Katarzyna A. Jadwiszczak

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.

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.

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 admixture zone of Betula humilis Schrk. phylogenetic lineages follows the eastern central European suture zone

Background: Contemporary genetic variation across species ranges reflects Pleistocene climatic changes. The highest genetic diversity is usually found within areas of known or presumed glacial refugia and within the admixture zones of phylogenetic lineages. Aims: The aim of our study was to evaluate the genetic diversity in the populations of Betula humilis, an endangered species, to distinguish between the refugial and suture zone hypotheses. Methods: We used the PCR-RFLP method to analyse the chloroplast DNA variation in populations of B. humilis, distributed across north-eastern Poland, western Belarus and Latvia. Rarity index (DW) was calculated for each population based on ‘frequency-down-weighted marker values’. We tested phylogeographic structure by using the Permut software. Results: The area studied was phylogeographically structured; DW values were low. Conclusions: Based on the low DW values, we rejected the hypothesis of a periglacial refugium in north-eastern Poland and Belarus. Most likely, the substantial genetic diversity in the area under study is a consequence of the mixing of phylogenetic lineages derived from distinct glacial refugia. The admixture zone of B. humilis follows the eastern central European suture zone.

Morphometric Differences Between the Phylogeographic Lineages of the Common Hamster Cricetus Cricetus in Poland

Morphometric Differences Between the Phylogeographic Lineages of the Common Hamster Cricetus Cricetus in Poland As the common hamster is endangered in the European part of its range, it is necessary to define the conservation units for successful management of natural populations. Here we describe the case of clear morphometric differentiation between phylogeographic lineages of the common hamster. The standard external measurements were taken from 209 common hamsters collected during the period 2005-2007 from the present species range in Poland. The studied populations belong to different phylogeographic lineages P3 (Polish Pannonia) and E1, and the hamsters of P3 lineage are smaller with longer feet and tails than the hamsters of E1 lineage. The phylogeographic lineages of the common hamster can be defined as evolutionary significant units (ESU) due to the significant genetic differentiation and as management units (MU) with the evidence for ecological differentiation. Morfometryczne Zróżnicowanie Pomiędzy Liniami Filogeograficznymi Chomika Europejskiego Cricetus Cricetus W Polsce Chomik europejski jest gatunkiem zagrożonym w całej europejskiej części zasięgu, istnieje więc konieczność zdefiniowania jednostek ochrony w obrębie gatunku w celu skutecznego zarządzania naturalnymi populacjami. Opisujemy tutaj przypadek wyraźnej różnicy morfologicznej pomiędzy liniami filogeograficznymi chomika europejskiego. Standardowe pomiary zewnętrzne zostały wykonane na 209 chomikach odłowionych w latach 2005-2007 z obecnego zasięgu gatunku w Polsce. Badane populacje należą do różnych linii filogeograficznych: P3 (Pannonia w Polsce) i E1 i stwierdzono, że chomiki linii P3 są mniejsze z dłuższymi stopami i ogonami niż chomiki linii E1. Linie filogeograficzne chomika europejskiego mogą być więc zdefiniowane jako jednostki o znaczeniu ewolucyjnym (ESU), w związku z istotnym zróżnicowaniem genetycznym, i jednostki zarządzania (MU), z wykazanym zróżnicowaniem ekologicznym.

Sexual reproduction efficiency and genetic diversity of endangered Betula humilis Schrk. populations from edge and sub-central parts of its range

Outcrossed mating systems play a very important role in the persistence of endangered, self-incompatible plants such as shrub birch, Betula humilis Schrk. The goal of this study was to estimate, for the first time, the effectiveness of sexual reproduction in threatened edge and sub-central populations of shrub birch. The amplified fragment length polymorphism (AFLP) method revealed that all of the individuals at each locality had different genotypes. The matrix incompatibility count (MIC) suggested that the effectiveness of recombination was similar among all the populations of shrub birch under study. However, taking into account the greater germination ability of seeds in sub-central populations, we conclude that sexual reproduction in those populations can be more efficient. The germination capacity of seeds depends on their mass, which was significantly lower in dry or more shaded sites compared to wet or more exposed sites. Non-significant results of multiple regression models suggest that chemical parameters of the habitat (pH, EC, NH4+, PO43−) had no influence on the reproductive output of B. humilis. The discrepancy between the still quite substantial genetic diversity and the poor sexual reproduction in shrub birch populations can be explained by the production of a few phosphorus-rich seeds, insufficient time for a decrease in genetic variation in the disappearing part of the range or hybridization with close congeners.

Disappearing population of Betula humilis Schrk. on the Maliszewskie Lake, NE Poland

Abstract Betula humilis Schrk. is an endangered glacial relict inhabiting wet meadows, natural and drained fens. One of its declining populations is located on the Maliszewskie Lake (the Wizna swamp, north-eastern Poland). The goal of the present study was to estimate the number of B. humilis individuals in this locality. In the Maliszewskie Lake population, 59 ramets, grouped into three clusters, were found. Twelve nuclear microsatellite loci were chosen to genotype 52 ramets. The analysis revealed that all the shoots within the single cluster had the same genotypes at the loci considered. This means that each cluster constituted one genetically distinct individual; thus, there were only three individuals of B. humilis in the studied population. The maintenance of the B. humilis population in the Maliszewskie Lake area requires urgent active protection involving removal of the shading vegetation. In fact, the entire Maliszewskie Lake is worthy of protection because of its hitherto unexplained origin and the occurrence of many endangered bird species.

Unfavourable habitat conditions can facilitate hybridisation between the endangered Betula humilis and its widespread relatives B. pendula and B. pubescens

ABSTRACT Background: Hybridisation can be a threat for the survival of a rare species because, in the case of insufficient numbers of appropriate mates, a rare form is much more likely to cross with a widespread taxon. Aims: In the present study, we tested hypotheses concerning the level of hybridisation between endangered Betula humilis and its widespread congeners: B. pendula and B. pubescens as a function of habitat conditions. Methods: We genotyped 312 individuals of three species using AFLP markers. B. humilis specimens were sampled in populations with low and high groundwater levels. Morphological identification of B. pubescens and B. pendula was verified using the Atkinson discriminant function. Results: Altogether, 15 individuals (4.8%) were indicated as putative hybrids. The B. humilis hybrids were found in dry habitats and they could be classified as F1 or F2 generation. Tree hybrids could represent backcrosses to either B. pendula or B. pubescens. Conclusions: Genetic analyses contradicted the idea that hybridisation between B. humilis and its close relatives was extensive. On the other hand, the presence of introgressed individuals in the populations in areas with low groundwater levels implied that pollen swamping might be a threat for declining B. humilis stands.