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Marcelo Weksler - One of the best experts on this subject based on the ideXlab platform.
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on the taxonomic status of Oryzomys curasoae mcfarlane and debrot 2001 rodentia cricetidae sigmodontinae with remarks on the phylogenetic relationships of o gorgasi hershkovitz 1971
Caribbean Journal of Science, 2009Co-Authors: Robert S Voss, Marcelo WekslerAbstract:A BSTRACT. — The type material of Oryzomys curasoae McFarlane and Debrot, 2001, an allegedly extinct species from the island of Curacao, Netherlands Antilles, is morphologically indistinguishable from O. gorgasi Hershkovitz, 1971, a Recent mangrove-inhabiting species from mainland Venezuela. A phylogenetic analysis suggests that the latter belongs to the genus Oryzomys in its strictest sense, and that “ curasoae ” is not close to Oecomys (formerly ranked as a subgenus of Oryzomys ) as previously suggested. Evidence that Rattus rattus may now be displacing O. gorgasi from coastal habitats in Venezuela suggests that black rats might have been directly responsible for the extinction of the insular population of O. gorgasi on Curacao. K EYWORDS. — extinct , oryzomyines , rodents , Curacao , Venezuela
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redescription of the enigmatic long tailed rat sigmodontomys aphrastus cricetidae sigmodontinae with comments on taxonomy and natural history
Proceedings of the Biological Society of Washington, 2007Co-Authors: Christy M Mccain, Robert M Timm, Marcelo WekslerAbstract:ABSTRACT Sigmodontomys aphrastus, the long-tailed rat, is an exceedingly rare rodent species from montane regions of Central and South America of which very little is known ecologically or systematically. It has been variously placed in the genera Oryzomys, Nectomys, and Sigmodontomys based on the five previously known specimens. Two new individuals were collected in northwestern Costa Rica's Cordillera de Tilaran. These new specimens and the other five known specimens are used to redescribe the species, detail measurements of external and cranial morphology, and compare S. aphrastus to similarly appearing sympatric species (Nephelomys albigularis and N. devius) and proposed closely related species (Sigmodontomys alfari, Mindomys hammondi, and Melanomys caliginosus). New ecological data is presented and the general knowledge of its natural history is summarized. The phylogenetic relatedness of S. aphrastus with purported sister taxa remains unresolved until combined molecular and morphological analyses ar...
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ten new genera of oryzomyine rodents cricetidae sigmodontinae
American Museum Novitates, 2006Co-Authors: Marcelo Weksler, Alexandre Reis Percequillo, Robert S VossAbstract:Abstract In order to achieve a monophyletic classification of oryzomyine rodents, 10 new genera are described for species or species groups previously referred to the polyphyletic genus Oryzomys. The following names are proposed: Aegialomys, n.gen. (for the “xanthaeolus group” of authors); Cerradomys, n.gen. (for the “subflavus group”); EremOryzomys, n.gen. (for polius); EuryOryzomys, n.gen. (for the “nitidus group”); Hylaeamys, n.gen. (for the “megacephalus group”); Mindomys, n.gen. (for hammondi); Nephelomys, n.gen. (for the “albigularis group”); OreOryzomys, n.gen. (for balneator); Sooretamys, n.gen. (for angouya); and Transandinomys, n.gen. (for bolivaris and talamancae). All of the new genera thus constituted are morphologically diagnosable and have distinct ecogeographic distributions. Pending revisionary work that is currently in progress by other researchers, six species belonging to the “alfaroi group” (herein construed as including alfaroi, chapmani, melanotis, rhabdops, rostratus, and saturatio...
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phylogeny of neotropical oryzomyine rodents muridae sigmodontinae based on the nuclear irbp exon
Molecular Phylogenetics and Evolution, 2003Co-Authors: Marcelo WekslerAbstract:Sigmodontine rodents are the most diverse family-level mammalian clade in the Neotropical region, with about 70 genera and 320 recognized species. Partial sequences (1266 bp) from the first exon of the nuclear gene encoding the Interphotoreceptor Retinoid Binding Protein (IRBP) were used to infer the phylogenetic relationships among 44 species representing all 16 currently recognized genera of the largest sigmodontine tribe, the Oryzomyini. Monophyly of the tribe was assessed relative to 15 non-oryzomyine sigmodontine taxa representing all major sigmodontine lineages. Twelve taxa from seven muroid subfamilies were used as outgroups. The resulting matrix included 71 taxa and 386 parsimony-informative characters. Phylogenetic analysis of this matrix resulted in 16 equally parsimonious cladograms, which contained the following well-supported groups: (i) a monophyletic Oryzomyini, (ii) a clade containing all oryzomyines except Scolomys and Zygodontomys, (iii) a clade containing Oecomys, Handleyomys, and several species of forest-dwelling Oryzomys, and (iv) a clade containing the remaining oryzomyine taxa. The last clade is composed of two large subclades, each with lower nodal support, containing the following taxa: (i) MicrOryzomys, OligOryzomys, Neacomys, and Oryzomys balneator; (ii) Holochilus, Lundomys, PseudOryzomys, Nectomys, Amphinectomys, Sigmodontomys, and several species of open-vegetation or semiaquatic Oryzomys. Regarding relationships among non-oryzomyine taxa, sigmodontines, neotomines, and tylomyines do not form a monophyletic group; a clade containing Rheomys and Sigmodon is basal relative to all other sigmodontines; and the remaining sigmodontines are grouped in three clades: the first containing Thomasomyini, Akodontini, and Reithrodon; the second containing Abrothrichini, and Phyllotini, plus Wiedomys, Juliomys, Irenomys, and Delomys; and the third containing the oryzomyines. No conflict is observed between IRBP results and previous robust hypotheses from mitochondrial data, while a single case of incongruence is present between the IRBP topology and robust hypothesis from morphological studies.
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a new species of Oryzomys rodentia sigmondontinae from southeast brazil with comments on the classification of the o capito species group
Zoological Journal of the Linnean Society, 1999Co-Authors: Marcelo Weksler, Lena Geise, Rui CerqueiraAbstract:Abstract A new species of Oryzomys is described for the coastal Atlantic region of Brazil. Oryzomys seuanezi sp. nov. was collected in eight localities throughout the Atlantic Forest from the south of the State of Bahia to the State of the Rio de Janeiro, mostly in lowlands. Belonging to the O. capito species group, O. seuanezi differs from the other species by its karyotype equal 2 n =48, FN=60. A morphometric analysis of populations of some species of the group indicates a split between the samples of the Atlantic Forest and those from O. capito from Cerrados and Amazon in relation to size, the former being larger. The population from Amazonia and from the Cerrados belongs to the same species, O. goeldii being a synonym of O. capito. O. seuanezi sp. nov. is the sister taxon of O. oniscus , forming an Atlantic Forest clade. The close relationship of this group and some Peruvian populations of O. capito , probably a new species, is postulated.
Milton H Stetson - One of the best experts on this subject based on the ideXlab platform.
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pineal gland and melatonin affect testicular status in the adult marsh rice rat Oryzomys palustris
General and Comparative Endocrinology, 1995Co-Authors: Kent E Edmonds, Milton H StetsonAbstract:The effects of the presence or absence of the pineal gland and of melatonin administration were examined on testicular maintenance, regression, and recrudescence in adult male rice rats. Pinealectomy at the beginning of the study caused significant testicular regression in animals housed on both long (16L:8D) and short (12L:12D) photoperiods (Experiment 1). Sham-operated males maintained testicular weight on 16L:8D and underwent testicular regression on 12L:12D. The magnitude of testicular regression in pinealectomized animals was reduced relative to that of sham-operated animals housed on a short photoperiod and occurred on a different time course. Animals pinealectomized after testicular regression had occurred on 12L:12D demonstrated delayed photostimulated testicular recrudescence when housed on 16L:8D, while spontaneous testicular recrudescence was unaffected in animals maintained on 12L:12D (Experiment 2). Administration of melatonin via subcutaneous implants at the beginning of the study (Experiment 3) produced similar effects on testicular function attributed to pinealectomy in Experiment 1. Finally, melatonin implants administered after the testes regressed on 12L:12D delayed both photostimulated and spontaneous testicular recrudescence in animals housed on long or short photoperiods, respectively (Experiment 4). These results suggest a role for both the pineal gland and melatonin at various stages of the annual reproductive cycle of the male rice rat.
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effects of photoperiod on pineal melatonin in the marsh rice rat Oryzomys palustris
Journal of Pineal Research, 1995Co-Authors: Kent E Edmonds, Mark D Rollag, Milton H StetsonAbstract:Pineal melatonin content was examined under four different photoperiods (10L:14D, 12L:12D, 14L:10D, and 16L:8D) in adult female rice rats (Experiment 1). Pineal melatonin was basal during the light and increased beginning 1 hr after lights off. Within 2 hr after lights off, melatonin increased to levels that were maintained throughout the dark period. In all but one photoperiod (10L:14D), melatonin remained elevated prior to light onset and decreased markedly within one hour after lights on. In addition, the duration of pineal melatonin was inversely related to the length of the photoperiod. In Experiment 2, the time course of pineal melatonin content on 16L:8D was examined every 20 min during the first hour after lights off and the first hour after lights on. Melatonin content increased gradually during the first hour and decreased markedly within 20 min after lights on. These data show that pineal melatonin in female rice rats is regulated by photoperiod.
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photoperiod and melatonin affect testicular growth in the marsh rice rat Oryzomys palustris
Journal of Pineal Research, 1994Co-Authors: Kent E Edmonds, Milton H StetsonAbstract:Edmonds KE, Stetson MH. Photoperiod and melatonin affect testicular growth in the marsh rice rat (Orgzonys palustris). J. Pineal Res. 1994: 17: 86–93. ©Munksgaard 1994 Abstract Reproduction in rice rats is subject to photoperiodic control and the pineal gland mediates this effect. We examined the effects of the pineal gland hormone melatonin on testicular weight when administered via implants, injections, and infusions. Testicular weight was modified by photoperiod and the size of the melatonin implant. Twenty-millimeter implants suppressed testicular weight in rice rats housed on 12- and 16-hr photoperiods, while those housed on a 14-hr photoperiod were more sensitive to melatonin; in these animals 10- and 20-mm implants inhibited testicular weight. Melatonin implants also prevented rice rats from responding to a change in photoperiod with the appropriate alteration of testicular growth. Melatonin injections inhibited testicular growth when administered before lights out on LD 14: 10, but not on LD 16: 8. Morning injections had no effect on either photoperiod. Finally, 12-hr duration melatonin infusions inhibited testicular growth in pinealectomized rice rats on LD 16: 8, while 6-hr duration infusions were without effect. These data show that the pineal, through the secretion of melatonin, is a phototransducing organ intimately involved in testicular growth in rice rats.
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the rice rat Oryzomys palustris in a delaware salt marsh annual reproductive cycle
Canadian Journal of Zoology, 1993Co-Authors: Kent E Edmonds, Milton H StetsonAbstract:A population of the rice rat Oryzomys palustris inhabiting the Canary Creek salt marsh in Lewes, Delaware, was sampled on a monthly basis from September 1988 to December 1990. Males were assigned t...
Kent E Edmonds - One of the best experts on this subject based on the ideXlab platform.
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pineal gland and melatonin affect testicular status in the adult marsh rice rat Oryzomys palustris
General and Comparative Endocrinology, 1995Co-Authors: Kent E Edmonds, Milton H StetsonAbstract:The effects of the presence or absence of the pineal gland and of melatonin administration were examined on testicular maintenance, regression, and recrudescence in adult male rice rats. Pinealectomy at the beginning of the study caused significant testicular regression in animals housed on both long (16L:8D) and short (12L:12D) photoperiods (Experiment 1). Sham-operated males maintained testicular weight on 16L:8D and underwent testicular regression on 12L:12D. The magnitude of testicular regression in pinealectomized animals was reduced relative to that of sham-operated animals housed on a short photoperiod and occurred on a different time course. Animals pinealectomized after testicular regression had occurred on 12L:12D demonstrated delayed photostimulated testicular recrudescence when housed on 16L:8D, while spontaneous testicular recrudescence was unaffected in animals maintained on 12L:12D (Experiment 2). Administration of melatonin via subcutaneous implants at the beginning of the study (Experiment 3) produced similar effects on testicular function attributed to pinealectomy in Experiment 1. Finally, melatonin implants administered after the testes regressed on 12L:12D delayed both photostimulated and spontaneous testicular recrudescence in animals housed on long or short photoperiods, respectively (Experiment 4). These results suggest a role for both the pineal gland and melatonin at various stages of the annual reproductive cycle of the male rice rat.
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effects of photoperiod on pineal melatonin in the marsh rice rat Oryzomys palustris
Journal of Pineal Research, 1995Co-Authors: Kent E Edmonds, Mark D Rollag, Milton H StetsonAbstract:Pineal melatonin content was examined under four different photoperiods (10L:14D, 12L:12D, 14L:10D, and 16L:8D) in adult female rice rats (Experiment 1). Pineal melatonin was basal during the light and increased beginning 1 hr after lights off. Within 2 hr after lights off, melatonin increased to levels that were maintained throughout the dark period. In all but one photoperiod (10L:14D), melatonin remained elevated prior to light onset and decreased markedly within one hour after lights on. In addition, the duration of pineal melatonin was inversely related to the length of the photoperiod. In Experiment 2, the time course of pineal melatonin content on 16L:8D was examined every 20 min during the first hour after lights off and the first hour after lights on. Melatonin content increased gradually during the first hour and decreased markedly within 20 min after lights on. These data show that pineal melatonin in female rice rats is regulated by photoperiod.
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photoperiod and melatonin affect testicular growth in the marsh rice rat Oryzomys palustris
Journal of Pineal Research, 1994Co-Authors: Kent E Edmonds, Milton H StetsonAbstract:Edmonds KE, Stetson MH. Photoperiod and melatonin affect testicular growth in the marsh rice rat (Orgzonys palustris). J. Pineal Res. 1994: 17: 86–93. ©Munksgaard 1994 Abstract Reproduction in rice rats is subject to photoperiodic control and the pineal gland mediates this effect. We examined the effects of the pineal gland hormone melatonin on testicular weight when administered via implants, injections, and infusions. Testicular weight was modified by photoperiod and the size of the melatonin implant. Twenty-millimeter implants suppressed testicular weight in rice rats housed on 12- and 16-hr photoperiods, while those housed on a 14-hr photoperiod were more sensitive to melatonin; in these animals 10- and 20-mm implants inhibited testicular weight. Melatonin implants also prevented rice rats from responding to a change in photoperiod with the appropriate alteration of testicular growth. Melatonin injections inhibited testicular growth when administered before lights out on LD 14: 10, but not on LD 16: 8. Morning injections had no effect on either photoperiod. Finally, 12-hr duration melatonin infusions inhibited testicular growth in pinealectomized rice rats on LD 16: 8, while 6-hr duration infusions were without effect. These data show that the pineal, through the secretion of melatonin, is a phototransducing organ intimately involved in testicular growth in rice rats.
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the rice rat Oryzomys palustris in a delaware salt marsh annual reproductive cycle
Canadian Journal of Zoology, 1993Co-Authors: Kent E Edmonds, Milton H StetsonAbstract:A population of the rice rat Oryzomys palustris inhabiting the Canary Creek salt marsh in Lewes, Delaware, was sampled on a monthly basis from September 1988 to December 1990. Males were assigned t...
Charles F Fulhorst - One of the best experts on this subject based on the ideXlab platform.
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catacamas virus a hantaviral species naturally associated with Oryzomys couesi coues Oryzomys in honduras
American Journal of Tropical Medicine and Hygiene, 2006Co-Authors: Mary Louise Milazzo, Maria N B Cajimat, Delton J Hanson, Robert D Bradley, Miguel Quintana, Catalina Sherman, Reina Teresa Velasquez, Charles F FulhorstAbstract:The primary objective of this study was to extend our knowledge of the geographical distribution, genetic diversity, and natural host associations of the hantaviruses indigenous to North America. Antibody to a hantavirus was found in 5 (20.8%) of 24 Coues' Oryzomys (Oryzomys couesi) and none of 41 other rodents captured near the town of Catacamas in eastern Honduras, and a hantavirus was isolated from one of the antibody-positive Coues' Oryzomys. Analyses of nucleotide and amino acid sequence data indicated that the viral isolate is a strain of a novel hantaviral species (proposed species name "Catacamas virus") that is phylogenetically most closely related to Bayou virus, a hantaviral species that is principally associated with Oryzomys palustris (marsh Oryzomys) in the southeastern United States. Catacamas virus is the first evidence for the occurrence of a hantaviral species in Honduras and the first evidence that a hantaviral species is naturally associated with an Oryzomys species other than O. palustris.
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isolation characterization and geographic distribution of cano delgadito virus a newly discovered south american hantavirus family bunyaviridae
Virus Research, 1997Co-Authors: Charles F Fulhorst, Nuris De Manzione, Thomas G. Ksiazek, Martha C Monroe, Rosa Alba Salas, Gloria Duno, Antonio Utrera, Stuart T Nichol, Duilia Tovar, Robert B. TeshAbstract:Abstract Rodents collected from the Venezuelan llanos (plains) during field studies of viral hemorrhagic fever were tested for evidence of hantavirus infection. Hantavirus antibody was found in one (7.7%) of 13 Oryzomys bicolor , one (3.4%) of 29 Rattus rattus , 10 (6.0%) of 166 Sigmodon alstoni and one (2.2%) of 45 Zygodontomys brevicauda . Hantavirus-specific RNA was detected in lung tissues from four antibody-positive rodents: two S. alstoni from Portuguesa State and one S. alstoni each from Cojedes and Barinas States. A hantavirus isolate (herein identified as VHV-574) was recovered from lung tissue from a hantavirus RNA-positive S. Alstoni collected from Portuguesa State. The results of serological tests and analyses of small and medium RNA segment nucleotide sequence data indicated that VHV-574 represents a novel hantavirus (proposed name ‘Cano Delgadito’) that is distinct from all previously characterized hantaviruses. The results of analyses of nucleotide sequence data from the four hantavirus RNA-positive S. alstoni suggested that Cano Delgadito virus is widely distributed in the Venezuelan llanos .
Eric C Hellgren - One of the best experts on this subject based on the ideXlab platform.
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comparing permeability of matrix cover types for the marsh rice rat Oryzomys palustris
Landscape Ecology, 2015Co-Authors: Scott A Cooney, Eric M Schauber, Eric C HellgrenAbstract:Matrix land cover types differ in permeability to animals moving between habitat patches, and animals may actually move faster across less-suitable areas. Marsh rice rats are wetland specialists whose dispersal crosses upland matrix. Our objectives were to (1) compare matrix permeability for the marsh rice rat among upland cover types, (2) compare permeability within versus outside perceptual range of the wetland, and (3) explore intrinsic and extrinsic features influencing matrix use and permeability. We quantified permeability of grassland, crop field, and forest to the marsh rice rat during 2011–2012, by marking rats in wetlands and estimating the slope of capture rate versus distance (0–95 m) into the matrix. We also compared permeability within (0–15 m) and beyond the perceptual range of rice rats, and tested whether age, sex, time, water depth, rice rat abundance, and vegetation density influenced matrix use and permeability. Permeability was greater for soybean fields than grassland or forest but did not appear to differ within versus beyond rice rats’ perceptual range. Matrix capture rates were higher early in the study and in times and locations with thick ground vegetation and high rice rat abundance in the wetlands. Rice rats captured in the matrix were younger than those in wetland patches. Our findings expand known matrix use by marsh rice rats, and support permeability being high in matrix types dissimilar to suitable habitat. Studying individual movements will help identify mechanisms underlying enhanced permeability in crop fields.
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habitat associations of the marsh rice rat Oryzomys palustris in freshwater wetlands of southern illinois
Journal of Mammalogy, 2011Co-Authors: Bryan W Eubanks, Eric C Hellgren, Jack R Nawrot, Robert D BluettAbstract:The marsh rice rat (Oryzomys palustris) is a semiaquatic rodent occurring in wetland habitats throughout the southeastern United States and along the Atlantic Coast. A lack of understanding of its ecology and distribution in inland parts of its range limits our ability to assess the species’ status and needs. We trapped rice rats at random and previously occupied, wetland-dominated sites in 5 southern Illinois watersheds during 2007–2009 to determine key variables affecting habitat occupancy by the species. We detected rice rats within 3 of 5 watersheds, 16 of 48 sites, and at 5 new locations. Most rice rats were captured in permanent or semipermanent emergent wetlands (n 5 89; 46.3% of total captures) or roadside ditches in wetland patches (n 5 73; 38.0%). Habitat associations determined using logistic regression and occupancy modeling provided similar results. Percent herbaceous cover and percent visual obstruction (0.0–0.5 m) were the most important microhabitat variables positively influencing rice rat occurrence. In areas surrounding wetlands, the proportion composed of upland grass was the best predictive variable of rice rat occurrence among landcover models. Estimates of daily detection probability were high (0.44–0.87). The likelihood of occupancy increased with the proportion of upland grass cover adjacent to wetland complex and percent herbaceous cover at the microhabitat scale. Inland metapopulations of rice rats are clustered throughout the southeastern United States in appropriate wetland complexes. Construction, restoration, and protection of emergent wetlands, and consideration of connectivity and adjacent grasslands, should benefit rice rat populations.