Animal Series #18: A Natural Born Superhero

Picture By Bernard DUPONT - Flickr (CC BY-SA 2.0)

It's has been ages since I've dedicated myself to write about animals hence today, I will try to find that kind of enthusiasm again. There are a lot of superheroes among us but when it comes to the ocean, we hardly notice that there is a certain animal which is big, long-lived, can heal relatively quick, strong and almost free of diseases. Today, we are going to talk about one of the greatest superheroes of the ocean, the great white shark. Pretty much straight forward, I have written an article about the great white shark months ago but today, I'm going to do it again with a different style. On February 18th (last week), a group of scientists have published a paper entailing some unusual genomic sequences in great white sharks compared to other vertebrates. Mind you there are approximately 4 billion great white shark genomic sequences out there thus this particular finding is no small feat. You have to be meticulous and patient with all of the necessary step to reach the ultimate conclusion.

Compared to humans, great white shark genomes exhibit a higher number of a certain repeated sequence (which is called LINES) that loves to make copies of themselves and slip through in between their DNA structure rendering the latter unstable thus making them prone to mutations and cancers. So why haven't they? Well, they have a greater number of genes which are responsible for maintaining stability, just like what we (humans) have although I would like to stress out that they might have a much-sophisticated genetic maintenance system courtesy of evolutionary adaptation. This maintenance gene has been found to have a tiny modification to their own genomic sequence compared with analogous genes of other vertebrates. For more than a century, humans know that even with their tough exterior and superior strength, sharks do get cancer but studies have shown that they were the least animals which have been recorded with such biological problems.

People have been involved in promoting and selling shark's parts telling people that they could provide therapeutic benefits of treating cancer although no such documentation has been published to suggest such benefits. What do you think will happen next? People have been killing on average 100 million sharks per year for the sake of their unproven therapeutic benefits and a bowl of shark fin soup. It's not that they didn't get cancer, they rarely do. In November 2015, a paper was published in the Journal of Fish Diseases regarding a great white shark which has found to have a tumour protruding from its mouth measuring about 30 cm in diameter. It provides some perspectives to the notion that this particular animal doesn't experience such anomaly. The cause for that tumour can be multifactorial. For the past few decades, we have seen the rising statistic of animals being diagnosed with cancers. Environmental pollutants can be one of the reasons why this particular shark species suffered from such malignancy.

There are a few species of sharks which have been found swimming in the area of the sea near to either a factory or a power plant suffered from cancer which confirms the role of environmental pollutants. Even with all of the genomic stability that can be provided by various genes, sharks are not immune from getting cancers; they are just protected and have an incredibly low chance of developing such anomalies. Nevertheless, it is quite a useful perk don't you think?

Affinity To Electricity And Acute Sense Of Smell

Picture By Sharkdiver - Wikipedia (CC0)

Ever heard of the rumour that a shark can pick up blood from miles away? Yeah, me too. Well, they do have a relatively acute sense of smell but the rumour that said they can do it from miles away is a complete exaggeration. Although we can consider the myth of smelling blood from a distance to be not entirely true, great white sharks still are lethal and can detect their victims from a significant distance of origin. This ability, however, is not influenced by their acute sense of smell but rather their sensitivity to electric impulse. The ampullae of Lorenzini or I would like to call a network of jelly-filled pore located on this predator's snout is a great thing, they can sense muscle movement from a few couple metres away (not miles), allowing them to hunt their prey rather effectively.

If you ever watch the movie "The Meg" you would know the fact that sharks are particularly attracted to panic motion. When we are panicking, our brains send a relatively quick electrical signal to our muscles making us splashing the water around us in an effort to swim away from this particular predator. The fact that if a shark is swimming towards you, they can be thought as either being aggressive or just curious about what is lying ahead. According to an article published in the Huffington Post, most of the time when sharks were approaching divers, they would back out once they took a proper closer look to their target. They hate humans meat but if you were splashing around like a madman, you would seem more like a distressed fish or seal which motivate them to launch a test bite.

Their ampullae of Lorenzini is really interesting by the way. One of the most profound skills of this sea predator is their ability to navigate and swim across the ocean in a straight line. We know that the ocean is vast and without a proper navigation system, one could get lost easily. People have been curious regarding this fact; how do sharks swim in a straight line when there are no landmark or anything which could have assisted them to do so? Nevertheless, scientist realised that they weren't swimming in a straight line in a randomised pattern. They were thought to swim along the magnetic field of the earth. I can't seem to find any article which could have supported that hypothesis but one of the most popular speculations made was that any shark species are able to convert the magnetic field of the earth into electrical energy. This would later be used by their own ampullae of Lorenzini to perceive the direction of swim and eventually translated into a straight line swimming behaviour. Cool, huh?

What about their acute sense of smell? Can they really smell your blood from miles away? Well, not likely but that's not entirely impossible. Any smell would be carried by the currents which usually takes some times to reach the nearest shark's nostrils. If eventually, they smell you, they would only come to identify what kind of creature you are. Are you a potential victim? Believe it or not, some shark species are picky eaters. They would come close, smell you and if you are not what they were looking for, they would just swim away. For whatever reason, I would say that the probability of you getting attack by a shark is minimal as long as you are not panicking but that doesn't mean you will absolutely not get bitten. It's difficult for us to be calm in the worst case scenario ever unless you have done this before, a few times.

No Partner? No Problem

Picture By Steve Pomeroy - Flickr (CC BY-SA 2.0)

Well, I'm not sure if we can think this ability as something worthy of a superhero but once again, the ocean is vast. We wouldn't know where we going to turn up and whether there is a potential partner nearby to reproduce. It's important to guarantee the continuation of this particular species so I would say the ability to reproduce without needing a male, is quite awesome. Apart from mating, sharks can reproduce in a few ways, either with sperms that they have been keeping for years after the last mating session or reproduce without it. Let see, just imagine, you've decided to travel east and before starting your journey, you met this guy and everything seems to move so fast. Eventually, you do it and later decide to keep the sperm for two years before conceiving one. After all, proper spacing is important. After a long journey, you couldn't find any male to procreate with. That's when your sperm storage comes into play.

In a situation whereby female sharks would live in solitary or failed to find a mate, keeping sperm for future use seems to be quite useful. There are a few species of sharks which utilised such strategy and the longest sperm keeping is currently held by a captive bamboo shark in California (3.5 years). This will not only allow the shark to produce offspring in a certain location but also to control the number of litter they would want to reproduce. What about parthenogenesis then? Is it an option. Yes, it is. Even without keeping sperms or had any sexual intercourse with the other male shark, it still possible for a shark to have a baby without male shark genetic contribution. It's not clear how this happens with sharks but we do know that shark offsprings which are reproduced this way are often fragile and not long-lived. They required constant care like a premature infant.

Sharks are really interesting. There are a number of species out there and a few of them are considered so rare that the probability to encounter them were less than 1%. Obviously, this is not the end of the shark chapter of my Animal Series. I would be back with some more interesting fact soon so stay tuned.

References

• Here's Why Great White Sharks Are Natural-Born Superheroes. Retrieved on 25th February 2019.
• Sharks Do Get Cancer: Tumor Found in Great White. Retrieved on 25th February 2019.
• What is electroreception and how do sharks use it?. Retrieved on 25th February 2019.
• Sharks Can Detect a Single Drop of Blood in the Ocean!. Retrieved on 25th February 2019.
• What Not To Do Around Sharks, According To The Experts. Retrieved on 25th February 2019.
• Can A Shark Really Smell A Drop Of Blood From A Mile Away?. Retrieved on 25th February 2019.
• Shark Set New Sperm Storage Record. Retrieved on 25th February 2019.
• Parthenogenesis Of A Shark. Retrieved on 25th February 2019.

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