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Emperor scorpion - Pandinus imperator
Topic Started: Jan 9 2012, 03:36 PM (2,366 Views)
Taipan
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Emperor scorpion - Pandinus imperator

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Facts
Kingdom Animalia
Phylum Arthropoda
Class Arachnida
Order Scorpiones
Family Scorpionidae
Genus Pandinus
Size
Length: 20 cm
Weight 30 g

Status
The emperor scorpion is listed on Appendix II of CITES.

Description
The largest of scorpions, but not the longest, the emperor scorpion has a dark body ranging from dark blue/green through brown to black. The large pincers are reddish and have a granular texture. The thorax is made up of four sections, each with a pair of legs. Behind the fourth pair of legs are comb-like structures known as pectines – these are longer in males and are used to distinguish the sexes. The tail, known as the metasoma, is long and curves back over the body. It ends in the large recepticle containing the venom glands and tipped with the sharp, curved sting. Sensory hairs cover the pincers and tail, enabling the scorpion to detect prey through air and ground vibrations. When pregnant, the body of a female expands to expose the whitish membranes connecting the segments. The emperor scorpion fluoresces greenish-blue under ultraviolet lights.

Pincer
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Sting
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Range
The emperor scorpion is found in Africa, including Benin, Chad, Côte d'Ivoire, Democratic Republic of Congo, Ghana, Guinea, Togo, Guinea-Bissau, Liberia, Nigeria, and Sierra Leone.

Habitat
Inhabits both tropical forest and open savannas. It burrows beneath soils and hides beneath rocks and debris.

Biology
The emperor scorpion engages in an elaborate courtship dance in which the male holds on to the female's pincers and moves around to find a suitable place on the ground to deposit his spermatophore. Once deposited, he manoeuvres the female over the area so she can receive the sperm. The female gives birth to between 9 and 32 live young after a seven to nine month gestation period, and they remain with her for some time. This semi-social behaviour is unusual in scorpions, although the mother is sometimes cannibalistic, eating her own young. The young are white when born, but darken with each moult, reaching sexual maturity at four months.

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Emperor scorpion second moult nymph

Diet
The emperor scorpion feeds on insects, arachnids, mice and small lizards, hunting them at night using its sensory hairs. It has poor eyesight and is preyed upon by bats, birds, small mammals, large spiders, centipedes and large lizards. It uses its pincers to catch prey and will only use the sting in self-defence.

Threats
This species is thought to be threatened by over-collection for the pet trade.

Conservation
Little conservation action is taking place for this species, which has yet to be assessed by the IUCN and occurs in some of the world's poorest countries where conservation is not a priority.

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Taipan
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How the scorpion's venomous sting evolved

By Jeremy Coles
Reporter, BBC Nature
15 January 2014 Last updated at 02:14

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Humble beginnings for a deadly sting

The sting in a scorpion's tail has been connected to common defensive proteins by scientists.

Defensins are proteins common to many plants and animals that fight off viral, bacterial and fungal pests.

Researchers investigated the relationship between these proteins and the neurotoxins present in scorpion venom.

Their results showed how just a single genetic mutation could convert such a protein into a deadly toxin.

The findings, published in the journal Molecular Biology and Evolution, are the first evidence of an evolutionary relationship between these defensins and toxins, according to scientists.

A scorpion's venom is a potent mix of genetically-encoded toxic proteins used to kill or paralyse prey and defend against predators or competitiors.

Previous evidence suggested a common ancestor between a family of neurotoxins found in this venom and defensins, insect proteins which defend against tiny pests known as microbes.

But Prof Shunyi Zhu from the Chinese Academy of Sciences, who undertook the study, explained that the similarity of the two in terms of their genetic structure was relatively low which "left a puzzle for more than 20 years" for researchers.

In order to confirm the functional link, the team of researchers from China and Belgium analysed the scorpion neurotoxin to find its "signature" - the region of the protein responsible for its structure and function.

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A 3D model of Navitoxin - the toxin engineered from defensive insect protein

They then searched for this key sequence in some of the insect defensive proteins.

It was found in green shield bugs, spined soldier bugs and three species of backswimmer.

"It is surprising that only insect defensins from venomous insects contain scorpion toxin signatures," said Prof Zhu.

"These defensins clearly represent an evolutionary intermediate and could have the potential to develop into a toxin with similar action to scorpion toxins."

To test this theory, the researchers went on to engineer the insect defensive protein to give it scorpion neurotoxin function. They were able to do so by deleting just one single loop in the protein's genetic structure.

"This is a typical example of divergent evolution," said Prof Zhu describing how the shift from microbe immunity to predator defence is a key element in the evolutionary origins of scorpions and their stings.

http://www.bbc.co.uk/nature/25683544




Experimental Conversion of a Defensin into a Neurotoxin: Implications for Origin of Toxic Function
Shunyi Zhu, Steve Peigneur, Bin Gao, Yoshitaka Umetsu, Shinya Ohki, and Jan Tytgat
Mol Biol Evol (2014)
doi: 10.1093/molbev/msu038

Abstract
Scorpion K+ channel toxins and insect defensins share a conserved three-dimensional structure and related biological activities (defense against competitors or invasive microbes by disrupting their membrane functions), which provides an ideal system to study how functional evolution occurs in a conserved structural scaffold. Using an experimental approach, we show that the deletion of a small loop of a parasitoid venom defensin possessing the “scorpion toxin signature” (STS) can remove steric hindrance of peptide-channel interactions and result in a neurotoxin selectively inhibiting K+ channels with high affinities. This insect defensin-derived toxin adopts a hallmark scorpion toxin fold with a common cysteine-stabilized α-helical and β-sheet motif, as determined by nuclear magnetic resonance (NMR) analysis. Mutations of two key residues located in STS completely diminish or significantly decrease the affinity of the toxin on the channels, demonstrating that this toxin binds to K+ channels in the same manner as scorpion toxins. Taken together, these results provide new structural and functional evidence supporting the predictability of toxin evolution. The experimental strategy is the first employed to establish an evolutionary relationship of two distantly related protein families.

http://mbe.oxfordjournals.org/content/early/2014/01/09/molbev.msu038.abstract?sid=921822c4-c8f7-49f7-872a-f207df23d376
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