Flight of the Dragonfly

By Rachel Baxter

"Pantal flavescens at Kavadoor" 

© 2010 Jeevan Jose 

Commonly known as the “globe skimmer”, it is no surprise that Pantala flavescens, a unique species of dragonfly, can travel long distances. Despite being less than 2 inches long, these tiny insects have the ability to fly across oceans, making some of the greatest migratory journeys on Earth.

However, only recently have scientists had an insight into just how often these voyages are occurring. A recent study, by biologists at Rutgers University, published in the journal PLOS One, has shown that Pantala dragonflies all over the world are genetically very similar. This is unusual in nature, as geographically segregated populations of the same species tend to vary genetically to some extent.

Jessica Ware, one of the paper’s authors, explains, "If North American Pantala only bred with North American Pantala, and Japanese Pantala only bred with Japanese Pantala, we would expect to see that in genetic results that differed from each other.”

Nevertheless, in the case of the Pantala dragonfly, highly similar genetic profiles have been found in individuals across the world, ranging from the USA and South America, to Japan, India and Korea. The fact that they seem to share one common global gene pool suggests that individuals from different continents are not only interbreeding, but doing so on a regular basis. This would mean that they are travelling around the world annually, if not more often.

The purpose of the vast migrations of these dragonflies is simple; they follow the weather, allowing them to reproduce in the ideal environment. For example, when the dry season hits India, they will move across to Africa for the wet season, as they require moisture to breed.

So, how do they do it? Pantala dragonflies have specialised wings that are perfectly adapted to long-distance travel, with minimum energy expenditure. They have relatively large wings that enable them to fly high up in the air, and glide in the wind. This mechanism is what allows them to cross entire oceans, and is referred to as “passive dispersal”, as they rely on the wind to do most of the work for them. Furthermore, as they are so small, weight is not a problem.

However, their size does cause a problem to the scientists studying them. Genetic analyses were used in the recent study because the dragonflies are too small for researchers to attach GPS trackers or tagging equipment to them. The weight of any existing technologies would be too overpowering, reducing their abilities to fly. Therefore, scientists thus far have no way of tracking the exact routes of the dragonflies, to assess exactly how long they are travelling for and where exactly they are travelling to and from.

Perhaps future technologies will provide trackers light enough to attach to the back of the minute dragonflies, allowing scientists to unlock further information about them. Until then, many key details of one of the greatest migrations on the planet will remain a mystery.  

Jaws: the impact of media on shark declines by Rachel Baxter

One of Hollywood’s favourite villains, sharks have always been dubbed as horrifying man-eaters. However, this is more fictional creation than fact, and as shark populations rapidly decline, are creations like ‘Jaws’ partly to blame?  

In 1975 when ‘Jaws’ hit our screens, sharks swam into the spotlight as malevolent killers lurking in the deep. Following the film’s release, shark fishing increased rapidly, especially in the USA, as many wanted to emulate the heroic protagonists, whilst others wanted to cull sharks to make the seas safer. This reduced shark populations and 40 years later they are still deteriorating, due to overfishing for sport and meat, particularly for use in shark fin soup, a traditional Asian delicacy.

Scientists estimate that shark finning kills up to 100 million sharks a year. Finning involves catching any shark, regardless of species or size, and removing its fin and discarding the body back into the water. This is often carried out whilst the shark is still alive and subsequently leaves the animal to die a slow and painful death. The heightened demand for shark fins is due to increasing prosperity in Asian countries such as China. This has resulted in a higher demand for expensive delicacies like shark fin soup, which costs up to $100 a bowl. Consequently, the value of shark fins has soared, meaning that thousands of sharks are killed for their fins daily. As a result, many shark species such as tiger sharks and hammerheads have experienced population decreases of over 90% in recent years.

Sharks are an apex predator throughout the world’s oceans. This means that they are at the top of the food chain and significant decline in their numbers has the potential to impact nearly every organism living in our seas. One issue is that in the absence of shark predation prey species populations will proliferate, thus decimating populations of their own prey. An example of this is already occurring in the eastern Pacific Ocean, spanning from California to Tierra del Fuego, at the southern tip of South America. The decline of sharks here has led to a huge increase in Humboldt squid, a predatory species of squid whose populations were historically controlled by sharks. However, due to the reduction in their natural predators, their populations have expanded rapidly and this is having an impact on fish stocks, as the squid will consume nearly any fish that they come across. The true impact of shark declines is still unknown but it is likely to change population numbers of a vast variety of different species and seriously upset the balance of marine ecosystems, all over the world.

Therefore, the conservation of sharks is key. Current conservation efforts include discouragement of shark consumption, especially in shark fin soup through methods such as petitions. Also, more and more sharks are becoming protected. In 1991 South Africa became the first country to protect great white sharks. Furthermore, many countries, including the UK, have now implemented restrictions on shark fishing and finning. Therefore there is hope for sharks, but attitudes need to be changed in order to increase support of conservation efforts.

To change attitudes, it is essential that people understand that sharks pose very little danger to humans; in fact we pose much more danger to them. Whilst an average of 4.2 humans may be killed by sharks each year, humans kill an estimated 100 million sharks annually. There are over 400 species of shark, whilst only 4 of these species have ever been involved in attacks on humans (great white, tiger, bull and oceanic whitetip), yet almost all shark species are affected by fishing. In fact, the chance of a shark attack is minute. Millions of people swim in the sea every year whilst only about 4 fatalities occur annually. In contrast, every year 150 people die due to falling coconuts, 10,000 die by lightning strike, and 24 are killed by flying champagne corks!

What’s more, many shark attacks on humans are thought to be accidental. Shark attacks often occur on surfers. This is because from below, a surfboard with four legs resembles the shape of a seal. In fact, sharks are never out to get humans, as we are not their natural prey. Humans are much larger and bonier than prey organisms such as fish and seals, and wetsuits are not part of a shark’s ideal diet! Also, the vast majority of shark attacks on humans involve only one bite. This is interesting as hunting sharks use an initial bite to weaken their prey, and then use further bites to kill. This indicates that most sharks that attack humans immediately realise that they have made an error, and consequently back away. So, is the revengeful, human-hunting shark from ‘Jaws’ simply an entertaining invention?

It is true that ‘Jaws’ is based on real events; the Jersey Shore attacks of 1916. These attacks involved four fatalities and one injury during the summer of 1916 off the Jersey Coast in North America. However, scientists concur that these attacks were a freak incident, and the same scenario has never been repeated. Ironically, Peter Benchley, the author of ‘Jaws’, became a keen shark conservationist, regretting his portrayal of sharks as monsters as it had such a significant impact on the world’s perception of them.

Perhaps, one day, films will undo what they have done and depict sharks in a new light. Swimmers will no longer be haunted by ‘ba-dum ba-dum’ and more people will be concerned by shark declines. This could reduce shark fishing and improve attitudes towards conservation, so that shark populations are saved before it is too late and the balance of our oceans changes forever.

Tortoises master the tablet

by Daisy Dunne

A team of tortoises from the University of Lincoln have successfully learnt to use touchscreen technology to win treats from scientists, who hope to learn more about the reptile's unique method of processing spatial navigation. Whilst mammals use the hippocampus for matters of geography, reptiles are thought to use a similar enigmatic structure known as the reptilian medial cortex.

"Tortoises are perfect to study as they are considered largely unchanged from when they roamed the world millions of years ago,” says Anna Wilkinson, who trained the tortoises using strawberry rewards, “this research is important so we can better understand the evolution of the brain and the evolution of cognition."

Impressively, two of the tortoises even went on to use the information they had learnt in a real life scenario. After learning to peck blue circles on one side of a screen in exchange for a reward, the reptiles chose to approach the same side of an experimental chamber when presented with two empty blue bowls similar to the virtual circles.

This outcome suggests that like the majority of animals, reptiles rely on 'landmarks', and not just simple motor processing, to orientate in their environment. Wilkinson hopes this study will open the door for a wider adoption of touchscreens in animal behavioural studies.

“The touchscreen is a brilliant solution as all animals can interact with it, whether it is with a paw, nose or beak. This allows us to compare the different cognitive capabilities", she says.

It’s Worse in the Water

by Rob Cooper

The vast majority of the surface of planet earth is covered by water and considering this it should be no surprise that whilst terrestrial (living on land) creatures can get rather frighteningly large, the denizens of the depths are always one step ahead. In this article I’ll examine ten of the most fearsome, peculiar and benign ocean creatures with the hope of showing just how fantastic the diversity of ocean live has been over time.

1. Dunkleosteus
Back in the Devonian a peculiar group called the Placoderms developed to truly monstrous sizes. Characterised by their armoured bodies and bony plates instead of the teeth the Placoderms reached their most terrifying in the killer whale sized Dunkleosteus. Strangely for such a large predator the 8 metre long Dunkleosteus could suck prey towards its mouth by rapidly opening its jaws (in less than 1/15th of a second). Unhealed bite marks on the head guard of younger Dunkleosteus also lend evidence to a theory of cannibalism.

2. Helicoprion
If you thought Dunkleosteus had strange teeth you may be surprised to learn far stranger tooth morphologies existed in the prehistoric seas. Helicoprion is a fantastic example of this having a ‘toot whorl’ that looked remarkably like a circular saw inspiring many strange artists’ impressions of the creature. The function of the peculiar teeth has yet to be determined but it is thought that the successive rings of teeth are analogous to growth rings in trees and that teeth successively pushed up to replace those that were lost, similar to how its modern day relatives sharks replace their teeth today.

3. Megamouth Shark
To continue from shark like animals to true sharks we next encounter a very rare modern shark colloquially known as the ‘Megamouth shark’. Since its discovery in 1976 only 55 specimens of this elusive shark have been seen or caught. Like its larger relatives, the basking and whale sharks, the Megamouth has an enormous mouth full of very small teeth that are ideal for sieving plankton from the ocean. As it follows the movement of plankton down to over 200 metres in depth it has small photophores (light emitting organs) to attract plankton and small fish to its 1.3 metre wide mouth.

4. Megalodon
It would be an insult not to mention the mightiest of all ocean predators in this article and Megalodon certainly fits that title handsomely. Well respected as the largest and most powerful predator in the history of all life (with one competitor) megalodon is now estimated at lengths of at least 14-18 metres and up to 20 metres and weights of slightly over 100 tonnes. Megalodon has the largest jaws ever discovered in the animal kingdom large enough for a full grown man to walk through without bending down and an estimated bite force of over 180,000 Newtons. This, along with other palaeontological evidence, suggests that Megalodon preyed on large whales until its extinction 1.5 million years ago.

5. Livyatan 'the great whale'
But what animal was big and ferocious enough to rival Megalodon? Strangely enough the answer comes from a contemporary of Megalodon’s the titanic Livyatan. Livyatan was a raptorial sperm whale which lived between 12-13 million years ago in the Eocene period. Akin to megalodon Livyatan remains have been found alongside those of baleen whales, sharks, dolphins, porpoises and many other sea creatures supporting the hypothesis of Livyatan being an apex predator alongside Megalodon. Unlike modern sperm whales Livyatan had the largest teeth of any animal yet discovered (bar the tusks of elephants and walrus) at up to 36cm in length. Livyatan was thought to ambush prey swimming at the surface from beneath much like the modern great white shark.

6. Leedsichthys 'monster fish'
From two rather fear inducing giants to a rather more benevolent one. Meet Leedsichthys, the largest bony fish to have ever lived. Leedsichthys ranged from around 10 to nearly 15 metres in length so probably rivaled the modern whale shark in size although a heavier bone skeleton likely made Leedsichthys considerably heavier. A strange tendency in large oceanic animals is that of eating remarkably small prey and Leedsichthys was no different and likely fed on plankton either by pumping water through its huge mouth or actively swimming to filter small organisms from the water around it.

7. Giant Manta Ray
Benevolent giants still exist today in the form of the majestic manta ray. Gliding through the waters like marine birds these gentle giants can have a wingspan of up to seven metres and weigh over a tonne. Manta’s are also filter feeders and typically herd their tiny prey into tight balls and swim through at speed with their large rectangular mouths open. On occasion Manta’s have been observed somersaulting through particularly tight balls of prey presumably to catch more prey.

8. Predator X
Leaping back 155 years to the late Jurassic period we come to a group of marine reptiles called the Pliosaurs. Pliosaurs were characterised by short necks and immensely powerful large jaws, the largest specimens having estimated bite forces comparably or far greater than Tyrannosaurus rex. Predator X was one of the largest of all Pliosaurs reaching between 12-15 metres long and possibly weighing up to 45 tonnes. Strangely, compared to modern day marine species, Pliosaurs used their four flippers for locomotion and had no tail fins to speak of; two of these fins would be used for normal locomotion whilst the other two would be used to create a burst of speed when ambushing prey.

9. Plesiosuchus
Crocodiles are often said to be living fossils and quite rightly so for modern crocodilians have hardly changed at all for hundreds of millions of years. However back in the Jurassic period, something very strange happened in crocodilian evolution… They began to adapt fully to living in the sea. At around 6.8 metres in length Plesiosuchus was one of the largest marine crocodiles and like its kin had shed the heavy, restricting armour of its forebears in favour of a streamlined body. The skull of Plesiosuchus shows many similarities to modern killer whales implying it regularly predated on large marine reptiles of the time.

10. Shastasaurus 'ocean giant'
On the topic of marine reptiles, it would be immensely uncharitable of me to finish this article without mentioning the largest marine reptile yet discovered. Shastasaurus was a primitive ichthyosaur, a group of marine reptiles that in their later stages would bear many similarities to dolphins yet the primitive forms were quite unique. The prey base and feeding method of Shastasaurus remains a mystery as it seems to have had no teeth and the suggestion that it fed on soft bodied molluscs is generally not supported by ichthyosaur skull morphology, what this strange animal was specialised for we may never know but that hardly makes it a less thrilling creature to imagine.

The oceans simultaneously offer some of the most fearsome and most benevolent creatures that planet earth has ever harboured. From gentle filter feeding giants to titanic ambush predators lurking beyond the reach of light the oceans are a place where life has fully explored the limits of size. No dinosaur has even come close to the largest baleen whales of today and whilst we may be thankful that many of their huge predators such have Megalodon have finally passed on; we do ourselves a great service by remembering just how rich the oceans are and how important they are as an ecosystem to us and other terrestrial species.

Life Without a Backbone

by Rob Cooper

It is a strange turn of phrase common today that having no backbone implies weakness and lack of stoicism. Whilst many of our most impressive contemporary animal species do have well developed backbones there are many critically important animals that lack such a feature. In this article I will attempt to illustrate and expose the diversity and nature of several extinct and extant species lacking said backbone and try to show why they should certainly glean more attention than they have until now.

1. The Colossal Squid 

A wonderfully accurately named animal, the colossal squid is the largest known invertebrate that has ever lived stretching to 14 meters and weighing up to half a tonne. Like all squid the colossal squid is equipped with arms and tentacles covered in suckers, but in contrast to the slightly smaller giant squid, this giant also has sharp hooks for catching large fish and bioluminescent squid species up to 1km below the waves. Once they are fully grown they are only predated regularly by sleeper sharks and sperm whales and still manage to give both predators nasty wounds with their hooks and suckers.

2. The Japanese Spider Crab
The largest member of the arthropod phylum (which includes: insects, arachnids and crustaceans) the Japanese spider crab can have a leg span of up to 3.8 metres and despite it’s rather fearsome appearance it is reported to have a rather gentle disposition. The crab acts as an omnivorous scavenger on the sea floor and like many crustaceans has very small planktonic larvae with transparent bodies and no arms or legs that floats in the water column.

3. The Japanese hornet
Sticking with the Japanese theme we move to a rather less benevolent creature; the Japanese hornet. The sting of the hornet reportedly induces the feeling of your flesh melting and releases a pheromone cocktail that attracts all the hornets in the local area. This pheromone is also used by hornets hunting bees. European bees, which have no defence against the hornets, are often slaughtered by the hive. Japanese bees however have learned to surround the hornet with their bodies and essentially cook the animal with their body heat. 

4. The bullet Ant
If the Japanese hornet wasn’t quite enough to freak you out I invite you to check out the infamous bullet ant. Why is it called the bullet ant? Well the sting of the bullet ant is, according to the schmitd sting pain index, the most painful of all stings and feels akin to being shot. Or if you prefer a slightly more vivid description… The sting is described as ‘waves of burning, throbbing, all-consuming pain that continues unabated for up to 24 hours’. This potent sting is thought to have evolved as a defence against predators that unearth the ant.

5. Anomalocaris
Delving back over 500 million years into the deep past a rather remarkable arthropod called Anomalocaris or ‘abnormal shrimp’ led the way in the evolution of large multicellular predators that would change the evolution of all future life. Anomalocaris was a truly gigantic animal in its time reaching two metres in length and probably preying on soft bodied organisms. The eyes of Anomalocaris like other ancient and modern arthropods were compound eyes and consisted of 16,000 lenses which represents some of the earliest evolved complex eyes able to tell friend from foe and discern environmental factors, which is clearly an incredibly important evolutionary step.

6. Arthropleura
The past often presents us with monolithic, giant versions of creatures we know today. Such is the case with Arthropleura, an ancient relative of millipedes and centipedes that stretched up to 2.6 metres in length and lived in the carboniferous period over 300 million years ago. The carboniferous period was characterised by huge amounts of vegetation and photosynthesis leading to a very high partial pressure of oxygen allowing arthropods such as Arthropleura to grow so large and is also responsible for many of earths current coal deposits hence the nomenclature of the period.

7. The Crown of Thorns 
Skipping forwards 300 million years in time, large invertebrates are still vitally important ecological factors. There is no better example than the mesmerizing crown of thorns star fish, so named for the hundreds of poisonous spines that covers its aboral (opposite to the oral, mouth containing, surface) surface. The crown of thorns feeds on coral polyps and can cause great damage to reefs if they gather en masse. However ecology is rarely so black and white. The crown of thorns provides a vital role in maintaining reef biodiversity by feeding on rapidly growing corals allowing slower growing corals to grow out and allow variance in reef composition. 

8. The Horse Conch
Fearsome snail is a term rarely used. However it is a term that perfectly describes the horse conch. A huge sea snail that lives of the coast of Florida in shallow waters up to 6 metres deep, the horse conch has made a name for itself by feeding on all manner of marine gastropods and arthropods. The horse conch has even been observed cannibalising younger members of the same species. The bright orange flesh of the animal is very striking and is perhaps a reminder of the incredibly diverse forms that even seemingly mundane animals such as snail have and do take.

9. Jaekelopterus
Sea scorpions such as Jaekelopterus were formidable ocean going predators from 460 to 248 million years ago. Jaekelopterus was discovered from a single 46cm long claw by Simon Braddy and Markus Poschmann of Bristol University in 2007. The full animal is estimated at 2.5 metres in length. Whilst not true scorpions, the sea scorpions were some of the largest arthropods that have ever existed and had the common feature of two large claws presumably used to catch prey such as trilobites that shared their primordial seas.

10. The Hagfish

The hagfish is a living fossil; that is a species that has existed relatively unchanged for a very long time period. The hagfish represents a period in evolutionary history just after the vertebrate skull had evolved but before the backbone had become prominent. The hagfish has a cartilaginous skeleton meaning it can literally tie itself in knots, and indeed does in order to provide enough force to tear chucks of flesh of whale carcasses that sink to the deep sea where it lives. The hagfish can produce huge amounts of slime on contact which increases in volume when exposed to water. This slime could be argued to be the most successful predatory fish repellent ever evolved as it clogs the gills of attacking fish preventing them from ‘breathing’. This is evidenced in how almost all known predators of hagfish are birds or mammals.

I hope I’ve demonstrated here that while many of vertebrates we see around us are certainly fascinating and incredibly important, aesthetically, ecologically and commercially, the invertebrates and strange missing links like the hagfish are not only crucially important to the working of our natural world but just as intriguing, beautiful and in some cases even terrifying, despite their disadvantage in size and complexity.