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Cryptically beautiful: surprising observations of the scorpion Cercophonius squama
Abraham Miller (firstname.lastname@example.org), School of Zoology, University of Tasmania, GPO Box 252-05, Hobart TAS 7001; ph (03) 6223 3341
As biologists we try to explain the behaviours and adaptations demonstrated by organisms in our environment. Oftentimes little or nothing is known about the biology of an organism and simply observing its activity gives insight into the processes that may have shaped its ecology. As it is the first step in the scientific method, observation can yield very useful, but sometimes perplexing, information. This is the case with my current research on the scorpion Cercophonius squama here in Tasmania. My aims are to model its distribution within the State, outline its habitat preferences and investigate its population dynamics. It has been an exciting and unexpected journey with some early confusion and some extraordinary observations.
The story began in August 2001 when I commenced my Honours project investigating the biology of the scorpions in Tasmania. At first it seemed that there were two species of scorpion here, Cercophonius michaelseni and Cercophonius squama. Now it appears there is only one, C. squama. The confusion arose during my literature review, when I found that the Catalog of the Scorpions of the World (Fet et al., 2000) said both species occurred in Tasmania. It was not until I discovered an article by Acosta (1990) that I realised there was a problem. Acosta (1990) reviewed the taxonomy of the genus Cercophonius and included species distribution maps. In this paper there were no records of C. michaelseni from Tasmania. It was Acosta's paper, written in Spanish, that the authors of the Catalog used when compiling the distribution of Cercophonius species. Something was not adding up. Luckily, I had contact with one of the contributors to the book, and he said it was possible that an error had been made. The two species are similar but have distinct morphological differences separating them. After extensive examination of many specimens and only finding C. squama in Tasmania, I conclude that the Catalog is in error and that C. squama is the only Tasmanian scorpion.
After sorting out this taxonomic confusion, I have had the good fortune to observe many activities of the scorpion both in the field and the laboratory, the most amazing of which would have to the birth of young by several females. Five females have given birth in the laboratory, three of which I have taken notes on and observed throughout the process. All scorpions are viviparous but these are the first observations of birth in Cercophonius.
I realised the females were pregnant early on when they appeared swollen in the mesasoma region. These had been collected in early spring. It can be assumed from this that insemination took place before the winter, as scorpions are inactive for a short period at that season. As time passed, scorpion embryos could be seen developing through the mother's body wall. When I saw this, I kept a close eye on the females for any birthing activity. No previous information was available on the time of year they give birth.
The first birth occurred in early January but was unsuccessful. The newborn young appeared to be stillborn or even aborted by the female. I do not know if this happens in the wild but I suspect that this outcome was the result of stress under laboratory conditions. I also observed females selectively eating some of the young. Can the females distinguish between healthy and weak young? If so, what signals trigger the eating? I was unable to carry out any experiments to answer these questions because of lack of time and the risk of disturbing the few females that had given birth. Other females were successful in their parturition, and the young are still living.
Cercophonius squama with newborns
The females gave birth to between 20 and 30 live young over a period of several hours. The young emerge from the female's gonopore surrounded by what appears to be a membrane and take from just a few minutes to as long as an hour to begin moving. Once they have their 'feet' under them, they crawl onto their mother's back. The young are white in colour and soft-bodied at birth. This is a time of high vulnerability to predators and desiccation, which may help to explain why the females carry the young on their back for a period of two or more weeks. Adults are more mobile than newborns and more likely to find suitably moist shelters.
The mother and her young are fairly inactive for the next week, choosing to take refuge under a piece of bark or rock. This period of inactivity lasted for a minimum of one week. Around 10 days after the birth, the young's exoskeleton begins to sclerotise. At two weeks the young's exoskeleton fluoresces under ultraviolet light. This is an indication that the exoskeleton has completely formed. Generally, scorpions are considered to be in the second instar once sclerotisation has occurred, although in this case a molt was not observed between the soft and hard stage. Exuvia would be left behind if molting had occurred and a definite change would have been observed, literally overnight. This was not the case, but rather, the process was a gradual one over several days. At the time of writing, the young are six weeks old and have not molted again.
Other areas of my research include modeling the scorpion's distribution, estimating populations and studying microhabitat selection. The project should be completed by June of 2002. To give a preview of things, I expect the distribution will be wider than previously thought and I expect population sizes may be rather large in some areas. Scorpions have now been found in the centre of the State, at Bronte Park and Wayatinah. These are significant localities that will be very useful in modeling the scorpion's Statewide distribution. Few scorpion localities had previously been recorded very far from coastal areas. With respect to population sizes, I am currently in the middle of a capture-mark-recapture program. I cannot conclude anything from this work yet, but on some nights as many as 30 scorpions can be found along a 200 m path!
Acosta, L.E. 1990. El género Cercophonius Peters, 1861 (Scorpiones, Bothriuridae). Boletín de la Sociedad de Biología de Concepción (Chile) 61: 7-27.
Fet, V., Sissom, W.D. Lowe, G. & Braunwalder, M.E. 2000. Catalog of the Scorpions of the World (1758-1998). New York: New York Entomological Society.
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