Agata Banaszek

Genetic differentiation of polish populations of Sorex araneus L. III : Interchromosomal recombination in a hybrid zone

Two parapatric chromosomal races of the common shrew (Sorex araneus) in Poland differ in their complement of metacentric arm combinations: hk, io, gr, nm (race IV), and hi, ko, gm, np (race II). In hybrids, these eight race‐diagnostic metacentrics form two randomly segregating complexes. The first complex (C1) occurs in the form of a ring configuration ok/kh/hi/io, or a chain o/ok/kh/hi/i (when there is Robertsonian polymorphism of the element io). The second complex (C2) always takes the form of a six‐element chain configuration r/rg/gm/mn/np/p. The C2 complex may be shortened to five or even four elements, when acrocentrics g, m and n are present. In the contact zone we found shrews of pure races (race II or IV), as well as hybrids with C1 or C2 complexes, and recombinants hi, ko, gr, nm. Complex heterozygotes are likely to suffer reduced fertility due to malsegregation at meiosis. However, the C1 hybrids with ring configurations occur with a high frequency throughout the contact zone. This suggest that their fitness is only slightly lowered relative to pure race individuals, in contrast to the hybrids with C1 or C2 chain configurations, which presumably have a more heavily reduced fertility. On the other hand, at the center of the zone there is a high proportion of recombinants, which, being chromosomal homozygotes, should display normal meiotic segregation. Furthermore, the high frequencies of recombinants within the contact zone should facilitate gene flow between the races. The occurrence of recombinants plays a similar role as the appearance of the maximum frequencies of acrocentric homozygotes described in several contact zones of S. araneus.

The evolutionary history of the two karyotypic groups of the common shrew, Sorex araneus , in Poland

Genetic variability within and among two karyotypic groups and five chromosome races of the common shrew (Sorex araneus) in Poland was assayed by sequencing a 1023 bp part of the cytochrome b gene (mtDNA) from 28 individuals. Thirty-four variable positions defined 21 distinct haplotypes with a maximum sequence divergence of 0.88%. No significant differentiation in the cytochrome b gene between Western and Eastern Karyotypic groups was found. Haplotype diversity estimates within the races and groups sampled were high (h = 0.800–0.928), while nucleotide diversity estimates were low (π = 0.0034–0.0053). The distribution of pairwise nucleotide differences fits well with expectations of a ‘sudden expansion’ model. High haplotype diversity was accompanied by relatively high expected heterozygosity (HE) values in nuclear genes (calculated over 47 enzyme loci: HE = 0.031 – 0.049), giving no evidence for a recent bottleneck after the process of post-Pleistocene recolonization of Poland by the shrews. Thus, for S. araneus chromosome races in Poland, the data on the cytochrome b gene variability support the hypothesis assuming the Robertsonian fusions having spread into an ancestral acrocentric distribution.

Chromosomal rearrangements do not seem to affect the gene flow in hybrid zones between karyotypic races of the common shrew (Sorex araneus).

Chromosomal rearrangements are proposed to promote genetic differentiation between chromosomally differentiated taxa and therefore promote speciation. Due to their remarkable karyotypic polymorphism, the shrews of the Sorex araneus group were used to investigate the impact of chromosomal rearrangements on gene flow. Five intraspecific chromosomal hybrid zones characterized by different levels of karyotypic complexity were studied using 16 microsatellites markers. We observed low levels of genetic differentiation even in the hybrid zones with the highest karyotypic complexity. No evidence of restricted gene flow between differently rearranged chromosomes was observed. Contrary to what was observed at the interspecific level, the effect of chromosomal rearrangements on gene flow was undetectable within the S. araneus species.

A comparison of spermatogenesis in homozygotes, simple Robertsonian heterozygotes and complex heterozygotes of the common shrew (Sorex araneus L.)

Spermatogenesis was studied in 56 shrews (Sorex araneus L.) from two chromosomal hybrid zones in Poland. The hybrid zones were formed between chromosome races that differed in Robertsonian metacentrics. Shrews were compared in four classes: homozygotes, simple Robertsonian heterozygotes, complex heterozygotes forming four-element rings in meiosis I, and complex heterozygotes forming four- or five-element chains. There was a significant effect of karyotype on the level of germ-cell death and chain-forming complex heterozygotes suffered the greatest germ-cell loss. However, the estimated level of germ-cell death is probably insufficient to influence the fertility of these males.

Chloroplast DNA variation of Betula humilis Schrk. in Poland and Belarus

Betula humilis is an endangered plant species in Central Europe. In order to protect this species, it is necessary to document its genetic diversity in this region and to identify areas for conservation prioritisation. As molecular investigations conducted throughout the ranges of many plant species have shown that the highest genetic diversities are found within former glacial refugia and/or within the contact zones of different phylogenetic lineages, we investigated the reasons underlying the considerable genetic variation of B. humilis in northeastern Poland revealed previously using nuclear microsatellites. We analysed 365 individuals of B. humilis from 19 populations and 67 specimens of Betula pendula and Betula pubescens sampled in four geographical regions in Poland and Belarus for polymorphism in chloroplast PCR-restriction fragment length polymorphism markers. Genetic data strongly suggested that B. humilis could have survived the Last Glacial Maximum at higher latitudes, but the hypothesis of a refugium in southeastern Poland was rejected. Chloroplast DNA analysis confirmed high genetic diversity in some populations in northeastern Poland. This phenomenon can likely be explained in terms of a suture zone, as the high haplotypic richness was followed by hT ≤ vT. Similar patterns of haplotype distributions in the birches under study and high introgression ratio (IG = 0.71) among B. humilis and congeneric trees suggested that postglacial recolonisation of the shrub birch was complicated by haplotype sharing with other birches.

Low genetic diversity and significant structuring of the common hamster populations Cricetus cricetus in Poland revealed by the mtDNA control region sequence variation

The genetic diversity of 12 populations in the present range of the common hamster Cricetus cricetus (Linnaeus, 1758) in Poland was established. The 366 bp of the mtDNA control region was sequenced for 195 individuals. As few as seven haplotypes were found and their distribution was geographically structured. The large geographic areas were fixed or almost fixed for a single haplotype and three groups of populations, that do not share any haplotypes, have been defined. Proportions of genetic diversity attributable to variation between groups of populations, between populations within groups and within populations were 93.64, 1.92 and 4.45% (SAMOVA: p < 0.001 for all estimates), respectively. Such pattern of variation is most probably the result of historical, postglacial bottlenecks and present genetic drift after the population decline in the last few decades.

Meiotic studies of male common shrews (Sorex araneus L.) from a hybrid zone between chromosome races

Thirty-three adult male common shrews (Sorex araneus L.) were collected from a hybrid zone between two chromosomal races that differed in Robertsonian metacentrics. Anaphase I nondisjunction frequencies were estimated on the basis of metaphase II counts. RIV and CV complex heterozygotes (four-element rings and five-element chains at meiosis I, respectively) had substantially higher nondisjunction rates than homozygotes and simple Robertsonian heterozygotes. However, at least in the case of RIV-forming hybrids, increased nondisjunction frequency did not result from malsegregation of the heterozygous complex. Extra elements found in hyperploid spreads were most frequently acrocentrics, that could not originate from a fully metacentric multivalent. Complex heterozygotes were also characterized by higher frequencies of univalents observed at diakinesis I. However, univalents did not originate from complex configurations, which were regularly formed with usually one chiasma per chromosome arm. Hence, we suppose that the presence of multivalents in the cell affects pairing and segregation of other elements at meiosis I.

Could Betula humilis have survived the last glaciation at a current margin of its distribution? Testing the hypothesis of a glacial refugium using nuclear microsatellites

The probability of population extinction seems to differ within the species range. Populations occupying former glacial refugia could harbor substantial genetic resources, hence they should be less prone to extirpation. It was hypothesized that the shrub birch Betula humilis could have survived the Last Glacial Maximum (LGM) at the current southwestern margin of its range. Using ten nuclear microsatellites, we studied genetic variation within and between 18 localities of B. humilis situated in marginal and subcentral areas. Six marginal populations were located in areas covered by an ice sheet during the LGM, and the remaining samples came from unglaciated areas. Analysis of private allele frequencies as well as hierarchical AMOVAs conducted for geographical regions, marginal versus central populations, and glaciated versus unglaciated areas did not confirm the hypothesis of glacial isolate of the shrub birch in southeastern Poland. On the other hand, very high genetic variation in some localities in northeastern Poland was found. Survival in periglacial areas followed by broad-fronted colonization or the existence of an admixture zone of phylogeographic lineages was proposed to explain this phenomenon.

The common hamster (Cricetus cricetus) in Ukraine: evidence for population decline

Abstract. The common hamster (Cricetus cricetus L.) is supposed to be an abundant species in Eastern Europe including Ukraine. However, the current data on hamsters occurrence in Ukraine from 1990 till nowadays show that the species became rare. The common hamster can be found in the West, North-East Ukraine and the Crimean peninsula. The species have declined in the forest-steppe zone and became extinct in most part of the steppe zone. Its actual distribution range has thus been strongly reduced. One of the possible causes of this decline is the habitat loss due to changes in agricultural management.

The distribution of the common hamster (Cricetus cricetus) in western Ukraine

Abstract The aim of this study was to determine the current range of the common hamster (Cricetus cricetus) in western Ukraine by checking the points of occurrence known from literature, personal reports and museum collections. According to RUSIN et al. (2013) the common hamster was reported from 23 localities grouped in 12 areas in 7 oblasts of Western Ukraine. In total, we confirmed eight areas of hamster occurrence from RUSIN et al. (2013) and found one new locality. The highest densities of the common hamster occured around Hrymailiv, Ternopol oblast and Halych, Ivano- Frankovsk oblast. The areas located in the vicinity of Lutsk in Volyn oblast, Chernovtsy and between Sambir and Old Sambir in Lvov oblast represent medium density populations. Low and very low densities were found in areas close to Lvov and Kamieniec Podolski, and Khmelnitskiy oblast. In general, it can be stated that the Volyn Upland and Podolia are still inhabited by the common hamster. Moreover, habitat conditions that support the existence of the common hamster and possibilities of contact with hamster populations from neighboring countries are also discussed in this paper. STRESZCZENIE Celem niniejszych badań było określenie aktualnego rozmieszczenia populacji chomika europejskiego (Cricetus cricetus) na terenie zachodniej Ukrainy. W tym celu sprawdzono obszary dotychczas uważane za zamieszkane przez chomika, znane z dostępnej literatury, indywidualnych obserwacji i informacji pochodzących ze zbiorów muzealnych. Zgodnie z badaniami opublikowanymi przez Rusin i in. (2013), chomik Europejski występuje w 23 lokalizacjach zgrupowanych w 12 głównych obszarach położonych łącznie na terenie 7 obwodów zachodniej Ukrainy. Podczas tegorocznych badań potwierdzono obecność chomika europejskiego na terenie 8 z 12 obszarów opisanych przez Rusin i in. (2013) oraz znaleziono jedną nową lokalizacją występowania tego gatunku. Największe zagęszczenie populacji chomika odnotowano w okolicy miejscowości Grzymałów, obwód Tarnopolski oraz miejscowości Halicz, obwód Ivano-Frankowski. Obszar zlokalizowany w sąsiedztwie Łucka w obwodzie Wołyńskim, Czemiowiec w obwodzie Czemiowieckim i pomiędzy Sambirem a Starym Sambirem w obwrodzie Lwowskim charakteryzuje średnie zagęszczenie populacji chomika europejskiego. Niski i bardzo niski stopień zagęszczenia stwierdzono w populacjach zamieszkujących teren w okolicach Lwrowra i Kamieńca Podolskiego położonego w obwrodzie Chmielnickim. Dodatkowo w przedło- żonej pracy omówione zostały wrarunki siedliskowa preferowane przez badany gatunek oraz możliwości kontaktu populacji zamieszkujących tereny przygranicze z populacjami chomika europejskiego z sąsiednich krajów.