17 February, 2020

Are trichobothria really necessary in scorpion prey capture?

It is a well known fact that the scorpion trichobothria on their pedipalps are very important in how the scorpions sense their environment. They use these small hairs to detect vibrations in the air and in the substrate, but direct behavioral studies on the use of trichobothria and natural prey capture are scarce.

Gabriel Pimenta Murayama and Rodrigo Hirata Willemart have recently published an interresting  study where they tested if the trichobothria are important in prey capture in Tityus serrulatus Lutz & Mello, 1922 (Buthidae). I must admit I assumed the answer was yes, but surprisingly their results suggested that the trichobothria of T. serrulatus was not essential to capture terrestrial prey.

It is important to remember that scorpions do have other types of sensory hairs (sensilla) on different parts of their body and these may play a role in detecting prey in the scorpions vicinity.

Many arachnids rely on substrate-borne vibrations and air displacement to detect prey. Air-flow stimuli may be detected by long setae called trichobothria, which occur on scorpion pedipalps, but seldom have their functions been addressed in these animals. We tested the hypothesis that trichobothria on scorpion pedipalps are important for capturing terrestrial prey in the scorpion Tityus serrulatus. We predicted that scorpions with trichobothria experimentally removed would be less successful in capturing terrestrial prey than the control groups. We also predicted that scorpions without trichobothria would have a higher number of capture attempts, that the latency to detect prey and to the first capture attempts would be higher, and the number of times that scorpions oriented their body towards the prey would be lower. We used an experimental subject and a cricket in an arena with a paper sheet as substrate. We did not find differences in the measured variables between the groups. Other sensory organs, such as basitarsal compound slit sensilla and tarsal hairs would enable scorpions to detect prey by substrate-borne vibrations, compensating for the lack of trichobothria. Our results suggest that the trichobothria of T. serrulatus may not be essential to capture terrestrial prey.

Murayama GP, Willemart RH. Are trichobothria used in terrestrial prey capture by the yellow scorpion Tityus serrulatus Lutz & Mello, 1922 (Buthidae)? Arachnology. 2019;18(3):287-90.

14 February, 2020

The role of sexual dimorphism in prey capture in two scorpion genera with different degree of male and female dimorphism

Sexual differences in morphology and other traits occur in many scorpion species, while the male and female are quite similar in others. In scorpions, sexual dimorphism is usually associated with mating and associated behavior.

Morphological differences in pedipalps and cauda have an impact in prey capture tactics, sting use and venom use in scorpions. Scorpions with large, powerful pedipalps will often not use their stinger and rely on the power of the pedipalps compared to species with more slender pedipalp.

Julio Cesar Gonzalez-Gomez and co-workers have recently published an article combining the above mentioned characteristics in scorpions by looking into the role of sexual dimorphism in prey capture in one group of scorpions with large sex differences and another group with minor differences. As espected they found significant differences between males and females in the group with large sexual dimorphism, and no differences in the group with minor differences.

Morphological differences between the sexes are a common feature in many groups of animals and can have important ecological implications for courtship, mating, access to prey and, in some cases, intersex niche partitioning. In this study, we evaluated the role of sexual dimorphism in the performance of the two structures that mediate the ability to access prey, the pinchers or chelae and the venomous stinger, in two species of scorpions with contrasting morphologies: Chactas sp., which has marked sexual dimorphism in the chelae, and Centruroides sp., which does not have such marked dimorphism in the chelae. We evaluated aspects such as chela pinch force, toxicity to prey (LD50) and the volume of venom in males and females of each species. We found significant differences between males and females of Chactas sp. in the chela pinch force, volume of venom and LD50. In contrast, for Centruroides sp., no differences between males and females were found in any of these traits. We discuss several potential selective regimes that could account for the pattern observed.

González-Gómez JC, Valenzuela-Rojas JC, García LF, Franco Pérez LM, Guevara G, Buitrago S, et al. Sexual dimorphism in the biomechanical and toxicological performance in prey incapacitation of two morphologically distinct scorpion species (Chactas sp. and Centruroides sp.). Biological Journal of the Linnean Society. 2020;129(1):190-8. [Subscription required for full text]

Thanks to Luis Fer for sending me this article!

13 February, 2020

A description of the hemispermatophore and mating plug of Vaejovis lapidicola

The hemispermatophore and mating plug have become important structures in scorpion taxonomy. Brandon Myers and Richard Ayrey have now published a description of these structures in the vaejovid Vaejovis lapidicola Stahnke, 1940.

While doing research on an undescribed scorpion species, we needed to examine the hemispermatophore and mating plug of Vaejovis lapidicola Stahnke, 1940. Included are photographs and a description of these structures from a topotype specimen collected in the same “red sandstone quarry” (Flagstaff, Arizona, USA), from which Herbert Stahnke collected the original specimens in 1938.

Myers B, Ayrey RF. Vaejovis lapidicola Stahnke, 1940: hemispermatophore and mating plug from a topotype male (Scorpiones: Vaejovidae). Euscorpius. 2020(299):1-7. [Open Access]

Family Vaejovidae

07 February, 2020

Two new species of Compsobuthus from North Africa

Frantisek Kovarik and co-workers have recently publish a paper on species in the genus Compsobuthus Vachon, 1949 (Buthidae) from Arabia and North Africa. Two new species are described.

Compsobuthus turieli Kovarik, Lowe, Stockmann & Stahlavsky, 2020 (Western Sahara and Morocco)

Compsobuthus ullrichi Kovarik, Lowe, Stockmann & Stahlavsky, 2020 (Egypt)

The article has also a redescription of Compsobuthus arabicus Levy, Amitai & Shulov, 1973.

Two new species of Compsobuthus Vachon, 1949, are described: C. turieli sp. n. from Western Sahara and Morocco, and C. ullrichi sp. n. from Egypt. The species C. arabicus Levy et al., 1973 is redescribed based on analysis of the holotype plus extensive material from Oman and the United Arab Emirates. These species are compared to others from their respective regions: C. kabateki Kovařík, 2003, C. levyi Kovařík, 2012, and C. polisi Lowe, 2001, for which new illustrations and biometrics are provided based on types and topotypic material. The hemispermatophores of C. arabicus, C. turieli sp. n. and C. ullrichi sp. n. are illustrated and described. We also record the karyotypes of C. acutecarinatus, C. arabicus, C. maindroni and C. ullrichi sp. n. All examined specimens possess 2n=22 and chromosomes gradually decreasing in length.

Kovarik F, Lowe G, Stockmann M, Stahlavsky F. Notes on Compsobuthus: redescription of C. arabicus Levy et al., 1973 from Arabia, and description of two new species from North Africa (Scorpiones: Buthidae). Euscorpius. 2020(298):1-40.

Congratulations on your "own" species, Carlos and Alex! :)

Family Buthidae

A new species of Ananteris from Panama

Roberto Miranda and Luis de Armas have recently published a new species of Ananteris Thorell, 1891 (Buthidae) from Panama.

Ananteris canalera Miranda & Armas, 2020

A new buthid species belonging to the genus Ananteris Thorell, 1891 is herein described from Panama Oeste Province, Panama. This is the second Ananteris species known from this Central American country and clearly differs from Ananteris platnicki Lourenço, 1993, distributed in Costa Rica and Panama, by its smaller size and male having a different hemispermatophore and telson similar to that of the female.

Miranda RJ, de Armas LF. A new species of Ananteris (Scorpiones: Buthidae) from Panama. Euscorpius. 2020(297):1-7. [Open Access]

Family Buthidae

21 January, 2020

Fossil of oldest scorpion known to science discovered

Scorpions have been around for a long time and researchers think they were among the first animals to become terrestrial. There is a debate going on whether these old scorpion ancestors were living in water or developed on land. Some think the latter, and that the water living species found developed later.

Andrew J. Wendruff and co-workers have discovered a 430 million years old preserved fossil scorpion from the Waukesha Biota (early Silurian, ca. 437.5–436.5 Ma) of Wisconsin, USA. This is the oldest scorpion fossil ever found. In their interesting article the authors discuss whether Parioscorpio venator, which is the name of grand, grand, grand .........father of today's scorpions, lived on land or in water. Their conclusion is that it probably could live in both environments, similar to today's horseshoe crabs.

Scorpions are among the first animals to have become fully terrestrialised. Their early fossil record is limited, and fundamental questions, including how and when they adapted to life on land, have been difficult to answer. Here we describe a new exceptionally preserved fossil scorpion from the Waukesha Biota (early Silurian, ca. 437.5–436.5 Ma) of Wisconsin, USA. This is the earliest scorpion yet reported, and it shows a combination of primitive marine chelicerate and derived arachnid characteristics. Elements of the circulatory, respiratory, and digestive systems are preserved, and they are essentially indistinguishable from those of present-day scorpions but share similarities with marine relatives. At this early point in arachnid evolution, physiological changes concomitant with the marine-to-terrestrial transition must have occurred but, remarkably, structural change in the circulatory or respiratory systems appear negligible. Whereas there is no unambiguous evidence that this early scorpion was terrestrial, this evidence suggests that ancestral scorpions were likely capable of forays onto land, a behavior similar to that of extant horseshoe crabs.

Wendruff AJ, Babcock LE, Wirkner CS, Kluessendorf J, Mikulic DG. A Silurian ancestral scorpion with fossilised internal anatomy illustrating a pathway to arachnid terrestrialisation. Sci Rep. 2020;10(1):14.  [Open Access]

17 January, 2020

Scorpions use different defensive behavior depending on sex, age and the threat level

Scorpions have developed multiple strategies for the defense against predators ranging from playing dead, running away to fighting back with the use of sting and venom. Interestingly, there seems to be differences in defensive behavior within the same species depending on the sex, age, size/strength of the threat and time of the day.

Andre Lira and co-workers published a study last Fall on the defensive behavior in the scorpion Tityus pusillus Lourenço, 2013 (Buthidae) from Brazil. A plasticity in defensive behavior was observed in this species, seeming to be influenced by the sex, age, diel period, and the body part targeted by the predator.

Differences in gender and age and the balance between aggressive behavior and the ability to escape are fundamental in predator–prey interactions, as well as for survival, foraging, and mating success. We investigated the defensive behavior of the scorpion Tityus pusillus and assessed possible differences in their behavior responses associated with sex, age, and diel period, by simulating a predation threat. Predator attacks were simulated by pressing the telsons with forceps, dropping the animals from a height of 25 cm on a plastic tray, restraining the pincers using large rubber-tipped tweezers, or restricting the prosoma. Tityus pusillus (Buthidae) showed five defensive behaviors: thanatosis, fleeing, stinging, standing still, and tail wagging. The scorpions responded with thanatosis or fleeing when their telsons were restricted. The frequency of these responses varied with sex and diel period. Stinging was the primary behavior response to prosoma restriction in both adults and juveniles while standing still was the most frequently observed behavior response to restraining pincers. These results indicate that the plasticity of defensive behavior in T. pusillus in response to predation is influenced by sex, age, diel period, and the body part targeted by the predator.

Lira AFA, Almeida FAF, Albuquerque CMR. Reaction under the risk of predation: effects of age and sexual plasticity on defensive behavior in scorpion Tityus pusillus (Scorpiones: Buthidae). Journal of Ethology. 2019;38(1):13-9. [Subscription required for full text]

Thanks to André for sending me this interesting article that I have been way to slow to read!