26 April, 2019

Tityus serrulatus - A natural born killer

A very tabloid headline for this post, but I felt I couldn't plagiarize the nice original article title "Selected to survive and kill". Scorpion stings in Brazil have increased in the last decade and the main culprit has been Tityus serrulatus Lutz and Mello, 1922 (Buthidae). This very invasive species has spread in Brazil in the last decades and has adapted very well to urban habitat. In addition, the species can reproduce by parthenogenesis, making this species a very expanding taxa.

Ricardo Jose Gonzaga Pimenta and co-workers have recently published a study on how well Tityus serrulatus handles food and water deprivation. The authors found that this medical important scorpion has an impressive capacity to survive starvation for long periods. Lack of water, on the other hand, caused a large decrease in survival rates. Reproduction occurred throughout the year for food-deprived scorpions and controls, but not in the water-deprived groups.

The results of this study have implications for how scorpion control should be conducted for this expanding, hard to kill, dangerous species in urban areas.

Annually, more than 1.2 million scorpion stings and more than 3,000 deaths occur worldwide. Tityus serrulatus Lutz and Mello, 1922 (Scorpiones, Buthidae) is the most medically relevant species in Brazil where it is spreading rapidly and causing over 90,000 cases of envenomation yearly. We monitored T. serrulatus longevity and ability to reproduce under conditions of food and/or water deprivation. We found that T. serrulatus is highly tolerant to food deprivation, with individuals enduring up to 400 days without food. On the other hand, access to water played a pivotal role in T. serrulatus survival. Food and water deprived scorpions showed weight reduction. Reproduction occurred throughout the year for fooddeprived scorpions and controls, but not in the water-deprived groups. Remarkably, fooddeprived animals were able to give birth after 209 days of starvation. Tityus serrulatus resistance to food and water deprivation is likely to be an additional factor underlying this species’ geographic expansion and the difficulties encountered in controlling it.

Pimenta RJG, Brandao-Dias PFP, Leal HG, Carmo AOD, Oliveira-Mendes BBR, Chavez-Olortegui C, et al. Selected to survive and kill: Tityus serrulatus, the Brazilian yellow scorpion. PLoS One. 2019;14(4):e0214075. [Open Access]

Thanks to Matt Simon for informing me about this article!

The origin of the buthid scorpion fauna of the Caribbean islands

The Caribbean islands have a large scorpion population where many species are endemic for this area. But how did this unique fauna originate? There have been three theories of the origins of the flora and fauna diversity seen in The Caribbean: 1. Connections via land bridges, 2. Vicariance events, 3. Overwater dispersal from continents and among islands.

Lauren Esposito and Lorenzo Prendini have now published a study investigating the biogeographical diversification of the New World buthid scorpion subfamily Centruroidinae Kraus, 1955 and trying to understand the origin of the Caribbean populations of these taxa.

The results of this study show that the centruroidine scorpions colonized the Caribbean islands on two independent occasions (35 mya ago from South America and the Greater Antilles and 20 mya ago North America, probably via Cuba). Interestingly, the results also point to a case of "reverse-colonization" event for the genus Heteroctenus Pocock, 1893. This genus seems to have a Caribbean ancestor, which subsequently colonized Central America and North America, and eventually re-colonized the Greater Antilles.

Scorpions are an excellent system for understanding biogeographical patterns. Most major scorpion lineages predate modern landforms, making them suitable for testing hypotheses of vicariance and dispersal. The Caribbean islands are endowed with a rich and largely endemic scorpion fauna, the origins of which have not been previously investigated with modern biogeographical methods. Three sets of hypotheses have been proposed to explain present patterns of diversity in the Caribbean: (1) connections via land bridges, (2) vicariance events, and (3) overwater dispersal from continents and among islands. The present study investigates the biogeographical diversification of the New World buthid scorpion subfamily Centruroidinae Kraus, 1955, a clade of seven genera and more than 110 species; infers the ancestral distributions of these scorpions; and tests the relative roles of vicariance and dispersal in the formation of their present distributions. A fossil calibrated molecular phylogeny was estimated with a Bayesian criterion to infer the dates of diversification events from which ancestral distributions were reconstructed, and the relative likelihood of models of vicariance vs. dispersal, calculated. Although both the timing of diversification and the ancestral distributions were congruent with the GAARlandia land-bridge hypothesis, there was no significant difference between distance-dependent models with or without the land-bridge. Heteroctenus Pocock, 1893, the Caribbean-endemic sister taxon of Centruroides Marx, 1890 provides evidence for a Caribbean ancestor, which subsequently colonized Central America and North America, and eventually re-colonized the Greater Antilles. This ‘reverse colonization’ event of a continent from an island demonstrates the importance of islands as a potential source of biodiversity.

Esposito LA, Prendini L. Island Ancestors and New World Biogeography: A Case Study from the Scorpions (Buthidae: Centruroidinae). Sci Rep. 2019;9(1):3500. [Open Access]

25 April, 2019

Scorpions as environmental indicators

Andre Lira and co-workers have recently publised a study looking into how scorpion diversity, species richness, and species composition respond to bioclimatic changes (like forests with different gradients of humidity).

The study indicated that much of the scorpion composition and diversity in the study area were explained by a longitudinal bioclimatic gradient (wet-dry forest) and that species richness increased with increasingly dry conditions along the longitudinal gradient. Based on the results presented in this study, the authors belive that scorpions can be used as environmental indicators due to the high detectability, sensitivity to environmental attributes, and well known and stable taxonomy.

Understanding large-scale patterns of biological diversity is one of the most important issues in ecology. Parameters of scorpion assemblages may serve as a proxy to understand how arthropods respond to bioclimatic changes by adjusting their spatially structured distribution. We analysed how scorpion species richness, abundance, and composition respond to climatic variations found along a longitudinal gradient between wet (Atlantic Forest) and dry (Caatinga hypo and hyperxerophilic) forests in Brazil. A total of 20 sites were sampled four times along a 712 km longitudinal wet-dry bioclimatic gradient in north-eastern Brazil. We recorded 2653 scorpions from 12 species, belonging to five genera and two families. Environmental variables associated with precipitation and temperature had a strong effect on scorpion distribution, resulting in a distinct faunal composition at both extremes of the gradient. Species composition presented a turnover along the bioclimatic gradient, with beta diversity increasing towards the drier sites. The increase of dryness coincide with increases in temperature, moisture reduction, and a general environmental harshness. Our study, therefore, indicates that species sensitivity to climatic variation determines scorpion distribution in Neotropical forests.

Lira AFA, Salomão RP, Albuquerque CMR. Pattern of scorpion diversity across a bioclimatic dry-wet gradient in Neotropical forests. Acta Oecologica. 2019;96:10-7. [Subscription required for full text]

Thanks to Andre Lira for sending me their study!

24 April, 2019

A review of the scorpion fauna of Greece

Since Aristoteles first mentioned the presence of scorpions in Greece, the number of taxa belonging to this country have increased very much in the last decade thanks to more studies and better taxonomical and phylogentic tools.

Victor Fet and co-workers have written av chapter in book published last Fall summing up the current knowledge of the scorpion fauna in Greece.

A remarkable diversity of scorpion fauna and its distribution in Greece is discussed. The current list of Greek scorpions includes 32 confirmed species belonging to three families (one of Buthidae, seven of Iuridae, and 24 of Euscorpiidae), as well as a number of unassigned euscorpiid taxa. Uncovered only in the last decade, mainly through the use of DNA markers, ‘cryptic’ scorpion fauna of Greece is the most diverse in Europe and rivals that of many other countries.

Fet V, Parmakelis A, Stathi I, Tropea G, Kotsakiozi P, Kardaki L, et al. Fauna and zoogeography of scorpions in Greece. In: Sfenthourakis S, Pafilis P, Parmakelis A, Poulakakis N, Triantis KA, editors. Biogeography and Biodiversity of the Aegean In honour of Prof Moysis Mylonas. Nicosia: Broken Hill Publishers Ltd; 2018. p. 123-34. [Full text available on Victor Fet's Research gate profile]

01 April, 2019

Scorpion envenomations in South Africa during a 10-year period

South Africa harbors a large diversity of scorpions, including many species in the medical important genus Parabuthus Pocock, 1890 (Buthidae). Carine J. Marks and co-workers have recently published a retrospective analysis of the scorpion cases managed by the Tygerberg Poisons Information Centre over a 10 year period.

The main conclusion is that the incidence of severe scorpionism were low in this period. 65% of the sting cases had no or minor symptoms, mainly local pain. As usual, children may be more vulnerable and extra vigilance is needed in cases involving small children. The species involved in the study were usually not involved, but it is well known that Parabuthus granulatus (Ehrenberg, 1831) and P. transvaalicus (Purcell, 1899) are the most dangerous species in South Africa.

Introduction: South Africa has a wide distribution of scorpion species, yet limited data are available regarding the incidence and severity of scorpion envenomation. The aim of this study was to analyse South African epidemiological data of scorpion stings and envenomation as reported to the Tygerberg Poisons Information Centre (TPIC).
Methods: A retrospective analysis was conducted of scorpion-related telephonic consultations to the TPIC over a ten year period (1 January 2005 to 31 December 2014). Data were entered onto a Microsoft Excel® spreadsheet and descriptive statistics are presented for all variables. Associations with severity of envenomation are presented as odds ratios (OR) with 95% confidence intervals (95%CI).
Results: During the study period 52,163 consultations were processed by the TPIC of which 740 (1.4%) cases involved scorpion stings. Of these, 146 (19.7%) cases were deemed serious envenomations. Antivenom was recommended to be administered in 131 (90%) of these cases. Healthcare professionals made most calls (63%), but were less likely to phone for non-serious cases (OR 0.16; 95%CI 0.09 to 0.29). The Western Cape Province had the highest incidence of calls (6.9 scorpion-related calls/100 000 people). Adults (> 20 years) were victims in 71.4% of cases, and were more likely to experience less serious stings (OR 0.57; 95%CI 0.37 to 0.86). The TPIC was consulted within six hours of the sting occurring in 356 (48.1%) cases with a significant association to less severity (OR 3.51; 95%CI 1.9 to 6.3). Only 2% (15) of the scorpions were available for identification.
Conclusion: The incidence of severe scorpionism to the TPIC was low. Care should be taken when children are involved and when calls are received more than six hours after the sting. TPIC consultants as well as healthcare professionals working in semi-arid regions should be aware of these high risk populations.

Marks CJ, Muller GJ, Sachno D, Reuter H, Wium CA, Du Plessis CE, et al. The epidemiology and severity of scorpion envenoming in South Africa as managed by the Tygerberg Poisons Information Centre over a 10-year period. African journal of emergency medicine : Revue Africaine de la Medecine d'Urgence. 2019;9(1):21-4. [Open Access]

Jaguajir rochae is able to perceive differences between small and large prey and make decisions regarding venom usage

Several studies have shown that scorpions have different strategies for optimizing the venom use. The reason for this is of course because it take times to renew the venom and it is costly as the venom is a mixture of complex proteins. This is often called the venom optimization hypothesis. This also means that optimizing venom usage might directly affect the predatory behavior and physiology of scorpions.

Meykson Alexandre da Silva and co-workers have recently published an article showing that the amount of venom available for individuals of Jaguajir rochae (Borelli, 1910) (Butidae) did have an effect on their prey capture behavior. Individuals with depleted venom glands did not attack large prey, but did try to catch smaller prey that could be handled with pedipalps only. The study shows that this scorpion is able to perceive differences between small and large prey and make decisions regarding venom usage. These results are in accordance with the the venom optimization hypothesis

Animal venom is composed of a complex mixture of protein-rich chemicals. Synthesis of animal venom incurs a high metabolic cost and is a prolonged process; consequently, animals use their venom cautiously and economically. Some studies have shown that venomous animals modulate the amount and/or type of venom used depending on certain factors, such as prey size or the intensity of predation threat. Here, we investigated how the quantity of venom that is available for use by the scorpion Jaguajir rochae interferes with its choice of prey.We used two types of prey of contrasting size (small 200–300-mg and large 600–700-mg cockroaches). The results showed that the amount of venom influences the feeding behavior of this species. Most scorpions without venom exhibited a low interest when large prey was present, but frequently attacked small prey. The scorpions also showed a distinct pattern in the time between venom extraction and the initiation of hunting behavior. In conclusion, J. rochae is able to perceive differences between small and large prey and make decisions regarding venom usage, supporting the "venom optimization hypothesis" (or "venom metering hypothesis"), by minimizing the venom use due to it being an energetically expensive resource.

Silva MA, Silvia NA, Lira AFA, Martins RD. Role of venom quantity in the feeding behavior of Jaguajir rochae (Scorpiones: Buthidae). Acta Ethologica. 2019;Published Online 09 March 2019. [Subscription required for full text]

Thanks to Meykson Alexandre da Silva for sending me their interesting article which confirm some of the assumptions that I did in my old studies of sting use in scorpions.