Giant sea scorpions.. ..and other foods

In his book Why Not Eat Insects? Vincent M. Holt [1] does not confine himself to this group of invertebrates. In addition to remarks about slugs and snails, he also has this to say:

..Spiders have been relished as tid-bits, not only by uncivilized nations, but by Europeans of cultivation. For Reaumur tells of a young lady who was so fond of spiders that she never saw one without catching and eating it. Lalande, the French astronomer, had similar tastes; and Rosel speaks of a German who was in the habit of spreading spiders, like butter, upon his bread.

Spiders are chelicerates and, had Holt travelled to China, Thailand or Vietnam he would have been aware of other chelicerates, scorpions, being eaten, often as “street food”. Scorpions have a sting that is used to inject venom but, when cooked, the venom becomes denatured and the whole animal can be eaten. A common method of preparation is to line scorpions on skewers that can then be grilled (see below), or they can be stir fried. Those who eat scorpions compare their flavour to

that of crabs, or shrimps, and scorpions are rich in protein, so provide a readily available and nutritious food [2].

The largest chelicerates, the eurypterids, became extinct about 250 million years ago, so there is no possibility that they co-existed with humans, or close human ancestors. However, just as we like to imagine co-existing with reptilian dinosaurs (equally impossible), it is fun to think what our attitude to eurypterids would be should they still be present today.

In the image above, adapted from an illustration in a paper by Braddy, Poschmann and Tetlie [3] we see the body form of the eurypterid Jaekelopterus.  It is typical of the “sea scorpions” in having four pairs of walking legs, chelicerae (limbs with claws), a pair of paddles and a segmented body ending in a flattened extension. Two compound eyes are present and, in a comparative study of the fossilised remains of eurypterids of several types, it is concluded that Jaekelopterus was likely to be an active predator and that competition with more successful vertebrate types led to its extinction [4], alongside all the other eurypterids.

The location of fossils shows that Jaekelopterus lived in “marginal marine environments” [3] so, had these creatures survived to modern times, they would have been easily accessible to humans and, no doubt, would have been made extinct by human hunting. At this point, we need to consider the size of the animals: the scale bar in the illustration shows 1 metre, so specimens of Jaekelopterus were up to 2 metres long and thus substantially longer than the average human (2 metres being equivalent to 6 feet 6 inches). If their chelicerae were disabled, they would be easy to catch and they did not have the defensive sting present in today’s scorpions (they are not closely related).

Letting our imagination free, we can fantasise that Jaekelopterus, with its long and muscular body, would be good to eat, especially when prepared using the cooking skills of modern humans – “eurypterid thermidor” anyone? Nonsense of course, but what fascinating creatures they must have been, had we been able to observe them.

[1] Vincent M. Holt (1885) Why Not Eat Insects? Faringdon, E.W.Classey Ltd.

[2] http://survival-mastery.com/skills/scouting/eating-scorpions.html

[3] S. J. Braddy, M. Poschmann and O. E. Tetlie (2008) Giant claw reveals the largest ever arthropod. Biology Letters 4: 106-109.

[4] V. E. McCoy, J. C. Lamsdell, M. Poschmann, R. P. Anderson and D. E. G. Briggs (2015) All the better to see you with: eyes and claws reveal the evolution of divergent ecological roles in giant pterygotid eurypterids. Biology Letters 11: 2015.0564.

We can't exist without slime

What is your reaction to slime? Most people find the substance, and even the thought of it, distasteful and yet we would not be alive if it was not for slime in one form or another.

Slime consists of chemical polymers that expand on contact with water, producing a clear, sticky substance that is ubiquitous and which we recognise from its slipperiness and its ability to stick to surfaces. The compounds that make up slime are referred to as exopolymers, or EPS, by those that study them and they consist principally of carbohydrates and proteins, although many other chemicals may also be found in the EPS produced by different organisms. They are truly ubiquitous: bacteria using them to attach to substrates; single-celled algae release them when producing an excess of carbohydrate during photosynthesis; and multicellular organisms use them for protection, locomotion, to aid in feeding, to aid buoyancy, and as a means of attachment [1].

During evolution, some cells in multicellular organisms became adapted to have the sole function of producing the EPS that result in slime. These goblet cells (see above) discharge their contents to become hydrated and we are familiar with the resulting sliminess of animals like worms, slugs and fish. 

I talked about EPS to an audience of trout fishers and this was recorded by the Wild Trout Trust [2] and one of the illustrations is shown below, together with the link to the video. I could only give a very few examples, but you get the drift of my talk: EPS are everywhere and yet they are largely ignored, even by scientists who should know better. Of course, there are prejudices to be overcome and at one conference dinner I was given a special prize for "the most revolting talk" given during the sessions. An award made in good humour, of course, but indicating that the subject was one that most find unpleasant. This is a pity, because EPS are one of the most important families of chemicals known.

It is fair to say that humans would not exist if it was not for slime. This argument has two components: one that develops ideas on the evolution of humans and the other on the very important role slime plays in allowing our survival. Our most distant ancestors lived in water and left this medium when fish transitioned into the amphibians (and then into reptiles and mammals). Reptiles and mammals have body coverings that reduce the loss of moisture, something that is a threat to amphibians and also the first fish making visits to land. Anyone handling a fish is aware that they have a slippery covering and this protects the animal from attack by parasites and may aid locomotion: it is a feature that is retained by amphibians and serves to reduce water loss from their bodies when they are exposed to the air for long periods. It is also a common feature among soft-bodied terrestrial invertebrates such as worms and slugs, while others, like the arthropods, have an impervious exoskeleton that much reduces the threat of desiccation.

Fish slime protects the gills from abrasion and also provides a barrier against osmotic stress, a feature that is very important to salmon as they migrate from the sea to fresh waters. Yet gas exchange occurs from the water to the mucus and then to the tissue of the gill surface and this is a feature retained through the evolution of respiratory organs of amphibians, reptiles and mammals. Human lungs and nasal passages have a coating of mucus, moved by cilia that are a throwback to our very ancient protozoan ancestors, and it can be so plentiful that it has to be removed by blowing, coughing, or swallowing, the latter normally being a continuous and unconscious process. In addition to allowing gas exchange, this mucus acts as a trap for particles, both living and dead, and it is a convention that we blow an excess of the slime into handkerchiefs, often noting the extent of hydration once the mucus becomes dried, demonstrating admirably the extent to which the EPS had undergone considerable expansion when in contact with water. Larger quantities of slime than usual are produced when this first defence mechanism is triggered by infection.

It is not only nasal, and bronchial, tissue that produce mucus in humans, and other mammals, as slime is also found in the digestive tract and in the reproductive system. The slippery quality of mucus acts as a protection for the oesophagus and slime is produced elsewhere in the gut to allow smooth passage of the contents while protecting the wall of the digestive tract. The mucus is not broken down by enzymes and, when aqueous solutions of food chemicals are removed, characteristic compacted faeces result. These are bound with slime produced originally by the gut wall and also by EPS released by the many micro-organisms that are resident within the digestive tract; the microbes protecting themselves against digestion by secreting EPS that then become a binding material for the faeces.

The final use of slime in humans is in reproduction and, especially, in allowing the migration of sperm deposited within the female genital tract. Each sperm swims within seminal fluid that contains EPS and then traverses the cervical mucus and onwards into the uterus, where one sperm fertilises a waiting egg, if one is present. It should also be pointed out that mucus provides a lubricant to facilitate copulation. 

Vital rôles indeed and it is fair to say that we would not exist without slime in one form or another, nor would very many other organisms

Having read this far in the blog post, what are your reactions? Perhaps you agree that I deserve to be thought revolting in writing, and talking, about such things, even though I respect proper taboos in polite company? Yet I am only highlighting the remarkable diversity of uses for slime and EPS and this deserves to be much better known, rather than being given the "Ugh! response" that seems to be most people's reaction to the subject. Why do we feel that way?

[1] Roger S. Wotton (2005) The Essential Role of Exopolymers (EPS) in Aquatic Systems. Oceanography and Marine Biology: An Annual Review 42: 57-94.

[2] https://www.youtube.com/watch?v=XNN-NeSwQj0

The beginning and the end of the Anthropocene

Is there an Anthropocene? This question is being debated currently and a report is to be published in 2016 on whether a geological epoch created by the transformative activities of Homo sapiens should be defined, and what should mark its beginning. According to Richard Monastersky [1]:

A committee of researchers is currently hashing out whether to codify the Anthropocene as a formal geological unit, and when to define its starting point.. .. The push to formalize the Anthropocene upsets some stratigraphers.. ..One major question is whether there really are significant records of the Anthropocene in global stratigraphy.. ..Some researchers argue that it is too soon to make a decision – it will take centuries or longer to know what lasting impact humans are having on the planet.

Monastersky then quotes from Erle Ellis, a Geographer at the University of Maryland:

"We should set a time, perhaps 1000 years from now, in which we would officially investigate this.. ..Making a decision before then would be premature."

Discussion about the Anthropocene thus reflects a typical debate among scientists and other academics having different views of what marks a definable stratigraphic boundary.

As Monastersky points out, markers could be from the Industrial Revolution, or from the radioisotope signatures resulting from atmospheric testing of nuclear weapons that ceased in the 1960s. While supporting the case for 1964 as the beginning of the Anthropocene, Lewis and Maslin [2] also put forward a strong argument for using the measurable decrease in atmospheric carbon dioxide between 1570 and 1620 (with a minimum in 1610), something that they relate to the effects of New World colonisation and dramatic changes in human population density, changes in diet and agricultural practices brought by new foods, and the development of increased trade based on industrial production. Their selection of 1610 adds another part to the Anthropocene debate, but their paper also contains an interesting review of human impacts in the very short time that Homo sapiens has been the dominant species on the Earth.

In conclusion, Lewis and Maslin write [2]:

Past scientific discoveries have tended to shift perceptions away from a view of humanity as occupying the centre of the Universe. In 1543 Copernicus's observation of the Earth revolving around the Sun demonstrated that this is not the case. The implications of Darwin's 1859 discoveries then established that Homo sapiens is simply part of the tree of life with no special origin. Adopting the Anthropocene may reverse this trend by asserting that humans are not passive observers of Earth's functioning. To a large extent the future of the only place where life is known to exist is being determined by the actions of humans. Yet, the power that humans wield is unlike any other force of nature, because it is reflexive and therefore can be used, withdrawn or modified. More widespread recognition that human actions are driving far-reaching changes to the life-supporting infrastructure of Earth may well have increasing philosophical, social, economic and political implications over the coming decades.

Whether the Anthropocene should be defined, and what its definition should be, seem trifling issues compared with those raised in that last paragraph. Whether the Anthropocene began in 1610 or 1964, it has the potential to be one of the shortest epochs thus far. The end of a geological time period is usually marked by large-scale events such as asteroid impacts, widespread upheavals in the Earth’s crust, or dramatic changes in climate. We don’t know how the Anthropocene will end and it may be from one of these causes and thus be outside human control. Alternatively, the epoch may end as a direct result of human actions. We know how destructive we have already been, and continue to be; with wars, global warming, widespread removal of forests, extinction of populations, introduction of poisons and antibiotics, etc. all being major impacts. There are those who feel that we should be able to overcome the many difficulties we face using technological solutions but, while I admire human invention, I do not feel optimistic about the future. The dominant economic system is based on growth and growth cannot be sustained indefinitely, so those of us in the Developed World will no longer be able to cocoon ourselves in warmed (or cooled) buildings and we may need to hunt and forage to obtain food. The social crises that result from a catastrophic fall in living standards can be imagined.

This is preachy, but our way of life, and its characteristic complacency, is highly damaging for other organisms on Earth and, like all the others, our epoch will end. The Anthropocene will be followed by another epoch, but what organisms will dominate? After our controlling influence is no longer present, the environment will again be the main vehicle for selection of changes in genes (a natural mechanism that we override). Bacteria and other unicellular organisms are sure to survive the cataclysmic events at the end of the Anthropocene, but what about other organisms? Will evolution result inevitably in a dominant form that makes drastic changes to its surroundings, or will there be a less destructive solution to the relationship between organisms and their environment?

[1] Richard Monastersky (2015) The human age. Nature 519: 144-147.

[2] Simon L. Lewis and Mark A. Maslin (2015) Defining the Anthropocene. Nature 519: 171-180.