N. A. Shchipanov

Natural hybridization between extremely divergent chromosomal races of the common shrew (Sorex araneus, Soricidae, Soricomorpha): hybrid zone in European Russia

The Moscow and Seliger chromosomal races of the common shrew differ by Robertsonian fusions and possibly whole‐arm reciprocal translocations (WARTs) such that their F1 hybrids produce a chain‐of‐eleven configuration at meiosis I and are expected to suffer substantial infertility. Of numerous hybrid zones that have been described in the common shrew, those between the Moscow and Seliger races involve the greatest chromosomal difference. We collected 211 individuals from this zone to generate a total dataset of 298 individuals from 187 unique global positioning system (GPS) locations within the vicinity of interracial contact. We used a geographic information system (GIS) to map the location of the hybrid zone, which follows a direct route between two lakes, as would be anticipated from tension zone theory. Even within the central area of the hybrid zone, there is a much higher frequency of pure race individuals than hybrid, making this a clear example of a bimodal zone in the sense of Jiggins & Mallet (2000) . The zone runs through good habitat for common shrews, but nevertheless it is very narrow (standard cline widths: 3–4 km), as would be anticipated from low hybrid fitness. There is clear potential for an interruption to gene flow and build‐up of reproductive isolation. As found in some other hybrid zones, there is a high frequency of novel genetic variants, in this case, new chromosomal rearrangements. Here, we report a de novo Robertsonian fission and a de novo reciprocal translocation, both for the first time in the common shrew. There is an extraordinarily high frequency of de novo mutations recorded in F1 hybrids in the zone and we discuss how chromosomal instability may be associated with such hybrids. The occurrence of a de novo Robertsonian fission is of considerable significance because it provides missing evidence that fissions are the basis of the novel acrocentric forms found and apparently selected for in certain common shrew hybrid zones.

Distribution of two chromosome races of the common shrew (Sorex araneus L.) in the hybrid zone: Can a change of the dispersal mode maintain independent gene frequencies?

Combination of different dispersal modes may itself, without external obstacles, lead to the appearance of subdivided populations and maintain the existence of independent population systems. The common shrew, a mammal convenient for studying different levels of intraspecific differentiation, was the object of the study. Empirical data have been used for simulation taking into account the change of dispersal modes in the population area. The obtained results agree with empirical data on the distribution of races and hybrids in the hybrid zone of chromosome races Moscow and Seliger. Change of the dispersal mode may maintain independent population dynamics and, in the case of chromosome races, prevent the migration of parental individuals into the territory of the other race.

Cytogenetic control of a hybrid zone between two Sorex araneus chromosome races before breeding season

Two chromosome races of common shrew, Moscow and Seliger, differ in the arm combination in 11 diagnostic chromosomes (Robertsonian metacentrics/acrocentrics). Homozygotes of both pure races, simple Robertsonian heterozygotes of Seliger race, and complex heterozygotes (F1 hybrids) were detected in the found earlier hybrid zone of these races, in the spring before the breeding season. The g/o heterozygote was first discovered in race Seliger, whose chromosome formula typically contains acrocentrics g and o. The m/q heterozygote was recorded for the second time. Meiosis was studied in 16 males representing five detected karyotypic categories. No abnormal in pairing of homologs in either sex trivalent common for the species (XY1Y2) or autosome trivalents (g/o and m/q) was detected at diakinesis-metaphase I. Two hybrids displayed a theoretically expected and unimpaired meiotic configuration in a form of a very long chain comprising 11 monobrachial homologs (g/gm/mq/qp/pr/rk/ki/ih/hn/no/o). The results are discussed in terms of hypotheses on fertility of complex heterozygotes and limited gene flow in hybrid zone.

Phenotypic Variation across Chromosomal Hybrid Zones of the Common Shrew (Sorex araneus) Indicates Reduced Gene Flow

Sorex araneus, the Common shrew, is a species with more than 70 karyotypic races, many of which form parapatric hybrid zones, making it a model for studying chromosomal speciation. Hybrids between races have reduced fitness, but microsatellite markers have demonstrated considerable gene flow between them, calling into question whether the chromosomal barriers actually do contribute to genetic divergence. We studied phenotypic clines across two hybrid zones with especially complex heterozygotes. Hybrids between the Novosibirsk and Tomsk races produce chains of nine and three chromosomes at meiosis, and hybrids between the Moscow and Seliger races produce chains of eleven. Our goal was to determine whether phenotypes show evidence of reduced gene flow at hybrid zones. We used maximum likelihood to fit tanh cline models to geometric shape data and found that phenotypic clines in skulls and mandibles across these zones had similar centers and widths as chromosomal clines. The amount of phenotypic differentiation across the zones is greater than expected if it were dissipating due to unrestricted gene flow given the amount of time since contact, but it is less than expected to have accumulated from drift during allopatric separation in glacial refugia. Only if heritability is very low, Ne very high, and the time spent in allopatry very short, will the differences we observe be large enough to match the expectation of drift. Our results therefore suggest that phenotypic differentiation has been lost through gene flow since post-glacial secondary contact, but not as quickly as would be expected if there was free gene flow across the hybrid zones. The chromosomal tension zones are confirmed to be partial barriers that prevent differentiated races from becoming phenotypically homogenous.

Interracial and population variability of phenotypic (cranial) characters in the common shrew Sorex araneus L., 1758

Variability of the cranial properties of chromosomal races Serov, Manturovo and Petchora of the common shrew were studied. A consistent increase of scull size in the Serov race with moving from the plain to highlands and a skull size decrease from low to high latitudes was detected. Interpopulation variability among different races was shown to be comparable with interracial variability or to exceed it. This suggests microevolution at the level of local populations.

Ural chromosomal Serov race of common shrew Sorex araneus L. (Insectivora, Mammalia) that inhabits polydominant deep coniferous taiga in the north of European Russia.

The chromosomal race Serov of the common shrew ( Sorex araneus ) known in the Urals and Western Siberia was found for the first time in ten areas studied in the European Cis-Ural region at least 300 km west of the Ural Mountains. Diagnostic metacentrics (go, hn, ip, km, qr) were stable; karyotyping of 16 animals showed no polymorphism (2 n A = 18). This common shrew race proved to move through the European territory within an area of Siberian stone pine (the major edificator of the polydominant Siberian taiga) which suggests that this race is involved in the relationships with Siberian taiga biota. The closest Eastern European chromosomal races, Manturovo and Pechora, were beyond the boundaries of the territory occupied by this community.

Variability of a cytochrome b region in different chromosome races and populations of the common shrew Sorex araneus L., 1758

The nucleotide sequence (572 bp) of the cytochrome b gene of the common shrew Sorex araneus was analyzed. In total, 92 animals of five chromosome races from 12 localities were studied. The median haplotype network has a pronounced star-like structure. The central haplotype common for all samples, except for the southern island sample of the race Sok, accounts for about 36%. The main characteristics of molecular variation in our work correspond to those obtained in other studies. We revealed the lack of a correlation between the genetic and geographic distances and also population structurization of the species. On the basis of variation of the haplotypes in the samples, a scenario of colonization of the postglacial territories by females of one or several close matrilines with subsequent rapid subdivision of the population into independent populations is discussed.

Density-dependent processes determine the distribution of chromosomal races of the common shrew Sorex araneus (Lipotyphla, Mammalia)

The common shrew is subdivided into 74 chromosomal races, widely distributed in the postglacial area from the Britain Islands to Lake Baikal. Based on 1969 karyotypes from 216 localities, we present for the first time a map of ranges of 25 chromosomal races (except the Altai race) currently known in Russia. We revealed two centers of high karyotypic diversity: the western (near Baltic Sea) and the eastern (near Baikal Lake). The studied races were categorized as small-, medium-, and large-range races, and small-range races concentrated around those two centers of karyotypic diversity. We did not find any significant association between race range size and ecological zone, latitude, or the ambient temperature. Physical barriers, such as Ural Mountain or rivers, do not limit race distribution. The width of rivers that divide a range of a single race or ranges of two different races does not differ. We supposed that the occupation of an area by a race could limit the invasion of a different race from an adjacent area and expansion of its range, thus contributing to race parapatric distribution alone without additional effects of physical barriers. Based on karyotype similarity and geographic localization, we combined races into four “karyotypic chains,” in which the races can be derived from one another consequently by a single chromosomal translocation. The present distribution of the common shrew races in Russia supports the idea that it has resulted from recolonization from refugia governed by the density-dependent processes.

Importance of olfactory communication in the spiral search strategy of the common shrew Sorex araneus L.

367 The existence of two different settlement strategies, spiral search and direct search, was shown in the study of the common shrew [1]. The of spiral search strategy is a purposeful search of a suitable site nearest to the place of birth [2]. Such shrews mainly form the core of a population. The strategy of direct search entails rann dom dispersion of animals in space [3]. The strategy of direct search explains examples of ultraalonggrange movements of common shrews, particularly, the welll studied occupation of lake islands at a distance of 50– 820 m from the shore [4]. The strategy of spiral search is the most interested for us, because the part of the population space that mainly determines the level of population density is filled in this case. The spiral search implies two opposite tendencies: the centripetal tendency, i.e., the tendency to keep at the minimal distance from natal plots; and the centriff ugal tendency, i.e., the tendency to avoid interference competition. We suggest a hypothesi, explaining the mechanism of spiral search in common shrews on the basis of indirect olfactory interactions of individuals (in the terminology of Rozhnov [5]). MATERIALS AND METHODS Regular observations of individually marked shrews were carried out in 2006 and 2007 in Staritsk raion of Tver oblast [6]. In parallel, experiments in opennair cages were conducted with these animals. Underryearlings temporary withdrawn from lines for the period up to 4 h were used. The animals were transs ferred to the place of experiment in individual cages with food and were kept until the beginning of the test 1.5–3 h in an individual cage of a larger size with food and nesting material. Chicken hearts were used as the main food; additionally, grasshoppers were given to animals (2–4 insects per individual). After testing, the shrews were released at the place of capture. Each anii mal was used in only one experiment. The experiment was conducted in the system of chambers of transparent plastic, sequentially joined though the wall via twoodirection stair passages so that four equal routes were available from the center. Singlee direction passages led into the end chambers, and a shrew that came there could not return back. For travv eling the whole route, an animal had to pass through three intermediate chambers 50 cm in length each. The intermediate chambers had a size of 50 × 25 cm; the central and end …

Small Mammals Disperse Micromycete Spores

Microscopic, mostly imperfect, fungi play an important role in the degradation of the organic matter, especially of lignin, cellulose, chitin, and keratin, which are difficult to degrade. Thus, because of the microscopic fungal activity, the substances return to the ecosystem cycle of matter in the form accessible to plants [1, 2], which is especially important in forest ecosystems, the dynamics of which depend to a great extent on the rate of litter degradation. The latter parameter is correlated with both the rodent population density [3] and development of their burrow network [4]. Special attaching devices on micromycete spores allow the latter to attach themselves to the animal fur [1]. Nevertheless, no direct evidence of animal-dependent dispersal of soil and litter fungi is available so far. We attempted to determine the spores of various micromycete species on animal fur and to assess preliminarily the distribution of the latter over various species of small mammals and in different plots of the area studied. The material was collected in the vicinity of Krutitsy village located at the border between the Staritskii and Zubovskii raions in the Tver oblast. Plot 1 covered a forest area about 1.5 × 2 km, in size which included a 60-year-old spruce forest (mostly greenmossy bilberry forest with spots of dead foliage, ferns, and low grass), a 50-year-old sphagnum long-mossy bilberry pine forest that covered a fire site, and a small 25to 35-year-old forest that was being overgrown with alder, fir underwood, and motley grass in the lower layer. Plot 2, separated from plot 1 with fields (400 m) was represented by a 50to 60-year-old forest, which covered an area 1.2 × 2 km in size and included an alder grove with a spruce underwood and motley grass in the lower layer. Plot 3 (3 × 4 km) was in general similar to plot 1 and represented by the same biotops. Spruce and pine groves on plots 1 and 3 were outwardly indistinguishable. Plot 3 was 400 m and 2 km away plots 2 and 1, respectively, and was separated with a field from them. Since 1995, monitoring of the population structures of small mammals has been performed in this area using lines of live traps set up in various habitats [5]. In 2001, soil–litter samples (ten from every habitat) and those of hair from the nape, belly, and sides of each animal were obtained at 20-m intervals along the trap lines. The following animals were examined: 16 common shrews ( Sorex araneous ), 37 medium shrews ( S. caecutiens ), 7 pigmy shrews ( S. minutus ), and 39 redbacked voles ( Clethrionomys glareolus ), which were caught into well-cleaned, dry live traps.