Genomic mosaicism underlies the adaptation of marine Synechococcus ecotypes to distinct oceanic iron niches

Phytoplankton are limited by iron (Fe) in ~40% of the world's oceans including high-nutrient low-chlorophyll (HNLC) regions. While low-Fe adaptation has been well-studied in large eukaryotic diatoms, less is known for small, prokaryotic marine picocyanobacteria. This study reveals key physiological and genomic differences underlying Fe adaptation in marine picocyanobacteria. HNLC ecotype CRD1 strains have greater physiological tolerance to low Fe congruent with their expanded repertoire of Fe transporter, storage and regulatory genes compared to other ecotypes. From metagenomic analysis, genes encoding ferritin, flavodoxin, Fe transporters and siderophore uptake genes were more abundant in low-Fe waters, mirroring paradigms of low-Fe adaptation in diatoms. Distinct Fe-related gene repertories of HNLC ecotypes CRD1 and CRD2 also highlight how coexisting ecotypes have evolved independent approaches to life in low-Fe habitats. Synechococcus and Prochlorococcus HNLC ecotypes likewise exhibit independent, genome-wide reductions of predicted Fe-requiring genes. HNLC ecotype CRD1 interestingly was most similar to coastal ecotype I in Fe physiology and Fe-related gene content, suggesting populations from these different biomes experience similar Fe-selective conditions. This work supports an improved perspective that phytoplankton are shaped by more nuanced Fe niches in the oceans than previously implied from mostly binary comparisons of low- versus high-Fe habitats and populations.     

Ecotypes of planktonic actinobacteria with identical 16S rRNA genes adapted to thermal niches in temperate, subtropical, and tropical freshwater habitats

Seven strains with identical 16S rRNA genes affiliated with the Luna2 cluster (Actinobacteria) were isolated from six freshwater habitats located in temperate (Austria and Australia), subtropical (People's Republic of China), and tropical (Uganda) climatic zones. The isolates had sequence differences at zero to five positions in a 2,310-nucleotide fragment of the ribosomal operon, including part of the intergenic spacer upstream of the 16S rRNA gene, the complete 16S rRNA gene, the complete 16S-23S internal transcribed spacer (ITS1), and a short part of the 23S rRNA gene. Most of the few sequence differences found were located in the internal transcribed spacer sequences. Two isolates obtained from habitats in Asia and Europe, as well as two isolates obtained from different habitats in the People's Republic of China, had identical sequences for the entire fragment sequenced. In spite of minimal sequence differences in the part of the ribosomal operon investigated, the strains exhibited significant differences in their temperature response curves (with one exception), as well as pronounced differences in their temperature optima (25.0 to 35.6 degrees C). The observed differences in temperature adaptation were generally in accordance with the thermal conditions in the habitats where the strains were isolated. Strains obtained from temperate zone habitats had the lowest temperature optima, strains from subtropical habitats had intermediate temperature optima, and a strain from a tropical habitat had the highest temperature optimum. Based on the observed temperature responses, we concluded that the strains investigated are well adapted to the thermal conditions in their home habitats. Consequently, these closely related strains represent different ecotypes adapted to different thermal niches.     

不同生境甘草的生态型研究

采用SDS-PAGE电泳的方法,对5种不同生境的甘草(G ly cy rrh iza ura lensis F isch.)幼苗进行了同工酶[过氧化物酶(POD)、酯酶(EST)、乳酸脱氢酶(LDH)和苹果酸脱氢酶(M DH)]研究,并利用PEG 6000进行了水分胁迫的生理响应实验.同时,对种植在相同生境下的2年生子代植株的地上部形态特征进行了观测.结果表明,5种生境的甘草至少已分化为2种生态型,且与它们的生境有显著的相关性,生长在生境干燥度较大的民勤甘草(M G)和酒泉甘草(JG)为一类,其幼苗的耐旱能力较强,而生长在干燥度相对小的大兴甘草(DG)、沙坡头甘草(SG)以及内蒙甘草(NG)归为另一类,幼苗的耐旱能力也低于前者,甘草生境中气候因素的水因子可能是影响其生态型分化的主导因子.由本研究结果得出以下推论,不同生境甘草的生态型分化是其适应环境进化的结果,甘草可能是甘草属的先锋种,由于长期适应不同的生态环境而产生了趋异变化,并形成了不同的生态型乃至新种.     

Nutritional differentiation among populations of the mediterranean shrub Dittrichia viscosa (Asteraceae) in siliceous and calcareous habitats

Summary Dittrichia (ex Inula) viscosa is a ruderal species that has recently become an invading plant in the northwest Mediterranean basin. A previous study failed to demonstrate the occurrence of morphologically differentiated ecotypes among populations of the species but suggested the existence of nutritional ecotypes. This latter possibility is examined here by comparing the ability of plants from contrasting habitats to control cation accumulation balance. Dittrichia viscosa plants, from eight siliceous habitats and nine calcareous habitats of southern France and neighbouring Spain and Italy, were cloned and grown together hydroponically with a solution simulating an acid soil with an aluminium constraint. Two independent hydroponic units containing solution supplemented with two levels of Al were used (2 Al levels x17 populations x3 genotypes x3 replicates). The growth and cation content (K, Ca, Mg and Na) of plant shoots and the chemical composition of the soil of each habitat were analysed. At the high Al level (1.1mm), populations differed in K, Ca and Mg plant proportions. Two groups could be distinguished: one containing all but one siliceous populations and the other containing all but one calcareous populations. Plants of the siliceous group accumulated proportionally more K and less Ca, and had better growth, than plants of the calcareous group, in the same way as calcifuge and calcicole species when grown on acid soil. At the lowest Al level (0.37mm), differences between siliceous and calcareous populations were less marked. The results suggest that differences in the ability of plants to control K and Ca balance, which appear to be of adaptive significance, could have arisen through selection, and that Dittrichia viscosa has evolved calcifuge and calcicole nutritional ecotypes in siliceous and calcareous habitats respectively. Various degrees of calcifugy, and to a lesser extent of calcicoly, can thus be suggested to occur among the studied populations, some in relation to the intensity of mineral stress in the natural habitats. So far, only functional traits have provided evidence of ecotypic differentiations within Dittrichia viscosa.deceased     

Ecotypes of Planktonic Actinobacteria with Identical 16S rRNA Genes Adapted to Thermal Niches in Temperate, Subtropical, and Tropical Freshwater Habitats

Seven strains with identical 16S rRNA genes affiliated with the Luna2 cluster (Actinobacteria) were isolated from six freshwater habitats located in temperate (Austria and Australia), subtropical (People's Republic of China), and tropical (Uganda) climatic zones. The isolates had sequence differences at zero to five positions in a 2,310-nucleotide fragment of the ribosomal operon, including part of the intergenic spacer upstream of the 16S rRNA gene, the complete 16S rRNA gene, the complete 16S-23S internal transcribed spacer (ITS1), and a short part of the 23S rRNA gene. Most of the few sequence differences found were located in the internal transcribed spacer sequences. Two isolates obtained from habitats in Asia and Europe, as well as two isolates obtained from different habitats in the People's Republic of China, had identical sequences for the entire fragment sequenced. In spite of minimal sequence differences in the part of the ribosomal operon investigated, the strains exhibited significant differences in their temperature response curves (with one exception), as well as pronounced differences in their temperature optima (25.0 to 35.6°C). The observed differences in temperature adaptation were generally in accordance with the thermal conditions in the habitats where the strains were isolated. Strains obtained from temperate zone habitats had the lowest temperature optima, strains from subtropical habitats had intermediate temperature optima, and a strain from a tropical habitat had the highest temperature optimum. Based on the observed temperature responses, we concluded that the strains investigated are well adapted to the thermal conditions in their home habitats. Consequently, these closely related strains represent different ecotypes adapted to different thermal niches.     

Evolution in extreme environments: replicated phenotypic differentiation in livebearing fish inhabiting sulfidic springs

We investigated replicated ecological speciation in the livebearing fish Poecilia mexicana and P. sulphuraria (Poeciliidae), which inhabit freshwater habitats and have also colonized multiple sulfidic springs in southern Mexico. These springs exhibit extreme hypoxia and high concentrations of hydrogen sulfide, which is lethal to most metazoans. We used phylogenetic analyses to test whether springs were independently colonized, performed phenotypic assessments of body and gill morphology variation to identify convergent patterns of trait differentiation, and conducted an eco-toxicological experiment to detect differences in sulfide tolerances among ecotypes. Our results indicate that sulfidic springs were colonized by three different lineages, two within P. mexicana and one representing P. sulphuraria. Colonization occurred earlier in P. sulphuraria, whereas invasion of sulfidic springs in P. mexicana was more recent, such that each population is more closely related to neighboring populations from adjacent nonsulfidic habitats. Sulfide spring fish also show divergence from nonsulfidic phenotypes and a phenotypic convergence toward larger heads, larger gills, and increased tolerance to H(2) S. Together with previous studies that indicated significant reproductive isolation between fish from sulfidic and nonsulfidic habitats, this study provides evidence for repeated ecological speciation in the independent sulfide spring populations of P. mexicana and P. sulphuraria.     

Intraspecific differences in thermal tolerance of Etheostoma spectabile (Agassiz) in constant versus fluctuating environments

The critical thermal maximum (CTM) of Etheostoma spectabile differed significantly among four populations whose habitats ranged from thermally constant to highly fluctuating conditions. Mean CTM of the population at the most fluctuating location was highest, populations in intermediate thermal environments were intermediate in thermal tolerance, and a population in a constant temperature spring run had thelowest CTM. The results support the view that thermal physiology can be evolutionarily labile within a species, and that changes respond to directional selection.     

Ecotypic differentiation in relation to soil nitrogen in northern Scandinavian Cochlearia officinalis

Ecotypic differentiation of Cochlearia officinalis L. was studied in four populations, roughly described as "beach", "bird cliff", "spring" and "estuary", which occupy different habitats in the northern part of Norway. The plants were cultivated under controlled conditions on soil to which nitrogen was applied at various amounts (0, 0.2 and 1.0 g N pot⁻¹). The above ground part of the "bird cliff" population showed the highest dry weight and nitrogen uptake at the highest nitrogen concentration. No effect of nitrogen treatment and the lowest dry weight were found in the "estuary" population. The differences in population response to added nitrogen were correlated to the nitrogen content of the soil in their natural habitat. Morphological features of the populations were also significantly different. The "estuary", "beach" and "bird cliff" populations showed differences in all characteristics measured – ratio of length/width of the leaves, shape of the leaf base, and length of the petiole. "Beach" and "spring" differed significantly in petiole length, while "bird cliff" and "spring" differed significantly in both leaf ratio and shape of the leaf base. These morphological features were not significantly altered by the application of nitrogen to the soil. This study shows that the four populations of Cochlearia officinalis are discrete biotypes characteristic of distinct habitats, and therefore, should be considered ecotypes.     

Genetic differentiation of the millipede Pycnotropis epiclysmus inhabiting seasonally inundated and non-flooded Amazonian forests

The millipede Pycnotropis epiclysmus Hoffman, 1995 (Diplopoda: Polydesmida: Platyrhacidae) is frequently found in Central Amazonian white-and mixed-water inundation forests along the Solimöes-Amazon River near Manaus, Brazil. It also inhabits non-flooded disturbed forest areas adjacent to this river. Populations from both biotopes were genetically studied. The specific pPeP172 satellite DNA family identified in P. epiclysmus has been analyzed in order to elucidate the systematic rank of morphologically indistinguishable individuals from the different habitat types. Nucleotide sequence data, sequence variability and copy number estimates of the pPeP172 satellite DNA do not discriminate the respective populations into genetically different ecotypes. The study of enzyme variability, however, revealed genotypic differences among the three populations: the populations from two geographically more distant inundation forests are genetically rather similar; and the geographically closer populations, one found in a non-flooded and the other in an inundation forest, have a genetic distance which is of similar magnitude to that of the two geographically more distant populations. The genetic data suggest that individuals from different habitats belong to populations of a single species. Genotypic structuring among and within local populations indicates processes of genetic differentiation which can be the result of the migration ability of this millipede.     

Zur Keimungsphysiologie des Wildhafers (Avena fatua L.)

The density of the phytophagous curculionid weevil complex belonging to one family and four subfamilies was determined in three different ecotypes including date‐palm, vegetable and natural (fallow) habitats in Western Saudi Arabia. Different densities were observed in the three habitats during 1996–1997. However, the date palm habitat showed high number of curculionid weevils. This may be attributed to the availability of food source, vegetational cover and shaded environment in the available niche. Chi square test showed that there were significant differences in density numbers between the three habitats. Three peaks were observed in the date‐palm habitat during December, March and May.     

不同生态型芦苇种群对盐胁迫的生长和光合特性

土壤盐渍化是影响我国土壤利用效率的主要因素之一,芦苇是改良土壤盐渍化的良好实验材料,但芦苇有着多种的生态型,比较各生态型芦苇的耐盐差异成为亟待解决的问题。通过设置淡水(0.00%)与加盐(质量浓度2.00%)处理控制实验,测量芦苇的生长指标和光合指标,比较河口型芦苇与内陆型芦苇耐盐性,寻找合适生态型的芦苇作为改良土壤盐渍化的生物材料。在实验中,与淡水条件相比,加盐(2.00%)处理条件下,河口型芦苇和内陆型芦苇的株高(height)、蒸腾速率(E)均显著性下降,但是两种生态型的芦苇的水分利用效率(WUE)明显提高;河口型的芦苇相对生长速率(RGR)和气孔导度(Gs)都明显高于内陆型芦苇。在淡水环境中,河口型芦苇的相对生长速率(RGR)和净光合速率(A)都显著性地高于内陆型芦苇。结果表明两种生态型的芦苇在进化过程中存在一定程度上的分化,盐胁迫会抑制两种芦苇的生长,两种生态型芦苇的相对生长速率和气孔导度在盐胁迫下出现明显地差异,表明两种生态型的芦苇对盐度的响应机制有所差异。相比于内陆型芦苇,河口型芦苇有着更强的耐盐性,内陆型及河口型芦苇的表型性状差异主要是由于其原生境的差异所决定的。     

Evolution of Ribosomal DNA (Rdna) Genetic Structure in Colonial Californian Populations of Avena Barbata

DNA samples from 980 plants of Avena barbata from 48 ecologically diverse sites in California and Oregon were assayed to determine their genotype for two duplicated loci governing rDNA variants. More than 40 different rDNA genotypes were observed among which 5 made up 96% of our sample in environmentally homogeneous sites; predominant genotypes were less frequent and recombinant genotypes were more frequent in environmentally heterogeneous sites. The spatial distribution of each predominant rDNA genotype was nearly an exact overlay on both macro- and microgeographical scales of a distinctive habitat and also of the distribution of an eight-locus morphological-allozyme variant genotype. In all, seven different habitat-genotype combinations (ecotypes) were distinguishable on the basis of their morphological-allozyme-rDNA genotypes. None of these seven genotypes has been found in ancestral Spanish populations; thus the above predominant multilocus genotypes (ecotypes) of the colonial populations evidently evolved subsequent to the recent introduction (within 150-200 generations) of A. barbata to California. The precise associations of specific alleles and genotypes of the morphological allozyme and rDNA loci with different specifiable habitats leads us to the conclusion that natural selection favoring particular multilocus combinations of alleles in different habitats was the main guiding force in shaping the internal genetic structure of local populations as well as the overall adaptive landscape of A. barbata over California and Oregon.     

坡地和沼泽地野牡丹(Melastoma candidum)叶片的解剖特征与气孔气体交换特性

对在坡地和沼泽地生长的野牡丹叶的解剖特征与气孔气体交换特性的研究表明：两者在形态结构方面存在着一定的差异,坡地野牡丹叶较窄,上表皮细胞小而排列紧密,气孔密度较大,上表皮厚,沼泽地野牡丹整个叶片和海绵组织比较厚,最大导管直径和栅栏细胞长度／宽度比值大,但栅栏组织厚／海绵组织厚比值较小。坡地野牡丹与沼泽地野牡丹的叶绿素a、叶绿素b的含量和类胡萝卜素的含量以及叶绿素a,b比值的差异都很小。沼泽地野牡丹净光合速率、蒸腾速率及气孔导度较高,常用的水分利用效率(Pn／Tr)接近,沼泽地野牡丹的内在水分利用效率(Pn／Gs)略高于坡地,但差异不显著。综合分析其生境条件,土壤与野牡丹叶片解剖结构和生理生态特性相关性密切。但实验结果不足以确定两种生境下生长的野牡丹为不同的生态型。     

Preliminary Observations on Resistance to Rust Diseases of Kentucky Bluegrass Ecotypes from Poland

Four hundred and forty-four ecotypes of Kentucky bluegrass ( Poa pratensis L.) collected from Poland were screened for rust resistance. A field experiment was established at Hof Steimke, DSV (Deutschen Saatveredelung), Germany. The ecotypes originated from the Polish Gene Bank, IHAR – Botanical Garden, Bydgoszcz. Sixty-two (13.9%) ecotypes that scored on average more than 5 were included in a group with high resistance. Ecotypes scored on average less than 5 were either included in a susceptible group (average scores 4.0–4.9) or a very susceptible group (average scores 2.0–3.9). There were 181 ecotypes in the susceptible group (40.8%) and 201 (45.3%) in the very susceptible group. Thirty-three (7.4%) ecotypes were more resistant and 29 (6.5%) ecotypes had resistance on the level of the most resistant control variety Ottos (score of resistance 5.3). Eight ecotypes (1.8%) with the highest level of resistance (score 7 or higher) were identified as especially promising sources of rust resistance. One ecotype (141858) showed reaction type 9 in both years and another one (141903) showed reaction type 9 in one year and reaction type 8 in another year (mean 8.5). Six ecotypes were scored on average 7 or 7.5. For 17 different habitats from which the tested ecotypes were collected only those ecotypes originating from 10 habitats (meadow, peat meadow, forest meadow, pasture, field, lakeside, waterside, ditch, roadside and gravel pit) showed high levels of resistance to rust. The value of newly identified resistant ecotypes for control of rusts on Kentucky bluegrass is discussed.     

Parallel evolution of dwarf ecotypes in the forest tree Eucalyptus globulus

Three small populations of a dwarf ecotype of the forest tree Eucalyptus globulus are found on exposed granite headlands in south-eastern Australia. These populations are separated by at least 100 km. Here, we used 12 nuclear microsatellites and a chloroplast DNA marker to investigate the genetic affinities of the dwarf populations to one another and to their nearest populations of tall E. globulus. Cape Tourville was studied in greater detail to assess the processes enabling the maintenance of distinct ecotypes in close geographical proximity. The three dwarf populations were not related to one another and were more closely related to adjacent tall trees than to one another. At Cape Tourville the dwarf and tall ecotypes were significantly differentiated in microsatellites and in chloroplast DNA. The dwarf and tall populations differed in flowering time and no evidence of pollen dispersal from the more extensive tall to the dwarf population was found. The three dwarf populations have evolved in parallel from the local tall ecotypes. This study shows that small marginal populations of eucalypts are capable of developing reproductive isolation from nearby larger populations through differences in flowering time and/or minor spatial separation, making parapatric speciation possible.     

Genetic and historical relationships among geothermally adapted Agrostis (bentgrass) of North America and Kamchatka: evidence for a previously unrecognized, thermally adapted taxon

Agrostis species have been known to evolve ecotypes rapidly in response to unusual edaphic conditions. The geographic distribution of Agrostis taxa in Lassen Volcanic National Park (California) and Yellowstone National Park (Wyoming) in the United States and the Valley of the Geysers (Kamchatka Peninsula) in Russia suggests that Agrostis scabra might have independently evolved morphologically similar ecotypes several times. We used RAPDs to show that, contrary to expectation, the thermal populations are not independently evolved, but instead constitute a single taxon that currently has four names. A UPGMA including the four thermal and nine nonthermal Agrostis taxa showed that the thermal cluster divides into geographically distinct subclusters, but that two morphologically distinct thermal taxa do not cluster independently. Even though currently confused with the thermal populations, nonthermal A. scabra is not closely related. An analysis of molecular variance (AMOVA) showed significant differentiation between the thermal populations and the nonthermal species sampled in this study. Splitting a hypothesized thermal operational taxonomic unit (OTU) into its components (geographically separated populations) does not greatly affect the partitioning of variation among OTUs. All thermal populations therefore should be assigned to the same taxon, but its taxonomic rank cannot be determined at this time.     

Phenotypic Plasticity and the Ecotypic Differentiation of Aggressive Behavior in Threespine Stickleback

The threespine stickleback fish, Gasterosteus aculeatus, has undergone a remarkable postglacial adaptive radiation in which an ancient oceanic ancestor has given rise to uncountable freshwater populations. The radiation is characterized by repeated, independent evolution of similar derived phenotypes under similar environmental conditions. A common pattern of divergence is caused by differences in habitat that favor morphological and behavioral features that enhance efficiency of feeding on plankton (limnetic ecotypes) vs. those that enhance efficiency of feeding on benthic invertebrates (benthic ecotypes). These two ecotypes exhibit consistently different patterns of courtship and of foraging and cannibalistic behavior (divergent behavioral syndromes). Here, we demonstrate that there also exist differences in aggression toward conspecifics that are likely to be characteristic of the ecotypes. We report differences in patterns of aggression toward rivals between the ecotypes and offer evidence of differences in the patterns of phenotypic plasticity (norms of reaction) for these traits across population types, and of differences in the incorporation of aggressive elements of behavior in courtship. These data support an earlier suggestion that differences in aggressive tendencies could have facilitated assortative mating between the four benthic–limnetic species pairs found in British Columbia lakes, and they demonstrate the need to evaluate divergent behavioral phenotypes in this radiation as phenotypic norms of reaction rather than as fixed traits.     

Geographic variation in thermal tolerance of a widespread minnow Notropis lutrensis of the North American mid-west

Eighteen populations of Notropis lutrensis , representing all of the major river systems occupied by this species across an 1100km north-south span of its range, showed no significant differences in mean critical thermal maximum (CTM), although general north-south differences in climatic temperatures exist. There were no clinal trends in CTMs, and CTMs were unrelated to stream size or any other discernible feature of the local habitats. Previous research has shown that N. lutrensis can adapt rapidly to an artificially altered thermal regime. The present results suggest that even though a species may have potentially 'labile' thermal physiology, it may nonetheless be 'static' or evolutionarily conservative in such characters when natural populations are examined empirically.     

Aestival and autumnal vicariads ofGentianella (Gentianaceae): A myth?

Plant samples were collected from 13 populations of the two speciesGentianella germanica andG. campestris. In addition, two samples from populations of grazed plants lacking their main stems were collected. A number of relevant morphological characters were measured, the flowering time, and the habitats of each population were studied. Some ecotypes ofG. germanica with clear differences in flowering time were recognized. Differences in flowering time and morphology between populations ofG. campestris seem to be clinal. The generally accepted theory of seasonal dimorphism with the assumption of separate aestival and autumnal vicariads proves to be inadequate. A hypothesis based upon the effect of human influences on the origin of this ecotypes is suggested.