Coevolution between mechanical patterns of predation and the venomous function in scorpions of the super-family Buthoidea

LOURENÇO, W.R.(1)

(1)Laboratoirede Zoologie (Arthropodes), Muséum National d’HistoireNaturelle, 61 rue de Buffon 75005 Paris, France

All of the extant scorpion species, which are assigned to 6 super-families and 16 to 20 families, possess venom glands. The presence of a telson + aculeus, and possibly tegumental glands, are also evident in fossil scorpions from the Palaeozoic, Mesozoic and Cenozoic(Lourenço, 2001, Lourenço& Weitschat, 2001, Jeram, 2001).

            At present the following points can be suggested:

            1. Originally, the telson played a major mechanical role in predation, with the aculeus acting rather as a “spear-head” (Lourenço, 2001, 2002).

            2. Over the course of evolutionary time, tegumentalglands evolved in the telson’s vesicle, however, their primitive role was certainly only digestive.

            3. Many, if not most, non-buthid scorpions (i. e. ischnurids, scorpionids), evolved more sophisticated mechanical techniques of predation (e.g. development of strong pedipalps). The use of venom (toxins) for the capture of prey is rather facultative in these groups.

            4. Buthoids are the most complex group of scorpions, with 3 families and about 80 genera. These cannot be considered as a homogeneous (monophyletic) unit, but instead represent 4 or 5 different evolutionary levels (Lourenço, 2000).

5. Within buthoids, only a few species of buthidspossess venoms formed of complex mixtures of highly specific toxins. These are represented by species of genera such as Androctonus, Buthus, Centruroides, Leiurus, Mesobuthusand Tityus, all of which can be placed in the highest evolutionary level within buthoids. These groups have been the subject of intensive biochemical and molecular research (Loret & Hammock, 2001).

To interpret the evolution of buthoid scorpion toxins, studies must be conducted with the venoms of primitive extant lineages. These are represented by species of the Malagasy microcharmidsand some relictualbuthidssuch as Ananteris, Anomalobuthus, Akentrobuthus, Birulatus, Himalayotityobuthus, Lychasiodes, Microtityus, Pseudouroplectes, Sabinebuthus and Tityobuthus.

CORRESPONDENCE TO:

LOURENÇO, W.R., Laboratoirede Zoologie (Arthropodes), Muséum National d’HistoireNaturelle, 61 rue de Buffon 75005 Paris, France. Email: arachne@mnhn.fr