Jelena Blagojević

B chromosomes in populations of mammals

B chromosomes (Bs) have been found in 55 out of 4629 living species of mammals. The summarized data show great variability in types of mammalian Bs, including differences in size, shape and molecular composition. This variability extends to the origin, mode of transmission and population dynamics. In general, B chromosomes in mammals do not differ from Bs found in other animal or plant species, but some peculiarities do exist. Most species in which Bs are found are widespread. Some data support the view that Bs may contribute to the successful expansion of some of these species, but it is possible that Bs are just more easily scored in them due to their frequent occurrence. Most of these species are also characterized by cycling fluctuations of abundance and characteristic social organization that produce conditions favorable for Bs to spread. All areas of research on Bs in mammals suffer from lack of data, emphasizing the necessity for intensified research on the molecular structure and ways of maintenance of Bs in populations.

Skull variation in Dinaric–Balkan and Carpathian gray wolf populations revealed by geometric morphometric approaches

Abstract Dinaric–Balkan and Carpathian gray wolf (Canis lupus L., 1758) populations, although geographically separated, occupy closely situated areas in the territory of Serbia. We studied morphological variation in the skull to investigate whether the two populations are distinguishable despite the animals being very large and highly mobile and seeming to form one continuous population. The size and shape of the mandible and cranium in the lateral view were compared between sexes and populations using landmark-based geometric morphometrics. Significant differences between sexes and populations were found for size and shape of both structures. Males were larger than females in both populations, and Carpathian were larger than Dinaric–Balkan wolves. Principal component analysis revealed the cranium to be a highly discriminative skull structure. Zygomatic arches were located anteriorly in males and posteriorly in females. Dinaric–Balkan wolves had a more elevated snout and sagittal crest than Carpathian wolves. Difference between Dinaric–Balkan and Carpathian wolves in the cranial flexion was observed for the first time in a comparative study of wolf populations. Present-day separation of Dinaric–Balkan and Carpathian wolf populations could have originated from 2 different glacial refuges. We presume that the observed morphometric divergence between the populations is not only a relic of the last glacial maximum but was further strengthened and shaped by synergistic effects of environmental factors and social behavior (territoriality and a dispersal mechanism influenced by the natal habitat).

B chromosomes and cranial variability in yellow-necked field mice (Apodemus flavicollis)

Abstract B chromosomes (Bs) are supernumerary chromosomes relative to the standard karyotype. The maintenance of Bs in the yellow-necked field mice (Apodemus flavicollis) was reconsidered by examining their effects on 3 components of cranial variability: canalization, developmental stability, and morphological integration. Bs do not disturb developmental homeostasis in their carriers. Moreover, Bs play a significant role in structuring cranial variation. We suggest that direct interactions between developmental pathways in mice without Bs might be a dominant mechanism for generating covariation of cranial traits, and integration of cranial traits in B carriers could be generated primarily by parallel variation of separate developmental pathways. Integration due to parallel variation is more predisposed to modifications by natural selection than integration caused by direct interactions, which could be beneficial to B carriers under variable environmental conditions. By contributing to the genetic variability of species possessing them, Bs provide themselves with long-term presence in populations. Therefore, the Bs of A. flavicollis should be considered as symbiotic genomic elements.

Two-module organization of the mandible in the yellow-necked mouse: a comparison between two different morphometric approaches.

Mandibles of yellow‐necked mouse (Apodemus flavicollis) were used to explore modularity. We tested a biological hypothesis that two separate modules (alveolar region and ascending ramus) can be recognized within the mandible. As a second research goal, we compared two different morphometric procedures under the assumption that methodological approaches that use either geometric or traditional morphometric techniques should give similar results. Besides confirmation of the predicted hypothesis of modularity, the application of both approaches revealed that: (i) modularity was somewhat more evident when it was analysed on the asymmetric (fluctuating asymmetry, FA) than on the symmetric (individual variation) component of variation; (ii) there is correspondence in the patterns of individual variation and FA, which indicates that integration of mandibular traits among individuals is primarily due to direct developmental interactions; and (iii) allometry does not obscure the hypothesized modularity for individual variation or for FA. In addition, traditional morphometric method allowed us to check whether allometry influenced each module to the same extent and to conclude that the ascending ramus is more heavily influenced by general size than the alveolar region. In studies of modularity, differences in methods can lead to discrepancies in the results, and therefore, some caution is required when comparing findings from different investigations. The substantial agreement between our results provides evidence that, when considering two‐module organization of the mouse mandible, direct comparison among studies that use the methods applied herein is, in great part, reliable.

Morphological Integration of the Mandible in Yellow-Necked Field Mice: the Effects of B Chromosomes

Abstract As a complex skeletal organ consisting of 2 functional and developmental units (ascending ramus and alveolar region), the mandible represents a well-established model in morphological integration studies. The concept of morphological integration assumes that developmentally or functionally related traits are more correlated than others and hence evolve together. We compared the level and pattern of mandibular morphological integration between groups of adult yellow-necked field mice (Apodemus flavicollis), with and without B chromosomes (Bs) in a population from Mt. Avala, Serbia. Bs are dispensable supernumerary chromosomes characterized by irregular and non-Mendelian modes of inheritance. The level of morphological integration was higher in animals with Bs. One of the 2 regions of the mandible tested (alveolar region) was significantly more affected by the presence of Bs than the other, with an increase in intensity of integration of 41.61% versus 15.86%. The hypothesis of morphological integration, which postulates disunion of the mandible into 2 distinct functional and developmental modules, was confirmed in animals with Bs. Bs probably have a function because they affect mandible phenotype (although the mechanism is unknown), increase variability within populations, and could lead to selective advantage.

Comparative cytogenetic analysis of European brown frogs: Rana temporaria, R. dalmatina and R. graeca

SUMMARYA cytogenetic study, based on the comparative analysis of chromosome morphology, amount and distribution of C-positive heterochromatin and positions of NORs, was undertaken on three species of brown frogs (Rana temporaria, R. dalmatina and R. graeca) from different Balkan localities. In contrast to their uniform karyotypes with respect to chromosome number, important interspecies differences have been observed in centromeric indices, the amount of constitutive heterochromatin, the distribution of C-bands and the positions of NORs. Analysis of these karyotype characteristics suggests that mostly intrachromosomal rearrangements occurred during karyotype differentiation of the examined species.

Molecular characterization and phylogenetic analysis of full-genome HBV subgenotype D3 sequences from Serbia

Hepatitis B virus (HBV) is classified into 8 genotypes with distinct geographical distribution. Genotype D (HBV/D) has the widest distribution area and is comprised of 7 subgenotypes. Subgenotypes D1, D2 and D3 appear worldwide, while D4-D7 have a more restricted distribution. Within the Mediterranean area, HBV/D and subgenotype D3 are the most prevalent. The purpose of this study was to characterize the full genome of Serbian HBV/D3 isolates by comparison and phylogenetic analysis with HBV/D3 sequences (66 samples) found in GeneBank/DDBJ databases from different parts of the world. Isolates were obtained from three patients diagnosed with chronic hepatitis B (HBsAg+). All three isolates have two very rare nucleotide substitutions, A929T and T150A, which indicate the same ancestor. Phylogenetic analysis of HBV/D3 genome sequences throughout the world follows an ethno-geographical origin of isolates with rare exceptions, which could be explained by human travelling and migration. The geographically close but ethnically different Serbian and Italian isolates clustered in the same subnode, and on a common branch with strains from Northern Canada. To test the apparently close HBV phylogenetic relationship between completely separated patients from Serbia and Northern Canada we analyzed in depth a 440 bp region of the HBsAg from Canadian (n=73) and Serbian (n=70) isolates. The constructed parsimony tree revealed that strains from Serbia and Northern Canada fell along the same branch which indicates independent evolution within regions of each country. Considering that HBsAg sequence has limited variability for phylogenetic analyses, our hypothesis needs further confirmation with more HBV complete genome sequences.

Comparative study of the phylogenetic structure in six Apodemus species (Mammalia, Rodentia) inferred from ISSR-PCR data

The utility of the Inter Simple Sequence Repeat-Polymerase Chain Reaction (ISSR-PCR) was explored in order to determine genetic variation in six species of the genus Apodemus (A. flavicollis, A. sylvaticus, A. uralensis, A. agrarius, A. mystacinus and A. epimelas) at the individual level, population level, in separate geographic samples and in the species as a whole. Six optimized primers produced highly reproducible and polymorphic DNA markers with 98.3% polymorphic bands on a total sample of 91 individuals from 32 localities in Europe and Asia. Moreover, each primer allowed for an exact diagnosis of each of the six Apodemus species and thus provides a simple and reliable tool for the hitherto problematic discrimination of species from the subgenus Sylvaemus. Genetic distances between species ranged from 0.079, among the closely related A. flavicollis and A. sylvaticus, to 0.203 between A. mystacinus and A. agrarius. A. flavicollis, A. uralensis and A. sylvaticus display a strong population substructure. The range of genetic distances among geographic samples within last two species reaches the values obtained for closely related species. ISSR markers proved to be a simple and reliable tool for species diagnosis, as well as for estimating genetic diversity below the species level and for closely related species, but they showed questionable reliability for larger genetic distances.

Potential genotoxic effects of melted snow from an urban area revealed by the Allium cepa test

The presence of well-known atmospheric pollutants is regularly screened for in large towns but knowledge about the effects of mixtures of different pollutants and especially their genotoxic potential is largely missing. Since falling snow collects pollutants from the air, melted snow samples could be suitable for evaluating potential genotoxicity. For this purpose the Allium cepa anaphase-telophase test was used to analyse melted snow samples from Belgrade, the capital city of Serbia. Samples of snow were taken at two sites, characterized by differences in pollution intensity, in three successive years. At the more polluted site the analyses showed a very high degree of both toxicity and genotoxicity in the first year of the study corresponding to the effects of the known mutagen used as the positive control. At the other site the situation was much better but not without warning signals. The results showed that standard analyses for the presence of certain contaminants in the air do not give an accurate picture of the possible consequences of urban air pollution because the genotoxic potential remains hidden. The A. cepa test has been demonstrated to be very convenient for evaluation of air pollution through analyses of melted snow samples.

Evolutionary genetics and systematics of the garden dormouse, Eliomys Wagner, 1840. 4 ‐ Karyotype and allozyme analyses of E. quercinus dalmaticus from Yugoslavia

Abstract The results of karyological and electrophoretic analyses of the garden dormouse, Eliomys quercinus dalmaticus, collected at two localities in Yugoslavia are reported. The karyotype consists of 48 chromosomes (FNa = 86). The chromosome morphology, as revealed by differential staining, is the same as in Eliomys quercinus pallidus from central Italy, but differs in two pairs of chromosomes from E. quercinus lusitanicus from Spain. Comparison between E. g. dalmaticus and other chromosomal races of the garden dormouse, by electrophoretic analysis of 41 gene loci, suggests a different origin for central European and Alpine populations