Retrotransposon‐based genetic diversity of Deschampsia antarctica Desv. from King George Island (Maritime Antarctic)

Deschampsia antarctica Desv. can be found in diverse Antarctic habitats which may vary considerably in terms of environmental conditions and soil properties. As a result, the species is characterized by wide ecotypic variation in terms of both morphological and anatomical traits. The species is a unique example of an organism that can successfully colonize inhospitable regions due to its phenomenal ability to adapt to both the local mosaic of microhabitats and to general climatic fluctuations. For this reason, D. antarctica has been widely investigated in studies analyzing morphophysiological and biochemical responses to various abiotic stresses (frost, drought, salinity, increased UV radiation). However, there is little evidence to indicate whether the observed polymorphism is accompanied by the corresponding genetic variation. In the present study, retrotransposon‐based iPBS markers were used to trace the genetic variation of D. antarctica collected in nine sites of the Arctowski oasis on King George Island (Western Antarctic). The genotyping of 165 individuals from nine populations with seven iPBS primers revealed 125 amplification products, 15 of which (12%) were polymorphic, with an average of 5.6% polymorphic fragments per population. Only one of the polymorphic fragments, observed in population 6, was represented as a private band. The analyzed specimens were characterized by low genetic diversity (uH_e = 0.021, I = 0.030) and high population differentiation (F_ST = 0.4874). An analysis of Fu's F_S statistics and mismatch distribution in most populations (excluding population 2, 6 and 9) revealed demographic/spatial expansion, whereas significant traces of reduction in effective population size were found in three populations (1, 3 and 5). The iPBS markers revealed genetic polymorphism of D. antarctica, which could be attributed to the mobilization of random transposable elements, unique features of reproductive biology, and/or geographic location of the examined populations.     

Identification of exotic genetic components and DNA methylation pattern analysis of three cotton introgression lines from <Emphasis Type="Italic">Gossypium bickii</Emphasis>

The impact of alien DNA fragments on plant genome has been studied in many species. However, little is known about the introgression lines of Gossypium. To study the consequences of introgression in Gossypium, we investigated ∼2000 genomic and ∼800 epigenetic sites in three typical cotton introgression lines, as well as their cultivar (Gossypium hirsutum) and wild parents (Gossypium bickii), by amplified fragment length polymorphism (AFLP) and methylation-sensitive amplified polymorphism (MSAP). The results demonstrate that an average of 0.5% of exotic DNA segments from wild cotton is transmitted into the genome of each introgression line, with the addition of other forms of genetic variation. In total, an average of 0.7% of genetic variation sites is identified in introgression lines. Simultaneously, the overall cytosine methylation level in each introgression line is very close to that of the upland cotton parent (an average of 22.6%). Further dividing patterns reveal that both hypomethylation and hypermethylation occurred in introgression lines in comparison with the upland cotton parent. Sequencing of nine methylation polymorphism fragments showed that most (7 of 9) of the methylation alternations occurred in the noncoding sequences. The molecular evidence of introgression from wild cotton into introgression lines in our study is identified by AFLP. Moreover, the causes of petal variation in introgression lines are discussed.     

Molecular analysis of genomic changes in synthetic autotetraploid Phlox drummondii Hook

Polyploidization is a major force that has shaped the evolution of flowering plants. Newly‐generated polyploids have been used to investigate the changes that occur in genomes immediately after polyploidization. The present research programme created colchitetraploids in Phlox drummondii and followed them through different generations (C₀, C₁, C₂, and C₃) to determine genomic changes. Genomic changes that followed autopolyploidization were investigated using amplified fragment length polymorphism (AFLP) and methylation‐sensitive amplified polymorphism (MSAP) technologies. The markers for which variation was evident were characterized by cloning and sequencing. Dot‐blotting was used to confirm increased or decreased abundance of the fragments for which variation was noted. We used bisulfite sequencing to determine changes in the levels of DNA methylation in the vicinities of the fragments that show variation. Our data indicate that these areas were more methylated in C₂ and C₃ colchitetraploids than in C₀ and C₁ colchitetraploids. The overall levels of methylation polymorphism found in C₂ and C₃ colchitetraploids were 1.0% and 1.65%, respectively. Changes were observed in both coding and noncoding regions. Some MSAP fragments that showed variation were similar to retrotransposons. Bisulfite sequencing indicated that CHH sites accounted for all the observed variation, whereas CG and CHG did not show any variation. The present study suggests that the genomic changes that accompany polyploidization in synthetic autopolyploids resemble those in allopolyploids. However, the extent of variation is lower in synthetic autopolyploids than in allopolyploids. These changes may help in the stabilization of the genomes of neo‐autopolyploids. © 2013 The Linnean Society of London, Biological Journal of the Linnean Society, 2013, 110 , 591–605.     

Seasonal variation in soil CO<Subscript>2</Subscript> efflux in evergreen coniferous and broad-leaved deciduous forests in a cool-temperate forest,central Korea

We measured the soil surface CO₂ efflux (R _S) from January 2005 to December 2006 in two neighboring stands in Gwangneung Forest, central Korea: evergreen coniferous forest (Abies holophylla, stand A) and broad-leaved deciduous forest (Quercus-dominated, stand Q). Regarding seasonal variation, R _S rate was low during the winter and early spring months in each stand and peaked in late July [1170 (stand A) and 1130 (stand Q) in 2005, and 1000 (stand A) and 740 (stand Q) mg CO₂ m⁻² h⁻¹ in 2006]. R _S rate was higher in stand A than in stand Q during most of the growing season. The pattern of summer rainfall differed between 2005 and 2006. R _S rate for both stands was suppressed significantly by the droughts in June 2005 and September 2006. After the heavy rainfall of July 2006, R _S rate was lower than in July 2005 in both stands, but this decrement was much greater in stand Q than in stand A. In midsummer (August) 2006, under higher soil temperature (ST) and lower soil water content (SWC) conditions than in August 2005, R _S rate of stand A was lower than that in August 2005, whereas stand Q showed no marked change. The exponential relationship between ST and R _S accounted for approximately 91–97% of the R _S variability in each stand and in each year. In stand A, the application of a second-order polynomial function indicated a significant correlation between SWC and R _S when the soil was warm (ST > 15°C). Our results suggest that the seasonality of R _S is strongly affected by the pattern of summer rainfall even in an Asia monsoon climate regime. In addition, the vegetation type (i.e., evergreen coniferous forest vs. broad-leaved deciduous forest) plays a significant role in response of R _S to various environmental fluctuations such as drought, heavy rainfall, and hot-dry condition.     

Diversity and genetic connectivity among populations of a threatened tree (<Emphasis Type="Italic">Dalbergia nigra</Emphasis>) in a recently fragmented landscape of the Brazilian Atlantic Forest

In this study we evaluated the influence of recent landscape fragmentation on the dynamics of remnant fragments from the Brazilian Atlantic Forest. This biome is one of the richest in the world and has been extensively deforested and fragmented. We sampled five populations of the threatened Dalbergia nigra, a tree endemic to the Brazilian Atlantic Forest, two located in a large reserve of continuous forest and three in fragments of different sizes and levels of disturbance. In order to assess historical changes, considering the longevity of the analyzed species, 119 adults and 116 saplings were genotyped for six microsatellite loci. Lower levels of genetic diversity were found in the most impacted fragments when compared to the most preserved population located inside the reserve, and there was significant genetic structure among the populations studied (pairwise F _ST = 0.031–0.152; pairwise D _EST = 0.039–0.301). However, genetic structure among saplings (F _ST = 0.056; D _EST = 0.231) was significantly lower than among adults (F _ST = 0.088; D _EST = 0.275). Estimates of contemporary gene flow based on assignment tests corroborated this result, suggesting that fragmentation led to an increase in gene flow. This connectivity among remnant fragments could mitigate the loss of genetic diversity through a metapopulation dynamic, but the high rate of habitat loss and the unknown long-term genetic effects add uncertainty. These results, taken together with the presence of private alleles in disturbed populations, highlight the importance of preserving the extant fragments.     

Approximation of the Basic Reproduction Number <Emphasis Type="Italic">R</Emphasis><Subscript>0</Subscript> for Vector-Borne Diseases with a Periodic Vector Population

The main purpose of this paper is to give an approximate formula involving two terms for the basic reproduction number R ₀ of a vector-borne disease when the vector population has small seasonal fluctuations of the form p(t) = p ₀ (1+ε cos (ωt − φ)) with ε ≪ 1. The first term is similar to the case of a constant vector population p but with p replaced by the average vector population p ₀. The maximum correction due to the second term is (ε²/8)% and always tends to decrease R ₀. The basic reproduction number R ₀ is defined through the spectral radius of a linear integral operator. Four numerical methods for the computation of R ₀ are compared using as example a model for the 2005/2006 chikungunya epidemic in La Réunion. The approximate formula and the numerical methods can be used for many other epidemic models with seasonality. MSC 92D30 ⋅ 45C05 ⋅ 47A55     

Conservation of long-lived perennial forest herbs in an urban context: <Emphasis Type="Italic">Primula elatior</Emphasis> as study case

Urban forests are generally fragmented in small isolated remnants, embedded in an inhospitable human-used matrix, and incur strong anthropogenic pressures (recreational activities, artificialization, pollution and eutrophication). These lead to particularly high constraints even for common forest herbs, whose genetic response may depend on life-history traits and population demographic status. This study investigated genetic variation and structure for 20 allozyme loci in 14 populations of Primula elatior, a self-incompatible long-lived perennial herb, occurring in forest fragments of Brussels urban zone (Belgium), in relation to population size and young plants recruitment rate. Urban populations of P. elatior were not genetically depauperate, but the small populations showed reduced allelic richness. Small populations showing high recruitment rates—and therefore potential rejuvenation—revealed lower genetic diversity (H _o and H _e) than those with low or no recruitment. No such pattern was observed for the large populations. There was a significant genetic differentiation among populations within forest fragments (F _SC = 0.052, P < 0.001), but not between fragments (F _CT = 0.002, P > 0.10). These findings suggest restricted gene flow among populations within fragments and local processes (genetic drift, inbreeding) affecting small populations, strengthened when there is recruitment. Urban forest populations of long-lived perennial herbs can be of conservation value. However, restoration of small populations by increasing population size through regeneration by seedling recruitment may lead to negative genetic consequences. Additional management, aiming to restore gene flow among populations, may need to be applied to compensate the loss of genetic diversity and to reduce inbreeding.     

Patterns of DNA sequence variation at candidate gene loci in black poplar (<Emphasis Type="Italic">Populus nigra</Emphasis> L.) as revealed by single nucleotide polymorphisms

Black poplar (Populus nigra L.) is an economically and ecologically important tree species and an ideal organism for studies of genetic variation. In the present work, we use a candidate gene approach to infer the patterns of DNA variation in natural populations of this species. A total of 312 single nucleotide polymorphisms (SNPs) are found among 8,056 bp sequenced from nine drought-adaptation and photosynthesis-related gene loci. The median SNP frequency is one site per 26 bp. The average nucleotide diversity is calculated to be θ_W = 0.01074 and π_T = 0.00702, higher values than those observed in P. tremula, P. trichocarpa and most conifer species. Tests of neutrality for each gene reveal a general excess of low-frequency mutations, a greater number of haplotypes than expected and an excess of high-frequency derived variants in P. nigra, which is consistent with previous findings that genetic hitchhiking has occurred in this species. Linkage disequilibrium is low, decaying rapidly from 0.45 to 0.20 or less within a distance of 300 bp, although the declines of r ² are variable among different loci. This is similar to the rate of decay reported in most other tree species. Our dataset is expected to enhance understanding of how evolutionary forces shape genetic variation, and it will contribute to molecular breeding in black poplar.     

Evidence for gametoclonal variation in potato (<Emphasis Type="Italic">Solanum tuberosum</Emphasis> L.)

Gametoclonal variation that occurs in gametic cells in culture and is recovered in their regenerated derivatives has not been reported in potato (Solanum tuberosum L.). Based on a set of 24 differentiating phenotypic traits, canonical variates analysis genetically distinguished the androgenic (di)haploid (2n = 2x = 24) D4 from its tetraploid (2n = 4x = 48) anther-derived sibs and anther donor JTH/C-107. Nuclear microsatellite analysis over six polymorphic loci indicated that meiotic rearrangements and mutant alleles were primarily associated with the release of gametoclonal variation. The incidence of null alleles in D4 at the loci STACCAS3 and STM0031 was also indicative of mutations occurring within the priming sequence. Microsatellite results were supported by random amplified polymorphic DNA (RAPD) assays that characterized a total of 567 loci (bins) representing 4,258 amplified fragments. Sixty-five new RAPDs that were absent in the anther donor and in either of its parents, viz., S. phureja Juz. & Buk. IVP-35 and S. tuberosum cv. Kufri Jyoti were present in D4, indicating the occurrence of extensive recombinational events. The results have been discussed in the context of microsatellite null alleles providing the most conclusive evidence for gametoclonal variation.     

Factors influencing the radiative surface temperature of grey seal (<Emphasis Type="Italic">Halichoerus grypus</Emphasis>) pups during early and late lactation

The aim of this study was to examine the variation in body surface temperature of grey seal (Halichoerus grypus) pups throughout lactation in response to different environmental conditions. Radiative surface temperatures (T _r, °C) of pups were measured on the Isle of May (56°11′N, 02°33′W), southeast Scotland from 29 October to 25 November 2003. Records were obtained from a total of 60 pups (32 female and 28 male) from three different pupping sites during early and late lactation. Pups were sheltered from high wind speeds but air temperature, humidity and solar radiation at pupping sites were similar to general meteorological conditions. The mean T _r of all pups was 15.8°C (range 7.7–29.7°C) at an average air temperature of 10.2°C (range 6.5–13.8°C). There was no difference in the mean T _r of pups between early and late lactation. However, the T _r varied between different regions of the body with hind flippers on average 2–6°C warmer than all other areas measured. There was no difference in mean T _r of male and female pups and pup body mass did not account for the variation in T _r during early or late lactation. Throughout the day there was an increase in the T _r of pups and this explained 20–28% of the variation in T _r depending on stage of lactation. There was no difference in the mean T _r of pups between pupping sites or associated with different substrate types. Wind speed and substrate temperature had no effect on the T _r of pups. However, solar radiation, air temperature and relative humidity accounted for 48% of the variation in mean T _r of pups during early lactation. During late lactation air temperature and solar radiation alone accounted for 43% of the variation in T _r. These results indicate that environmental conditions explain only some of the variation in T _r of grey seal pups in natural conditions. Differences in T _r however indicate that the cost of thermoregulation for pups will vary throughout lactation. Further studies examining intrinsic factors such as blubber thickness and activity levels are necessary before developing reliable biophysical models for grey seals.     

Past bottlenecks and current population fragmentation of endangered huemul deer (<Emphasis Type="Italic">Hippocamelus bisulcus</Emphasis>): implications for preservation of genetic diversity

Small populations in fragmented habitats can lose genetic variation through drift and inbreeding. The huemul (Hippocamelus bisulcus) is an endangered deer endemic to the southern Andes of Chile and Argentina. Huemul numbers have declined by 99% and its distribution by 50% since European settlement. The total population is estimated at less than 2,000 individuals and is highly fragmented. At one isolated population in Chilean Patagonia we sampled 56 individuals between 2005 and 2007 and genotyped them at 14 microsatellite loci. Despite low genetic variability (average 2.071 alleles/locus and average H _O of 0.341), a low inbreeding coefficient (F _IS) of 0.009 suggests nearly random mating. Population genetic bottleneck tests suggest both historical and contemporary reductions in population size. Simulations indicated that the population must be maintained at 75% of the current size of 120 individuals to maintain 90% of its current genetic diversity over the next 100 years. Potential management strategies to maintain genetic variability and limit future inbreeding include the conservation and establishment of habitat corridors to facilitate gene flow and the enlargement of protected areas to increase effective population size.     

Study of mitochondrial genomes of allopllasmic recombinant wheat lines constructed on the basis of barley-wheat hybrids

Using RFLP analysis with three probes homologous to specific regions of mitochondrial DNA genes and PCR analysis of the mitochondrial recombining-repeat-sequence 18S/5S region of cereals, five alloplasmic wheat lines of different origin and fertility expression were studied. These lines are self-pollinated progeny of BC₁-BC₄ generations of barley–wheat hybrids Hordeum geniculatum All. (2n = 28) × Triticum aestivum L. (2n = 42). It was found that recombinant alloplasmic lines characterized by partial fertility contain either maternal (barley) DNA fragments or maternal and paternal (wheat) DNA fragments simultaneously (heteroplasmy). In lines with stable expression of self-fertility, fragments of only paternal mitochondrial DNA were detected. It is assumed that in alloplasmic lines, there is the interrelation between the presence of definite fragments of the mitochondrial genome belonging to either parental type and fertility expression.Translated from Genetika, Vol. 41, No. 3, 2005, pp. 349–355.Original Russian Text Copyright © 2005 by Trubacheeva, Salina, Pershina.     

Genetic variation and differentiation of <Emphasis Type="Italic">Abies alba</Emphasis> Mill. populations from Ukrainian Carpathians

Using electrophoretic analysis of 11 enzyme systems, we studied the genetic structure and differentiation of eight natural populations of silver fir Abies alba Mill. in the Ukrainian Carpathians. Of 24 isozyme loci identified, 66.8% proved to be polymorphic. The mean numbers of alleles and genotypes per locus in the populations were respectively 3.1 and 4.5. Each A. alba tree was on average heterozygous at 15.9% of genes. In six populations, the genotypic distribution for all of the loci examined corresponded to Hardy-Weinberg proportions. The populations studied had low levels of subdivision (F _ST = 0.018; G _ST = 0.019 ) and differentiation. Neis genetic distances between the A. alba populations in the region ranged from 0.002 to 0.009, being on average 0.006.Translated from Genetika, Vol. 41, No. 3, 2005, pp. 356–365.Original Russian Text Copyright © 2005 by Korshikov, N. Pirko, Ya. Pirko.     

Recruitment failure in Florida Keys <Emphasis Type="Italic">Acropora palmata,</Emphasis> a threatened Caribbean coral

Recovery of Acropora palmata from its currently imperiled status depends on recruitment, a process which is poorly documented in existing Caribbean coral population studies. A. palmata is thought to be well adapted to proliferate through the recruitment of fragments resulting from physical disturbances, such as moderate intensity hurricanes. This study monitored fifteen 150 m² fixed study plots on the upper Florida Keys fore-reef for asexual and sexual recruitment from 2004 to 2007. Between July and October 2005, 4 hurricanes passed by the Florida Keys, producing wind speeds on the reef tract of 23 to 33 m s⁻¹. Surveys following the hurricanes documented an average loss of 52% estimated live tissue area within the study plots. The percentage of “branching” colonies in the population decreased from 67% to 42% while “remnant” colonies (isolated patches of tissue on standing skeleton) increased from 11% to 27%. Although some detached branches remained as loose fragments, more than 70% of the 380 fragments observed in the study plots were dead or rapidly losing tissue 3 weeks after Hurricane Dennis. Over the course of the study, only 27 fragments became attached to the substrate to form successful asexual recruits. Meanwhile, of the 18 new, small encrusting colonies that were observed in the study, only 2 were not attributable to asexual origin (i.e., remnant tissue from colonies or fragments previously observed) and are therefore possible sexual recruits. In summary, the 2005 hurricane season resulted in substantial loss of A. palmata from the upper Florida Keys fore-reef from a combination of physical removal and subsequent disease-like tissue mortality, and yielded few recruits of either sexual or asexual origin. Furthermore, the asexual and sexual fecundity of the remaining population is compromised for the near future due to the lack of branches (i.e., “asexual fecundity”) and overall loss of live tissue.     

Accelerated soil CO<Subscript>2</Subscript> efflux after conversion from secondary oak forest to pine plantation in southeastern China

Soil respiration (R _s) is an important component of the carbon cycle in terrestrial ecosystems, and changes in soil respiration with land cover alteration can have important implications for regional carbon balances. In southeastern China (Xiashu Experimental Forest, Jiangsu Province), we used an automated LI-8100 soil CO₂ flux system to quantify diurnal variation of soil respiration in a secondary oak forest and a pine plantation. We found that soil respiration in the pine plantation was significantly higher than that in the secondary oak forest. There were similar patterns of soil respiration throughout the day in both the secondary oak forest and the pine plantation during our 7-month study (March–September 2005). The maximum of R _s occurred between 4:00 pm and 7:00 pm. The diurnal variations of R _s were usually out of phase with soil surface (0.5 cm) temperature (T _g). However, annual variation in R _s correlated with surface soil temperature. Soil respiration reached to a maximum in June, and decreased thereafter. The Q₁₀ of R _s in the secondary oak forest was significantly higher than that in the pine plantation. The higher Q₁₀ value in the secondary oak forest implied that it might release more CO₂ than the pine plantation under a global-warming scenario. Our results indicated that land-use change from secondary forest to plantation may cause a significant increase in CO₂ emission, and reduce the temperature sensitivity of soil respiration in southeastern China.     

Airborne <Emphasis Type="Italic">Aspergillus</Emphasis> and <Emphasis Type="Italic">Penicillium</Emphasis> in the atmosphere of Szczecin, (Poland) (2004–2009)

The investigation into airborne fungal spore concentrations was conducted in Szczecin (Poland) between 2004 and 2009. The objective of the studies was to determine a seasonal variation in concentrations of amerospores on the basis of meteorological parameters. The presence of spores in Szczecin was recorded using a volumetric method. Fungal spores were present in the air in high numbers in late summer and early autumn. The highest concentrations were noted in September, October and November. The peak period was recorded in August, September, October and November. The highest annual number of spores occurred in 2005 and 2007 and the lowest in 2006. High values of daily concentration of amerospores occurred during the afternoon and late at night. In 2005 and 2007 the late-night maximum was overdue about 1 or 2 h. For daily values of dew point temperature and relative humidity, the coefficients were positive, significant for p = 0.001 and ranged from 0.342 to 0.258. The average wind speed was positively correlated for p = 0.01 and the coefficient was 0.291. The similar relations were noted for hourly values of spore concentrations for p = 0.05, p = 0.01 and p = 0.001. For these spore types, the dew point temperature and relative humidity appeared to be the most influential factor.     

An ecological study of association between coronary heart disease mortality rates in men and the relative frequencies of common allelic variations in the gene coding for apolipoprotein E

Three common alleles, ɛ ₂ , ɛ ₃ , and ɛ ₄ , of the gene coding for apolipoprotein E (apoE) have been identified as predictors of interindividual variation in measures of lipid and lipoprotein metabolism, and ultimately risk of coronary heart disease (CHD), within many populations. Here we evaluated the utility of the geographic distribution of these alleles for prediction of interpopulation variation in average level of serum total cholesterol and other traditional risk factors, and CHD mortality rate. We employed published estimates of the relative frequencies of the three common apoE alleles, average levels of risk factors such as serum total cholesterol, systolic and diastolic blood pressure, body mass index, smoking prevalence and CHD mortality rate for nine population-based samples of middle-aged males studied by the international WHO MONICA Project. There was approximately a 10-fold difference between the highest and lowest CHD mortality rate. Of the traditional risk factors, variation in the average level of serum total cholesterol was the best predictor (approximately 33%) of the observed interpopulation variation in estimates of CHD mortality rate (Pr=0.10). Variation in the relative frequency of the ɛ ₄ allele predicted approximately 50% of interpopulation variation in average serum total cholesterol level (Pr=0.02) and 75% of the variation in CHD mortality rate (Pr=0.002) when information about variation in the other risk factors and the ɛ ₂ andɛ ₃ alleles is ignored. Furthermore, variation in the relative frequency of the ɛ ₄ allele predicted approximately 40% of the variation in CHD mortality rate (Pr=0.02) after considering the contribution of variation in average serum total cholesterol level. Average serum total cholesterol level was estimated to increase by 0.114 mmol/l (4.405 mg/dl), and CHD mortality rate by 24.5/100 000, for an increase of 0.01 in the relative frequency of the ɛ ₄ allele. The predictive utility of the ɛ ₂ andɛ ₃ alleles was considerably less than that of the ɛ ₄ allele. For the sample of populations considered, the geographic distribution of the apoE alleles can be a statistically significant predictor of interpopulation variation in both the average serum total cholesterol level and CHD mortality rate. In particular, the ɛ ₄ allele may confer valuable ecological risk information. Received: 2 December 1997 / Accepted: 28 May 1998     

Long‐term monitoring of B‐chromosome invasion and neutralization in a population of Prospero autumnale (Asparagaceae)

B chromosomes have been reported in about 15% of eukaryotes, but long‐term dynamics of B chromosomes in a single natural population has rarely been analyzed. Prospero autumnale plants collected in 1981 and 1983 at Cuesta de La Palma population had shown the presence of B chromosomes. We analyze here seven additional samples collected between 1987 and 2015, and show that B frequency increased significantly during the 1980s and showed minor fluctuations between 2005 and 2015. A mother–offspring analysis of B chromosome transmission, at population level, showed significant drive on the male side (k_B = 0.65) and significant drag on the female side (k_B = 0.33), with average B transmission rate being very close to the Mendelian rate (0.5). No significant effects of B chromosomes were observed on a number of vigor and fertility‐related traits. Within a parasite/host framework, these results suggest that B chromosomes’ drive on the male side is the main pathway for B chromosome invasion, whereas B chromosome drag on the female side might be the main manifestation of host genome resistance in this species. Prospero autumnale thus illuminates a novel evolutionary pathway for B chromosome neutralization by means of a decrease in B transmission through the nondriving sex.     

<Emphasis Type="Italic">In vitro</Emphasis> clonal propagation of <Emphasis Type="Italic">Holarrhena antidysenterica</Emphasis> (L.) wall. through nodal explants from mature trees

Summary In vitro clonal propagation of 18–20-yr-old Holarrhena antidysenterica tress has been achieved by employing nodal explants. The tree explants showed marked seasonal variation in their morphogenic response under in vitro conditions. Maximum response was obtained from the beginning of May to the end of July, followed by a gradual decline, finally dropping to zero from October to February. The explants induced multiple shoots only on cytokinin-containing medium. Several cytokinins [N⁶-benzyladenine (BA), N⁶-(2-isopentenyl) adenine (2ip), 6-furfuryl aminopurine (Kn), and adenine sulfate (Ads)] were assayed. The best response was achieved with 15 μM BA in which 62.5% of cultures produced 2.75±0.2 shoots per explant with 3.56±0.2 cm average length. Amongsth the three heavy metals assayed, silver nitrate (AgNO₃) significantly improved the response. This compound enhanced both the percentage of responding cultures (86.6%) and the average shoot number (4.73±0.2) at a concentration of 20mgl⁻¹. Further improvement in the morphogenic response occurred when explants from in vitro shoots were employed instead of mature trees. In this case, the percentage of morphogenic cultures was increased to 100% at the third subculture with an average of 11.45±0.3 shoots per explant. Regenerated shoots were rooted in half-strength Murashige and Skoog medium with 10 μM indole-3-acetic acid. The plantlets were successfully acclimatized in soil.     

Effective Size of the Early-Run Sockeye Salmon <Emphasis Type="Italic">Oncorhynchus nerka</Emphasis> Population of Lake Azabach’e,Kamchatka Peninsula Evaluation of the Effect of Interaction between Subpopulations within a Subdivided Population

The effect of subdivision on the effective size (N _e) of the early-run sockeye salmon Oncorhynchus nerka population of Lake Azabach’e (Kamchatka Peninsula) has been studied. The mode of this effect is determined by the relative productivity of the subpopulations and its magnitude, by the rate of individual migration among subpopulations and genetic differentiation. If the contributions of subpopulations (offspring numbers) are different, genetic differentiation can reduce the N _e of the subdivided population. At equal subpopulation contributions, genetic differentiation always increases the N _e of the subdivided population in comparison with a panmictic population. We have found that all sockeye salmon subpopulations of Azabach’e Lake produce equal offspring numbers contributing to the next generation. The genetic differentiation between sockeye salmon subpopulations is low, and the subdivision increases the N _e of the early-run race with reference to the sum of the effective sizes of the subpopulations by as little as 2%.__________Translated from Genetika, Vol. 41, No. 5, 2005, pp. 680–685.Original Russian Text Copyright © 2005 by Efremov.