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PubMed1994

The testis-determining gene, SRY, exists in multiple copies in Old World rodents.

SRY is a unique gene on the Y chromosome in most mammalian species including the laboratory mouse, Mus musculus, and the closely related European wild mouse species M. spicilegus, M. macedonicus, and M. spretus. In contrast, SRY is present in 2-6 copies in the more distantly related Asian mouse species M. caroli, M. cervicolor, and M. cookii and in 2-13 copies in the related murid species Pyromys saxicola, Coelomys pahari, Nannomys minutoides, Mastomys natalensis, and Rattus norvegicus. Copy numbers do not correlate with known phylogenetic relationships suggesting that SRY has undergone a rapid and complex evolution in these species. SRY was recently proposed as a molecular probe for phylogenetic inferences. The presence of multiple SRY genes in a wide range of murid species and genera, and at least one cricetid species, necessitates caution in the use of SRY for phylogenetic studies in the Rodentia unless it is ascertained that multiple SRY genes do not exist.

Animals↗
PubMed2003

Bisbalia vossi n. g., n. sp. (Nematoda: Onchocercidae), a filarial worm from a geomyoid rodent, Heteromys anomalus, in Venezuela.

Bisbalia vossi n. g., n. sp. is described from Heteromys anomalus (Rodentia: Geomyoidea: Heteromyidae) in northern Venezuela (Aragua). The filariae were found in a membranous pocket in the pleural cavity, and almost all had ingested red blood cells of their host. The morphology of this onchocercine species is highly evolved (advanced reduction of head and caudal papillae; short undivided oesophagus). Its very short microfilariae (60 microm) and the shape of the tail of the female (two terminal median pairs of bosses) suggest that this species could be derived from Ackertia Vaz, 1934, a South American genus parasitic in caviomorph rodents which is related to the Dipetalonema-line, but Ackertia has several pairs of precloacal papillae, which are absent in the new genus. In North America, where the geomyoid rodents originated and diversified, the two previously described filarial species differ from this new material and show affinities with Old World bat parasites (Litomosa van Beneden, 1871).

Animals↗
PubMed2003

Quinolizidine alkaloids in Ormosia arborea seeds inhibit predation but not hoarding by agoutis (Dasyprocta leporina).

Quinolizidine alkaloids (QAs) are secondary compounds found in seeds of many species of plants, possibly protecting them against pathogens and seed predators. QAs were isolated from Ormosia arborea seeds and bioassayed against red-rumped agoutis (Dasyprocta leporina, Rodentia: Caviomorpha) to verify if they inhibit seed predation and food hoarding (seed dispersal). Three treatments were used: (1) seeds of O. arborea, (2) palatable seeds of Mimusops coriacea (Sapotaceae) treated with MeOH, and (3) seeds of M. coriacea treated with QAs dissolved in MeOH in similar concentration to that present in O. arborea. Palatable seeds were significantly more preyed upon than seeds treated with QAs and Ormosia seeds, but QAs did not influence hoarding behavior. QAs in O. arborea may have a strong effect in avoiding seed predation by rodents, without reducing dispersal.

Adaptation, Physiological↗
PubMed2001

Do big-brained animals play more? Comparative analyses of play and relative brain size in mammals.

It has been hypothesized that play is more likely to be present in larger brained species. We tested this hypothesis in mammals using independent contrasts, a method that controls for phylogenetic relatedness. Comparisons across 15 orders revealed that the prevalence and complexity of play was significantly correlated with brain size, with larger brained orders having more playful species. Three orders, Rodentia, Marsupialia, and Primates, were used for within-order comparisons among species and, where possible, among families. The comparisons were not significant for rodents or primates, and those for marsupials yielded inconsistent results. Therefore, although a strong relationship is present at the highest taxonomic level of comparison, it diminishes or evaporates at lower level comparisons.

Animals↗
PubMed1991

Is the guinea-pig a rodent?

The guinea-pig (Cavia porcellus), traditionally classified as a New World hystricomorph rodent, often shows anomalous morphological and molecular features in comparison with other eutherian mammals. For example, its insulin differs from that of other mammals in anabolic and growth-promoting activities and in its capability to form hexamers. Indeed, the literature about the molecular evolution of guinea-pigs abounds in references to 'convergent evolution', 'extremely rapid rates of substitution', and 'unique evolutionary mechanisms'. These claims are based on the assumption that the guinea-pig is a rodent. Our phylogenetic analyses of amino-acid sequence data, however, imply that the guinea-pig diverged before the separation of the primates and the artiodactyls from the myomorph rodents (rats and mice). If true, then the myomorphs and the caviomorphs do not constitute a natural clade, and the Caviomorpha (or the Histricomorpha) should be elevated in taxonomical rank and regarded as a separate mammalian order distinct from the Rodentia. If, as suggested by recent data, the myomorphs branched off before the divergence among the carnivores, lagomorphs, artiodactyls and primates, then the new order would represent an early divergence in eutherian radiation.

Animals↗
PubMed1994

Primitive fossil rodent from Inner Mongolia and its implications for mammalian phylogeny.

The evolutionary origin of rodents is obscured by the group's sudden and highly transformed first appearance in the fossil record in the latest Paleocene. We report here the discovery of nearly complete dental remains of an extraordinary new primitive rodent from strata of transitional Paleocene-Eocene age in Inner Mongolia, China. The strikingly conservative morphological features of this taxon, Tribosphenomys minutus, gen. et sp. nov., substantially modify previous ideas about the ancestral rodent morphotype, which in turn has important implications for understanding the origin of rodents and their relationship to other eutherian mammals. This new fossil, in conjunction with recent morphological and molecular evidence confirming rodent monophyly, indicates the need for a reassessment of phylogenetic affinities among gliriform eutherians. Our results indicate a sister-group position of the new taxon to other rodents, and support the alliance of lagomorphs (rabbits) and rodents (cohort Glires). They also suggest that paraphyly of an extinct assemblage, the 'Eurymylidae', and reveal an unexpectedly complex pattern of character evolution near the ancestry of Rodentia.

Animals↗
PubMed1996

Phylogenetic position of the order Lagomorpha (rabbits, hares and allies)

Ever since they have been classified as ruminants in the Old Testament (Leviticus 11:6, Deuteronomy 14:7) and equated with hyraxes in the vulgate Latin translation, rabbits and their relatives (order Lagomorpha) have frequently experienced radical changes in taxonomic rank. By using 91 orthologous protein sequences, we have attempted to answer the classical question "What, if anything, is a rabbit?". Here we show that Lagomorpha is significantly more closely related to Primates and Scandentia (tree shrews) than it is to rodents. This newly determined phylogenetic position invalidates the superordinal taxon Glires (Lagomorpha + Rodentia), and indicates that the morphological 'synapomorphies' previously used to cluster rodents and lagomorphs into Glires, may actually represent symplesiomorphies or homoplasies that are of no phylogenetic value. This raises the possibility that the ancestral eutherian morphotype may have possessed many rodent-like morphological characters.

Animals↗
PubMed1986

Coypu insulin. Primary structure, conformation and biological properties of a hystricomorph rodent insulin.

Insulin from a hystricomorph rodent, coypu (Myocaster coypus), was isolated and purified to near homogeneity. Like the other insulins that have been characterized in this Suborder of Rodentia, coypu insulin also exhibits a very low (3%) biological potency, relative to pig insulin, on lipogenesis in isolated rat fat-cells. The receptor-binding affinity is significantly higher (5-8%) in rat fat-cells, in rat liver plasma membranes and in pig liver cells, indicating that the efficacy of coypu insulin on receptors is about 2-fold lower than that of pig insulin. The primary structures of the oxidized A- and B-chains were determined, and our sequence analysis confirms a previous report [Smith (1972) Diabetes 21, Suppl. 2, 457-460] that the C-terminus of the A-chain is extended by a single residue (i.e. aspartate-A22), in contrast with most other insulin sequences, which terminate at residue A21. In spite of a large number of amino acid substitutions (relative to mammalian insulins), computer-graphics model-building studies suggest a similar spatial arrangement for coypu insulin to that for pig insulin. The substitution of the zinc-co-ordinating site (B10-His----Gln) along with various substitutions on the intermolecular surfaces involved in the formation of higher aggregates are consistent with the observation that this insulin is predominantly 'monomeric' in nature. The c.d. spectrum of coypu insulin is relatively similar to those of casiragua insulin and of bovine insulin at low concentration.

Amino Acid Sequence↗
PubMed2004

[Three new species of the genus Medwayella Traub, 1972 (Insecta: Siphonaptera: Pygiopsyllidae) from Sabah (eastern Malaysia, Borneo)].

Medwayella traubiana n. sp., M. pfeifferi n. sp. and M. sabahae n. sp. (Pygiopsyllidae) are described from Sabah (north of Borneo island), the first two on Tupaia tana (Scandentia), the last on Sundasciurus lowii (Rodentia). Sex male is only identified, because these fleas have been collected in sympatry, or even in syntopy. Their determination is based on segment IX and aedeagus. If M. traubiana and M. pfeifferi are related to some known species, M. sabahae is clearly distinct from other Medwayella.

Animals↗
PubMed2006

Cellular scaling rules for rodent brains.

How do cell number and size determine brain size? Here, we show that, in the order Rodentia, increased size of the cerebral cortex, cerebellum, and remaining areas across six species is achieved through greater numbers of neurons of larger size, and much greater numbers of nonneuronal cells of roughly invariant size, such that the ratio between total neuronal and nonneuronal mass remains constant across species. Although relative cerebellar size remains stable among rodents, the number of cerebellar neurons increases with brain size more rapidly than in the cortex, such that the cerebellar fraction of total brain neurons increases with brain size. In contrast, although the relative cortical size increases with total brain size, the cortical fraction of total brain neurons remains constant. We propose that the faster increase in average neuronal size in the cerebral cortex than in the cerebellum as these structures gain neurons and the rapidly increasing glial numbers that generate glial mass to match total neuronal mass at a fixed glia/neuron total mass ratio are fundamental cellular constraints that lead to the relative expansion of cerebral cortical volume across species.

Animals↗
PubMed1990

DNA "fingerprinting" reveals high levels of inbreeding in colonies of the eusocial naked mole-rat.

Using the technique of DNA fingerprinting, we investigated the genetic structure within and among four wild-caught colonies (n = 50 individuals) of a eusocial mammal, the naked mole-rat (Heterocephalus glaber; Rodentia: Bathyergidae). We found that DNA fingerprints of colony-mates were strikingly similar and that between colonies they were much more alike than fingerprints of non-kin in other free-living vertebrates. Extreme genetic similarity within colonies is due to close genetic relationship (mean relatedness estimate +/- SE, r = 0.81 +/- 0.10), which apparently results from consanguineous mating. The inbreeding coefficient (F = 0.45 +/- 0.18) is the highest yet recorded among wild mammals. The genetic structure of naked mole-rat colonies lends support to kin selection and ecological constraints models for the evolution of cooperative breeding and eusociality.

Animals↗
PubMed1993

An examination of the generation-time effect on molecular evolution.

By using DNA sequences of 17 mammalian genes, the generation-time effect is estimated separately for synonymous substitutions and nonsynonymous substitutions. Star phylogenies composed of rodentia, artiodactyla, and primates are examined. The generation-time effect is found to be more conspicuous for synonymous substitutions than for non-synonymous substitutions, by using the methods of (i) Nei and Gojobori, (ii) Li, and (iii) Ina. The proportion of accepted amino acid substitutions in evolution is estimated to be about twice as large in the primate lineage as in the rodent lineage. This result is in accord with the nearly neutral theory of molecular evolution.

Animals↗
PubMed1991

The effect of diet on microfaunal population and function in the caecum of a subterranean naked mole-rat, Heterocephalus glaber.

The effect of dietary fibre and starch content on digestibility, microfaunal population and caecal function was investigated in a subterranean mole-rat, Heterocephalus glaber (Rodentia). Mole-rats were fed on a diet of either sweet potato (neutral-detergent fibre (NDF) 65 g/kg dry matter (DM), starch 638 g/kg DM) or carrot (NDF 157 g/kg DM, starch 258.7 g/kg DM) for 4 weeks. Daily intake and faecal output were monitored. Thereafter caecal microfaunal population, density and function were assessed using light and scanning electron microscopy and by measuring both gas and short chain fatty acid (SCFA) production. A 2.4-fold increase in fibre and 2.5-fold decrease in starch content resulted in a decrease in caecal DM content (390 g/kg). A concomitant dramatic decline (by 93%) in ciliate protozoa with a corresponding 2-fold increase in bacteria also accompanied this change in diet. Fermentative efficiency as indicated by gas production was 2.6 times greater on a carrot diet than on sweet potato. Microbial fermentation resulted in higher SCFA concentrations on the carrot diet, with a 42% reduction in SCFA concentration on the sweet potato diet. Here, SCFA contributed 5.1% of daily energy expenditure and this increased 5.0-fold on the carrot diet. Caecal micro-organism function, therefore, played an important role in the nutritional physiology of these naked mole-rats, and enabled maximum utilization of the food substrate.

Animals↗
PubMed2001

Molecular phylogeny and divergence time estimates for major rodent groups: evidence from multiple genes.

The order Rodentia contains half of all extant mammal species, and from an evolutionary standpoint, there are persistent controversies surrounding the monophyly of the order, divergence dates for major lineages, and relationships among families. Exons of growth hormone receptor (GHR) and breast cancer susceptibility (BRCA1) genes were sequenced for a wide diversity of rodents and other mammals and combined with sequences of the mitochondrial 12S rRNA gene and previously published sequences of von Willebrand factor (vWF). Rodents exhibit rates of amino acid replacement twice those observed for nonrodents, and this rapid rate of evolution influences estimates of divergence dates. Based on GHR sequences, monophyly is supported, with the estimated divergence between hystricognaths and most sciurognaths dating to about 75 MYA. Most estimated dates of divergence are consistent with the fossil record, including a date of 23 MYA for Mus-Rattus divergence. These dates are considerably later than those derived from some other molecular studies. Among combined and separate analyses of the various gene sequences, moderate to strong support was found for several clades. GHR appears to have greater resolving power than do 12S or vWF. Despite its complete unresponsiveness to growth hormone, Cavia (and other hystricognaths) exhibits a conservative rate of change in the intracellular domain of GHR.

Animals↗
PubMed1998

Complete mitochondrial DNA sequence of the fat dormouse, Glis glis: further evidence of rodent paraphyly.

The complete mitochondrial genome of the fat dormouse, Glis glis, has been sequenced (16,602 bp). A total of 23 complete mitochondrial mammalian genomes have been taken into account for phylogenetic reconstruction. Phylogenetic analyses were performed with parsimony, distance (stationary Markov model), and maximum-likelihood methods. In all cases, data strongly support the paraphyly of rodents, with dormouse and guinea pig in a different clade from rat and mouse, reaching bootstrap values of 95%. Rodent monophyly and the existence of Glires (Rodentia and Lagomorpha) are weakly supported, with maximum bootstrap values of 11% and 8.6%, respectively. This result agrees with the analyses of isochore patterns in the nuclear genome and the B2 and B2-like retroposons, which show a close relationship between dormice and guinea pigs rather than between dormice and rats and mice.

Animals↗
PubMed2002

Enhanced selection for MHC diversity in social tuco-tucos.

To explore the effects of behavior and demography on balancing selection at major histocompatibility complex (MHC) loci, we examined allelic diversity at exon 2 of the MHC class II DQbeta locus in a social and a solitary species of tuco-tuco (Rodentia: Ctenomyidae: Ctenomys), both of which occur in the same valley in southwestern Argentina. By comparing patterns of diversity at this MHC gene to the diversity evident at fifteen microsatellite loci, we demonstrate that balancing selection at the DQbeta locus is enhanced in the social species compared to its solitary congener. These findings have intriguing implications for the role of behavioral and demographic parameters in maintaining diversity at MHC loci.

Animals↗
PubMed1993

Molecular evidence for mating asymmetry and female choice in a pocket gopher (Thomomys) hybrid zone.

This paper presents circumstantial evidence that the mating system of the North American pocket gophers (Rodentia: Geomyidae) is a promiscuous one, with female choice at its base. A molecular marker (a length variant in the mitochondrial Control region [D-loop]) is used to show mating asymmetry in a hybrid zone between the species Thomomys bottae and Thomomys townsendii in north-eastern California. All hybrids result from a bottae mother x townsendii father cross. Because of significant differences in body size and resulting burrow diameter, bottae females must have actively sought their respective townsendii mates for the asymmetry in mating to have occurred, signalling female choice in these subterranean mammals that are otherwise characterized by exclusive-use territories, skewed adult sex ratio in favour of females, and high variance in male reproductive success.

Animals↗
PubMed2003

The anatomy of the world's largest extinct rodent.

Phoberomys is reported to be the largest rodent that ever existed, although it has been known only from isolated teeth and fragmentary postcranial bones. An exceptionally complete skeleton of Phoberomys pattersoni was discovered in a rich locality of fossil vertebrates in the Upper Miocene of Venezuela. Reliable body mass estimates yield approximately 700 kilograms, more than 10 times the mass of the largest living rodent, the capybara. With Phoberomys, Rodentia becomes one of the mammalian orders with the largest size range, second only to diprotodontian marsupials. Several postcranial features support an evolutionary relationship of Phoberomys with pakaranas from the South American rodent radiation. The associated fossil fauna is diverse and suggests that Phoberomys lived in marginal lagoons and wetlands.

Animals↗