06 October, 2017

An update on the medical important scorpions of Mexico

Mexico has a very high diversity of scorpions, but also many medical important species in the genus Centruroides Marx, 1890 (Buthidae). Several of these species have an urban distribution making scorpions a significant health problems in some areas.

Lidia Riano-Umbarila and co-workers have recently published a major study of the medical importance of several Centruroides species based on LD50 tests (a controversial test from a animal welfare and ethics point of view). The article add more knowledge to the list of potential dangerous scorpions species in Mexico (click on the picture to see the species mentioned in this study).

The increment in the number of scorpion envenoming cases in Mexico is mainly associated to the rapid growth of the urban areas, and consequently, to the invasion of natural habitats of these arachnids. On the other hand, there is a great diversity of scorpion species, so it is indispensable to identify those of medical importance, which we now know are many more than the 7-8 previously reported as dangerous to humans. Because different LD50 values have been reported for the venom of the same species, probably due to variations in the experimental conditions used, in this work we determined the LD50 values for the venoms of 13 different species of scorpions using simple but systematic procedures. This information constitutes a referent on the level of toxicity of medically important scorpion species from Mexico and establishes the bases for a more comprehensive assessment of the neutralizing capacity of current and developing antivenoms.

Riano-Umbarila L, Rodriguez-Rodriguez ER, Santibanez-Lopez CE, Guereca L, Uribe-Romero SJ, Gomez-Ramirez IV, et al. Updating knowledge on new medically important scorpion species in Mexico. Toxicon. 2017;138:130-7. [Subscription required for full text]

American "superbat" (Antrozous pallidus) is immune against scorpion venom

The Pallid Bat (Antrozous pallidus). Photo: Courtesy by Connor Long (C)

A few weeks ago an article by  Bradley Hopp and co-workers presented a study of the Pallid Bat (Antrozous pallidus) using the Arizona Bark Scorpion (Centruroides sculpturatus Ewing, 1928) as prey. The Arizona Bark Scorpion is the most venomous scorpion in the US, and the researchers observed that the hunting bats were stung by their prey without any serious symptoms.

Systematic observations and experiments with injections of scorpion venom in the bats confirmed that The Pallid Bat is probably resistant to the venom of the bark scorpion. An altered sodium ion channel function may partly be the mechanism for this resistance.

The pallid bat (Antrozous pallidus), a gleaning bat found in the western United States and Mexico, hunts a wide variety of ground-dwelling prey, including scorpions. Anecdotal evidence suggests that the pallid bat is resistant to scorpion venom, but no systematic study has been performed. Here we show with behavioral measures and direct injection of venom that the pallid bat is resistant to venom of the Arizona bark scorpion, Centruroides sculpturatus. Our results show that the pallid bat is stung multiple times during a hunt without any noticeable effect on behavior. In addition, direct injection of venom at mouse LD50 concentrations (1.5 mg/kg) has no effect on bat behavior. At the highest concentration tested (10 mg/kg), three out of four bats showed no effects. One of the four bats showed a transient effect suggesting that additional studies are required to identify potential regional variation in venom tolerance. Scorpion venom is a cocktail of toxins, some of which activate voltagegated sodium ion channels, causing intense pain. Dorsal root ganglia (DRG) contain nociceptive neurons and are principal targets of scorpion venom toxins. To understand if mutations in specific ion channels contribute to venom resistance, a pallid bat DRG transcriptome was generated. As sodium channels are a major target of scorpion venom, we identified amino acid substitutions present in the pallid bat that may lead to venom resistance. Some of these substitutions are similar to corresponding amino acids in sodium channel isoforms responsible for reduced venom binding activity. The substitution found previously in the grasshopper mouse providing venom resistance to the bark scorpion is not present in the pallid bat, indicating a potentially novel mechanism for venom resistance in the bat that remains to be identified. Taken together, these results indicate that the pallid bat is resistant to venom of the bark scorpion and altered sodium ion channel function may partly underlie such resistance.

Hopp BH, Arvidson RS, Adams ME, Razak KA. Arizona bark scorpion venom resistance in the pallid bat, Antrozous pallidus. PLoS One. 2017;12(8):e0183215. [Open Access]

Thanks to Matt Simon for informing me about this article.

27 September, 2017

Increased predator exposure changes scorpion venom cocktail to become a more effective weapon

I just came across a very interesting article on phenotypic plasticity in scorpion venom. Scorpion venom is a cocktail of different toxins having different effects on different targets (e.g. one toxin is effective against invertebrates, another against mammals and a third against both). The matter in question in the current study is if scorpions are able to modify the ‘recipe’ of its venom cocktail, and thereby optimizing the fitness benefits of its costly venom, in different environments exhibiting differences in densities and types of predators and prey.

The Australian species Hormurus waigiensis (Gervais, 1843) (Hormuridae) was used in this study.

And interestingly, the results showed that simulated predator exposure appeared to decrease relative production of strong invertebrate toxins, while generally increasing the production of a section of the venom profile with activity towards mammalian cells. Put in other words, it seems that at least in Liocheles waigensis, increased interactions with a potential predator will cause the venom to become more effective (dangerous) against the predator and less effective against invertebrate prey.

So don't provoke your scorpions! This may make them more dangerous ;)

Animals embedded between trophic levels must simultaneously balance pressures to deter predators and acquire resources. Venomous animals may use venom toxins to mediate both pressures, and thus changes in this balance may alter the composition of venoms. Basic theory suggests that greater exposure to a predator should induce a larger proportion of defensive venom components relative to offensive venom components, while increases in arms races with prey will elicit the reverse. Alternatively, reducing the need for venom expenditure for food acquisition, for example because of an increase in scavenging, may reduce the production of offensive venom components. Here, we investigated changes in scorpion venom composition using a mesocosm experiment where we manipulated scorpions’ exposure to a surrogate vertebrate predator and live and dead prey. After six weeks, scorpions exposed to surrogate predators exhibited significantly different venom chemistry compared with naive scorpions. This change included a relative increase in some compounds toxic to vertebrate cells and a relative decrease in some compounds effective against their invertebrate prey. Our findings provide, to our knowledge, the first evidence for adaptive plasticity in venom composition. These changes in venom composition may increase the stability of food webs involving venomous animals.

Gangur AN, Smout M, Liddell MJ, Seymour JE, Wilson D, Northfield TD. Changes in predator exposure, but not in diet, induce phenotypic plasticity in scorpion venom. Proc Biol Sci. 2017;284(1863). [Subscription required for full text]

18 September, 2017

A new, extinct species of Centruroides found in amber from Mexico

Wilson Lourenco has recently described a new species of Centruroides Marx, 1890 (Buthidae) found in amber from Chiapas, Mexico.

Centruroides knodeli Lourenco, 2017

The new species is extinct. Please note that this species is not listed in The Scorpion Files as the species list only list extant species.

The article also includes criticisms of a recent article published by Rolando Teruel where two extinct species of Tityus C. L. Koch, 1836 (Buthidae) also found in amber were synonymized with Tityus geratus Santiago-Blay & Poinar, 1988. The following two species are restored as valid species.

Tityus azari Lourenço, 2013

Tityus (Brazilotityus) hartkorni Lourenço, 2009

Centruroides knodeli sp. n., a new species of fossil scorpion, is described from a specimen in amber from Chiapas, Mexico. The new species is clearly related to the extant fauna of the Neotropical region and is placed in the genus Centruroides Marx, 1890, presently distributed in North, Central and South America and in the Caribbean region. Also, the fossil species Tityus hartkorni Lourenço, 2009 and Tityus azari Lourenço, 2013, described from Dominican amber and inappropriately regarded by Rolando Teruel as junior synonyms of Tityus geratus Santiago-Blay & Poinar, 1988, are herein restored as valid taxa.

Lourenco WR. A new species of Centruroides Marx, 1890 from Chiapas amber, Mexico (Scorpiones: Buthidae). Revista Iberica de Arachnologia. 2017(30):100-6.

14 September, 2017

Two new species of Grosphus from Madagascar

Wilson Lourenco and co-workers have recently published an article describing two new species of Grosphus Simon, 1880 (Buthidae) from Madagascar.

Grosphus halleuxi Lourenço, Wilme, Soarimalala & Waeber, 2017

Grosphus rakotoariveloi Lourenço, Wilme, Soarimalala & Waeber, 2017

Grosphus simoni Lourenco, Goodman & Ramilijaona, 2004 is redescribed. The biogeography of the mentioned species is also discussed.

A reanalysis of the type material of Grosphus simoni Lourenço, Goodman & Ramilijaona, 2004, associated with new material of this species from the northeast of Madagascar, has led to the conclusion that the male paratype of G. simoni belongs to a new, undescribed species. A large series of specimens collected in the Ambatovy-Analamay-Torotorofotsy humid forests, at around 1000 m, revealed the presence of another new species, also associated to G. simoni. Thanks to the supplementary material, with males and females, a new diagnosis is proposed for G. simoni and two new species are here described. Some general comments on the biogeography of the two new species and G. simoni are also provided.

Lourenco WR, Wilme L, Soarimalala V, Waeber PO. Species of Grosphus Simon, 1880 associated to Grosphus simoni Lourenço, Goodman & Ramilijaona, 2004 with description of two new species (Scorpiones: Buthidae). Revista Iberica de Arachnologia. 2017(30):61-9.

Family Buthidae

12 September, 2017

A new species of Broteochactas from Brazil

Wilson Lourenco has recently described a new species of Brotheochactas Pocock, 1893 (Chactidae) from Brazilian Amazonia.

Broteochactas purus Lourenco, 2017

A new contribution to the knowledge of the scorpions belonging to the genus Broteochactas Pocock, 1893 is proposed and a new species is described, Broteochactas purus sp. n., based on one female specimen collected in the region of Beruri near the River Purus in the State of Amazonas, Brazil. The new species is characterized by a small size, an intense reddish to reddish yellow coloration, body and appendages with punctation and metasomal segment V and telson with conspicuous spinoid granulations.

Lourenco WR. One more new species of Broteochactas Pocock, 1893 (Scorpiones: Chactidae) from Brazilian Amazonia. Revista Iberica de Arachnologia. 2017(30):11-4.

Family Chactidae

08 September, 2017

A new species of Ananteris from Brazil

Andre Felipe de Araujo Lira and co-workers have recently described a new species of Ananteris Thorell, 1891 (Buthidae) from the Caatinga biome in Brazil.

Ananteris otovianoi Lira, Pordeus & Ribeiro de Albuquerque, 2017

We describe a new species of scorpion from the Caatinga of the state of Pernambuco, Brazil. Ananteris otovianoi sp. nov. can be distinguished from other Ananteris by the following combination of characters: blackish brown spots up to the medical surface of the chelicerae; pectinal tooth count and some structures measurements. In addition, data on natural history are showed and discussed. 

Lira AFA, Pordeus LM, Ribeiro de Albuquerque CM. A New species of Ananteris (Scorpiones: Buthidae) from Caatinga biome, Brazil. Acta Arachnologica. 2017;66(1):9-15. [Open Access, but pdf for this issue is not yet available]

Thanks to Andre Lira for sending me their article!

Family Buthidae