Exceptional Chromosomal Evolution and Cryptic Speciation of Blind Mole Rats Nannospalax leucodon (Spalacinae, Rodentia) from South-Eastern Europe

Mole rats are exclusively subterranean and highly specialized rodents. Their long lifespans, remarkable anti-cancer mechanisms, and various distinctive adaptive features make them a useful research model. Moreover, opposing convergence of morphological traits, they have developed extremely high karyotype variability. Thus, 74 chromosomal forms have been described so far and new ones are being revealed continuously. These evolved during the process of rapid radiation and occur in different biogeographical regions. During research into their reproductive biology we have already provided substantial evidence for species-level separation of these taxa. Here, we review diverse chromosomal forms of the lesser blind mole rat, Mediterranean Nannospalax leucodon, distributed in South-eastern Europe, their karyotype records, biogeography, origin, and phylogeny from our extensive research. In the light of new data from molecular genetic studies, we question some former valuations and propose a cryptospecies rank for seven reproductively isolated chromosomal forms with sympatric and parapatric distribution and clear ecogeographical discrepances in their habitats, as well as new experimental and theoretical methods for understanding the courses of speciation of these unique fossorial mammals.Genes (2017), 8(11): 29

Do B chromosomes affect fecundity in yellow-necked mice Apodemus flavicollis (Rodentia, Mammalia)?

The effects of the presence of B chromosomes on fecundity of the yellow-necked mouse Apodemus flavicollis were studied in 46 females without and 28 with Bs from four localities in Serbia. Uterine inspection showed that there was no significant difference in the mean number of scars and embryos between females with and those without Bs. Thus, B chromosomes do not appear to affect the fecundity of females carrying them, indicating that the presence of Bs does not affect fitness characteristics.B hromozomi su dodatni hromozomi u odnosu na standardni komplement i nisu neophodni za preživljavanje. Javljaju se u gotovo svim taksonima kod oko 15% vrsta. Održavanje B hromozoma objašnjava se, u parazitskom modelu, kao balans suprotnih delovanja mehanizama akumulacije i eliminacije. U heterotičnom modelu, ravnoteža se postiže zahvaljujući pozitivnim efektima malog broja B hromozoma. U ovom radu ispitivani su efekti prisustva B hromozoma na fekunditet žutogrlog miša, Apodemus flavicollis, i to kod 46 ženki sa i 28 bez B hromozoma sa 4 lokaliteta u Srbiji. Analiza uterusa pokazala je da nema značajnih razlika u prosečnom broju ožiljaka i embriona među jedinakama sa i bez B hromozoma. Prema tome, B hromozomi nemaju efekte na fekunditet ženki koje su nosioci, odnosno njihovo prisustvo ne deluje na ovu značajnu fitnes karakteristiku. Prethodni nalazi, zajedno sa našim rezultatima, podržavaju heterotički model održavanja B hromozoma kod analizirane vrste.nul

Do B chromosomes affect fecundity in yellow-necked mice Apodemus flavicollis (Rodentia, Mammalia)?

The effects of the presence of B chromosomes on fecundity of the yellow-necked mouse Apodemus flavicollis were studied in 46 females without and 28 with Bs from four localities in Serbia. Uterine inspection showed that there was no significant difference in the mean number of scars and embryos between females with and those without Bs. Thus, B chromosomes do not appear to affect the fecundity of females carrying them, indicating that the presence of Bs does not affect fitness characteristics.B hromozomi su dodatni hromozomi u odnosu na standardni komplement i nisu neophodni za preživljavanje. Javljaju se u gotovo svim taksonima kod oko 15% vrsta. Održavanje B hromozoma objašnjava se, u parazitskom modelu, kao balans suprotnih delovanja mehanizama akumulacije i eliminacije. U heterotičnom modelu, ravnoteža se postiže zahvaljujući pozitivnim efektima malog broja B hromozoma. U ovom radu ispitivani su efekti prisustva B hromozoma na fekunditet žutogrlog miša, Apodemus flavicollis, i to kod 46 ženki sa i 28 bez B hromozoma sa 4 lokaliteta u Srbiji. Analiza uterusa pokazala je da nema značajnih razlika u prosečnom broju ožiljaka i embriona među jedinakama sa i bez B hromozoma. Prema tome, B hromozomi nemaju efekte na fekunditet ženki koje su nosioci, odnosno njihovo prisustvo ne deluje na ovu značajnu fitnes karakteristiku. Prethodni nalazi, zajedno sa našim rezultatima, podržavaju heterotički model održavanja B hromozoma kod analizirane vrste.nul

Distribution of B chromosomes in age categories of the yellow-necked mouse Apodemus flavicollis (Mammalia, Rodentia)

The presence of B chromosomes (Bs) is frequently found in populations of yellow-necked mouse, Apodemus flavicollis. Differences in frequencies of Bs in age categories were analyzed in 717 animals in order to clarify the mechanisms of their maintenance in populations of A. flavicollis. The absence of statistically significant differences in the frequency of Bs between six age categories indicates that the maintenance of Bs in populations can be explained by in terms of their contribution to overall genetic diversity of the species rather than by parasitic behavior.Prekobrojni hromozomi nazivaju se B hromozomi ako zadovoljavaju tri kriterijuma: nisu neophodni za preživljavanje, ne sparuju se sa hromozomima A seta i ne nasleđuju se mendelovski. B hromozomi su vrlo često prisutni u populacijama žutogrlog miša, Apodemus flavicollis. Njihovo održavanje u populacijama objašnjava se sa dva suprostavljena modela. Model označen kao parazitski tvrdi da se B hromozomi održavaju zahvaljujući mehanizmu akumulacije uprkos štetnim efektima na fitnes nosilaca. S druge strane, heterotički model sugeriše da u odsustvu akumulacije mali broj B hromozoma ima adaptivnu prednost za nosioce, dok veći broj može biti štetan. Ako B hromozomi, koji su označeni kao parazitski, redukuju fitnes kod jedinki koje su njihovi nosioci, onda je očekivano da frekvenca jedinki sa B hromozomima opada sa starošću. Analizirana je razlika u frekvenci B hromozoma u uzrasnim kategorijama kod 717 jedinki sa ciljem da se razjasne mehanizmi njihovog održavanja u populacijama A. flavicollis. Odsustvo statistički značajnih razlika u frekvenci B hromozoma između 6 uzrasnih kategorija ukazuje da se održavanje B hromozoma u populacijama ove vrste može objasniti njihovim doprinosom ukupnoj genetičkoj raznovrsnosti pre nego parazitskim ponašanjem.Projekat ministarstva br. 14301

Discrimination of the sibling species Apodemus flavicollis and A-sylvaticus (Rodentia, Muridae)

Karyotyping and several molecular methods have allowed successful identification of two morphologically similar wide-ranging Western Palearctic species, the yellow-necked field mouse Apodemus flavicollis (Melchior, 1934) and the long-tailed wood mouse A. sylvaticus (Linnaeus, 1758), but reliable species diagnosis on the basis of morphometric characters is particularly problematic. Although they are easily morphologically distinguishable in Central and Northern Europe, this is not the case in southern parts of their distribution areas. Despite that, we have successfully discriminated A. flavicollis and A. sylvaticus from Serbia (Southern Europe) using geometric and traditional morphometric methods on a data set for ventral crania of specimens previously genotyped by the Inter Simple Sequence Repeat-PCR (ISSR-PCR). Discrimination power of applied approaches was more or less similar. The majority of our results were consistent with those obtained for specimens collected across the Czech Republic (Central Europe). Morphological differences observed herein, as well as those already reported between A. flavicollis and A. sylvaticus from the central and northern parts of their distribution areas, could be the outcome of their biology, i.e. ecological discrepancies, different assumed evolutionary scenarios considering biogeography, phylogeny, history and ontogeny. (C) 2014 Elsevier GmbH. All rights reserved.Ministry of Education, Science and Technological Development of Serbia {[}173003

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.nul

Morphological integration of the mandible in yellow-necked field mice: The effects of B chromosomes

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

Molecular phylogeny and distribution of three Apodemus species (Muridae, Rodentia) in Serbia

Phylogenetic relationships among three species of the genus Apodemus (A.. avicollis, A. sylvaticus and A. agrarius) from seven different localities in Serbia were estimated using arbitrarily primed PCR (AP-PCR) pro. ling, which allowed clear distinction between the sibling species A.. avicollis and A. sylvaticus. Eight oligonucleotide primers out of the 22 screened, gained a total of 397 amplified bands. The average pairwise genetic distances within Apodemus species ranged from 0.51 between A.. avicollis and A. sylvaticus, to 0.74 between A. sylvaticus and A. agrarius. The large genetic distances obtained among populations of A.. avicollis (0.13) indicate that this part of the Balkan Peninsula was probably a refuge during the last glaciation. Furthermore, differences obtained between populations south and north from the river Danube suggest that this species survived the Last Glacial Maximum in at least two separate refuges. Although our data for molecular markers are from a limited number of localities, extended analyses of C-band distribution on chromosomes from previously studied localities south of the rivers Danube and Sava, indicate that distribution of A. sylvaticus is limited to northern Serbia. Therefore, it is possible that this part of the Balkan Peninsula was not a refuge for this species during the last glaciation.nul

Molecular phylogeny and distribution of three Apodemus species (Muridae, Rodentia) in Serbia

Phylogenetic relationships among three species of the genus Apodemus (A.. avicollis, A. sylvaticus and A. agrarius) from seven different localities in Serbia were estimated using arbitrarily primed PCR (AP-PCR) pro. ling, which allowed clear distinction between the sibling species A.. avicollis and A. sylvaticus. Eight oligonucleotide primers out of the 22 screened, gained a total of 397 amplified bands. The average pairwise genetic distances within Apodemus species ranged from 0.51 between A.. avicollis and A. sylvaticus, to 0.74 between A. sylvaticus and A. agrarius. The large genetic distances obtained among populations of A.. avicollis (0.13) indicate that this part of the Balkan Peninsula was probably a refuge during the last glaciation. Furthermore, differences obtained between populations south and north from the river Danube suggest that this species survived the Last Glacial Maximum in at least two separate refuges. Although our data for molecular markers are from a limited number of localities, extended analyses of C-band distribution on chromosomes from previously studied localities south of the rivers Danube and Sava, indicate that distribution of A. sylvaticus is limited to northern Serbia. Therefore, it is possible that this part of the Balkan Peninsula was not a refuge for this species during the last glaciation.nul

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.Ministry of Education and Science of Serbia [173003