It’s that time of year again… SHARK WEEK! Just as you start to pop your popcorn and sit down on your sofa to see if Michael Phelps can out swim a great white shark, scientists are returning from the annual Joint Meeting of Ichthyologists and Herpetologists. This year, shark, fish, reptile, and amphibian biologists converged on Austin, Texas to discuss their newest findings – and I’m here to share some of that science with you. With four days filled with talks, it would be impossible to tell you about all the incredible science being conducted, but here are just a few of the highlights.
What fish are teaching us about romance!
In his talk “Beauty and the brains: Insights from frogs and fishes,” Dr. Mike Ryan discussed the research that has been conducted in his lab over the past few years using fishes and frogs. The work on fishes focuses on a unisexual species called the Amazon Molly (Poecilia formosa). The species is composed entirely of females – that’s right men, a society of nothing but ladies! Even though the females essentially produce clones of themselves without any genetic input from a male, they still require sperm from a male to trigger the egg’s development into a baby. To receive this sperm donation, the females mate with males of another species, the Sailfin Molly (Poecilia latipinna; Figure 1).
You may not be at a point in your life where you want children, but biologically you are hardwired with a desire to spread your genes to the next generation. This is the case for all organisms, so why would a male Sailfin Molly mate with an Amazon Molly that won’t pass the male genes down to the babies? To investigate this, the first question Dr. Ryan asked was “do the males know that they are mating with an Amazon Molly and not a female of their own species?” The answer is yes – and when given the choice, males preferred to mate with their own species.
The next question Dr. Ryan’s lab focused on was “if males prefer to mate with their own species, why mate with the female Amazon Mollies at all?” This is where it gets interesting! The scientists exposed female Sailfin Mollies to two different males to determine their mate preference. When only shown the two males, the females had a clear preference for one over the other. However, when the scientists showed the female Sailfin Molly those same two males but put a female Amazon Molly in with the less desirable male, the female Sailfin Molly preferred the previously less desirable male. Essentially, mating with an Amazon Molly might make a male Sailfin Molly more attractive to females of his own species!
Can sharks help us fight cancer?
We already know that sharks are incredible predators that have been on our planet for millions of years. One of the reasons sharks and their relatives are so successful likely stems from their remarkable healing abilities. Previous research has shown that some shark cells can even suppress the growth of cancer cells in human tumors! Obviously, this is a very exciting find worth digging into. The problem is that scientists can only keep the shark cells alive for a limited time in the lab when conducting research. With shark populations already threatened, it isn’t feasible to continuously collect sharks to supply scientists with fresh cells.
Dr. Carl Luer gave a talk on some of the new research going on in his lab. He and his colleagues are trying to solve this conundrum by engineering a continuous (i.e. immortal) line of shark cells that scientists would be able to use for conducting cancer research. Cells have a life span. After a certain amount of time they are pre-programmed to self-destruct (with the exception of cancer cells, which have mutated to continually grow unchecked by normal cellular processes). If scientists can “reprogram” a cell to turn off the self-destruct mechanism, they can keep a cell line alive for longer periods of time, allowing them to conduct research without continually isolating new cells.
There are a few ways a cell can become immortal: a random mutation can arise in the genome altering cellular life cycles (such as with cancer cells) or a viral infection may induce a cell to become cancerous and turn off the self-destruction programming. With the lower instance of cancer in shark populations, however, it is not as easy for scientists to hijack these already immortal cells in sharks. Dr. Luer is using a technique called cellular fusion, which allows him to induce two cells to hybridize (merge together) to try to make a longer living shark cell line. This could lead to some really exciting biomedical research! In the meantime, you can learn more about shark immune systems at http://motemarine.org/~rhueter/sharks/cancer.phtml .
Shark body temperatures may help us predict pupping ranges
Dr. Aaron Carlisle gave a talk about how some sharks can regulate their body temperatures. This may not seem altogether fascinating considering we regulate our own body temperature constantly. When it is cold outside, your body does not automatically drop because humans, and all mammals, are endotherms. Fish, however, with a few notable exceptions, rely on the surrounding water to regulate their body temperatures. However, some sharks, such as the salmon shark and the great white shark (Figure 2), are regional endotherms – meaning they are able to regulate temperatures in a portion of their body. This can help keep muscles warm for faster swimming, for instance, and may keep critical organs warm to allow sharks to hunt prey in cold regions.
Even though regional endotherms can withstand colder waters, they still undergo extensive migrations to warm water each year, and scientists have no clear idea why. Dr. Carlisle and colleagues examined how size might impact body temperature regulation and found that smaller sharks would not be able to regulate body temperatures as efficiently as larger sharks. Now, let’s think about how sharks are born: these regionally endothermic sharks give birth to live young (rather than laying eggs). After months of growing and developing in a warm mother, these small pups would not be large enough to regulate their body temperatures in the cold waters the mothers typically inhabit. Just think how unpleasant it would be to spend an hour in a hot tub and get thrown into an ice cold swimming pool – not fun! In fact, the heat difference the newly born pups would experience could be enough to induce shock or even cause mortality.
Scientists observe that regionally endothermic fishes migrate to waters that are closer to their own body temperature. While we do not know for sure that the sharks are going to these warm waters to give birth to their pups, this research certainly gives good support to the hypothesis that mothers are swimming to warmer waters to reduce the stress of cold waters on their newly born pups. Knowing this may allow researchers to find the ever-elusive pupping grounds for several shark species.
Want to learn more about sharks? You can take a class for free! Dr. William Bemis gave an opening talk on how he collaborated with shark biologists and dedicated individuals from Cornell University and the University of Queensland Australia to develop a completely online, widely accessible class on shark biology. This four week long course is free from edX and open to anyone to enroll. You can learn more about the course at https://www.edx.org/course/sharks-global-biodiversity-biology-cornellx-uqx-bioee101x-0 .
I received my Master’s degree from the University of Rhode Island where I studied the sensory biology of deep-sea fishes. I am fascinated by the amazing animals living in our oceans and love exploring their habitats in any way I can, whether it is by SCUBA diving in coral reefs or using a Remotely Operated Vehicle to see the deepest parts of our oceans.