Functional morphology and bite performance of raptorial chelicerae of camel spiders (Solifugae)

Abstract

SUMMARYSolifugae are an understudied group of relatively large arachnids with well over 1000 species distributed on almost all major continents. These highly active predators utilize their large chelicerae for feeding, defense, burrowing and mating. We investigated the differences in cheliceral morphology and performance of two ecologically divergent species from North Africa; the cursorial Galeodes sp. and the burrowing Rhagodes melanus. Morphological data show differences in aspect ratio between the two species. Bite force measurements show Rhagodes (N11) to be a much stronger biter than Galeodes (N8), in terms of both absolute maximum force (Rhagodes 5.63N, Galeodes 2.12N) and force relative to cheliceral size. Synchrotron microtomographs of one specimen for each species reveal large differences in physiological cross-sectional area (PCSA) and estimated muscle stress, resulting in a much higher muscle stress in Rhagodes. This species also showed a longer muscle fiber length. Muscle volume and PCSA were found to differ between the two chelicerae in the two scanned specimens. Whereas Rhagodes reflects this morphological asymmetry in having a higher bite force in the right chelicera, Galeodes shows no such bias.

Biomechanical determinants of bite force dimorphism inCyclommatus metalliferstag beetles

“…As mentioned, this should be accompanied by further adaptations of the mandibular system, e.g. as observed for the cheliceral system in camel spiders (van der Meijden et al, 2012). In this regard, the specific working hypotheses that we tested are: (1) males have prolonged input levers to compensate for their long output levers, (2) male mandibular muscles are geometrically advantageous compared with those of females (in terms of size and working direction), and (3) these muscles are intrinsically stronger than female muscles.…”

Cheliceral Morphology in Solifugae (Arachnida): Primary Homology, Terminology, and Character Survey

“…1). The manus contains the cheliceral muscles, which extends somewhat into the fixed finger along with the trachea (Klann, 2009;Van der Meijden, et al, 2012). Sørensen (1914: 161) mentioned adipose tissue inside the fingers in engorged specimens.…”

“…The bicondylar hinge restricts movement of the fingers to the dorsoventral plane, allowing the teeth to overlap in a scissor-like manner and transforming the chelicerae into the powerful offensive and defensive appendages they are (Roewer, 1934: 54). The two interdigital condyli determine the rotation axis of the fingers ( Van der Meijden et al, 2012). The movable finger closes prolateral to the fixed finger.…”

“…MATING BEHAVIOR: The size and shape of the chelicerae is often associated with reproduction (e.g., Hrušková-Martišová et al, 2010a;Van der Meijden et al, 2012). For example, Van der Meijden et al (2012) speculated that a reproductive function (e.g., male-male antagonism) might explain the apparently larger chelicerae reported for male Rhagodidae (although how this was measured was not mentioned).…”

“…For example, Van der Meijden et al (2012) speculated that a reproductive function (e.g., male-male antagonism) might explain the apparently larger chelicerae reported for male Rhagodidae (although how this was measured was not mentioned). Others (e.g., Hrušková-Martišová et al, 2010a) have suggested that cheliceral shape may be adapted for direct involvement during copulation.…”