Laelapine Mite (Acari: Laelapidae) Morphometric Analysis Reflects Taxonomic and Geographic Clusters of South American Oryzomyines (Rodentia: Sigmodontinae)

Ongoing efforts to survey and inventory nonvolant small mammals across the Neotropics are beginning to reveal a highly structured and diverse fauna of rodents and marsupials. By increasing the foundation of specimens in museums around the world, it has become possible, for the first time, to evaluate and quantify the similarities and differences among small mammals collected from a broad range of geographic localities, ecoregions, and habitats. Because ectoparasites were sampled in the process of collecting mammalian voucher specimens, we are able to study the laelapine mites (Acari: Laelapidae) associated with well-identified and verifiable host specimens. Here, we evaluate morphometric variation of two nominal mite species, Laelaps acuminata and Gigantolaelaps oudemansi (Acari: Laelapidae), that are widespread and appear to infest a wide range of both terrestrial (Hylaeamys and Euryoryzomys) and arboreal (Oecomys) oryzomyine rodents. Mites were collected from seven species (three genera) of oryzomyines, E. macconnelli, E. nitidus, E. russatus, H. megacephalus, Oe. bicolor, Oe. concolor, and Oe. mamorae, from a number of localities from Bolivia, Brazil, and Paraguay. Results of both UPGMA clustering and principal component analyses, for both mite species, indicate that each rodent species hosts distinct mite species (with one possible exception—Euryoryzomys nitidus and E. russatus), and that each of these two nominal mite species is actually a complex of species, heretofore unrecognized, and awaiting formal description. Our results add to the growing body of evidence that laelapine mite species are host-specific, rather than pleioxenous, as has been the paradigm developed in the parasitological literature. Finally, we discuss the implications of our results for oryzomyine taxonomy, including the status of Euryoryzomys nitidus and E. russatus. These morphometric studies indicate that the diversity of the laelapine mite fauna associated with oryzomyine rodents has been underestimated.