Luis A. Ruedas

Mammalian Reservoirs of Arenaviruses

Arenaviruses are negative-stranded RNA viruses that have been isolated from several species of mammals in various parts of the world. With two exceptions, these viruses have all been isolated from rodents of the family Muridae — sensu Musser and Carleton (1993). Tacaribe virus was originally isolated from fruit-eating bats of the genus Artibeus, while Sabia virus has no known wild reservoir. Arenavirus infections in their rodent reservoirs are characterized by persistent shedding of infectious virus in the urine (Johnson 1970).

Increased host species diversity and decreased prevalence of Sin Nombre virus.

Prevalence of infection was highest where fewer animal species carried the virus.

Host switch during evolution of a genetically distinct hantavirus in the American shrew mole (Neurotrichus gibbsii)

A genetically distinct hantavirus, designated Oxbow virus (OXBV), was detected in tissues of an American shrew mole (Neurotrichus gibbsii), captured in Gresham, Oregon, in September 2003. Pairwise analysis of full-length S- and M- and partial L-segment nucleotide and amino acid sequences of OXBV indicated low sequence similarity with rodent-borne hantaviruses. Phylogenetic analyses using maximum-likelihood and Bayesian methods, and host-parasite evolutionary comparisons, showed that OXBV and Asama virus, a hantavirus recently identified from the Japanese shrew mole (Urotrichus talpoides), were related to soricine shrew-borne hantaviruses from North America and Eurasia, respectively, suggesting parallel evolution associated with cross-species transmission.

Flow cytometry for monitoring contaminant exposure in black-crowned night-herons

The flow cytometry method (FCM) was employed to determine cellular DNA content of black-crowned night-heron (Nycticorax nycticorax) embryos and 10-day-old chicks collected at sites differing in types of chemical contamination. The coefficient of variation of DNA content (CV) in blood collected from embryos suggested cytogenetic damage at a site in Louisiana known to be contaminated with petroleum. Blood CV from chicks suggested genetic damage at a site in Texas also known to be contaminated with petroleum. Spleen CVs in chicks were significantly lower than respective means from the reference site. The CVs of chick blood and liver and spleen negatively correlated, suggesting recovery of spleen and liver cells after exposure to a clastogenic compound. Thus, the lower CVs may also have been indicative of genetic damage. Based on the findings of this study, FCM is a potential indicator of certain environmental contaminants in black-crowned night-herons.

Epidemiological considerations of rodent community composition in fragmented landscapes in Panama

Abstract We predicted that more-fragmented habitats are associated with lower diversity of small mammals and higher densities of populations of rodents that are hosts of hantaviruses. We compared diversity and distribution of small mammals that are either hosts or nonhosts of hantaviruses in 6 Panamanian national parks and adjacent areas with varying degree of human impacts. We sampled forest, edge, and anthropogenically disturbed habitats. The generalist rodents Oligoryzomys fulvescens (reservoir of Choclo virus) and Zygodontomys brevicauda (reservoir of Calabazo virus) were more abundant in disturbed habitats, especially in smaller and more isolated patches, where population density and diversity of other rodent species was lowest. In contrast, these 2 species had lower abundances in larger forested areas with more nonreservoir species of small mammals. Our results suggest that the change in the natural environment resulting from tropical deforestation is increasing the abundance and distribution of species that are reservoirs for hantaviruses. Therefore, it is likely that forest fragmentation has contributed to recent outbreaks of hantavirus pulmonary syndrome in tropical areas. Conservation of natural resources becomes all the more imperative, not only for protecting fauna and flora but also for human health.

Systematics of Sylvilagus Gray, 1867 (Lagomorpha: Leporidae) from Southwestern North America

A multivariate morphological analysis of 26 cranial, mandibular, and dental characters was carried out on five taxa of cottontails: Sylvilagus floridanus chapmani (J. A. Allen, 1899), S.f. cognatus (Nelson, 1907), S. f. holzneri (Mearns, 1896), S. f. robustus (Bailey, 1905), and S. nuttallii pinetis (J. A. Allen, 1894). Discrete characters of upper P2 and P3 and lower p3 were examined in the above taxa, S. n. grangerii (J. A. Allen, 1895), and S. a. audubonii in the context of cladistic analyses. In the latter series of analyses, particular attention was paid to inter- and intrapopulational variation in the S. f. floridanus (J. A. Allen, 1890) and robustus taxa and in S. audubonii (Baird, 1857). I describe dental variation among holotypes and topotypes of these three taxa. My principal objective was to assess whether or not S. robustus was a subspecies of S. floridanus . An analysis of variance indicated that robustus differed from other taxa in six characters (greatest length of skull, condylobasal length, breadth of rostrum, interbasioccipital length, width of tympanic bullae, and mastoid breadth). Principal component analysis indicated ontogenetic differences between robustus and remaining taxa. Neighbor joining analysis in every case correctly classified each specimen examined to its predetermined taxon. Besides a large difference in size, several discrete differences in cranial and dental morphology separated S. robustus from the parapatric S. f. chapmani and from the nominal subspecies, S. f. floridanus ;, characters based on premolar enamel pattern in particular differentiated between S. f. floridanus and robustus . In phylogenetic analyses of 24 dental characters, S. cognatus , S. robustus , and S. holzneri were successive sister taxa to an unresolved clade consisting of two paraphyletic S. nuttallii “subspecies” and two subspecies of S. floridanus (sensu stricto). I propose that Sylvilagus robustus is a species distinct from S. floridanus and its subspecies, some of which probably also constitute distinct species. These results help clarify biogeographic problems inherent in the genus Sylvilagus under the current taxonomic framework.

Efficacy of Three Types of Live Traps Used for Surveying Small Mammals in the Pacific Northwest

Abstract Capture rates of 3 trap types were compared at 5 sites in and around Portland, Oregon, USA: Sherman traps, custom-made steel-mesh traps, and pitfall traps. Simpson and Shannon diversity indices were calculated for various combinations of trap types and compared for differences. Sherman and mesh traps also were evaluated for mortality rates before and after the use of a rain shield during the rainy winter months. Of the 5 species of small mammals caught in all 3 types of traps, pitfalls were the most effective trap, followed by Sherman traps, with mesh traps a very distant third. Sherman traps significantly outperformed mesh traps overall when compared for larger species that were not contained by pitfall traps. Different combinations of trap types yielded significantly different Simpson and Shannon diversity indices, with pitfalls having the highest measures for small mammals, and a combination of Sherman and pitfall traps having the highest measures when considering both larger and smaller mammals. Use of rain shields with Sherman and mesh traps did not affect mortality rates. However, mortality was affected by trap type, with significantly higher death rates in mesh than Sherman traps.

Serosurvey of Wild Rodents for Hantaviruses in Panama, 2000–2002

Five hundred fifty-six samples representing 24 species of small mammals (two species of marsupials and 22 rodents) were collected in Panama between February 2000 and July 2002. The samples were examined for antibodies to hantaviruses by means of enzyme-linked immunosorbent assay or immunoblot assays. The serologic results indicated that several rodent species might act as hantaviral reservoirs in Panama: Costa Rican pygmy rice rat (Oligoryzomys fulvescens costaricensis), four positive of 72 tested (5.6%); Cherries cane rat (Zygodontomys brevicauda cherriei), five of 108 (4.6%); Mexican deer mouse (Peromyscus mexicanus), one of 22 (5%); Mexican harvest mouse (Reithrodontomys mexicanus), one of seven (14%); Chiriquí harvest mouse (Reithrodontomys creper), one of two (50%); and Sumichrasts harvest mouse (Reithrodontomys sumichrasti), three of four (75%). Hantavirus infection in Peromyscus mexicanus and the three species of Reithrodontomys was caused by Rio Segundo hantavirus, a species of virus not previously reported from Panama. At least three hantaviruses, therefore, are known to infect populations of wild rodents in the country. However, given the total number of animals tested, the role of these rodent species in the epidemiology and epizootiology of hantavirus infections remains unclear.

Phylogenetic relationships of the cuscuses and brushtail possums (Marsupialia : Phalangeridae) using the nuclear gene BRCA1

The family Phalangeridae comprises approximately two dozen extinct and extant species that include the brushtail possums (Trichosurus), scaly-tailed possum (Wyulda) and cuscuses (Phalanger, Strigocuscus, Spilocuscus and Ailurops). Morphological studies have suggested that Ailurops ursinus is the sister taxon to all other phalangerids. Another species of interest is Strigocuscus celebensis, whose morphologically based taxonomic affinity has habitually been with trichosurins. Mitochondrial 12S rRNA results, however, found moderate support for an Ailurops and Strigocuscus celebensis clade and placed A. ursinus and S. celebensis as sister to Phalanger and Spilocuscus. This study uses nuclear sequence data from the breast cancer and ovarian cancer susceptibility gene 1 (BRCA1) to test previous mitochondrial DNA results and uses relaxed molecular clock methods to estimate divergence dates. The results support Ailurops as sister taxon to S. celebensis and this clade as sister to Phalangerini. Relaxed molecular-dating methods suggest a date of 23–29 million years for the split between Trichosurini and the remaining phalangerids and 19–24 million years for the split between Ailurops + Strigocuscus celebensis and Phalangerini. Several vicariant/dispersal events are necessary to explain the geographic distribution of the Phalangeridae and our estimated molecular divergence dates are congruent with previously proposed south-east Asian geological events.

EVOLUTIONARY RELATIONSHIPS AMONG GENERA OF PHALANGERIDAE (METATHERIA: DIPROTODONTIA) INFERRED FROM MITOCHONDRIAL DNA

Abstract We sequenced the 12S rRNA gene of 2 elusive and morphologically plesiomorphic species of phalanger: the small Sulawesi cuscus (Strigocuscus celebensis—Gray, 1858) and the Sulawesi bear cuscus (Ailurops ursinus—Temminck, 1824). The sequences were integrated with previously existing data on the same gene in other species of phalangerids, as well as newly derived data from Wyulda Alexander, 1918. In contrast to current wisdom, we resolve S. celebensis not as a member of the tribe Trichosurini, but rather as a taxon sister to Ailurops in a reconstituted Ailuropinae in turn successively sister to Phalangerinae. Examination of our data supports an evolutionary origin for the family approximately 34 million years ago (mya), in the northwestern region of the Sahul Shelf, the continental mass underlying Australia and New Guinea. The radiation of the most plesiomorphic genera in the family, Trichosurus and Wyulda, is restricted to that region. S. celebensis, resolved as sister to A. ursinus in a clade ingroup to trichosurines, diverged from remaining ingroup lineages between 21.1 and 23.3 mya, a time when Sulawesi was available for colonization and sea currents would have enhanced the colonization potential from the east of Sulawesi and neighboring islands. We recommend Trichosurinae as a subfamilial level entity on par with Ailuropinae and Phalangerinae, circumscription of Trichosurinae to Trichosurus and Wyulda, and removal of Strigocuscus into Ailuropinae, leaving only Phalanger and Spilocuscus in Phalangerinae.