A phylogenetic analysis of the arachnid orders based on morphological characters

Morphological evidence for resolving relationships among arachnid orders was surveyed and assembled in a matrix comprising 59 euchelicerate genera (41 extant, 18 fossil) and 202 binary and unordered multistate characters. Parsimony analysis of extant genera recovered a monophyletic Arachnida with the topology (Palpigradi (Acaromorpha (Tetrapulmonata (Haplocnemata, Stomothecata nom. nov. )))), with Acaromorpha containing Ricinulei and Acari, Tetrapulmonata containing Araneae and Pedipalpi (Amblypygi, Uropygi), Haplocnemata (Pseudoscorpiones, Solifugae) and Stomothecata (Scorpiones, Opiliones). However, nodal support and results from exploratory implied weights analysis indicated that relationships among the five clades were effectively unresolved. Analysis of extant and fossil genera recovered a clade, Pantetrapulmonata nom nov. , with the topology (Trigonotarbida (Araneae (Haptopoda (Pedipalpi)))). Arachnida was recovered as monophyletic with the internal relationships (Stomothecata (Palpigradi, Acaromorpha (Haplocnemata, Pantetrapulmonata))). Nodal support and exploratory implied weights indicated that relationships among these five clades were effectively unresolved. Thus, some interordinal relationships were strongly and/or consistently supported by morphology, but arachnid phylogeny is unresolved at its deepest levels. Alternative hypotheses proposed in the recent literature were evaluated by constraining analyses to recover hypothesized clades, an exercise that often resulted in the collapse of otherwise well-supported clades. These results suggest that attempts to resolve specific nodes based on individual characters, lists of similarities, evolutionary scenarios, etc., are problematic, as they ignore broader impacts on homoplasy and analytical effects on non-target nodes.  © 2007 The Linnean Society of London, Zoological Journal of the Linnean Society , 2007, 150 , 221–265.     

Substitution patterns in congeneric arachnid species in the northern Alps

Complementary abundance gradients of substituting congeneric arachnids along the northern margin of the Alps are described, and the possible historical and contemporary factors that have produced these distributions are explored. The intensities of activity of epigeous arachnids were determined in pitfall traps along seven altitudinal transects approximately 35 km apart in the Bavarian Alps (Germany) and in the county of Salzburg (Austria). No supraregional gradient of physical factors exists within the region investigated. Six pairs of congeners show vicariances or alternating abundance gradients. For each species pair, the abundance gradient is represented in diagrams and compared with a graphic model of substitution types. Three patterns are evident: strict vicariances, abrupt replacement in a narrow belt, and gradual substitution over a wide zone of sympatric occurrence. The different extent of range overlap suggests distinctive classes and intensities of interspecific interactions. With regard to biogeographic histories, one prevailing pattern emerged: endemic species of the eastern Alps are replaced by Eurosiberian counterparts towards the west. It appears that geographical abundance variation reflects colonization history.