The plan is very old, as is the scorpion base plan. Look at the wings. The four large wings with complex venation is a very old plan, as more modern insects have gone the way of reducing venation complexity, losing or reducing the rear wing, or at times locking the rear and forewing together as is often seen in the Hymenoptera. The most extreme alteration is seen in the Dipterans, where the rear wing no longer functions as a wing, having completely altered its morphology to become a specialised flight stabilising organ called a haltere, along with this the wing venation has been greatly reduced. You can’t have a dragonfly with a short tail, it wouldn’t be able to fly, nor a dragonfly with a small thorax, there wouldn't be enough muscle mass to drive the large wings at high speed. This plan works extremely well, but, it is also largely locked-in, in some ways having reached an evolutionary dead end. However, within this base plan there is enormous variation as a result of the plasticity of morphology. Many weird and wonderful base plans have existed, but most have gone the way of the dinosaur, those remaining have either been very lucky or very well adapted.

What is adaptation? What is morphology? Adaptation really means change, or the ability to make alterations in order to improve the genetic fitness of the organism. The genetic fitness of an individual is a measure of the likelihood of offspring surviving to reproductive age, it has nothing to do with running the mile. Morphology is the word used to describe the structure of an organism. Adaptive morphology therefore means changes in the structure of an organism in order to better fit its environment which then gives rise to improved genetic fitness. There are two major driving forces at play here, one is the inability of DNA to exactly replicate itself 100% of the time, otherwise known as a genetic mutation and the other is natural selection, whereby one form has an improved genetic fitness over the other. Other factors also come into pay such as luck, but this is not a genetics lecture, so lets not get too bogged down in that, collectively though, the entire process is known as evolution.

What has this got to do with Liocheles? I very much enjoy investigating how an animals morphology plays a role in the way in which it lives its life. Liocheles is a marvelous example of adaptive morphology. I could have chosen any scorpion group or species for this article, but chose Liocheles because of their extreme morphology and thought keepers might be interested to learn a little of the meaning of this adaptive morphology. Another good reason is that this genus is largely unstudied and the few presently recognised species will only be a subgroup of that which really exists. Being aware of adaptive morphology might help you to recognise a potentially undescribed species.

Lets look at the base plan of Liocheles. As with all scorpions, the base plan is the same, a combined head and thorax or prosoma, an abdomen split into two different structures, the mesosoma (body) and metasoma (tail), the arm-like pedipalps, hand-like chelicerae, eight walking legs and menacing post abdominal telson. The base plan is no different to any other scorpion and if it wasn't, well, it wouldn’t be a scorpion. However, minor adjustments to the plan allow adaptation to varying environments and ways of life. Liocheles would have to be the most distinctive scorpion in Australia. The combination of very large pedipalps, tiny metasoma and flattened cross section is not seen in any other Australian scorpion.

So, what are the driving forces behind the key features of the adaptive morphology of Liocheles? Why does a scorpion evolve such large arms? Why does this scorpion have such a small metasoma (tail)? Many people will enthusiastically tell me the small tail is the result of not needing to sting prey due to the very large and powerful arms and hands, and yet, this is not necessarily true as I have seen Liocheles sting prey many times. They have also retained a relatively large telson, which would not be expected if its use had been greatly reduced. In engineering there is a well known saying that, ‘form follows function’, the same principle is recognised in biology. Many scorpions have large pedipalps, look at some of the Urodacids for example. The Flinders Ranges scorpion, Urodacus elongatus has quite large pedipalps, very much on a par with Liocheles, it’s just that the tail is not diminished as it is with the latter. Why hasn’t U. elongatus evolved a diminished tail? The answer is quite simple if we compare the home sites of both species. Liocheles are mostly crevice dwellers, they occupy very tight flat places and as a result have evolved a dorso-ventrally flattened morphology in the same fashion as Hemicloea major, the flat-rock spider. However, not all Liocheles occupy rock crevices, some live under bark and rocks and some have even become burrowers. Notice I used the word ’become’. The plesiomorphic or base character state for Liocheles is representative of an animal having originally evolved in tight crevice-like home sites. As the animal has become more and more abundant and widespread, competition for home sites has forced individuals to live outside their preferred sites, resulting in speciation. So, why the diminished tail? The ability to squeeze back into the deepest void of a rock crevice will increase the chances of escaping a predator. A large tail would disallow this, while a small diminished tail will allow the scorpion to back farther away from potential danger. On top of this defence, the large pedipalps can be folded across the face of the body to form an impenetrable wall. Natural selection has acted on two major morphological changes here, the large shield-like pedipalps and the diminished tail for backing into tight spots. Urodacus elongatus also use their pedipalps to block the entrance to their rock scrape, but as they do not retreat back into the deepest crevice there has been no pressure on the tail to become smaller, in fact in the sexually dimorphic male its gone the opposite way.

What else can be said about the tail of Liocheles? Most scorpions have ridges running down the tail segments, these are known as carinae or keels. In Liocheles, these are all but gone. They exist, but have become quite smooth and rounded off, more than likely as a result of the tight crevice existence. My observations have shown me that scorpions regularly use the tail for soil moving and excavation activities. The carinae act to aid in this behaviour by behaving as scraping edges. Liocheles would have had no need to remove any soil when occupying a rock or bark crevice and carinae might even act to hinder backing into a deep crevice. The greatest deviation from the base plan here is small diameter, rounded metasomal segments, with little to no carination. Along with this adaptive morphology is the interesting behaviour whereby envenomation of prey nearly always takes place laterally with the tail brought around the side of the body, rather than over the top as is common with scorpions which wander in search of prey.

What of the sexual dimorphism displayed by Liocheles? One of the first things a keeper might notice or learn about Liocheles is that males often have much longer pedipalps than their female counterpart. Not only that but they also usually have a tooth and notch mechanism on the hand not present in females. It’s very common in scorpions to see differences in the hands of the sexes. This comes about as a result of the promenade-a-deux, whereby the male must grasp the often reluctant female using his hands and drag her to a suitable substrate in order to complete a successful spermatophore deposition. The selective pressure is so great here that all kinds of bumps, notches, curves etc have evolved in order to achieve a better grip of the female, but its rare to see such a big difference in the total length of the pedipalp. Once again, we only need to look carefully at the home site to see what is happening. A reluctant female will respond to an intruding male in the same manner she would to a predator, she will back into the deepest recess of her rock refuge she can. The male with the longer arms will be more likely to reach the female and drag her out, this along with the locking tooth and notch mechanism affords him a good chance of exchanging gametes, far more so than his short armed competitor. This unique adaptation to an unusual home site has given rise to a unique form of sexual dimorphism.

The above isn't the case for all Liocheles as a recently discovered population has shown. A population from North Queensland shows a form where there is little to no difference in the length of the pedipalps between sexes. This form lives right alongside another more typical rock crevice dweller, but occupies rotting logs and the like where natural selection no longer gives males with long pedipalps any advantage. When a selective pressure no longer exists a character will often return to its prior state, this is especially true of sexually dimorphic characters. Each population of scorpion will display its own range of characters and unique adaptive morphologies. An organism can never be perfect, it can never evolve to the point where every aspect of its morphology and physiology perfectly fits its way of life; error is the seed of evolution, it allows adaptation to changing conditions and situations and is the reason organisms have become so diversified on this planet.

If we continue to look at Liocheles we will undoubtedly discover more adaptive morphologies and behaviors suited to its way of life, nearly every aspect of the animal will in some way have been affected by natural selection. Have you ever noticed how Liocheles has the ability to move in any direction without turning, in a similar fashion to a crab, brilliantly suited for crevice survival. The strongly curved ungues or tarsal claws are well made for clinging to vertical rock surfaces. The common dark colouration affords good visual protection while pale forms exist amongst much lighter coloured rocks. Each leg femur has an anterior face showing a row of hardened denticles, I can only speculate, but presumably these may well aid in grip to resist removal. The alterations to the base plan have given Liocheles a good foothold over its crevice and bark habitats, but have greatly reduced its capacity outside this environment and no doubt explains why it has made little headway into other habitats.

If you study an animal carefully enough and think long and hard you will be able to make determinations for yourself as to what might be going on, some of it will be pure speculation and some of it you might be able to support with data or observations, either way, it is a great way to get to know the animal you are studying—good luck with your observations.