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PubMed2000

Lung morphology in rodents (Mammalia, Rodentia) and its implications for systematics.

A new nomenclature of the lung lobes and of the bronchial tree is presented, with which the lungs in 40 species of 11 rodent families are described. Whole, fixed lungs and silicone casts of the bronchial tree are tested for 23 characters, based on the distribution of lung lobes, the number and geometry of first order bronchi, the pulmonary blood supply, and lung symmetry. Ten lung morphotypes are recognized, seven of them representing one or more families: Castor type (Castoridae), Cryptomys type (Bathyergidae), Ctenodactylus type (Ctenodactylidae), Eliomys type (Gliridae), Myocastor type (Myocastoridae), Octodon type (Octodontidae and Echimyidae) and Rattus type (Sciuridae, Muridae pt. and Dipodidae). The Hydromys type is found only in Hydromys chrysogaster (Muridae), while Galea type A and B both appear in Galea musteloides (Caviidae). The data are phylogenetically analyzed by the program PAUP 4.0 using as outgroup Lagomorpha or Insectivora. On the species level, there are no well-resolved cladograms. On the family level, the cladograms do not contradict traditional rodent systematics with one exception: the Caviidae do not fall within Caviomorpha or even within the Hystricomorpha, but form a sister group to Dipodidae (Myomorpha). This appears to be a result of convergence. The lungs of Gliridae are more similar to those of Muridae than to those of Sciuridae. Included in the ingroup, Oryctolagus (Lagomorpha) forms a clade with Caviidae + Dipodidae. Thus, the "Glires hypothesis" is neither supported nor refuted.

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PubMed1994

Functional allometry of the semicircular ducts in subterranean mole-rats Cryptomys (Bathyergidae, Rodentia).

BACKGROUND: Since the spatial mobility of subterranean mole-rats is restricted and their skull strongly modified, morpho-functional regression of their vestibular organ may be expected. On the other hand, vestibular sense may be indispensable for orientation in a world deprived of most external sensory cues. Since vestibular sensitivity is determined by the size of the labyrinth, morphometrical analysis may be employed to assess the sensitivity and to test whether the organ is degenerate or progressively specialized. METHODS: We analyzed the shape and size of the membranous labyrinth of vestibular organs in toto in three species of African subterranean blind mole-rats of the genus Cryptomys (Bathyergidae) differing in body size yet not in habitats, ways of life, or employed orientation and locomotory strategies. The mechanical sensitivity of the cupula was estimated according to Oman et al. (1987. Acta Otolaryngol. (Stockh.), 103:1-13) for each of the three semicircular ducts. RESULTS: The size and shape of the vestibular organ changed predictably depending on species-specific (yet not individual) body mass. In some aspects, particularly the cross-sectional area, the ducts were larger than expected for a mammal of a comparable body size. In all species examined, the anterior semicircular ducts exhibited the highest sensitivity. CONCLUSIONS: The vestibular organs of blind subterranean mole-rats are not regressed morpho-functionally.

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PubMed1992

Ultrasonic vocalization and body temperature maintenance in infant voles of three species (Rodentia: Arvicolidae).

Infant voles thermoregulate poorly and produce ultrasonic vocalizations when cooled. Vocalizing and the ability to maintain body temperature in isolated pups cold-challenged at 5 degrees C or 22 degrees C were studied in nestling Clethrionomys glareolus, Microtus agrestis, and Arvicola terrestris. The tendency to vocalize varied with age, since pups vocalized more in their 2nd week than in their 1st or 3rd weeks. Rate of vocalizing was correlated with sound pressure level of vocalizations. Their was no apparent relation between vocalizing rate and deep body temperature. M. agrestis pups vocalized most and A. terrestris pups least, and all three species vocalized more at the lower temperature. Maximal vocalizing occurred in mid aged M. agrestis (at 5 degrees C) with mean of 1291 vocalizations/20 min and mean SPL of 80 dB (decibels re: 20 microN/m2). It is suggested that the vocalizing response is an adaptation related to risk from hypothermia in infant voles.

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PubMed1985

Cross fertilization in vivo and in vitro between three species of vesper mice, Calomys (Rodentia, Cricetidae).

Cross fertilization was tested between oocytes of Calomys callidus and spermatozoa from C. callidus, C. musculinus and C. laucha by both in vivo and in vitro insemination. After in vivo and in vitro insemination, respectively, percentages of oocytes fertilized were 68.8 and 46.6 (C. callidus X C. callidus), 20.3 and 12.7 (C. callidus X C. musculinus), 26.7 and 4.3 (C. callidus X C. laucha). Thus, the percentages obtained after in vitro insemination were always lower than those obtained with in vivo insemination. It was found that 23.9% and 44.4% of two-cell hybrid embryos were present in oviducts 30 hr after in vivo insemination of C. callidus females with C. musculinus or C. laucha spermatozoa, respectively. At a later stage (56 hr postinsemination), development did not progress further, and abnormal embryos were found both at 30 and 56 hr postinsemination, suggesting some kind of cleavage arrest or degeneration of the embryos. We suggest that fertilization is not strictly species-specific, at least among the species we studied, but that there are some factors that reduce the efficiency of interspecific fertilization.

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PubMed1986

The effect of melatonin administration and short exposures to cold on body temperature of the blind subterranean mole rat (Rodentia, Spalax ehrenberghi, Nehring).

Improvement of the cold resistance capacity of the mole rat (Spalax ehrenbergi, Nehring), a blind subterranean rodent, was achieved following subcutaneous melatonin administration. Melatonin-treated mole rats exhibited reduction both in initial body temperature (Tbo) and in the decrease of body temperature (delta Tb) after 6 hours of exposure to cold. The tested mole rats were acclimated to and kept during the experiment, under long (16L/8D) photoperiod schedule while the effects of melatonin administration on body temperature simulated the effects of short photoperiod conditions. These results suggest that in mole rats, melatonin biochemically mediates photoperiodic information into body temperature physiological response. As a byproduct of the original experiment, it was found that frequently repeated short (6 hours) exposure to cold (Ta = 5 +/- 1 degrees C) can in itself initiate an improvement of cold resistance capacity similar to the effect of melatonin administration. This supports the idea that mole rats may improve their cold resistance in response to either photoperiodic or climatic changes.

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PubMed1992

The ear in subterranean insectivora and rodentia in comparison with ground-dwelling representatives. I. Sound conducting system of the middle ear.

Compared to acoustically unspecialized mammals (soricids and murids), the middle ear of subterranean insectivores and rodents (twelve species of six families examined) was clearly distinguished and characterized by many common features: rather round and relatively larger eardrum without a pars flaccida; reduced gonial; loose or no connection between the malleus and the tympanic bone; reduced and straightened transversal part of the malleus; enlarged incus; increased and rather flat incudo-mallear joint; rather parallel position of the mallear manubrium and incudal crus longum in some species (and their fusion in bathyergids); reduced or even missing middle ear muscles. Convergent occurrence of these structural features in taxa of different origin and their generally derived character suggest that they cannot be categorized as degenerative. The form of the stapes can be considered as a non-adaptive trait; it was taxon specific yet remarkably polymorphous in some species and exhibited no convergent features among subterranean mammals. Structural retrogression resulting in a columella-like stapes was observed in some species lacking the stapedial artery. The stapedial base was relatively larger than in unspecialized mammals. The subterranean mammals did not exhibit conspicuously enlarged eardrums as would be required for sensitive tuning to low frequencies. It is, however, argued that while selective pressures in the subterranean ecotope promoted hearing of low frequencies, hearing sensitivity did not have to be enhanced.

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PubMed1994

Trophoblastic invasion of the uterine epithelium in Calomys callosus (Rodentia, Cricetidae).

Implantation sites in the uterus of the cricetid rodent Calomys callosus were examined by light and electron microscopy at several points during day 4 of pregnancy to determine the changes occurring in the trophoblast and epithelial cells during the early blastocyst-endometrial relationship, particularly the epithelial removal phase. By morning, the blastocysts had already lodged in the antimesometrial region of the uterine crypts and the embryo-maternal interaction was limited to sparse contacts between the epithelial microvilli and the trophoblast surface. A few dense and altered epithelial cells were present. Three zones could be distinguished in the stromal region. In the subepithelial area, the stromal cells showed features similar to those found in other rodents during the early decidualization process. Effective epithelial invasion by the trophoblast occurred only in the evening, although at noon, apposition and attachment phases were identifiable. During invasion, the trophoblast processes were first seen insinuating between the epithelial cells, projecting towards the basal lamina, and finally replacing these cells. The epithelial cells in contact with the invading trophoblast exhibited severe disorganization similar to that found during the process of cell death by apoptosis. The removal of such cells occurred by trophoblast phagocytosis. Once in contact with the basal lamina, the trophoblast rapidly spread out both mesometrially and antimesometrially, phagocytosing the remaining epithelial cells. Trophoblast processes were also seen penetrating the basal lamina. Given that the epithelium breached and phagocytosed by the trophoblast habitually displays degenerative characteristics, we consider the mechanisms that might be involved in epithelial cell death and in the removal of the uterine epithelium, and the participation of the trophoblast in both these events.

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PubMedDate not supplied

Biochronological implications of the Arvicolidae (Rodentia, Mammalia) from the Lower Pleistocene hominid-bearing level of Trinchera Dolina 6 (TD6, Atapuerca, Spain).

Level TD6 of the Trinchera Dolina Section in the railway cutting of the Sierre de Atapuerca (Trinchera del Ferrocarril) has yielded a rich small mammal assemblage (26 species) in association with fossil human remains of Homo antecessor. The arvicolids of TD6 are identified as: Mimomys savini, Microtus seseae, Stenocranius gregaloides, Terricola arvalidens, Iberomys huescarensis, Allophaiomys chalinei, and Pliomys episcopalis. The rodent association also includes large rodents (i.e., Castor fiber, Marmota sp., and Hystrix refossa) and the small Allocricetus sp., Eliomys helleri, Micromys minutus, and Apodemus aff. flavicollis. The small vertebrate remains also include Insectivora (Beremendia fissidens, Sorex sp, Neomys sp., Crocidura sp., Galemys sp., Talpa sp., Erinaceus sp.), Chiroptera (Miniopterus schreibersii, Myotis sp., Rhinolophus sp.), and Lagomorpha (Oryctolagus sp., Lepus sp.), as well as lizards, birds and amphibians. The H. antecessor remains are derived from a 15 cm thick layer at the top of TD6 (TD6-T36-43), where A. chalinei, H. refossa and Marmota sp. do not occur. The paleomagnetic Matuyama/Brunhes boundary is found in the overlying level TD7 of the Gran Dolina Section. On the basis of the arvicolids, TD6 can be referred to the Biharian biochron. The Matuyama/Brunhes boundary is fixed in the late Biharian (Microtus-Mimomys rodent Superzone). The species M. savini (without M. pusillus), as well as the evolutionary stage of Microtus s.l., are characteristic of the Late Biharian. The evolutionary level of the species M. savini, T. arvalidens, S. gregaloides indicates that TD6 is older than West Runton (type Cromerian). In the Trinchera Dolina Section we are able to calibrate, for the first time, the evolutionary level of important biochronological markers with magnetostratigraphy. We propose that a radiation of Microtus s.l., along with the first appearance of primitive S. gregaloides, T. arvalidens and Iberomys, took place just before the Matuyama/Brunhes boundary. These species can be considered as characteristic elements of early Pleistocene faunas.

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PubMed1998

The molecular phylogenetics of tuco-tucos (genus Ctenomys, Rodentia: Octodontidae) suggests an early burst of speciation.

Variation in the nucleotide sequence of the entire mitochondrial cytochrome b gene (1140 bp) was examined for 27 individuals representing 13 species of South American rodents of the genera Ctenomys, Octodontomys, Tympanoctomys, and Spalacopus. Representatives of the family Echimyidae, Euryzygomatomys and Mesomys, were used as outgroups to test the monophyly of the Octodontinae and Ctenomyinae. Relationships among species of tuco-tucos (genus Ctenomys) were also examined including representatives of the three described subgenera and the two sperm morphs. Reciprocal monophyly of the Octodontinae and Ctenomyinae is strongly supported. Several basal relationships among species of the genus Ctenomys are poorly resolved, suggesting the possibility of a hard polytomy due to a rapid and potentially simultaneous radiation early in the history of the genus. In other cases, clades within the Ctenomyinae previously identified on the basis of allozymes, chromosomes, parasites, or skull morphology were supported. Calibrations based on the fossil record suggest that the mitochondrial cytochrome b of these caviomorphs has evolved at a rapid rate, comparable to those proposed for Mus-Rattus, and three to four times higher than ungulate rates.

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PubMed2002

Molecular systematics of sciurognathi (rodentia): the mitochondrial cytochrome b and 12S rRNA genes support the Anomaluroidea (Pedetidae and Anomaluridae).

Nucleotide sequence data from the mitochondrial 12S rRNA and cytochrome b genes were used to analyze phylogenetic relationships among sciurognath rodents. Our sample taxa included representatives of 11 sciurognath and 3 hystricognath families with two marsupial species, Didelphis virginiana and Macropus robustus, as outgroups. The dataset was analyzed using both maximum-parsimony (weighted and unweighted) and likelihood methods. Three suprafamilial groupings are strongly supported: Geomyidae + Heteromyidae (Geomyoidea), Sciuridae + Aplodontidae (Sciuroidea), and Pedetidae + Anomaluridae (Anomaluroidea). Although moderately supported, two sister group relationships were identified between Gliridae and Sciuroidea and between Castor and Geomyoidea. In contrast to previous nuclear DNA evidence, the evolutionary affinities between Ctenodactylidae and Hystricognathi (Ctenohystrica) and between Muridae and Dipodidae (Myodonta) are not supported by the mitochondrial data. Molecular divergence dates based on the combined data were estimated for suprafamilial groupings and are discussed in the light of current morphological and paleontological interpretations of rodent phylogeny.

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PubMed1988

[Chromosomes of the Cuming rat, Phloeomys cumingi Waterhouse, 1839 (Mammalia: Rodentia)].

The chromosome formula of Phloeomys cumingi is described for the first time. The diploid number is 40 in both sexes, the fundamental number is 60. The 38 autosomes are divided into 5 pairs of submetacentrics, 4 pairs of metacentrics, 6 pairs of large acrocentrics and 4 pairs of small acrocentrics. The sex chromosomes are large and rich in C-positive heterochromatin. The comparative analysis of the chromosomes of Phloeomys with those of Mus musculus and Rattus norvegicus puts forward numerous analogies between these 3 species. According to the comparison of the chromosomes of Phloeomys with the ancestral karyotype of the Cricetidae, eleven chromosome pairs at least have conserved their original G-banding pattern. Although chromosome data reveal a close relationship between Phloeomys and Muridae, they do not exclude the possible belonging of this species to a separate family, that of Phloeomyidae.

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