ABSTRACT

Pseudoscorpions are an ancient order of arachnids whose mating systems display an interesting mix of phylogenetic conservatism and evolutionary plasticity. A 400 millionyear– old pattern of indirect sperm transfer by means of spermatophores deposited on the substrate pervades all aspects of sexual selection in pseudoscorpions. Across families, mating behavior ranges from the ancestral condition, in which males deposit structurally simple spermatophores irrespective of the presence of females (non–pairing), to a derived condition in which males engage in elaborate courtship and assist females in the uptake of structurally complex spermatophores. In non–pairing taxa, sexual selection appears to be mediated through rapid male development and prolific spermatophore production. Males are invariably the smaller sex and do not fight over access to females. Why non–pairing has persisted in six of seven superfamilies remains an enigma. Cladistic analysis suggests that pair formation has evolved independently only once. Evidence from within the most diverse family, the Chernetidae, indicates that, once pair formation evolved, sexual dimorphism became a highly variable condition. Only in productive, and hence often ephemeral and patchily distributed, micro – habitats do populations reach densities at which selection for fighting ability outweighs the costs of attaining competitive size. The harlequin–beetle–riding pseudoscorpion, Cordylochernes scorpioides, has provided a model system both for assessing the influence of ecological factors on the operation of sexual selection and for identifying processes that can maintain variability in male sexually selected traits.