South American Rodents Research Articles

Renal Structural Characteristics as Indexes of Renal Adaptation for Water Conservation in the Genus Sylvilagus

Renal Structural Characteristics as Indexes of Renal Adaptation for Water Conservation in the Genus Sylvilagus

Variation in chromosome number within the genus Ctenomys and description of the male karyotype of Ctenomys talarum talarum Thomas.

Ctenomys is a highly diversified polytypic genus of South American Caviomorph rodents, of the family Octodontidae. With their burrowing habits, the species of this genus, commonly named tuco-tucos, are the South American equivalent of the subterranean North American pocket gophers (family Geomyidae).

Chromosomes of the coypu.

THE coypu, Myocastor coypus Molina (or Myopotamus coypus, Myopotamus bonariensis Commers, Hydromys coypus Geoff.), is a South American rodent that belongs to the family Octodentidae and sub-family Capromyidae. To-day it is found in all continents, living in swamps and fish ponds as a feral animal or raised in captivity for its fur1. So far as we know, no previous investigation of chromosome number and morphology has been carried out on this animal.

Chronic infection of rodents by Machupo virus.

Machupo virus, the etiologic agent of human hemorrhagic fever in Bolivia, induced chronic asymptomatic infection in laboratory hamsters and colonized individuals of the peridomestic, wild, South American rodent, Calomys callosus. Viruria was detected for more than 500 and 150 days, respectively, in the two species. Chronic viremia was shown only for Calomys. Virus-neutralizing substances were present in parenterally infected adult animals, but not in animals born to, and in contact with, an infected female. Chronic infection in wild rodents may be an important mechanism in the natural history of Machupo and related virus infections.

Leukaemia-inhibiting properties and L-asparaginase activity of sera from certain South American rodents.

GUINEA pig serum is known to exert a striking inhibitory effect on certain transplantable leukaemias of the mouse and rat1. Suppression may be seen, not only with long transplanted leukaemias, but also with recently derived spontaneous and radiation-induced leukaemias (preceding communication). Other sera have been tested, but none has shown unequivocal activity1,2. The only rodent other than the guinea pig, the serum of which has been examined and found to be negative, is the rat2. Up to the present time, however, no animal closely related to the guinea pig has been studied.

Are There Rodent Suborders?

THE rodents are the most numerous order of mammals, both in terms of genera and species, and of individuals, including over half of the described living species of mammals. They are much less well represented among the known fossils, but this is, to a very large extent, the result of their small size and hence lesser conspicuousness, rather than of a former lesser diversification, at least since the latter part of the Eocene. The basic characteristic of the order-the development of gnawing incisors-has restricted the number of ecologic niches that were open to rodents. Since rodents have become very successful in this limited direction, many lines have developed, tending to evolve in the same general direction, due to similar selective pressures acting on a similar genotype. This has produced a great deal of parallelism and convergence within the order, as is now acknowledged by all students of the group. Due to this parallelism and convergence, one is faced with the problem of differentiating between similarities indicative of close relationships and those that are not. Hence, there has been, and still is, considerable difference of opinion as to the proper classification of the order. The classical arrangement, involving a subdivision into the Sciuromorpha, Myomorpha and Hystricomorpha, fundamentally on the basis of the structure of the masseter muscle, dates from Brandt (1855), although similar but less formal arrangements had been proposed before. Simpson (1945) is the latest major review of classification to adopt this three-fold arrangement. Although this has been the standard classification, many investigators felt (as, indeed, did Simpson) that its use involved forcing some rodents into unnatural relationships for purposes of convenience. Therefore, greater or lesser variants were proposed (Tullberg, 1899; Miller and Gidley, 1918; Winge, 1924). Tullberg's scheme divided the rodents into two major groups, based on the structure of the angle of the jaw, and then divided each of these on the basis of the masseter. For his secondary divisions, he used Brandt's three groups, erecting a fourth group for the South African Bathyergidae. Neither Winge nor Miller and Gidley use Brandt's terminology, but, essentially, accepted his groups and added a fourth for the forms which did not fit well into this scheme. These fourth, or wastebasket, groups have never met with wide acceptance. Even in cases where the suborders seemed morphologically valid, parts of the Brandtian classification seemed unreasonable to some authors. For example, the Hystricomorpha included certain Old World (particularly African) families, and a large array of South American ones, which were assumed to be of ultimate Old World origin. For many years, this was interpreted as indicating a South Atlantic land bridge. With increasing knowledge of the character and distribution of fossil mammals, no such land bridge seemed possible as an invasion route for the South American rodents (Simpson, 1950), and the problem of the origin of the South American forms became a major stumbling block in accepting the unity of the Hystricomorpha. Wood (1950), in view of the known extensive parallelism among rodents, suggested that the similarities between the New and Old World forms could best be explained as parallelisms, and that the source of the South American forms should be sought in North America. Within the past few years, there has

PORCUPINES, PALEOGEOGRAPHY, AND PARALLELISM

One of the vexing problems of geographic distribution is the explanation of why one suborder of rodents, the Hystricomorpha, is characteristic of South America, the southern parts of Eurasia, and Africa, but does not seem ever to have been present in North America until very recent times. Few authors have doubted that the Hystricomorpha represent a natural group with a common ancestry. In order to explain this distribution, it has been necessary to invoke continental drift, land bridges, trans-oceanic floating, or other hypotheses which seem rather dubious to many students. An attempt will be made to show that an alternative interpretation, involving only more -orthodox and established migration routes, is at least as well supported by the available evidence. The Hystricomorpha include a basic group of recent-forms, together with their fossil relatives, which are almost universaly considered to be closely related. This group includes numerous South American rodents (porcupines, guinea pigs, chinchillas, agoutis, pacas, vizcachas, capybaras, etc.); our North American porcupine (Erethizon); the African, South Asiatic, and southern European porcupines (Hystricidae); and the African Petromyidae and Thryonomyidae. In addition, a number of other families, restricted to Africa, whose correct taxonomic position is very uncertain, are often placed here (Bathyergidae, Ctenodactylidae, Pedetidae and Anomaluridae).

Reproduction of a South American rodent, the mountain viscacha

American Journal of AnatomyVolume 84, Issue 1 p. 143-173 Article Reproduction of a South American rodent, the mountain viscacha Oliver P. Pearson, Oliver P. Pearson Biological Laboratories, Harvard University, Cambridge, MassachusettsSearch for more papers by this author Oliver P. Pearson, Oliver P. Pearson Biological Laboratories, Harvard University, Cambridge, MassachusettsSearch for more papers by this author First published: January 1949 https://doi.org/10.1002/aja.1000840105Citations: 30AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat Citing Literature Volume84, Issue1January 1949Pages 143-173 RelatedInformation

The Nutria, a South American Rodent, in Kansas

A feral nutria, Myocastor coypus, was captured in the fall of 1945 in central Kansas. The animal was cornered by a dog near a pond on the 0. A. Dunn farm, along Peace Creek, twenty-four miles west and two miles north of Hutchinson, in Reno County. The nutria, a semiaquatic, South American rodent, which resembles our native muskrat in size and habits, has been reared in recent years on fur farms in the United States. Although nutrias have occasionally escaped from such fur farms and become established in the wild, we know of no fur farms with captive nutria or other fur bearers in this part of Kansas, nor of nutria elsewhere in the state. Feral nutrias have been recorded elsewhere in the United States, as in Montana (Jellison, Jour. Mamm., 26:432, 1945), Washington and Oregon (Larrison, Murrelet, 24:3, 1943), Louisiana (Lowery, Occas. Papers Mus. Zool., La. State Univ., no. 13:248, 1943), and New Mexico (Sooter, Jour. Mamm., 24:503, 1943). In France, the nutria escaped from fur farms after World War I and now has become established in the wild over much of that country (see Bourdelle, Jour. Mamm., 20:288, 1939). Laurie (Jour. Animal Ecol., 15:22-34, 1946) gives a full account of the nutrias in England, many of which escaped from fur farms abandoned at the start of World

Nomenclature of South American Hystricoid Rodents

Nomenclature of South American Hystricoid Rodents

The Relation of Heredity to Spontaneous Thyroid Tumors in Mice: Studies in the Incidence and Inheritability of Spontaneous Tumors in Mice 25th Report

This intensive study of the occurrence of thyroid tumors was undertaken in order to demonstrate whether or not heredity bears the same relation to the tendencies to resistance and to susceptibility to these tumors which it has been found to bear to tumors in other organs (1–8). No report has been found of any spontaneous thyroid neoplasms in mice except those from this laboratory (9). Moreover, very few malignant growths in the thyroid have been reported in other rodents; 5 in rats (10, 11, 12) and one in a coypu (a South American rodent) (13) being all that have been found in the literature. We are, therefore, dealing with a type of tumor relatively rare in all reports of rodents and one nowhere else reported in mice. The occurrence therefore, of malignant thyroid tumors in any considerable numbers within a given strain of mice deliberately bred for these tumors, could not logically be attributed to chance. There have been to date in the entire stock of this laboratory twenty three mice that have shown enlargements of the thyroid gland. Of these, four have been simple colloid goiters, two have been papillary adenomas, and seventeen have been malignant growths. Some of these mice have died and the tissues have been examined since the publication of the pathological study of these thyroid growths. (Report 22 in this series.) This accounts for the difference in numbers.

Viannella viscaciæ n.sp., a Nematode Parasite of the South American rodent Viscacia viscacia

Two members of a collection of the South American rodent Viscacia viscacia received by the Zoological Society of London, died early this year, one of them about 10 days after arrival at the Gardens. At the post-mortem examination both were found to have the alimentary canal heavily parasitized with Trichostrongylid nematodes. In the stomach there occurred Graphidioides rudicaudatus and Trichostrongylus retortæformis, whilst in the small intestine there were a few specimens of Trichostrongylus retortæformis and large numbers of the worm which forms the subject of the present paper. To naked eye examination of the intestinal wall the worms appeared as small bright red spots about the size of a pin's head and it could be seen that each was spirally coiled.

XXIX.—New South-American Rodents

XXIX.—<i>New South-American Rodents</i>

LVII.—Four new South-American Rodents

LVII.—<i>Four new South-American Rodents</i>

XLIV.—Notes on South-American monkeys, bats, carnivores, and rodents, with descriptions of new species

(1903). XLIV.—Notes on South-American monkeys, bats, carnivores, and rodents, with descriptions of new species. Annals and Magazine of Natural History: Vol. 12, No. 70, pp. 455-464.