Vanja Bugarski-Stanojević

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 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.

B chromosomes in populations of yellow‐necked mice – stowaways or contributing genetic elements?

B chromosomes (Bs) are supernumerary elements to the standard chromosome set, characterized by a dispensable nature. They are maintained like parasites if they possess any mechanism of accumulation. Otherwise, they must confer some selective advantage to the carriers. Some evidence for a beneficial effect led to the dominating opinion that Bs are genomic parasites. Populations of the yellow‐necked mouse, Apodemus flavicollis, are characterized by a frequent presence of Bs, even though no mechanism for their accumulation has been found. Head morphology was compared in three populations of this species with different frequencies of animals with Bs (fB). Two of the localities (Mt. Avala, fB = 0.37 and Mt. Cer, fB = 0.31) are typical forest habitats and are about 100 km far from each other, while the third locality (Ada, fB = 0.19) is a quite different habitat located less than 5 km from Mt. Cer. Discriminant analysis of morphological traits separated the locality Ada from Mt. Avala, while the population from Mt. Cer, besides its internal variation, included variation from both other localities (Ada‐like and Mt. Avala‐like). The frequency of animals with Bs in the Ada‐like group (in the Mt. Cer population) was significantly different from that in the Ada population (0.19 vs. 0.43). Differences in fB, found in phenotypically/genotypically similar groups in different habitats, point to the existence of adaptive effects of Bs at the level of populations.

Habitat quality and B chromosomes in the yellow-necked mouse Apodemus flavicollis

The correlation between frequency of B chromosomes and quality of habitat was analysed in 680 specimens of yellow‐necked mice, Apodemus flavicollis, collected at six localities in Serbia. Animals with B chromosomes were present at all localities in frequencies ranging from 0.23 to 0.40. Quality of habitat was judged from an index of overall body size (BSI). At the studied localities, the frequency of animals with Bs was negatively correlated with the index of overall body size (r = −0.93), indicating that B chromosomes in this species are mentioned due to the effects that they exert at the level of populations. This finding supports the heterotic model of maintenance of B chromosomes.

Genetic differentiation in populations of the yellow-necked mouse, Apodemus flavicollis, harbouring B chromosomes in different frequencies

Two alternative models are used to explain maintenance of polymorphism of B chromosomes (Bs) in populations of a great number of species. The parasitic model suggests deleterious effects of Bs on fitness of carriers, while the heterotic model assumes that, in the absence of drive, equilibrium is produced by beneficial effects of Bs at low numbers. In order to determine the potential contribution of Bs to genetic differentiation and diversity, four populations of Apodemus flavicollis, differing in frequency of Bs (from 0.23 to 0.38) and settled in ecologically different habitats, were analyzed by 471 AFLP markers. Although numerous loci were demonstrated to be population specific, none of them was associated with individuals with Bs. AMOVA showed that the presence of Bs does not affect population differentiation, pointing to greater genetic similarity of Bs to A chromosomes. The greatest genetic diversity (0.241) was found in the population settled in optimal conditions for this species featured by the lowest frequency of animals with Bs (0.23). We found that the majority of loci marked as loci under directional selection, are characteristic of either a population with lower or one with a higher frequency of Bs. Several loci detected as outliers were associated with environmental variables that could directly and/or indirectly influence population dynamics of A. flavicollis. Thus, we suggest that the different frequency of Bs carriers in populations is related to adaptive differentiation to diverse habitats, which is in accordance with the heterotic model of Bs maintenance.

Genetic Analysis of Dobrava-Belgrade Virus from Western Serbia - A Newly Detected Focus in the Balkan Peninsula

Dobrava–Belgrade virus (DOBV) is a hantavirus species that causes the most severe form of haemorrhagic fever with renal syndrome (HFRS) in Europe. DOBV has been detected in three Apodemus rodents: A. flavicollis, A. agrarius and A. ponticus. These emerging viruses appear throughout the Balkan Peninsula including Serbia as its central part. In this study, we examined the seroprevalence, molecular epidemiology and phylogenetics of DOBV from A. flavicollis captured at six Serbian localities. Furthermore, we applied microsatellite typing of host animal genome to analyse the role of host kinship in DOBV animal transmission. The overall IgG seropositivity rate over 3 years (2008–2010) was 11.9% (22/185). All seropositive samples were subjected to RT‐PCR and DNA sequencing for S and L genome segments (pos. 291–1079 nt and 2999–3316 nt, respectively). DOBV was genetically detected in three samples from mountain Tara in western Serbia, a newly detected DOBV focus in the Balkans. No sequence data from human cases from Serbia are available for the studied period. However, collected DOBV isolates in this work phylogenetically clustered together with isolates from Serbian human cases dating from 2002, with 1.9% nucleotide divergence. We determined the level of kinship between seropositive and seronegative animal groups and found no significant difference, suggesting that horizontal virus transmission in the studied population was the same within and among the hatches. Our findings are the first genetic detection of DOBV in rodents in Serbia. We confirm wide and continuous hantavirus presence in the examined parts of the Balkans, underlying the necessity of continual monitoring of hantavirus circulation in A. flavicollis.