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PubMed2005

Ecomorphological diversification among South American spiny rats (Rodentia; Echimyidae): a phylogenetic and chronological approach.

The phylogeny of South American spiny rats (Rodentia; Echimyidae) was studied using the exon 28 of the von Willebrand Factor nuclear gene (vWF). Sequences were analysed separately and in combination with a mitochondrial dataset (cyt b, 12S and 16S rRNAs) used in previous publications. The basal polytomy of echimyids was partially resolved and unexpected intergeneric clades were recovered. Thus, the intimate nested position of Myocastor within echimyids is evidenced. A well-supported clade is identified, including all the arboreal genera, and a group formed by Myocastor, Thrichomys, and Proechimys+Hoplomys. The clustering of Euryzygomatomys+Clyomys with Trinomys is also suggested. On the opposite, the phylogenetic position of Capromys as well as the relationships among arboreal genera remain unclear. Molecular divergence times were estimated using a Bayesian relaxed molecular clock and suggest a Middle Miocene origin for most of modern genera. The ecomorphological diversification of echimyids is discussed in the light of these new results and past environmental modifications in South America.

Animals↗

PubMed1998

Chromatographic and immunological identification of GnRH (gonadotropin-releasing hormone) variants. Occurrence of mammalian and a salmon-like GnRH in the forebrain of an eutherian mammal: Hydrochaeris hydrochaeris (Mammalia, Rodentia).

The molecular variants of Gonadotropin releasing hormone (GnRH) in brain extracts of the eutherian mammal Hydrochaeris hydrochaeris (Mammalia, Rodentia) were characterized. An indirect method combining reverse-phase high-performance liquid chromatography (RP-HPLC) and radioimmunoassay (RIA) with different antisera was used. Two different forebrain regions (olfactory bulbs and preoptic-hypothalamic region) were analyzed. Characterization of RP-HPLC fractions from preoptic-hypothalamic extracts with three different RIA systems revealed two immunoreactive GnRH (ir-GnRH) peaks coeluting with mammalian GnRH (mGnRH) and salmon GnRH (sGnRH) synthetic standards. These results were additionally supported by serial dilution studies with specific antisera. Similar results were obtained from olfactory bulb extracts with the same methodology. However, a third ir-GnRH peak in a similar position to that of chicken GnRH II (cIIGnRH) synthetic standard was revealed. As far as we know, this is the first report showing chromatographic and immunological evidences for the presence of a second GnRH variant in the forebrain of an eutherian mammal.

Animals↗

PubMedDate not supplied

[Pseudophysaloptera kahmanni n. sp. (Nematoda: Physalopteridae), a parasite of the stomach of the dormouse Eliomys quercinus ophiusae Thomas, 1925 (Rodentia: Gliridae) in Formentera (Balearic Islands) (author's transl)].

A new Nematode Physalopteridae, Pseudophysaloptera kahmanni n. sp., parasitizing the stomach of the dormouse Eliomys quercinus ophiusae Thomas, 1925 (Rodentia: Gliridae) in Formentera (Balearic Islands, Spain) is described. It is the first and only species of the genus Pseudophysaloptera Baylis, 1934 to be known parasitizing Rodents in the nature.

Animals↗

PubMed1982

[Kahmannia eliomydis n. gen., n. sp. (Nematoda: Heteroxynematidae), an intestinal parasite of Eliomys quercinus (Linnaeus, 1766)(Rodentia: Gliridae) in Minorca (Balearic Islands)].

Description of Kahmannia eliomydis n. gen., n. sp., an Heretoxynematid Nematode parasitizing the intestine of the Garden dormouse Eliomys quercinus (Linnaeus, 1766) (Rodentia: Gliridae) in the island of Minorca (Balearies). Kahmannia n. gen. is proposed to include in the Heteroxynematinae the intestinal parasites from Rodents characterized by: oral opening circular without lips; buccal capsule triangular with small oesophageal teeth; oesophagus elongated with spherical bulb with strongly developed valves, clearly individualized and separated by a well-defined oesophageal isthmus; cephalic vesicle present, with sinuous peribuccal ornamentation forming slender crown with eight digitations; cuticular striations marked; lateral and cervical alae absent; male without caudal lateral alae, without precloacal cuticular ornamentation on ventral surface and without gubernaculum, but with single spicule; and thin-shelled eggs without operculum. It is the first Nematode Oxyuroidea known parasitizing Rodents Glirimorpha.

Animals↗

PubMed1977

Similarity of satilite DNA properties in the order Rodentia.

We have characterized satellite DNAs from 9 species of kangaroo rat (Dipodomys) and have shown that the HS-alpha and HS-beta satellites, where present, are nearly identical in all species as to melting transition midpoint (Tm), and density in neutral CsCl, alkaline CsCl, and Cs(2)SO(4)-Ag(+) gradients. However, the MS satellites exist in two internally similar classes. The satellite DNAs from three other rodents were characterized (densities listed are in neutral CsCl). The pocket gopher, Thomomysbottae, contains Th-alpha (1.713 g/ml) and Th-beta (1.703 g/ml). The guinea pig (Caviaporcellus) contains Ca-alpha, Ca-beta and Ca-gamma at densities of 1.706 g/ml, 1.704 g/ml and 1.704 g/ml, respectively. The antelope ground squirrel (Ammospermophilusharrisi) contains Am-alpha, 1.708 g/ml, Am-beta, 1.717 g/ml, and Am-gamma, 1.707 g/ml. The physical and chemical properties of the alpha-satellites from the above four rodents representing four different families in two suborders of Rodentia were compared. They show nearly identical Tm, nucleoside composition of single strands, and single strand densities in alkaline CsCl. Similar comparisons on the second or third satellite DNAs from these rodents also indicate a close relationship to each other. Thus the high degree of similarity of satellite sequences found in such a diverse group of rodents suggests a cellular function that is subject to natural selection, and implies that these sequences have been conserved over a considerable span of evolutionary time since the divergence of these rodents about 50 million years ago.

Animals↗

PubMed1995

Monophyly of the order Rodentia inferred from mitochondrial DNA sequences of the genes for 12S rRNA, 16S rRNA, and tRNA-valine.

A recent analysis of amino acid sequence data (Graur et al.) suggested that the mammalian order Rodentia is polyphyletic, in contrast to most morphological data, which support rodent monophyly. At issue is whether the hystricognath rodents, such as the guinea pig, represent an independent evolutionary lineage within mammals, separate from the sciurognath rodents. To resolve this problem, we sequenced a region (2,645 bp) of the mitochondrial genome of the guinea pig containing the complete 12S ribosomal RNA, 16S ribosomal RNA, and transfer RNA(VAL) genes for comparison with the available sciurognath and other mammalian sequences. Several methods of analysis and statistical tests of the data all show strong support for rodent monophyly (91%-98% bootstrap probability, or BP). Calibration with the mammalian fossil record suggests a Cretaceous date (107 mya) for the divergence of sciurognaths and hystricognaths. An older date (38 mya) for the controversial Mus-Rattus divergence also is supported by these data. Our neighbor-joining analyses of all available sequence data (25 genes) confirm that some individual genes support rodent polyphyly but that tandem analysis of all data does not. We propose that the conflicting results are due to several compounding factors. The unique biochemical properties of some hystricognath metabolic proteins, largely responsible for generating this controversy, may have a single explanation: a cascade effect resulting from inactivation of the zinc-binding abilities of insulin. After excluding six genes possibly affected by insulin inactivation, analyses of all available sequence data (7,117 nucleotide sites, 3,099 amino acid sites) resulted in strong support for rodent monophyly (94% BP for DNA sequences, 90% for protein sequences), which lends support to the insulin-cascade hypothesis.

Animals↗

PubMed2003

Molecular systematics of dormice (Rodentia: Gliridae) and the radiation of Graphiurus in Africa.

The phylogenetic relationships among the Gliridae (order Rodentia) were assessed using 3430 nucleotides derived from three nuclear fragments (beta-spectrin non-erythrocytic 1, thyrotropin and lecithin cholesterol acyl transferase) and one mitochondrial gene (12S rRNA). We included 14 glirid species, representative of seven genera of the three recognized subfamilies (Graphiurinae, Glirinae and Leithiinae) in our analysis. The molecular data identified three evolutionary lineages that broadly correspond to the three extant subfamilies. However, the data suggest that the genus Muscardinus, previously regarded as falling within the Glirinae, should be included in the Leithiinae. Molecular dating using local molecular clocks and partitioned datasets allowed an estimate of the timing of cladogenesis within the glirids. Graphiurus probably diverged early in the group's evolution (40-50 Myr ago) and the three subfamilies diverged contemporaneously, probably in Europe. The radiation within Graphiurus is more recent, with the colonization of Africa by this lineage estimated at ca. 8-10 Myr ago.

Africa↗

PubMed1992

An intriguing Y chromosome in Heteromys anomalus (Rodentia, Heteromyidae).

The mitotic chromosomes of the pocket mouse Heteromys anomalus (Rodentia, Heteromyidae) from Venezuela were analyzed by means of conventional staining and various banding techniques. The karyotype of this species is distinguished by a Y chromosome with exceptional banding properties. The very large heterochromatic Y long arm shows a remarkable bright quinacrine fluorescence, but only moderate or dull fluorescence when labeled with other AT base pair-specific fluorochromes. The implications of these findings are discussed.

Animals↗

PubMed1999

Autosomal and sex chromosomal polymorphisms with multiple rearrangements and a new karyotype in the genus Rhipidomys (Sigmodontinae, Rodentia).

Two diploid numbers and five karyomorphs were found in ten specimens of Rhipidomys (Sigmodontinae, Rodentia) from three states in Brazil: 2n = 50 from Amazonas, and 2n = 44 from Mato Grosso and Bahia. CBG, GTG, and RBG-banding and Ag-NOR analyses were performed, as well as fluorescence in situ: hybridization with (T2AG3)7 probes. The new diploid number of 2n = 50 was associated with two different fundamental numbers (FN = 71 and 72) as a result of pericentric inversions and addition/deletion of constitutive heterochromatin. The samples from two localities (Aripuanã and Vila Rica) in the state of Mato Grosso shared 2n = 44 and FN = 52, but their karyotypes differed because of pericentric inversions. Although the single specimen from Bahia had the same diploid number as the samples from Mato Grosso, its karyotype and FN were completely distinctive. Karyological comparison of GTG-banding patterns revealed total homology between the karyotypes of the specimens from Bahia and Mato Grosso, implying the occurrence of 14 autosomal pericentric inversions. Homologies between ten of the autosomes in the karyotypes with 2n = 50 (FN = 72) and 2n = 44 (from Vila Rica, MT) were demonstrated. The differentiation between 2n = 44 and 2n = 50 involved five pericentric inversions, addition/deletion of constitutive heterochromatin in both autosomes and sex chromosomes, at least one Robertsonian rearrangement and other not detected rearrangements. Despite the remarkable number of rearrangements, interstitial telomeric sites (ITS) were not detected. Sex chromosomes also exhibited polymorphism in size and morphology.

Animals↗

PubMed2001

Pericentric inversion in natural populations of Oligoryzomys nigripes (Rodentia: Sigmodontinae).

We analysed polymorphism for pericentric inversion in chromosome 3 of Oligoryzomys nigripes (Rodentia: Sigmodontinae) in several populations in Brazil and examined the meiotic behaviour of this chromosome in heterozygotes. We observed an orderly pairing of all chromosomes at pachytene in heterozygotes for the inverted chromosome 3. No indication of meiotic arrest and germ-cell death was found. Electron microscopy of synaptonemal complexes and conventional meiotic analysis indicated strictly nonhomologous synapsis and crossing-over suppression in the inverted region in the heterozygotes, which prevent the formation of unbalanced gametes. Thus, the pericentric inversion in chromosome 3 does not apparently result in any selective disadvantages in heterozygous carriers. In the majority of the populations studied, the frequencies of acrocentric homozygotes, metacentric homozygotes, and heterozygotes were in Hardy-Weinberg equilibrium. However, in some populations, we detected an excess of heterozygotes and a deficiency of acrocentric homozygotes.

Animals↗

PubMed2006

Reproductive isolation due to the genetic incompatibilities between Thrichomys pachyurus and two subspecies of Thrichomys apereoides (Rodentia, Echimyidae).

We tested intrinsic reproductive isolation between 3 taxa of the South American caviomorph rodent Thrichomys (Rodentia, Echimyidae): T. pachyurus, T. apereoides subsp. apereoides and T. apereoides subsp. laurentius. They were mated in captivity and produced viable progeny. Some F1 hybrid females were fertile, whereas all F1 males were sterile. Histological examination revealed meiotic arrest at the primary spermatocyte stage. No sperm was detected in testes or epididymes. Electron microscopic analysis of surface spread synaptonemal complexes revealed a complete failure of chromosome pairing in F1 hybrids of T. pachyurus with T. apereoides subsp. laurentius and T. apereoides subsp. apereoides. In the male hybrids between T. apereoides subsp. apereoides and T. apereoides subsp. laurentius, meiosis did not proceed beyond diplotene, although all of the chromosomes, including heteromorphic ones, paired in an orderly fashion. Backcross males with homomorphic karyotypes showed segregation in meiosis progression. This indicates that male hybrid sterility is due to genetic, but not chromosomal, incompatibility of the parental taxa.

Animals↗

PubMed2002

Chromosomal characterization of Arvicanthis species (Rodentia, Murinae) from western and central Africa: implications for taxonomy.

A chromosome study of unstriped grass rats of the genus Arvicanthis (Rodentia, Murinae) in western and central Africa is presented. The observations extend the data available to 242 specimens from 59 localities. All individuals karyotyped belong to four karyotypic forms, or cytotypes, earlier described as ANI-1, ANI-2, ANI-3, and ANI-4 and are presumed to correspond to four distinct species. In order to provide diagnostic characters for these western and one central African Arvicanthis species, we standardized the chromosomal data available and developed a G- and C-banded chromosome nomenclature that allows easy species identification. Each form is characterized by a distinct geographical distribution, roughly following the biogeographical domains of western Africa, although their precise limits remain to be assessed. The sole area of sympatry detected is the region of the inner delta of the Niger River, where both ANI-1 and ANI-3 can be found. It is proposed that the three western African species ANI-1, ANI-3, and ANI-4 be renamed as A. niloticus, A. ansorgei, and A. rufinus, respectively.

Animals↗

PubMed1993

Karyotype of the giant mole-rat, Cryptomys mechowi (Rodentia, Bathyergidae).

The karyotype of the giant mole-rat, Cryptomys mechowi (Rodentia, Bathyergidae), from Zambia was investigated in one male and one female by means of G-, C-, and AgNOR-banding techniques. The diploid chromosomal set consisted of 40 biarmed chromosomes (2n = 40, NF = 80). A pair of autosomes in the male and the X chromosomes in the female were heteromorphic. The sex chromosomes were unusually large.

Animals↗

PubMed2003

Retinal spectral sensitivity, fur coloration, and urine reflectance in the genus octodon (rodentia): implications for visual ecology.

PURPOSE: To determine the eye's spectral sensitivity in three species of the genus Octodon (order Rodentia; infraorder Caviomorpha), O. degus, O. bridgesi, and O. lunatus, as well as the spectral properties of the animals' fur and urine and of objects in their habitat. The genus is endemic in Chile and contains species with different habitats and circadian patterns (diurnal versus nocturnal). METHODS: The electroretinogram (ERG) was used to record scotopic and photopic spectral sensitivity. The reflectance of ventral and dorsal body parts, urine, and other objects from the natural microhabitat were measured with a fiber-optic spectrometer. RESULTS: In scotopic conditions, the maxima of sensitivity (lambda(max)) were at 505.7 +/- 7.7 nm in O. degus, 501 +/- 7.4 nm in O. bridgesi, and 510.1 +/- 7.4 nm in O. lunatus, representing the rod mechanism. In photopic conditions, only the diurnal species O. degus (common degu) was studied. The degu's photopic sensitivity had a lambda(max) at 500.6 +/- 1.2 nm and contained two cone mechanisms with lambda(max) at 500 nm (green, medium-wavelength-sensitive [M] cones) and approximately 360 nm (ultraviolet, short-wavelength-sensitive [S] cones). In all three Octodon species, dorsal body parts were more cryptically colored than ventral ones, and ventral body parts had a significant UV reflectance. The fresh urine of O. degus, used for scent marking in various behavioral patterns, was also high in UV reflectance. CONCLUSIONS: It is suggested that territorial urine marks are visual as well as pheromone cues for UV-sensitive species and hence may have favored the evolution of UV-cones in rodents.

Animal Communication↗

PubMed1990

The primary structures of gundi (Ctenodactylus gundi, Rodentia) hemoglobin and myoglobin.

The primary structures of the alpha- and beta-chains of hemoglobin and myoglobin from the gundi (Ctenodactylus gundi, Rodentia) are presented. The sequences were determined after enzymatic and chemical cleavages of the polypeptide chains and by sequencing of the peptides mainly by automated sequence analysis. The sequences of gundi hemoglobin chains and of myoglobin are compared with those of other rodents.

Amino Acid Sequence↗

PubMedDate not supplied

[Cutaneous leishmaniasis in Amazonia: isolation of Leishmania (Viannia) lainsoni from the rodent Agouti paca (Rodentia: Dasyproctidae), in the state of Pará, Brazil].

The isolation of Leishmania (V.) lainsoni is recorded for the first time from a wild animal, the rodent Agouti paca (Rodentia: Dasyproctidae), from Pará State, north Brazil. Isolates of the parasite were made from apparently normal skin of 3 specimens of this rodent captured on the Island of Tocantins, in the municipality of Tucuruí, an area subsequently flooded in the formation of the lake associated with the Tucuruí hydroelectric dam. No isolations were made from the viscera. Identification of the parasite was in each case based on morphology of the amastigotes and promastigotes, behavior of the organism in hamsters, isoenzymes profiles and the use of monoclonal antibodies. The inapparent nature of the infection leads us to suggest that the "paca", Agouti paca, represents a primitive host of L. (V.) lainsoni in the Amazon Region.

Animals↗

PubMed2001

Descriptions of two new species of Eimeria (Apicomplexa: Eimeriidae) and of Eimeria chinchillae-like oocysts from the plains vizcacha Lagostomus maximus (Desmarest, 1817) (Rodentia: Chinchillidae) from Argentina.

Of 163 fecal samples collected between March 1997 and February 1999 from the plains vizcacha, Lagostomus maximus (Rodentia: Chinchillidae), 19 (12%) were found to be positive for coccidia. All species are from the genus Eimeria and 2 are described here as new. The third species is consistent with the description of Eimeria chinchillae De Vos and Van der Westhuizen, 1968. Sporulated oocysts of Eimeria lagostomi n. sp. are ellipsoidal to subspheroidal, 35.7 x 30.9 (26-36 x 30-41), with a length:width (L/W) ratio of 1.2 (1.0-1.3), without a micropyle (M) or polar granule (PG), but with an oocyst residuum (OR) comprised of a round, compact mass of many small granules. The sporocysts are lemon-shaped, 14.2 x 10.2 (9-11 x 11-16), with an L/W ratio of 1.4 (1.2-1.7) and have a Stieda body (SB) and sporocyst residuum (SR). Eimeria vizcacho n. sp. has sporulated oocysts that are subspheroidal, 26.4 x 23.4 (21-27 x 23-31), with an L/W ratio of 1.1 (1.1-1.2), lack an M and OR, but have 1-2 PGs. Sporocysts are elongate-ellipsoidal, 14.3-9.0 (8-10 x 13-15), with an L/W ratio of 1.6 (1.4-1.8), lack an SB, but have 2 SR; the first a small mass of granules lying between the sporozoites in the middle or at 1 end, and the second also of many small granules, always at the opposite end. Sporulated oocysts of the E. chinchillae-like organism are ellipsoidal to subspheroidal, 20.7 x 17.5 (15-22 x 17-24) with an L/W ratio of 1.2 (1.0-1.3), lack an M and OR, but have 0-3 PGs. Sporocysts are ellipsoidal, 10.7-6.9 (6-8 x 8-13) with an L/W ratio of 1.55 (1.3-1.8) and have an SB and SR.

Animals↗

PubMed2005

Redescription of Trichuris pampeana (Nematoda: Trichuridae) from the South American subterranean rodent Ctenomys talarum Thomas, 1898 (Rodentia: Octodontidae).

Trichuris pampeana Suriano and Navone, 1994 (Nematoda: Trichuridae) is redescribed from voucher specimens from the type host Ctenomys azarae Thomas, 1903 (Rodentia: Octodontidae) and from parasites collected from 2 populations of the subterranean rodent C. talarum Thomas, 1898 from Mar de Cobo and Necochea, Buenos Aires Province, Argentina. After a revision of these nematodes, it was confirmed that the following characters were not considered in the original description: bacillary band, cells from the esophagointestinal junction, ejaculatory duct, vas deferens, adanal papillae, vagina, oviduct, and rectum. Additional information about the spicular sheath, vulva, uteri, and ovary is provided. The morphological features given in this redescription allow to confirm the identity of T. pampeana as a valid species and also to distinguish it more clearly from other species of the genus.

Animals↗