Environmental variability and population dynamics: do European and North American ducks play by the same rules?

Density dependence, population regulation, and variability in population size are fundamental population processes, the manifestation and interrelationships of which are affected by environmental variability. However, there are surprisingly few empirical studies that distinguish the effect of environmental variability from the effects of population processes. We took advantage of a unique system, in which populations of the same duck species or close ecological counterparts live in highly variable (north American prairies) and in stable (north European lakes) environments, to distinguish the relative contributions of environmental variability (measured as between‐year fluctuations in wetland numbers) and intraspecific interactions (density dependence) in driving population dynamics. We tested whether populations living in stable environments (in northern Europe) were more strongly governed by density dependence than populations living in variable environments (in North America). We also addressed whether relative population dynamical responses to environmental variability versus density corresponded to differences in life history strategies between dabbling (relatively “fast species” and governed by environmental variability) and diving (relatively “slow species” and governed by density) ducks. As expected, the variance component of population fluctuations caused by changes in breeding environments was greater in North America than in Europe. Contrary to expectations, however, populations in more stable environments were not less variable nor clearly more strongly density dependent than populations in highly variable environments. Also, contrary to expectations, populations of diving ducks were neither more stable nor stronger density dependent than populations of dabbling ducks, and the effect of environmental variability on population dynamics was greater in diving than in dabbling ducks. In general, irrespective of continent and species life history, environmental variability contributed more to variation in species abundances than did density. Our findings underscore the need for more studies on populations of the same species in different environments to verify the generality of current explanations about population dynamics and its association with species life history.     

The relationship between genetic variability and growth rate among populations of the pocket gopher, Thomomys bottae

Perhaps the oldest unresolved debate inconservation genetics is whether geneticvariability matters – in other words, whetherrelatively low average genetic variationcontributes to deficits in individual andpopulation level vigor and fitness. Using astatistically powerful paired sampling designin which each of three pairs of populationsconsisted of one high genetic variability andone low genetic variability population from aparticular subspecies of the pocket gopher,Thomomys bottae, we tested the hypothesisthat individuals from populations with lowergenetic variability have lower growth rates (acommonly used surrogate for fitness) than thosefrom populations with higher variability. Wemeasured genetic variability using averageallozyme heterozygosity and two measures of DNAfingerprint band sharing (Jeffreys 33.15 andMS1 probes). The population rankings of thelevels of genetic variability among the threemeasures were concordant. The least squaresmean growth rate (controlling for sex,subspecies and initial mass) of gophers fromlow variability populations (0.41 ± 0.06g/day, n = 48) was less than half that ofgophers from high variability populations (1.04± 0.07 g/day, n = 45). This result lendscredence to the premise that differences inpopulation level genetic variability havesignificant fitness consequences andunderscores the importance of maintaininggenetic variability in managed populations.     

Environmental colour affects aspects of single-species population dynamics

Single-species populations of ciliates (Colpidium and Paramecium) experienced constant temperature or white or reddened temperature fluctuations in aquatic microcosms in order to test three hypotheses about how environmental colour influences population dynamics. (i) Models predict that the colour of population dynamics is tinged by the colour of the environmental variability. However, environmental colour had no effect on the colour of population dynamics. All population dynamics in this experiment were reddened, regardless of environmental colour. (ii) Models predict that populations will track reddened environmental variability more closely than white environmental variability and that populations with a higher intrinsic growth rate (r) will track environmental variability more closely than populations with a low r. The experimental populations behaved as predicted. (iii) Models predict that population variability is determined by interaction between r and the environmental variability. The experimental populations behaved as predicted. These results show that (i) reddened population dynamics may need no special explanation, such as reddened environments, spatial subdivision or interspecific interactions, and (ii) and (iii) that population dynamics are sensitive to environmental colour, in agreement with population models. Correct specification of the colour of the environmental variability in models is required for accurate predictions. Further work is needed to study the effects of environmental colour on communities and ecosystems.     

Genetic variability, population size and isolation of distinct populations in the freshwater fish Cottus gobio L.

Analysis of allozyme data of the European freshwater fish Cottus gobio showed marked genetic differentiation across drainage basins in northeastern Bavaria, which points to the existence of at least two cryptic taxa. Genetic variability within populations differed significantly between these two taxa, which could be due to historical (bottlenecks) or ecological reasons (population size). To distinguish between these two hypotheses we sampled 12 distinct populations from Rhine, Elbe and Danube drainages. Using allozyme data we examined the influence of population size and isolation on genetic variability within populations. We used spatial extent of populations (patch size) as a measure for population size. To estimate isolation we calculated a compound measure which took into account patch size and distance to all neighbouring populations. Both patch size and isolation were highly correlated with genetic variability, explaining ≈95% of the variance of genetic variability within populations. Furthermore, analysis of covariance suggests that the difference in genetic variability between taxa may be explained by differences in population size.     

Fertilization and defoliation frequency affect genetic diversity of Festuca pratensis Huds. in permanent grasslands

Permanent pastures and meadows are species-rich vegetation systems that play an important role in the ecology and agriculture of temperate climates. Intensive management reduces species diversity and may also influence the genetic diversity within individual species and populations. The objective of this study was to assess genetic variability of meadow fescue, an important component of species-rich grasslands, and to determine whether fertilization and defoliation frequency influence genetic variability within natural populations. Genetic diversity of six natural populations and three cultivars of Festuca pratensis was investigated using randomly amplified polymorphic DNA (RAPD) markers and agronomic traits. Samples of natural populations were taken from two unrelated long-term experiments, where treatments had been applied for 11–38 years. RAPD analysis detected a clear genetic distinction of the cultivars from the natural populations. Genetic variability within cultivars was lower than within natural populations. Analysis of molecular variance ( AMOVA ) showed a significant effect of management on genetic variability. Fertilization and frequent defoliation led to a reduction in genetic variability within natural populations. Analysis of agronomic traits was only partially congruent with the results of RAPD analysis. This study shows that significant genetic variability exists within cultivars and natural populations of Festuca pratensis and can be reduced by intensive management.     

The Influence of Translocation Strategy and Management Practices on the Genetic Variability of a Reestablished Elk (Cervus elaphus) Population

Reintroduction of terrestrial vertebrates with the goal of ecosystem restoration typically establishes small and isolated populations that may experience reduced genetic variability due to founder effects and genetic drift. Understanding the genetic structure of these populations and maintaining adequate genetic diversity is important for long‐term restoration success. We quantified genetic variability at six microsatellite loci for a reintroduced population of Cervus elaphus (elk) restored to the tallgrass prairie ecosystem of northeastern Kansas. Allelic richness, observed and expected heterozygosity were intermediate to levels reported in other North American elk populations. Current levels of genetic variability in restored North American elk populations were not well explained by founding population size, number of founding populations, or number of years since the last translocation. Simulation results suggest that the retention of genetic variability in isolated populations is strongly influenced by mating system while also being impacted by temporal variability in population size and population growth rate. Our results have implications for understanding how translocation strategies and post‐reintroduction management may influence genetic variability in restored populations.     

Developmental stability is not disrupted by extensive hybridization and introgression among populations of the marine bivalve molluscs Mytilus edulis (L.) and M. galloprovincialis (Lmk.) from south-west England

The effects of hybridization and introzgression were assessed among two naturally hybridizing bivalve molluscs (the mussels Mytilus edulis and M. galloprovincialis) from western Europe to estimate how disruptive these processes are to developmental stability (measured in terms of morphological variability). Ten shell traits were measured for 392 mussels from four allopatric populations (two each of At. edulis and At. galloprovincialis) and two hybrid populations. An index of variability (defined as Z_i= |y_i–y_i where y_; is the population mean of the length-standardized trait, and y_i is the individualcar;s length-standardized trait value) was constructed for each trait, and for the sum of the traits. The hybrid populations did not exhibit greater mean variability than the allopatric populations for any of the indices. Upon pooling, the hybrid populations had significantly lower variability than the pooled M. edulis populations and the pooled M. galloprovincialis populations in two analyses, and had similar means in the remaining nine analyses. Where significant differences existed, the pooled M. galloprovincialis had lower levels of mean trait variability than the pooled M. edulis. Among the two hybrid populations, the putative Fl hybrids and backcross individuals exhibited means of trait variability which were similar to those of the parental types. Thus, extensive hybridization and introgression do not adversely affect developmental stability among these mussel populations. There was a strong significant correlation between the ranking of indices (based on the amount of variability) across all six populations, indicating that a large genetic component determines the measured morphological variability. It is concluded that the genes or gene complexes which control morphological development in M. edulis and M. galloprovincialis arc very similar, providing further evidence of the close evolutionary relatedness of these mussel taxa.     

Genetic variability in the endemic <Emphasis Type="Italic">Leucojum valentinum</Emphasis>

The genetic variability of Leucojum valentinum Pau (Amaryllidaceae), a vulnerable endemic species restricted to a small area in the region of Valencia (Eastern Spain), has been studied using random amplified polymorphic DNA (RAPD) markers. A total of 197 individuals from eleven populations were studied using 13 RAPD primers. Our results show high variability for the species, low differentiation among populations and uncorrelated levels of genetic variability and population size. Four groups in which three populations (SAG, PUG and COL) are separated from all the others were found, but without connection to geographical location.     

性选择、配偶外父亲身份确认程度、遗传变异性和保护

岛屿动物中的性选择强度不高,其原因可能是由于岛屿种群的遗传变异性水平较低。本文作者检验了鸟类岛屿种群是否具有较低的遗传变异性、性选择强度大的种群是否具有较高的突变输入率（rate of mutational input),在鸟类岛屿种群中是否具有较低的性选择强度（可以根据配偶外父亲身份的频率来估计）。小卫星共有谱带系数（minisatellite band sharing coefficient)可确定无亲源关系个体之间的遗传变异性,对与遗传变异性有关的雄性个体的父亲（paternity)进行了成对比较以检验如下假说：在具有较多遗传变异的种群中,雌性个体更经常地进行配偶外交配。在小卫星谱带系数较低的鸟类种群中,配偶外父亲的频次较高。对岛屿和大陆鸟类进行的第二个比较分析表明：岛屿种群中的配偶外父亲频次较低,遗传变异性也较低,其部分原因在于突变输入（mutational input)减少。上述发现表明：（1）父亲确认程度（parternity)随遗传变异性的数量而增加;（2）在遗传变异性较大的种群中,突变率较高,性选择的程度更激烈;（3）岛屿种群中性选择的强度一般比大陆种群弱。这对于理解遗传变异性的空间变异、理解岛屿种群和其它隔离种群的保护问题有重要启示。     

Genetic variability of Siberian fir (Abies sibirica Ledeb.) inferred from AFLP markers

Genetic variability of AFLP markers was studied in 20 populations of Siberian fir (Abies sibirica (Pinaceae) and in two populations of Far-Eastern Manchurian fir A. nephrolepis and Sakhalin fir A. sachalinensis each. Four pairs of selective primers were used. In total, 168 samples from three fir species were genotyped for 117 polymorphic loci. According to the AMOVA results, the variability proportion characterizing the differences between three Abies species was several times higher (F(CT) = 0.53) than that accounting for among-population differences within the species (F(SC) = 0.125). Differentiation of the A. sibirica populations based on AFLP markers exceeded 14% (F(ST) = 0.141). Significant correlation between the genetic distances calculated from the AFLP data and the geographic distances between populations was found. The results of AFLP variability analysis supported and supplemented the conclusions inferred previously from allozyme and cpSSR data: several genetically similar geographic groups of Siberian fir were identified. These groups differ both in allele frequencies and in the levels of genetic variation.     

Genetic variability is correlated with population size and reproduction in American wild-rice (Zizania palustris var. palustris, Poaceae) populations

American wild-rice (Zizania palustris var. palustris) has served as a staple for indigenous North Americans for thousands of years, but has had significant habitat losses in recent centuries. We investigated genetic variability among 17 wild-rice populations in northern Wisconsin using 13 isozyme markers. We then compared these genetic patterns to differences in habitat and population characteristics and phenotypic variation in plant growth and reproduction across sites. Wild-rice's mean genetic diversity (0.15) is moderate compared to wind-pollinated outcrossers but lower than the mean (0.20) reported for the Poaceae. Estimated inbreeding coefficients within populations (f) average 0.12 but vary greatly among the populations (from -0.44-0.52), suggesting heterogeneous population histories. Larger populations in larger lakes express higher levels of genetic variability and smaller inbreeding coefficients than smaller or more isolated populations. The number of panicles per plant is also higher in populations with greater genetic variability. Estimated genetic differentiation among the 17 populations (F(ST)) was high (0.30), suggesting limited gene flow among drainages. Wild-rice population size and degree of isolation have opposing effects on its genetic variability, and plant performance is positively associated with genetic variability.     

Morphometric analysis of populations of Centris aenea Lepeletier (Hymenoptera: Apidae) from Northeastern Brazil

Centris aenea Lepeletier is a solitary bee that has raised interest in management to pollinate crops, such as acerola, Malpighia emarginata. This study investigated the level of morphometric variability among populations of C. aenea from Northeastern Brazil. Traditional and geometric morphometric analyses were used. Head length, leg length, wing length, and wing shape were measured in samples (5-10 females) from eight localities. We did not find statistically significant differences among the populations (P > 0.01). The partial wing warps were similar in the populations and indicated that the bees were not morphometrically different. Our results suggest that C. aenea shows low population morphometric variability and highlight the need for further investigations on population variation in this species, preferably including populations sampled at the extremes of their geographic distribution. Significant insight into the population variation of C. aenea will probably require the use of molecular markers to allow a comparative approach between morphometric variability and genetic variability.     

Contrasting patterns of gene diversity between microsatellites and mitochondrial SNPs in farm and wild Atlantic salmon

Levels of genetic variability at 12 microsatellite loci and 19 single nucleotide polymorphisms in mitochondrial DNA were studied in four farm strains and four wild populations of Atlantic salmon. Within populations, the farm strains showed significantly lower allelic richness and expected heterozygosity than wild populations at the 12 microsatellite loci, but a significantly higher genetic variability with respect to observed number of haplotypes and haplotype diversity in mtDNA. Significant differences in allele- and haplotype-frequencies were observed between farm strains and wild populations, as well as between different farm strains and between different wild populations. The large genetic differentiation at mitochondrial DNA between wild populations (F_ST = 0.24), suggests that the farm strains attained a high mitochondrial genetic variability when created from different wild populations seven generations ago. A large proportion of this variability remains despite an expected lower effective population size for mitochondrial than nuclear DNA. This is best explained by the particular mating schemes in the breeding programmes, with 2–4 females per male. Our observations suggest that for some genetic polymorphisms farm populations might currently hold equal or higher genetic variability than wild populations, but lower overall genetic variability. In the short-term, genetic interactions between escaped farm salmon and wild salmon might increase genetic variability in wild populations, for some, but not most, genetic polymorphisms. In the long term, further losses of genetic variability in farm populations are expected for all genetic polymorphisms, and genetic variability in wild populations will be reduced if escapes of farm salmon continue.     

Genetic analysis of ecologically relevant morphological variability in Plantago lanceolata L.

Summary Morphological variability was studied in two populations of Plantago lanceolata using diallel analysis. In each population, reciprocal crosses between all possible pairs of ten plants were made. In the greenhouse, six members of each family were grown and many characters were measured. Using the model of Cockerham and Weir, the contributions of the different genetic variance components were calculated. From earlier papers it was postulated in advance to what extent and by which effect the characters in both populations were genetically determined. The populations had been differentiated for life history and morphological characters, and varied also in the relative contribution of genetic components to variability. In the Merrevliet (Me) population, where strong biotic selection was assumed, low levels of additive-genetic variability were present and the relative dominance appeared to be high. The contrasting population, Westduinen (Wd), which is abiotically controlled and shows strong environmental variability, possessed higher levels of additive-genetic variability and lower levels of relative dominance. It is possible that differential natural selection has diminished additive-genetic variability to different extents in both populations: plasticity and environmental heterogeneity prevented the loss of additive-genetic variability in Wd, whereas in the stable population, Me, natural selection had the opportunity of not only changing the means of the characters but also of diminishing additive-genetic variability to a great extent.Grassland Species Research Group Publication No. 146     

Detection of genetic polymorphism in the populations of brinjal shoot and fruit borer, Leucinodes orbonalis (Guenee)

In the present study six different populations of L. orbonalis were collected and subjected to analysis of genetic variability in terms of carboxylesterase isozyme pattern and DNA polymorphism using RAPD-PCR. Pattern of carboxylesterase revealed a similar isozyme cluster in the populations namely, sivaganga (population-3), dindigal (population-4), virudhunagar (population-5) and coimbatore (population-6). Similarly, the populations of L. orbonalis recorded 3 distinct randomly amplified polymorphic DNA markers in all populations grouped above. This pattern of genetic variability in the populations was also supported by the analysis of the similarity indices and UPGMA dendrogram.     

High-Throughput Sequencing of a South American Amerindian

The emergence of next-generation sequencing technologies allowed access to the vast amounts of information that are contained in the human genome. This information has contributed to the understanding of individual and population-based variability and improved the understanding of the evolutionary history of different human groups. However, the genome of a representative of the Amerindian populations had not been previously sequenced. Thus, the genome of an individual from a South American tribe was completely sequenced to further the understanding of the genetic variability of Amerindians. A total of 36.8 giga base pairs (Gbp) were sequenced and aligned with the human genome. These Gbp corresponded to 95.92% of the human genome with an estimated miscall rate of 0.0035 per sequenced bp. The data obtained from the alignment were used for SNP (single-nucleotide) and INDEL (insertion-deletion) calling, which resulted in the identification of 502,017 polymorphisms, of which 32,275 were potentially new high-confidence SNPs and 33,795 new INDELs, specific of South Native American populations. The authenticity of the sample as a member of the South Native American populations was confirmed through the analysis of the uniparental (maternal and paternal) lineages. The autosomal comparison distinguished the investigated sample from others continental populations and revealed a close relation to the Eastern Asian populations and Aboriginal Australian. Although, the findings did not discard the classical model of America settlement; it brought new insides to the understanding of the human population history. The present study indicates a remarkable genetic variability in human populations that must still be identified and contributes to the understanding of the genetic variability of South Native American populations and of the human populations history.     

Genetic variability in natural populations of Arabidopsis thaliana in northern Europe

Ten populations of the model plant Arabidopsis thaliana were collected along a north-south gradient in Norway and screened for microsatellite polymorphisms in 25 loci and variability in quantitative traits. Overall, the average levels of genetic diversity were found to be relatively high in these populations, compared to previously published surveys of within population variability. Six of the populations were polymorphic at microsatellite loci, resulting in an overall proportion of polymorphic loci of 18%, and a relatively high gene diversity for a selfing species (HE = 0.06). Of the overall variability, 12% was found within populations. Two of six polymorphic populations contained heterozygous individuals. Both FST and phylogenetic analyses showed no correlation between geographical and genetic distances. Haplotypic diversity patterns suggested postglacial colonization of Scandinavia from a number of different sources. Heritable variation was observed for many of the studied quantitative traits, with all populations showing variability in at least some traits, even populations with no microsatellite variability. There was a positive association between variability in quantitative traits and microsatellites within populations. Several quantitative traits exhibited QST values significantly less than FST, suggesting that selection may be acting to retard differentiation for these traits.     

Genetic Variability of Hymenoscyphus pseudoalbidus on Ash Leaf Rachises in Leaf Litter of Forest Stands in Poland

Two hundred and thirty cultures of Hymenoscyphus pseudoalbidus were obtained from ascospores created in apothecia on the previous years' ash leaf rachises in the stand floor. Fruiting bodies of the pathogen were collected in four regions of Poland differing by geographical location, the altitude above sea level and climatic conditions. Isolates were identified based on the sequences of ribosomal DNA (ITS1‐5.8S‐ITS2) and the calmodulin gene. Only the presence of H. pseudoalbidus was identified in the decaying ash stands in Poland; morphologically similar, saprotrophic species of H. albidus was absent. Intrapopulation and interpopulation genetic variability of isolates was determined based on 84 RAMS markers obtained using four primers. Genetic variability of the fungus populations, measured by the Dice coefficient of genetic similarity and the Shannon coefficient of genetic diversity, decreased along with a decrease in the location of isolate collection area above sea level. A significant dependency was shown between intrapopulation genetic variability of isolates and altitude of regions above sea level. The Mantel test excluded existence of dependence between geographical and genetic distance among populations (r = ?0.038, P = 0.55). A significant correlation was found between the genetic distances of individuals within populations and locations above sea level. Based on PCA and geographical location of populations, it was shown that populations create four distinct groups. amova showed that a majority of total genetic variability (65.80%) constitutes intrapopulation variability. Variability between populations was high (28.7%), and individual regions had a smallest influence (5.5%) on the level of total variability.     

Cryptic divergence and strong population structure in the colonial invertebrate Pycnoclavella communis (Ascidiacea) inferred from molecular data

We studied sequence variation in the mitochondrial gene cytochrome c oxidase subunit I (COI) for 135 individuals from eight Mediterranean populations of the colonial ascidian Pycnoclavella communis across most of its presently known range of distribution in the Mediterranean. Three haplotypes from Atlantic locations were also included in the study. Phylogenetic, phylogeographic and population genetic analyses were used to unravel the genetic variability within and between populations. The study revealed 32 haplotypes for COI, 29 of them grouped within two Mediterranean lineages of P. communis (mean nucleotide divergence between lineages was 8.55%). Phylogenetic and network analyses suggest the possible existence of cryptic species corresponding to these two lineages. Population genetic analyses were restricted to the five populations belonging to the main genetic lineage, and for these localities we compared the information gleaned from COI sequence data and from eight microsatellite loci. A high genetic divergence between populations was substantiated using both kinds of markers (COI, global Fst=0.343; microsatellite loci, global Fst=0.362). There were high numbers of private haplotypes (COI) and alleles (microsatellites) in the populations studied. Restricted gene flow and inbreeding occur in the present range of distribution of the species. Microsatellite loci showed a strong incidence of failed amplifications, which we attribute to the marked intraspecies variability that hampered the application of these highly specific markers. Our results show important genetic variability at all levels studied, from within populations to between basins, possibly coupled to speciation processes. This variability is attributable to restricted gene flow among populations due to short-distance dispersal of the larvae.     

Biochemical and DNA markers yield strikingly different results regarding variability and differentiation of roe deer (Capreolus capreolus, Artiodactyla: Cervidae) populations from northern Germany

Three mainland and two island roe deer ( Capreolus capreolus ) populations with a total sample size of 105 individuals from Schleswig–Holstein, northern Germany, were analysed with regard to genetic variability within and differentiation among populations as revealed by eight allozyme loci known to be polymorphic in roe deer, eight microsatellite loci and 404 bp of the mitochondrial control region. Surprisingly, the allozymes were completely monomorphic, but microsatellite and control region variability were high. Hypotheses as to demographic reasons for the variability patterns found, including bottlenecks, founder effects and translocations, are put forward. There were no statistically significant differences between the island and the mainland populations in terms of genetic variability as measured by expected heterozygosity, inbreeding coefficient and allelic richness. The correlations of the various variability indices were not statistically significant after Bonferroni correction. Nevertheless, there was a clear tendency for differentiation indices to yield concordant results for microsatellite and mitochondrial markers.