Mate-guarding in the genus Creutzeria (Astigmata: Histiostomatidae), an aquatic mite genus inhabiting the fluid-filled pitchers of Nepenthes plants (Nepentheaceae)

摘要

A number of genera of Histiostomatidae inhabit phytotelmata, being found fully submerged and filtering organic matter from the fluid. One such phytotelm habitat is the fluid-filled pitchers of species of Nepenthes, a carnivorous plant genus widely distributed in the Old World tropics. As in most histiostomatid species, males of Nepenthes-inhabiting mites seek out tritonymphal females and guard them from other males, a behavior termed "precopulatory mate-guarding". Upon ecdysis of the tritonymph to adult, mating takes place. Successful mate-guarding prevents other males from gaining access to a virgin female and helps ensure the guarding male's paternity of any resultant offspring.While most Nepenthes-inhabiting genera are ambulatory, walking about on decomposing arthropods in the pitchers, species of the genus Creutzeria are natatory and propel themselves through the fluid using legs greatly modified for this purpose. Males of purely ambulatory species typically climb onto the dorsum of a tritonymphal female and firmly clasp her idiosoma with their legs. Some species do not move about on their own accord, but rely on the female to carry them. In others, two pairs of legs are used for clutching the female; the other two pairs are very long, thereby allowing the male to walk about while holding the securely clasped female off the substrate. Swimming is a more laborious task, especially since the male must propel not only himself through the fluid but also the female. The mate-guarding behavior of Creutzeria spp. was studied by direct observation under a stereomicroscope and from videos filmed through a stereomicroscope. In addition, phase contrast and scanning electron microscopy were used to examine the morphological adaptations associated with mate-guarding and mating. Legs I of males are greatly modified for clasping a tritonymphal female during mate-guarding and legs III and IV for swimming. Legs II are a morphological compromise, being used for swimming as well as for grasping the substrate for resting when legs I are occupied with a female.