27 February, 2012

Functional implications of pedipalp chela shapes in scorpions

Arie van der Meijden and co-workers have previously published a paper on claw size and pincer force in scorpions. A follow-up paper is now in press on the functional implications of pedipalp chela shapes in scorpions.

Scorpions depend on their pedipalps for prey capture, defense, mating and sensing their environment. Some species additionally use their pedipalps for burrowing or climbing. Because the pincers or chelae at the end of the pedipalps vary widely in shape, they have been used as part of a suite of characters to delimit ecomorphotypes. We here evaluate the influence of the different chela cuticular shapes on their performance under natural loading conditions. Chelae of 20 species, representing seven families and spanning most of the range of chela morphologies, were assigned to clusters based on chela shape parameters using hierarchical cluster analysis. Several clusters were identified corresponding approximately to described scorpion ecomorphotypes. Finite element models of the chela cuticulae were constructed from CT scans and loaded with estimated pinch forces based on in vivo force measurements. Chela shape clusters differed significantly in mean Von Mises stress and strain energy. Normalized FEA showed that chela shape significantly influenced Von Mises stress and strain energy in the chela cuticula, with Von Mises stress varying up to an order of magnitude and strain energy up to two orders of magnitude. More elongate, high-aspect ratio chela forms showed significantly higher mean stress compared with more robust low-aspect ratio forms. This suggests that elongate chelae are at a higher risk of failure when operating near the maximum pinch force. Phylogenetic independent contrasts (PIC) were calculated based on a partly resolved phylogram with branch lengths based on an alignment of the 12S, 16S and CO1 mitochondrial genes. PIC showed that cuticular stress and strain in the chela were correlated with several shape parameters, such as aspect ratio, movable finger length, and chela height, independently of phylogenetic history. Our results indicate that slender chela morphologies may be less suitable for high-force functions such as burrowing and defense. Further implications of these findings for the ecology and evolution of the different chela morphologies are discussed.

van der Meijden A, Kleinteich T, Coelho P. Packing a pinch: functional implications of chela shapes in scorpions using finite element analysis. J Anat. 2012; Early View paper. [Subscription required for fulltext]

Thanks to Dr. van der Meijden for sending me this paper!

23 February, 2012

New Scorpion Files species biography: Tityus asthenes

Hard working scorpion enthusiast Michiel Cozijn has written a new, informative species biography for The Scorpion Files. This time he has looked at the South American Tityus asthenes (Pocock, 1893) in the Buthidae family.

Species biography for Tityus asthenes

You can find information about other species biographies written by Michiel by clicking on the blog tag "species biography".

A big thanks to Michiel for supporting The Scorpion Files!

10 February, 2012

Rumikiru - a new genus from northern Chile

Andres Ojanguren-Affilastro and co-workers have recently published a paper describing a new genus in the family Bothriuridae from northern Chile. A new species is also presented. In addition, an existing species is transferred into the new genus.

Rumikiru Ojanguren-Affilastro, Mattoni, Ochoa & Prendini, 2012 (new genus)

Rumikiru atacama Ojanguren-Affilastro, Mattoni, Ochoa & Prendini, 2012 (new species)

Rumikiru lourencoi (Ojanguren-Affilastro, 2003) (new combination - transfered from Orobothriurus)

Rumikiru is formed from the language Quechua and means "Stone tooth" (refering to the large large denticles on the movable fingers of the pedipalp chela in this genus (an unique character in Bothriuridae), and to the habitat of the two species (they are restricted to rocky slopes)).

Rumikiru, n. gen., a new bothriurid scorpion genus from the coastal Atacama Desert, Chile, is described. This is the first scorpion genus endemic to northern Chile. It is most closely related to Pachakutej Ochoa, 2004, from the inter-Andean valleys of Peru. Orobothriurus lourencoi Ojanguren-Affilastro, 2003, is transferred to the new genus and redescribed, creating Rumikiru lourencoi (Ojanguren-Affilastro, 2003), n. comb., and a second species of the genus, Rumikiru atacama, n. sp., is described.

Ojanguren Affilastro AA, Mattoni CI, Ochoa JA, Prendini L. Rumikiru, n. gen. (Scorpiones: Bothriuridae), a new scorpion genus from the Atacama Desert. American Museum Novitates. 2012(3731):1-43. [Free fultext]

Thanks to Rolando Teruel for informing me about this paper.

Family Bothriuridae

02 February, 2012

First arboreal (tree-dwelling) bothriurid scorpion

Jaime Pizarro-Araya and co-workers report about the first arboreal (tree-dwelling) species in the family Bothriuridae.

Urophonius tumbensis
Cekalovic, 1981 was observed and collected active on threes in temperate forests in southern Chile. The scorpions were walking on the trunk and major branches at heights ranger from 2 to 2 meters above ground.

We present the first observations of an arboreal bothriurid scorpion and the first report of an arboreal scorpion from the temperate forests of southern Chile. Urophonius tumbensis Cekalovic 1981 was observed and captured with ultraviolet (UV) light at a height of up to 6 meters on trunks of Cryptocarya alba (Molina) Looser trees in the Hualpén Botanical Reserve (Bío Bío Region, Chile).

Pizarro-Araya J, Ojanguren-Affilastro AA, Prendini L. First report of an arboreal scorpion (Bothriuridae: Urophonius) from the temperate forests of southern Chile. Gayana. 2011;75(2):187-91.

Thanks to Gerard Dupre for sending me this paper!