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.  

What Came First, Sponges or the Comb Jellies?

By Sam Firminger

The well-known chicken or the egg conundrum first posed by classical philosophers such as the likes of Aristotle asks a simple biological question. Reduced down to its very essence, it’s a concept often applied in the field of phylogenetics. Here, a range of tools available to biologists are used to study the evolutionary history and relationships of the entire biological scale, from genes to species and phyla. In the past, these tools utilised mainly morphological data but with recent progressions in gene sequencing and evolutionary modelling, genetic data is swiftly changing the landscape of phylogenetics. With this advent of new technologies, the phylogeny of the early complex multicellular organisms, the basal Metazoans (more widely known as the kingdom of Animalia or Animals) has been turned on its head with contentious results being presented to the scientific community.

The Basal Metazoans

The Cambrian Period (541 to 485.5 Mya) is well known for the ‘Cambrian explosion’, a remarkable event that encompassed the explosive radiation of organisms into most of the animal phyla we know and love today. Immediately predating this period however, is the Ediacaran, also commonly referred to as the Vendian (635-542 Mya). Fossil records have shown that this is actually when soft-bodied organisms first appeared on Earth. It is here that the Porifera (Sponges), Ctenophores (Comb jellies), Cnidarians (Jellyfish and corals) and Placozoans first emerged in the murky depths of the ancient oceans. Ctenophores could easily be mistaken for jellyfish with their layered, jelly-like bodies but instead move by the movement of ‘combs’, or cilia, running along the body. They also lack the stinging cells which Jellyfish are famous for. Species found at depth can often be seen to have wonderfully striking multi-coloured LED-like ripples along their bodies, caused by scattering of light through the moving combs. Similarly, most (but not all) Ctenophora species are capable of using proteins that cause bioluminescence: you may well have seen these curious creatures in a documentary or two.

Conflicting Phylogenies

                                                                     

The traditional phylogeny of these taxa places the Porifera as the most basal group, with the rest splitting off from this lineage and evolving later. This is probably the view a layman would also adopt, simply by looking at the organisms. Sponges are sessile and look relatively simple, even plant-like, due to the lack of any features that you might typically associate associates with animals, such as limbs, eyes or muscles. However, multiple academic groups in recent years have challenged this view using transcriptome data (sequenced data from all types of RNA found in a cell). They suggest that it was actually the Ctenophores which evolved first, placing them as a sister group and the most distant to all known animals. This controversial view of the evolutionary history of these animals immediately sent ripples through the scientific community, as it went against all previous textbooks and published papers, including a 2014 paper published in the highly revered Nature journal.

If one is to run with this hypothesis then there are some things that need explaining. Ctenophores have relatively complex epithelial nerve nets, along with muscles and a gut. These characteristics are absent in Porifera, suggesting that if the Ctenophores did in fact evolve first, there would have had to have been a secondary loss of these features to a simpler body plan found in the sponges, followed by another novel evolution of a nervous system into those found in Cnidarians (Jellyfish). An alternative explanation is that the Ctenophores evolved their nervous system independently of the other phyla. However, this has been proven to be unlikely due to both the Ctenophores and the Cnidarians having specific common features, including neuronal fate patterning genes and the presence of vital components for synaptic function. This provocative claim of the sponges no longer being viewed as the ancestral phyla led to widespread questioning of whether it was time for the history books to be rewritten, completely changing our understanding of evolution as we know it. Are they right?

The Recent Research

A team at the University of Bristol led by Dr Davide Pisani with colleagues from around the world published a paper in December 2015 using genomic data to tackle these controversial claims. The team used data sets from previous experiments suggesting Ctenophore-early hypotheses and showed that the choice of evolutionary models, which are run on data, is crucial for obtaining correct results, and in previous papers these were inappropriately chosen. They discuss how the previously used models had failed to take into account important biological factors which affect the rate of change of genes such as the hydrophobicity of bases.  Subsequent analyses by Dr Pisani and his team using more appropriate models along with powerful statistical methods lead to the conclusion that it was in fact the sponges which came first, not the Ctenophores, which supports and reinforces the classically held hypothesis: a sigh of relief for many scientists.

Dr Davide Pisani told the University of Bristol press team: “Knowing whether sponges or comb jellies came first is fundamental to our understanding of evolution.  Take the nervous system for example; this is the fundamental organ system that mediates our own perception of self.  It is what makes us human, so is pretty important!  Depending on whether sponges or comb jellies came first underpins entirely different evolutionary histories for this organ system.  If comb jellies came first, then the last common ancestor of all the animals might have had a nervous system, and as all comb jellies are predators this ancestor might have even been a predator.”

These results highlight the issue of revolutionary claims that all too often surface in the scientific community. Upon closer inspection with rigorous testing and analyses, they are not always what they seem. It begs the use of proper methodology with thorough self-analysis before publishing a paper. It seems as if the history books are safe, for now.

Dr Pisani’s paper can be found in full at: http://www.pnas.org/content/early/2015/11/24/1518127112.full.pdf

The Science of Taste

By David Morris

Structure of a taste bud

In 350 BC, the Greek philosopher Aristotle postulated that varying blends of two tastes, sweetness and bitterness, comprised all flavours. As the understanding of taste developed, it was shown that sourness and saltiness were also distinct tastes. In 1908 the Japanese chemist, Kikunae Ikeda, discovered a fifth subtle and now well established taste known as umami. Until recently, these tastes were universally accepted as the five fundamental detectable tastes that made up all flavours that can be experienced by humans.

The role of smell (olfaction) in flavour wasn’t fully appreciated until as late as 2004, when biologists Richard Axel and Linda Buck discovered the role of the nose in detecting and characterising odours. When you breathe in through your nose, millions of odorous molecules activate and inhibit olfactory receptors at the roof of the nasal cavity. Electrical impulses travel from these receptors to the brain, informing you of what you’re eating. This action is supported by taste buds in the mouth.

Molecules within certain foods can chemically activate senses that are responsible for the sensation of heat, pain or touch. This is known as chemesthesis. Despite being different from taste, chemesthesis can contribute to the flavour of a substance. Examples include the ‘tingle’ on the tongue from ingestion of carbonated drinks, the feeling of heat upon eating a chili pepper, and the cooling feeling from eating gum.

 Taste receptors are mounted on papillae, which are structures found on the front and back of the tongue, the roof and sides of the mouth, and even at the back of the mouth and throat. The idea of a ‘tongue map’ whereby certain areas of the tongue detect certain tastes is a myth, although the concentration of certain receptors may vary in different areas of the tongue.

           Saltiness and sourness are the simplest of the tastes. Sourness arises from the donation of hydrogen ions, which is a characteristic feature of acids. It has been postulated that detection of sour foods defends the body from ailments like indigestion. Similarly, saltiness arises from the dissociation of salt on the tongue, forming sodium and potassium ions. The taste response acts as a warning for your body to replenish electrolytes, but not too much, hence why we find salty foods appealing, but also repulsive in large amounts.

                  

           Bitterness, umami and sweetness are more complicated tastes. They all come from the binding of larger, more complex molecules to large proteins in the taste buds that are typically responsible for signal transduction throughout the body. Bitterness receptors can bind with molecules that are usually toxins or poisons. In this way, the bitter taste warns your body against ingesting molecules that can harm your body.

           Similarly, umami receptors detect glutamate (a component of monosodium glutamate, or MSG, a popular salt substitute), giving off a subtle savoury taste. The subtlety arises because the glutamate is usually bound to sodium, giving off a more powerful salty taste. Glutamate is useful to your body as a neurotransmitter and a catalyst to metabolism, so like salt, the taste warns your body to replenish glutamate, but not excessively.

Tomatoes are rich in umami

           In July of this year, academics at the University of Purdue published a paper in Chemical Senses describing the existence of a sixth taste called oleogustus. Usually, when the body ingests oil or fat, it is in the form of triglyceride, a molecule comprised of three fatty acids chemically bound through a glycerol molecule. This triglyceride is too large to fit into oleogustus receptors and thus can’t be tasted. However, when the fat spoils, the triglyceride is broken down into glycerol and the fatty acids. The fatty acid then binds to the oleogustus receptors and acts as a warning that the food is no longer suitable for ingestion, hence it smells and tastes rancid.

                  

           Each of the aforementioned tastes, as well as the olfactory and chemesthetic systems, have proven essential for the body to be able to consume the correct amount of different types of food, and to protect from ingesting harmful toxins and poisons.

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.