Decrease In Genetic Diversity Research Articles

Microenvironmental sensitivity of body weight at harvest in Nile tilapia: Genetic parameters, performance test traits, and genetic variability

Uniformity of body weight at harvest is a trait of great economic importance in Nile tilapia production. Studying the genetic aspects of microenvironment sensitivity proves to be a valuable instrument for enhancing the uniformity of production. The microenvironmental sensitivity of a given genotype can be quantified by analyzing the degree of genetic heterogeneity of environmental variance. This study involved the analysis of a database comprising phenotypic records of body weight at harvest for 10,207 individuals. It aimed to estimate genetic parameters, scrutinize the effects of direct selection, and evaluate how selection impacts the genetic variability within a Nile tilapia breeding program. Estimates of genetic parameters were obtained by Bayesian procedures using a two-step animal model in GIBBS1F90 (BLUPF90 family) software. The coefficients of variation for residual variance (0.29) and genetic correlation (−0.43) between body weight at harvest and microenvironmental sensitivity were deemed moderately favorable. Direct selection for microenvironmental sensitivity resulted in a 41% increase in the coancestry coefficient. The group chosen for low microenvironmental sensitivity exhibited a significant difference of 19.08% in the coefficient of variation from the group selected for high microenvironmental sensitivity. No significant differences in the coefficient of variation were observed between tilapia of the commercial line selected for growth rate and those selected for low microenvironmental sensitivity. Selection for microenvironmental sensitivity has the potential to enhance production uniformity. Significantly, directional breeding for performance achieves a comparable improvement in uniformity. Nevertheless, opting for direct selection for microenvironmental sensitivity could result in a decrease in genetic variability within Nile tilapia breeding programs.

Recurrent selection for Fusarium head blight resistance in a durum wheat population

AbstractFusarium head blight (FHB) is a devastating fungal disease of wheat. Since early 1990s, frequent FHB epidemics in major wheat‐growing regions have caused massive economic losses. Developing FHB‐resistant varieties is key to minimize the loss caused by the disease. In durum wheat (Triticum turgidum L. ssp. durum), however, it is challenged by lack of resistant sources. Introgression of resistance genes from wild relatives and bread wheat has resulted in some durum wheat lines with moderate resistance. Due to its complex genetic nature, integrating more resistance genes with moderate and even minor effects promises to provide high and durable FHB resistance. In this study, a base population was developed using diverse resistant lines and elite durum wheat breeding lines as founders and went through three cycles of phenotypic selection from 2019 to 2022, with FHB severity decreased by 34%. Six S0:1 lines in Cycle 2 and Cycle 3 populations exhibited significantly lower FHB severity than the moderately susceptible check variety ND Riveland. The results suggested that recurrent phenotypic selection could effectively improve FHB resistance. Analysis of the founders and Cycle 2 and Cycle 3 populations with 2706 single nucleotide polymorphism markers indicated that there was little decrease in genetic variation due to selection. Genome‐wide association analysis found no markers significantly associated with FHB severity. Genomic prediction accuracies based on cross‐validation for FHB severity, plant height, and days‐to‐flowering were 0.51, 0.69, and 0.61, respectively. Recurrent genomic selection can shorten the select cycle to 4 months and therefore is promising to accelerate genetic improvement of FHB severity.

Phenotypic plasticity of a winter-diapause mechanism copes with the effects of summer global warming in an ectothermic predator.

To adapt to changes in temperature, animals tend to invest more energy in thermal tolerance to enhance survival, which can have simultaneous costs on plastic traits. Would a decrease in genetic variability, due to global warming, affect the ability of populations with existing metabolic regulatory mechanisms to cope with extreme temperatures? To address this question, we conducted a series of experiments based on the A1B scenario of global warming, assessing within-population genetic variance in (a) morphological traits, (b) metabolic rate allometries, and (c) survival of a winter-diapausing predator ectotherm. Our study focused on the lacewing species Chrysoperla pallida, using both exogamic and endogamic artificial genetic lines. We discovered that both lines use their winter-diapausing phenotype to adapt to summer extreme temperatures caused by extreme heating conditions, but the exogamic line is prone to express phenotypic plasticity in metabolic scaling, with a trade-off between body size and mandible size, i.e. larger individuals tended to develop smaller mandibles to better survive. These findings highlight the significance of substantial phenotypic plasticity and pre-existing metabolic regulatory mechanisms in enabling ectotherms to cope with potential extreme heating occurring in global warming.

Genetic variation of gelam (Melaleuca cajuputi subsp. cumingiana) in southern Kalimantan peat swamp population based on isozyme marker

Gelam (Melaleuca cajuputi subsp. cumingiana) is highly utilized timber by local people for house construction, poles, firewood, and other uses. Over-exploitation without sufficient regeneration leads to population reduction and a decrease in genetic variation. Information about the genetic variation of gelam is needed to conserve or improve the species. The study’s objectives were to identify the polymorphism of the enzyme system and the genetic variation of gelam in southern Kalimantan. Seeds were collected from 7 populations in southern Kalimantan. Seedlings were used and assessed by an isozyme marker. Five enzyme marker screening was conducted to determine the genetic variation, only the EST and DIA enzymes showed polymorphic and consistent patterns, POD and SHD showed polymorphic, inconsistent patterns, while GOT did not show the pattern. Genetic variation of gelam in the southern Kalimantan population was quite high (He = 0.4115, Ho = 0.2996, HT = 0.4215), it was mostly distributed within the population (97.6%) Inbreeding (FIS=0.21) or non-random mating occurred and led to a reduction in heterozygosity of the population.

Genetic Variation of Ceiba pentandra (L.) Gaertn. from Three Populations in West Sumatra, Indonesia Based on RAPD Markers

Ceiba pentandra (L.) Gaertn. is one of the cotton-producing plants. However, there is a population decline in some areas, resulting in a decrease in genetic variation. This study aims to determine intrapopulation and interpopulation genetic variation and genetic differentiation of C. pentandra in three populations in West Sumatra. The research was conducted with the descriptive method using molecular data and sample collection with the survey method. Analysis of genetic variation using RAPD (Random Amplified Polymorphic DNA) markers on 15 individual plants collected from three populations, namely Solok, Pesisir Selatan, and Padang Pariaman. The results showed that primers OPA-01, OPA-02, and OPB-10 could detect polymorphism. The value of intrapopulation genetic variation was highest in the South Coastal population (H = 0.1857) and lowest in the Solok population (H = 0.1228). Interpopulation genetic variation (DST = 0.0326) was lower than intrapopulation genetic variation (Hs = 0.1607), with a low genetic differentiation value (GST = 0.1686) and a high gene flow value (Nm = 2.4660). Cluster analysis showed that the Pesisir Selatan and Solok populations had the farthest genetic distances (0.0580). UPGMA analysis shows that accessions do not cluster specifically based on their population.

Growth of Eucheuma cottonii seaweed from tissue culture with different time acclimatization in Hurun Bay

Constraints on the seaweed culture in Indonesia until now still rely on seeds obtained by vegetative propagation and have poor quality, which often causes a decrease in genetic variability. Planting seaweed seedlings from tissue cultures that have been acclimatized in a greenhouse laboratory is believed to improve the quality of the seaweed seeds. This research aimed to observe the growth of tissue culture acclimatized Eucheuma cottonii seaweed seedlings to different rearing times in greenhouses applied to floating raft cages. This study used a completely randomized design (CRD) with three treatments and three replications. Acclimatization treatment was conducted for 2 weeks, 4 weeks, and 6 weeks. Seaweed seedlings acclimatized in the greenhouse are reared on bamboo floating rafts in the sea, with an initial weight of 5 grams each. The length of maintenance at sea is 28 days. The resulting daily growth rate in two-week acclimatization was 2.92%, the four-week treatment was 2.93%, and the six-week treatment was 2.57%. in raising seedlings at sea, the highest daily growth rate value was in the four-week treatment of 7.25%, followed by the two-week treatment of 7.11% and the six-week treatment of 6.43%.

Paracoccidioides restrepiensis has undergone a severe population bottleneck

Genus Paracoccidioides now encompasses five species, P. lutzii, P. brasiliensis sensu stricto, P. americana, P. venezuelensis, and P. restrepiensis. All the paracoccidioidomycosis (PCM) cases reported in Colombia have been classified as P. restrepiensis, which was named in honor of Angela Restrepo, a leading researcher in the field of the biology of the fungus. Previous assessments of genetic diversity have suggested that Paracoccidioides species have differences in their level of polymorphism. To infer changes in effective population size, we used the Pairwise sequentially Markovian coalescent (PSMC) by generating two pseudodiploids for P. restrepiensis and one for P. brasiliensis sensu stricto. We found that P. restrepiensis diverged from its sister species recently, the divergence time from P. venezuelensis being 125,000 (± 42,000) years. The analyses using PSMC show a systematic reduction in the effective population size of P. restrepiensis with a rapid decrease in genetic variability compared to P. brasiliensis sensu stricto, which indicates that P. restrepiensis has undergone a systematic population bottleneck. None of the other two species show the dramatic effective population size reduction observed in P. restrepiensis. These comparisons suggest that the trajectory of P. restrepiensis is somehow different from the other Paracoccidioides species and poses the question regarding the biogeographic events that have led to such a dramatic population pattern.

Analysis of genetic diversity in two plantations of <i>Pinus caribaea</i> var. <i>hondurensis</i>

Forest tree breeding activities in plantations with exotic species implies several instances of material selection where genetic variation can be affected. The objective of the work was to verify the genetic variability present in two plantations of Pinus caribaea var. hondurensis by microsatellite markers, initially designed for Pinus taeda fluorescent-labeled. Thus, 299 individuals were analyzed using eight polymorphic microsatellite markers. The results indicate that both plantations have adequate levels of genetic diversity that are representative of the Pinus genus. Through the Bayesian method, it was possible to detect two different population genetic structures (K = 2) between both plantations analyzed. In conclusion, this study suggests that microsatellites markers are useful tools to monitor genetic variation in genetic breeding programs. The genetic diversity estimated in both plantations is similar and typical for Pinus plantations, and as expected, there was a slight decrease in genetic variability in the commercial plantation in comparation with the base plantation.

Variability and Genetic Structure of the Montezuma Quail Cyrtonyx montezumae in the Northern Limit of its Distribution

A species’ geographic distribution of genetic variability is influenced by different factors including size of geographic distribution, dispersal capability, mating system, and migration. For instance, a low migration rate among populations may cause a decrease in genetic variation. Such is the case of the Montezuma quail (Cyrtonyx montezumae), a popular game bird with a limited flight capacity that prevents long-distance dispersal. In the northern limit of the species’ distribution in Arizona, New Mexico, and Texas in the United States, the species inhabits oak forests that are separated from one another by deserts. Consequently, Montezuma quail populations are distributed in patches or islands. Knowledge of the species’ genetic structure is likely to help inform habitat management decisions. The objective of this study was to determine patterns of genetic variation in populations of the Montezuma quail using 9 microsatellite DNA loci. We genotyped 119 individuals harvested from 4 populations: Arizona (AZ), western New Mexico (WNM), eastern New Mexico (ENM), and west Texas (WTX). Montezuma quail populations had low observed heterozygosity (Ho = 0.22 ± 0.04) and a low number of alleles per locus (A = 2.41 ± 0.27) compared to other quail species. A global population genetic differentiation index (RST) of 0.045 suggests a weak genetic structure. Max(RST) occurred among pairwise comparisons AZ-WTX, AZ-ENM, and WNM-WTX. A Bayesian allocation analysis indicates that individuals were separated into 3 groups (K = 3), placing the populations of Arizona and Texas in distinct groups apart from the 2 populations of New Mexico, which are in the same group. Despite this differentiation, the Bayesian allocation analysis suggests admixture among populations, which may be an indicator of migration between them, especially between the populations in New Mexico and Arizona. An isolation-by-distance analysis indicates that there is a strong correlation (R2 = 0.84) and suggestive evidence (P = 0.08) of non-independence between geographical and genetic distances, though Montezuma quail populations in the southwestern United States may not be isolated. Climate change projections indicate an increase in aridity conditions in this region, especially in temperate ecosystems where the species occurs. In this scenario, corridors between the populations may disappear, thus causing their complete isolation.

Comparative Study of the Genetic Diversity of Local Steppe Cattle Breeds from Russia, Kazakhstan and Kyrgyzstan by Microsatellite Analysis of Museum and Modern Samples

The comparative molecular genetic study of museum and modern representatives of cattle breeds can help to elucidate the origin and maintenance of historical genetic components in modern populations. We generated the consensus genotypes for 11 microsatellite loci for 24 museum samples of Kalmyk, Kyrgyz, and Kazakh cattle, dated from the first quarter of the 20th century, and compared them with those of modern Kalmyk, Kyrgyz, and Kazakh white-headed breeds. The level of genetic diversity of the modern Kalmyk and Kyrgyz cattle (uHe = 0.771–0.778) was similar to those observed in the museum samples (uHe = 0.772–0.776), while a visible decrease in genetic variability in the modern Kazakh white-headed breed compared to museum Kazakh cattle was detected (uHe = 0.726 and 0.767, respectively). The PCA plot, FST- and Jost’s D-based networks, and STRUCTURE clustering provided strong evidence of the maintenance of the historical genetic background in modern populations of Kalmyk and Kyrgyz cattle. In spite of the allele pool of Kazakh white-headed cattle having undergone great changes compared to the museum Kazakh cattle, several animals still carry the visible aspect of the historical genetic components. Our results can be used for the selection of individuals for the creation of gene banks and may significantly improve the efficiency of conservation programs aimed at preserving genetic diversity in the national genetic resources of cattle.

Assessment of genetic diversity of Turkish maize landraces for phytic acid and total phenolic contents

Assessment of genetic diversity of Turkish maize landraces for phytic acid and total phenolic contents

Genetic diversity in tomato (Solanum lycopersicum L.) germplasm using fruit variation implemented by tomato analyzer software based on high throughput phenotyping

The decrease of genetic variation in crops like tomato (Solanum lycopersicum L.) due to domestication, breeding, and population bottle necks for fresh market consumptions has increased the need for this cash crop’s conservation and characterizations. To study the genetic variation of this valuable genetic resource in the National Plant Gene Bank of Iran, a collection of 589 tomato accessions from different regions was characterized using semi-automatic and high-throughput techniques. Based on the fruit shape, the studied accessions were classified into ten groups and significant differences for all the fruit characteristics studied indicated an abundant diversity within the germplasm collected from different regions. Studied tomato germplasm was grouped into nine main clusters based on hierarchical cluster analysis. More than 83% of data variation was explained by seven components in which the first two components explained for 50% of the variation where fruit shape index and proximal/distal fruit end shape showed a high contribution in the variation of the first component. This unique genetically divergent germplasm could be utilized to select tomato breeding lines of interest. Also, accessions belonged to the heterotic clusters could be selected for hybridization and conservation purpose as well as enrichment of pre-breeding programs of the tomato germplasm.

Coevolution fails to maintain genetic variation in a host–parasite model with constant finite population size

Coevolutionary negative frequency-dependent selection has been hypothesized to maintain genetic variation in host and parasites. Despite the extensive literature pertaining to host–parasite coevolution, the temporal dynamics of genetic variation have not been examined in a matching-alleles model (MAM) with a finite population size relative to the expectation under neutral genetic drift alone. The dynamics of the MA coevolution in an infinite population, in fact, suggests that genetic variation in these coevolving populations behaves neutrally. By comparing host heterozygosity to the expectation in a single-species model of neutral genetic drift we find that while this is also largely true in finite populations two additional phenomena arise. First, reciprocal natural selection acting on stochastic perturbations in host and pathogen allele frequencies results in a slight increase or decrease in genetic variation depending on the parameter conditions. Second, following the fixation of an allele in the parasite, selection in the MAM becomes directional, which then rapidly erodes genetic variation in the host. Hence, rather than maintain it, we find that, on average, matching-alleles coevolution depletes genetic variation.

Understanding photothermal interactions will help expand production range and increase genetic diversity of lentil (Lens culinarisMedik.)

Societal Impact StatementLentil is a staple in many diets around the world and growing in popularity as a quick‐cooking, nutritious, plant‐based source of protein in the human diet. Lentil varieties are usually grown close to where they were bred. Future climate change scenarios will result in increased temperatures and shifts in lentil crop production areas, necessitating expanded breeding efforts. We show how we can use a daylength and temperature model to identify varieties most likely to succeed in these new environments, expand genetic diversity, and give plant breeders additional knowledge and tools to help mitigate these changes for lentil producers.SummaryLentil (Lens culinarisMedik.) is cultivated under a wide range of environmental conditions, which has led to diverse phenological adaptations and resulted in a decrease in genetic variability within breeding programs due to reluctance in using genotypes from other environments.We phenotyped 324 genotypes across nine locations over three years to assess their phenological response to the environment of major lentil production regions and to predict days from sowing to flowering (DTF) using a photothermal model.DTF was highly influenced by the environment and is sufficient to explain adaptation. We were able to predict DTF reliably in most environments using a simple photothermal model, however, in certain site‐years, results suggest there may be additional environmental factors at play. Hierarchical clustering of principal components revealed the presence of eight groups based on the responses of DTF to contrasting environments. These groups are associated with the coefficients of the photothermal model and revealed differences in temperature and photoperiod sensitivity.Future climate change scenarios will result in increased temperature and/or shifts in production areas. The ability to use the photothermal model to identify genotypes most likely to succeed in these new environments has important social impacts with respect to traditional cropping systems.

Comparative genetic diversity of Cryptosporidium species causing human infections.

Parasites sometimes expand their host range and cause new disease aetiologies. Genetic changes can then occur due to host-specific adaptive alterations, particularly when parasites cross between evolutionarily distant hosts. Characterizing genetic variation in Cryptosporidium from humans and other animals may have important implications for understanding disease dynamics and transmission. We analyse sequences from four loci (gp60, HSP-70, COWP and actin) representing multiple Cryptosporidium species reported in humans. We predicted low genetic diversity in species that present unusual human infections due to founder events and bottlenecks. High genetic diversity was observed in isolates from humans of Cryptosporidium meleagridis, Cryptosporidium cuniculus, Cryptosporidium hominis and Cryptosporidium parvum. A deviation of expected values of neutrality using Tajima's D was observed in C. cuniculus and C. meleagridis. The high genetic diversity in C. meleagridis and C. cuniculus did not match our expectations but deviations from neutrality indicate a recent decrease in genetic variability through a population bottleneck after an expansion event. Cryptosporidium hominis was also found with a significant Tajima's D positive value likely caused by recent population expansion of unusual genotypes in humans. These insights indicate that changes in genetic diversity can help us to understand host-parasite adaptation and evolution.

Effects of inbreeding on growth and survival rates, and immune responses of ridgetail white prawn Exopalaemon carinicauda against the infection of Vibrio parahaemolyticus

Inbreeding could lead to a decrease in genetic variation within a population and subsequent depression of performance traits. The purpose of this study was to investigate the effects of inbreeding on the growth-related traits, immune responses, antioxidant status and the acute hepatopancreatic necrosis disease (AHPND) resistant capacity of ridgetail white prawn (Exopalaemon carinicauda) using a new inbred line named EC5. The results demonstrated that the genetic polymorphisms of EST-SSR markers decreased with an increase in artificial inbreeding, and there was less growth traits and a lower survival rate among inbred populations than the control population. Inbreeding effects on the immune responses and antioxidant status were studied in experimental full-sibling inbred populations of E. carinicauda at five levels of inbreeding coefficient (F = 0.785, F = 0.816, F = 0.859, F = 0.886, F = 0.908) under controlled laboratory conditions. Inbreeding affected the total haemocyte count, antibacterial activity and phenoloxidase (PO) activity, and the haemocyanin (HEM) concentration decreased after the ninth generation. Antioxidant status showed a similar pattern: superoxide dismutase (SOD) and catalase (CAT) activity in the cell-free haemolymph decreased. The effects of inbreeding on survival after infection with Vibrio parahaemolyticus were significant, as the cumulative mortality of shrimp in the control population (CP) was significantly lower than that in the F9 generation of EC5 inbred family during 24–72 h after infection with V. parahaemolyticus (P < .05). Additionally, the levels of antibacterial activity, immune enzymes including lysozyme (LZM) activity, alkaline phosphatase (AKP) activity and PO activity in cell-free haemolymph were significantly higher in the control population than those in the F9 generation 6 h after infection with V. parahaemolyticus (P < .05). Furthermore, the expression levels of anti-lipopolysaccharide factor (ALF), LZM, Tollip, evolutionarily conserved signaling intermediate in Toll pathway (ECSIT), Toll and signal transducer and activator of transcription (STAT) in the hepatopancreas, and Crustin, LZM and Tollip in haemocytes were significantly higher in the control population than those in the F9 generation after infection with V. parahaemolyticus (P < .05). These results suggested that the F9 generation has a weaker disease-resistant capability than the control population when infected with V. parahaemolyticus. In conclusion, this study demonstrates that a high level of inbreeding has a negative effect on growth-related traits and physiological health of E. carinicauda, thus highlighting the need to maintain genetic diversity in selective breeding programs.

Estimation of genetic parameters for some performance traits in a selected Barred Rock line

This study was conducted to determine the genetic correlation and heritability for age at sexual maturity, body weight at sexual maturity, egg yield, egg weight, egg shape index and L*, a*, b* values of egg shell in a Barred Rock line was applied selection. For this aim, a total of 1622 pedigreed Barred Rocks were selected. The present estimated heritability values for investigated traits were found between moderate-to-high. However, the heritability of egg yield, eggshell color and body weight at sexual maturity were found lower than those of other traits. It was calculated positive correlations among monthly egg yields, especially between egg yield at the second month with total egg yield. As a conclusion, selection studies did not cause much decrease in genetic variation of studied traits, except for egg yield and body weight at sexual maturity. Monthly egg yield data can be used selection studies.

Genome-wide estimates of genetic diversity, inbreeding and effective size of experimental and commercial rainbow trout lines undergoing selective breeding

BackgroundSelective breeding is a relatively recent practice in aquaculture species compared to terrestrial livestock. Nevertheless, the genetic variability of farmed salmonid lines, which have been selected for several generations, should be assessed. Indeed, a significant decrease in genetic variability due to high selection intensity could have occurred, potentially jeopardizing the long-term genetic progress as well as the adaptive capacities of populations facing change(s) in the environment. Thus, it is important to evaluate the impact of selection practices on genetic diversity to limit future inbreeding. The current study presents an analysis of genetic diversity within and between six French rainbow trout (Oncorhynchus mykiss) experimental or commercial lines based on a medium-density single nucleotide polymorphism (SNP) chip and various molecular genetic indicators: fixation index (FST), linkage disequilibrium (LD), effective population size (Ne) and inbreeding coefficient derived from runs of homozygosity (ROH).ResultsOur results showed a moderate level of genetic differentiation between selected lines (FST ranging from 0.08 to 0.15). LD declined rapidly over the first 100 kb, but then remained quite high at long distances, leading to low estimates of Ne in the last generation ranging from 24 to 68 depending on the line and methodology considered. These results were consistent with inbreeding estimates that varied from 10.0% in an unselected experimental line to 19.5% in a commercial line, and which are clearly higher than corresponding estimates in ruminants or pigs. In addition, strong variations in LD and inbreeding were observed along the genome that may be due to differences in local rates of recombination or due to key genes that tended to have fixed favorable alleles for domestication or production.ConclusionsThis is the first report on ROH for any aquaculture species. Inbreeding appeared to be moderate to high in the six French rainbow trout lines, due to founder effects at the start of the breeding programs, but also likely to sweepstakes reproductive success in addition to selection for the selected lines. Efficient management of inbreeding is a major goal in breeding programs to ensure that populations can adapt to future breeding objectives and SNP information can be used to manage the rate at which inbreeding builds up in the fish genome.

Genetic variability is preserved among strongly differentiated and geographically diverse almond germplasm: an assessment by simple sequence repeat markers

Eighty-six almond accessions of diverse geographic origin, ranging from Central Asia to the USA, were genotyped in 15 simple sequence repeat (SSR) loci to compare genetic diversity parameters, characterize genetic differentiation, and examine factors responsible for the maintenance of genetic diversity and population structure in almond. The mean allele number was 18.86 alleles per locus. All but one primer demonstrated polymorphic information content higher than 0.7. Almond genotypes clustered according to their pedigree and geographic origin. STRUCTURE analysis determined nine genetically distinct subgroups within the studied genotypes including the Kyrgyz, Akdamar, Bademli, Hungarian, Monor, Italian, Moroccan, and Californian accessions and wild species and an admixed group. An AMOVA analysis confirmed that considerable genetic variation occurred within populations (71.30%), and genetic variation among populations was also significant (28.70%). The mean values of the fixation index (FST) varied between 0.38 and 0.55, indicating marked genetic differentiation among the populations. The among-population genetic differentiation based on allele sizes (RST) was significantly higher than that based on allele identities (FST) between the most groups, suggesting that stepwise mutations have also contributed to genetic differentiation. A Mantel test and a neighbor-joining tree showed no significant correlation between the geographic distance and the genetic distance (Rxy = 0.173, P = 0.226) and indicated that geographic distance among the assessed populations has little influence on their genetic differentiation (Rxy = 0.248, P = 0.194). Our data show drift, mutations, and massive gene exchange between several wild species and cultivated P. dulcis as crucial components of genetic differentiation. Slight losses of genetic diversity are attributable to geographic isolation, human selection and not to the relatively recent occurrence of self-compatibility. There was no indication of a major decrease in genetic variability in almond germplasm from Asia to Europe. The present results reveal that almond domestication avoided the occurrence of a genetic bottleneck although its risk is present in many subpopulations.

Mitochondrial DNA Barcoding of the Pacific Oyster Crassostrea gigas (Thunberg, 1793) (Mollusca: Bivalvia: Ostreidae), Cultivated in the Black Sea

To clarify the taxonomic assignment of oysters bred at the nursery of the Kovalevsky Institute of Marine Biological Research, Russian Academy of Sciences (IMBR RAS), and to determine the genetic variability parameters, the sequence variation of oyster mitochondrial COI and 16S rRNA gene fragments was analyzed. Comparison with other species of the genera Crassostrea and Ostrea showed that oysters bred at the nursery belonged to Crassostrea gigas. The generation examined was characterized by considerable decrease in genetic variability.