There is a general perception that central and northern Europe were colonized by range expansion from Mediterranean refugia at the end of the last glaciation. Data from various species support this scenario, but we question its universality. Our mitochondrial DNA studies on three widespread species of small mammal suggest that colonization may have occurred from glacial refugia in central Europe^western Asia. The haplotypes on the Mediterranean peninsulae are distinctive from those found elsewhere. Rather than contributing to the postglacial colonization of Europe, Mediterranean populations of widespread small mammals may represent long-term isolates undergoing allopatric speciation. This could explain the high endemism of small mammals associated with the Mediterranean peninsulae.
Abstract:The Swedish Tundra Northwest Expedition of 1999 visited 17 sites throughout the Canadian Arctic. At 12 sites that were intensively sampled we estimated the standing crop of plants and the densities of herbivores and predators with an array of trapping, visual surveys, and faecal-pellet transects. We developed a trophic-balance model using ECOPATH to integrate these observations and determine the fate of primary and secondary production in these tundra ecosystems, which spanned an 8-fold range of standing crop of plants. We estimated that about 13% of net primary production was consumed by herbivores, while over 70% of small-herbivore production was estimated to flow to predators. Only 9% of large-herbivore production was consumed by predators. Organization of Canadian Arctic ecosystems appears to be more top-down than bottom-up. Net primary production does not seem to be herbivore-limited at any site. This is the first attempt to integrate trophic dynamics over the entire Canadian Arctic.Résumé : En 1999, l'Expédition suédoise de la toundra du nord-ouest à échantillonné 17 sites à travers l'arctique canadien. Nous avons utilisé différentes méthodes de trappage, des recensements visuels et des transects de décomptes de fèces pour estimer la biomasse végétale, ainsi que les densités des herbivores et des prédateurs aux 12 sites inventoriés plus en détail. Nous avons développé un modèle d'équilibre trophique à l'aide d'ECOPATH pour intégrer ces observations et déterminer le sort des productions primaire et secondaire de ces écosystèmes de toundra, entre lequels la biomasse végétale varie par un facteur de 8. Nous estimons qu'environ 13 % de la production primaire nette est consommée par les herbivores, tandis que plus de 70 % de la production des petits mammifères est consommée par les prédateurs. Seulement 9 % de la production des grands herbivores est consommée par les prédateurs. Ces écosystèmes semblent façonnés plus par les effets trophiques descendants (top-down) que par les effects trophiques ascendants (bottom-up). La production primaire nette de ces sites ne semble pas limitée par les herbivores. Notre étude constitue la première tentative pour intégrer les la dynamique trophique sur l'ensemble de l'arctique canadien. Krebs et al. 843
In 1996 the International Sorex araneus Cytogenetics Committee (ISACC) published a comprehensive list of 50 chromosome races of the common shrew Sorex araneus (Zima et . 1996). Since that time twenty one new races have been described and three races have been removed from the list. The present list summarises the data about races described since the 1996 publication. The rules introduced by Searle et ai (1991) and Hausser et al (1994) were followed in the compilation of the list. It can be considered a reference for further studies of evolutionary relationships between the chromosome races of Sorex araneus. A summary table of all the 68 known races, arranged alphabetically according to their names, is given. RESUMEEn suivant les principes de nomenclature des chromosomes de Sorex araneus (Searle et al. 1991) et ceux de la definition de ses races chromosomiques , PISACC (International Sorex araneus Cytogenetics Committee) a public en 1996 la premiere liste de races chromosomiques de 5. araneus (Zima et al., 1996). Elle comprenait 50 races chromosomiques. Depuis, 21 race nouvelles ont etc decrites et trois races ont etc eliminees de cette liste. Nous presentons ici la liste revisee des races chromosomiques de 5. araneus qui comprend actuellement 68 races.
The chromosomes were studied in 401 common shrews, Sorex araneus, from 91 localities in Scandinavia, the great majority in Sweden. Eight chromosome races were identified, each with its characteristic arm combination of metacentric chromosomes. Six races occur in Sweden and adjacent regions of Norway, and two in Denmark. The Swedish races are called, from north to south, Abisko, Sidensjö, Uppsala, Hällefors, Åkarp, and Öland, and the Danish races are called Sjaelland and Jutland. The geographic distribution of the races is described and discussed. Intrapopulation chromosome variation of Robertsonian type is common in the Abisko and Sidensjö, less common in the Uppsala and Öland, and absent in the Hällefors and Åkarp races. Polymorphism has not been demonstrated in the Danish races. All races but the Abisko race belong to the West European Karyotypic Group. The Abisko race is of eastern origin. The chromosome races in Denmark and Sweden form a series of whole arm reciprocal translocations with one exchange between adjacent races.
Both mouse and man have the common XX/XY sex chromosome mechanism. The X chromosome is of original size (5-6% of female haploid set) and the Y is one of the smallest chromosomes of the complement. But there are species, belonging to a variety of orders, with composite sex chromosomes and multiple sex chromosome systems: XX/XY1Y2 and X1X1X2X2/X1X2Y. The original X or the Y, respectively, have been translocated on to an autosome. The sex chromosomes of these species segregate regularly at meiosis; two kinds of sperm and one kind of egg are produced and the sex ratio is the normal 1:1. Individuals with deviating sex chromosome constitutions (XXY, XYY, XO or XXX) have been found in at least 16 mammalian species other than man. The phenotypic manifestations of these deviating constitutions are briefly discussed. In the dog, pig, goat and mouse exceptional XX males and in the horse XY females attract attention. Certain rodents have complicated mechanisms for sex determination: Ellobius lutescens and Tokudaia osimensis have XO males and females. Both sexes of Microtus oregoni are gonosomic mosaics (male OY/XY, female XX/XO). The wood lemming, Myopus schisticolor, the collared lemming, Dirostonyx torquatus, and perhaps also one or two species of the genus Akodon have XX and XY females and XY males. The XX, X*X and X*Y females of Myopus and Dicrostonyx are discussed in some detail. The wood lemming has proved to be a favourable natural model for studies in sex determination, because a large variety of sex chromosome aneuploids are born relatively frequently. The dosage model for sex determination is not supported by the wood lemming data. For male development, genes on both the X and the Y chromosomes are necessary.
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