9.8 feet) long.
They also have remarkable lifespans. Scientists recently used radiocarbon dating techniques on the eye lens of a Greenland shark, and found they can live for more than 272 years, making the species the longest living vertebrate on the planet.
While these are impressive traits, their age and large size leave Greenland sharks more vulnerable to stressors such as overfishing or habitat loss than other fishes.
Scientists know little about Greenland sharks living in the unfished waters of the eastern Canadian Arctic. To help collect information on sharks residing in this region, we baited cameras with squid and dropped them into the deep waters of Nunavut.
After two summer field seasons, we had more than 250 hours of high-resolution video recorded from 31 locations.
Greenland sharks arrived at 80 percent of our deployments. We used the video to distinguish one individual from the next based on their unique skin markings, a method researchers also use to identify for whale sharks and great white sharks. Altogether, we identified 142 individual sharks.
The videos also gave us additional information about the sharks, including their length and swimming speeds. In some locations, the sharks were relatively small—less than 1.5 meters (approximately 4.9 feet) long—in others, they were over three meters long, but nearly all of them were likely still too young to reproduce.
Researchers are increasingly using video to survey marine wildlife. Baited-camera surveys eliminate the adverse effects of scientific longline surveys, where fish are caught on hooks. Even though the sharks are later released, many suffer from the stress of capture or can become entangled in the fishing gear, which can lead to death.
New Information for a Changing Arctic
We did most of this work within the region of Tallurutiup Imanga (Lancaster Sound), which could become Canada's largest marine protected area.
This area is known as a vital feeding and nursery ground for many Arctic species of both ecological and Inuit cultural significance, including whales, seabirds, polar bears, seals and walruses. Our video data now shows that this area might of be important to Greenland sharks too, at least in summer months.
Map of baited camera deployments where Greenland sharks were observed, with symbol sizes proportional to the number of individuals distinguished from each set. The 'X' indicates sets where no sharks were observed.http://www.nature.com/articles/s41598-017-19115-x, CC BY
In addition, given the significance of top predators in controlling the dynamics of high latitude marine ecosystems, the role of Greenland sharks may represent an important link in Arctic food webs.
At a time when oceans are rapidly warming, Arctic sea-ice cover is shrinking and there is increasing interest in Arctic fisheries and conservation, it's important that we understand the domains of these large, ancient creatures.
Reposted with permission from our media associate The Conversation.
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By Jacob L. Steenwyk and Antonis Rokas
From the mythical minotaur to the mule, creatures created from merging two or more distinct organisms – hybrids – have played defining roles in human history and culture. However, not all hybrids are as fantastic as the minotaur or as dependable as the mule; in fact, some of them cause human diseases.
When Looking Through a Microscope Isn’t Close Enough.<p>For the last few years, <a href="http://www.rokaslab.org/" target="_blank">our team at Vanderbilt University</a>, <a href="https://www.researchgate.net/lab/Gustavo-Goldman-Lab" target="_blank">Gustavo Goldman's team at São Paulo University in Brazil</a> and many other collaborators around the world have been collecting samples of fungi from patients infected with different species of <em>Aspergillus</em> molds. One of the species we are particularly interested in is <a href="https://doi.org/10.1006/rwgn.2001.0082" target="_blank"><em>Aspergillus nidulans</em>, a relatively common and generally harmless fungus</a>. Clinical laboratories typically identify the species of <em>Aspergillus</em> causing the infection by examining cultures of the fungi under the microscope. The problem with this approach is that very closely related species of <em>Aspergillus</em> tend to look very similar in their broad morphology or physical appearance when viewing them through a microscope.</p><p>Interested in examining the varying abilities of different <em>A. nidulans</em> strains to cause disease, we decided to analyze their total genetic content, or genomes. What we saw came as a total surprise. We had not collected <em>A. nidulans</em> but <em>Aspergillus latus</em>, a close relative of <em>A. nidulans</em> and, as we were to soon find out, <a href="https://doi.org/10.1016/j.cub.2020.04.071" target="_blank">a hybrid species that evolved through the fusion of the genomes</a> of two other <em>Aspergillus</em> species: <em>Aspergillus spinulosporus</em> and an unknown close relative of <em>Aspergillus quadrilineatus</em>. Thus, we realized not only that these patients harbored infections from an entirely different species than we thought they were, but also that this species was the first ever <em>Aspergillus</em> hybrid known to cause human infections.</p>
Several Different Fungal Hybrids Cause Human Disease.<p>Hybrid fungi that can cause infections in humans are well known to occur in several different lineages of single-celled fungi known as yeasts. Notable examples include multiple different species of <a href="https://doi.org/10.1002/yea.3242" target="_blank">yeast hybrids</a> that cause the human diseases <a href="https://rarediseases.info.nih.gov/diseases/6218/cryptococcosis" target="_blank">cryptococcosis</a> and <a href="https://www.cdc.gov/fungal/diseases/candidiasis/index.html" target="_blank">candidiasis</a>. Although pathogenic yeast hybrids are well known, our discovery that the <em>A. latus</em> pathogen is a hybrid is a first for molds that cause disease in humans.</p>
(Left) Candida yeasts live on parts of the human body. Imbalance of microbes on the body can allow these yeasts, some of which are hybrids, to grow and cause infection. (Right) Cryptococcus yeasts, including ones that are hybrids, can cause life-threatening infections in primarily immunocompromised people. Centers for Disease Control and Prevention<p><a href="https://doi.org/10.1371/journal.ppat.1008315" target="_blank">Why certain <em>Aspergillus</em> species are so deadly</a> while others are harmless remains unknown. This may in part be because <a href="https://doi.org/10.1016/j.fbr.2007.02.007" target="_blank">combinations of traits, rather than individual traits</a>, underlie organisms' ability to cause disease. So why then are hybrids frequently associated with human disease? Hybrids inherit genetic material from both parents, which may result in new combinations of traits. This may make them more similar to one parent in some of their characteristics, reflect both parents in others or may differ from both in the rest. It is precisely this mix and match of traits that hybrids have inherited from their parental species that <a href="https://www.nytimes.com/2010/09/14/science/14creatures.html" target="_blank">facilitates their evolutionary success</a>, including their ability to cause disease.</p>
The Evolutionary Origin of an Aspergillus Hybrid.<p>Multiple evolutionary paths can lead to the emergence of hybrids. One path is through mating, just as the horse and donkey mate to create a mule. Another path is through the merging or fusion of genetic material from cells of different species.</p><p>It is this second path that appears to have been taken by our fungus. <em>A. latus</em> appears to have two of almost everything compared to its parental species: twice the genome size, twice the total number of genes and so on. But unlike other hybrids, which are often sterile like the mule, we found that <em>A. latus</em> is capable of reproducing both asexually and sexually.</p><p>But how distinct were the parents of <em>A. latus</em>? By comparing the parts contributed by each parent in the <em>A. latus</em> genome, we estimate that its parents are approximately 93% genetically similar, which is about as related as we humans are with lemurs. In other words, <em>A. latus</em>, an agent of infectious disease, is the fungal equivalent of a human-lemur hybrid.</p>
How A. Latus Differs From its Parents.<p>Elucidating the identity of closely related fungal pathogens and how they differ from each other in infection-relevant characteristics is a key step toward reducing the burden of fungal disease. For example, we found that <em>A. latus</em> was three times more resistant than <em>A. nidulans</em>, the species it was originally identified as using microscopy-based methods, to one of the most common antifungal drugs, <a href="https://www.drugbank.ca/drugs/DB00520" target="_blank">caspofungin</a>. This result provides a clear example of the potential importance of accurate identification of the <em>Aspergillus</em> pathogen causing an infection.</p><p>We also examined how <em>A. latus</em> and <em>A. nidulans</em> interact with cells from our immune system. We found that immune cells were less efficient at combating <em>A. latus</em> compared to <em>A. nidulans</em>, suggesting the hybrid fungus may be trickier for our immune systems to identify and destroy.</p><p>In the midst of the COVID-19 pandemic, our quest to understand <em>Aspergillus</em> pathogens is becoming more urgent. Growing evidence suggests that <a href="https://doi.org/10.1111/myc.13096" target="_blank">a fraction of COVID-19 patients are also infected with <em>Aspergillus</em>.</a> More worrying is that these <a href="https://doi.org/10.3201/eid2607.201603" target="_blank">secondary <em>Aspergillus</em> infections</a> can worsen the clinical outcomes for those infected with the novel coronavirus. That being said, we stress that little is known about <em>Aspergillus</em> infections in COVID-19 patients due to a lack of systematic testing, and none of the infections identified so far appear to have been caused by hybrids.</p><p>So, when it comes to hybrids, some are fantastic (the minotaur), some are helpful (the mule) and some are dangerous (<em>Aspergillus latus</em>). Understanding more about the biology of <em>Aspergillus latus</em> may help in our understanding of how microbial pathogens arise and how to best prevent and combat their infections.</p>
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