Sexual dimorphism of body size and sternopleural bristle number: a comparison of geographic populations of an invasive cosmopolitan drosophilid

Zaprionus indianus is a cosmopolitan drosophilid, of Afrotropical origin, which has recently colonized South America. The sexual dimorphism (SD) of body size is low, males being almost as big as females. We investigated 10 natural populations, 5 from America and 5 from Africa, using the isofemale line technique. Three traits were measured on each fly: wing and thorax length and sternopleural bristle number. Two indices of SD were compared, and found to be highly correlated (r > 0.99). For the sake of simplicity, only the female/male (F/M) ratio was further considered. A significant genetic variability of SD was found in all cases, although with a low heritability (intra-class correlation of 0.13), about half the value found for the traits themselves. For size SD, we did not find any variation among continents or any latitudinal trend, and average values were 1.02 for wing length and 1.01 for thorax length. Bristle number SD was much greater (1.07). Among mass laboratory strains, SD was genetically much more variable than in recently collected populations, a likely consequence of laboratory drift. Altogether, SD, although genetically variable and prone to laboratory drift, is independent of size variations and presumably submitted to a stabilizing selection in nature.     

Geographical Clines for Quantitative Traits in Natural Populations of a Tropical Drosophilid: Zaprionus Indianus

We analyzed natural populations of Zaprionus indianusin 10 Indian localities along a south-north transect (latitude: 10–31°3 N). Size traits (body weight, wing length and thorax length) as well as a reproductive trait (ovariole number) followed a pattern of clinal variation, that is, trait value increased with latitude. Wing/thorax ratio, which is inversely related to wing loading, also had a positive, but non-significant correlation with latitude. By contrast, bristle numbers (sternopleural and abdominal) exhibited a non-significant but negative correlation with latitude. Sex dimorphism, estimated as the female/male ratio, was very low in Z. indianus, contrasting with results already published in other species. Genetic variations among populations were also analyzed according to other geographic parameters (altitude and longitude) and to climatic conditions from each locality. A significant effect of altitude was found for size traits. For abdominal bristles, a multiple regression technique evidenced a significant effect of both latitude and altitude, but in opposite directions. Genetic variations were also correlated to climate, and mainly with average year temperature. Taking seasonal variations into account failed however to improve the predictability of morphometrical variations. The geographic differentiation of Z.indianusfor quantitative traits suggests adaptive response to local conditions, especially to temperature, but also reveals a complex situation according to traits investigated and to environmental parameters, which does not match results on other drosophilid species.     

Geographic variation in phenotypic plasticity in response to dissolved oxygen in an African cichlid fish

Genetic adaptation and phenotypic plasticity are two ways in which organisms can adapt to local environmental conditions. We examined genetic and plastic variation in gill and brain size among swamp (low oxygen; hypoxic) and river (normal oxygen; normoxic) populations of an African cichlid fish, Pseudocrenilabrus multicolor victoriae. Larger gills and smaller brains should be advantageous when oxygen is low, and we hypothesized that the relative contribution of local genetic adaptation vs. phenotypic plasticity should be related to potential for dispersal between environments (because of gene flow’s constraint on local genetic adaptation). We conducted a laboratory‐rearing experiment, with broods from multiple populations raised under high‐oxygen and low‐oxygen conditions. We found that most of the variation in gill size was because of plasticity. However, both plastic and genetic effects on brain mass were detected, as were genetic effects on brain mass plasticity. F₁ offspring from populations with the highest potential for dispersal between environments had characteristically smaller and more plastic brains. This phenotypic pattern might be adaptive in the face of gene flow, if smaller brains and increased plasticity confer higher average fitness across environment types.     

Reaction norms and the genetic basis of phenotypic plasticity in the wing pattern of the butterfly Bicyclus anynana

The genetic basis of the dry-wet season polyphenism of wing pattern in response to temperature shown by Bicyclus anynana was studied, using a split-family design over four temperatures. Reaction norms crossed, but were only linear in the three highest temperatures, and only when larval development time was used as the environmental axis. Significant full-sib additive variances (V_A) and heritabilities (h²) for plasticity were found using slopes of reaction norms in a bootstrap procedure. Heritabilities were lower in intermediate temperatures, mainly due to differences in the residual variances (V_R). There was no clear trend in V_A across temperatures, contrary to the expectation that V_A would have been depleted by natural selection at the extreme temperatures and not depleted at the intermediate temperatures which occur less frequently in the field. Unpredictability in the onset of the following season at intermediate temperatures might lead to selection for diverse flresponses resulting in relatively high V_Rs. Theoretical models linking reaction norms to genetic parameters in separate environments were difficult to apply in this study, particularly because they are based on the assumption that V_Rs are constant. However the reaction norm approach combined with quantitative genetics provided a valuable insight into the evolution of the observed polyphenism.     

表型可塑性和局域适应在紫茎泽兰入侵不同海拔生境中的作用

紫茎泽兰是我国危害最严重的外来入侵物种之一,为探讨表型可塑性和局域适应在其入侵中的作用,在高、低海拔的两个样地内,测定了来自云南南部640～2450 m海拔范围的6个种源的紫茎泽兰种群的株高、冠宽、分枝数和高温半致死温度(HSLT).结果表明,在高海拔样地,各种群紫茎泽兰株高、冠宽、分枝数和HSLT(2130 m的哀牢山种群除外)均显著低于在低海拔样地,紫茎泽兰各种群的株高、冠宽和分枝数的可塑性指数(0.881～0.975)均较大,而HSLT的可塑性(0.052～0.200)较小.无论在高还是低海拔样地,紫茎泽兰的株高、冠宽和分枝数在种群间的差异均不显著,而HSLT在种群间的差异达极显著水平,表现出明显的遗传分化,但其在种群间的差异仍小于其在样地间的差异.在高海拔样地,紫茎泽兰各种群的分枝数与种源海拔呈显著正相关;在低海拔样地,紫茎泽兰的HSLT与种源海拔呈显著负相关,表现出明显的局域适应特征.表型可塑性和局域适应均与紫茎泽兰的入侵有关,但前者的作用可能更大.     

Reaction norms across and genetic parameters at different temperatures for thorax and wing size traits in Drosophila aldrichi and D. buzzatii

Reaction norms across seven constant and one fluctuating temperature of development were measured for thorax length and several wing size traits for up to 10 isofemale lines of each of the cactophilic Drosophila species, D. aldrichi and D. buzzatii, originating from the same locality. Maximum thorax length was reached at different low to intermediate temperatures for the two species, whereas wing length was highest at the lowest temperature in both species. Various ratio parameters showed pronounced species differences. The reaction norm for the wing loading index (wing length/thorax length) decreased monotonically with temperature in both species, but was much steeper and spanned a wider range in D. aldrichi than in D. buzzatii, suggesting either that wing loading is not a good characterization of flight capacity or, more likely, that flight optimization does not occur in the same manner in both species. The vein ratio (distal length/proximal length of the third vein) increased with temperature in D. buzzatii but decreased in D. aldrichi. Wing development in the two species thus is very different, with the proximal part of the wing in D. buzzatii more closely allied to the thorax than to the distal part. Among line variation was significant for all traits in both species, and most pronounced for thorax length and the ratio parameters. Coefficients of variation were significantly different between the species for all traits, with those in D. aldrichi higher than in D. buzzatii. Genetic variance in plasticity was significant for all traits in D. buzzatii, but only for seven out of 12 in D. aldrichi. Additive genetic variances for all traits in both species were significantly larger than zero. Genetic correlations between thorax length and several wing length parameters, and between these and wing area, were positive and generally significant in both species. The genetic correlation between the distal and the proximal length of the third vein was not significantly different from zero in D. aldrichi, but negative and significant in D. buzzatii. Heritabilites varied significantly among temperatures for almost all traits in both species. Phenotypic variances were generally higher in D. aldrichi than in D. buzzatii, and commonly highest at the extreme temperatures in the former species. At the high temperature the genetic variances also were usually highest in D. aldrichi. The data clearly suggest that the process of thermal adaptation is species specific and caution against generalizations based on the study of single species.     

Adaptation to an extraordinary environment by evolution of phenotypic plasticity and genetic assimilation

Adaptation to a sudden extreme change in environment, beyond the usual range of background environmental fluctuations, is analysed using a quantitative genetic model of phenotypic plasticity. Generations are discrete, with time lag τ between a critical period for environmental influence on individual development and natural selection on adult phenotypes. The optimum phenotype, and genotypic norms of reaction, are linear functions of the environment. Reaction norm elevation and slope (plasticity) vary among genotypes. Initially, in the average background environment, the character is canalized with minimum genetic and phenotypic variance, and no correlation between reaction norm elevation and slope. The optimal plasticity is proportional to the predictability of environmental fluctuations over time lag τ. During the first generation in the new environment the mean fitness suddenly drops and the mean phenotype jumps towards the new optimum phenotype by plasticity. Subsequent adaptation occurs in two phases. Rapid evolution of increased plasticity allows the mean phenotype to closely approach the new optimum. The new phenotype then undergoes slow genetic assimilation, with reduction in plasticity compensated by genetic evolution of reaction norm elevation in the original environment.     

不同种源羊草表型差异性

研究植物因环境变化产生的表型差异,对于其适应未来全球气候变化具有重要的意义。羊草具有广泛的地理分布,是研究表型差异的理想材料。将白城市镇赉种源地羊草(ZL),白城市洮北种源地羊草(TB),吉林大安市种源地羊草(DA)和大安市姜家甸草场种源地羊草(JC)进行同质园移栽培养,分析了4个种源羊草的表型特征。结果表明,不同种源间羊草表型特征株高、叶长、叶宽、茎直径和生理特征蒸腾速率(Tr)、水分利用效率(WUE)和生物量分配均存在显著差异。在同质园环境培养下,这些表型特征均存在显著的种源差异。从总体上来看,TB种源地的羊草具有最高的株高、叶长和叶宽,分别为72.2 cm、34.4 cm、和10.34 mm。ZL种源有着最高的生物量(46.05 g)和WUE(3.06μmolCO₂/mmol H₂O)。ZL种源叶鲜重和干重均表现出了较高值,分别为2.88 g和0.96 g。不同种源羊草经移栽到同质园环境下,因为对源地气候长期的适应,产生了明显的表型差异,进而引起形态、生理特征的差异。这有利于羊草适应未来剧烈的气候变化,进一步揭示了羊草适应环境的策略。     

Adaptive phenotypic plasticity and local adaptation for temperature tolerance in freshwater zooplankton

Many organisms have geographical distributions extending from the tropics to near polar regions or can experience up to 30°C temperature variation within the lifespan of an individual. Two forms of evolutionary adaptation to such wide ranges in ambient temperatures are frequently discussed: local adaptation and phenotypic plasticity. The freshwater planktonic crustacean Daphnia magna, whose range extends from South Africa to near arctic sites, shows strong phenotypic and genotypic variation in response to temperature. In this study, we use D. magna clones from 22 populations (one clone per population) ranging from latitude 0° (Kenya) to 66° North (White Sea) to explore the contributions of phenotypic plasticity and local adaptation to high temperature tolerance. Temperature tolerance was studied as knockout time (time until immobilization, T_imm) at 37°C in clones acclimatized to either 20°C or 28°C. Acclimatization to 28°C strongly increased T_imm, testifying to adaptive phenotypic plasticity. At the same time, T_imm significantly correlated with average high temperature at the clones’ sites of origin, suggesting local adaptation. As earlier studies have found that haemoglobin expression contributes to temperature tolerance, we also quantified haemoglobin concentration in experimental animals and found that both acclimatization temperature (AccT) and temperature at the site of origin are positively correlated with haemoglobin concentration. Furthermore, Daphnia from warmer climates upregulate haemoglobin much more strongly in response to AccT, suggesting local adaptation for plasticity in haemoglobin expression. Our results show that both local adaptation and phenotypic plasticity contribute to temperature tolerance, and elucidate a possible role of haemoglobin in mediating these effects that differs along a cold–warm gradient.     

Genetic differences and phenotypic plasticity in body size between high- and low-altitude populations of the ground beetle Carabus tosanus

The body size of a univoltine carabid beetle Carabus tosanus on Shikoku Island, Japan, was clearly smaller in higher‐altitude populations (subspecies), which possibly represents incipient speciation. To explore the determinants of altitudinal differences in body size in this species, we studied the degree of phenotypic plasticity by conducting rearing experiments at two constant temperatures and examined genetic differences through interpopulation crosses. At 15 °C, C. tosanus had a longer developmental period and a shorter adult body than at 20 °C. Nevertheless, variation in body size due to temperature effects (phenotypic plasticity) was small compared to the interpopulation differences, which suggests substantial genetic differences between populations (subspecies) at different altitudes. In F₁ offspring from crosses between a low‐altitude (subspecies tosanus) and a high‐altitude population (subspecies ishizuchianus), adult body length was affected by the genotypes of both parents, with an interaction effect of parental genotype and offspring sex. Further analyses revealed that adult body length was affected by sex‐linked factors in addition to autosomal factors. These genetic differences in body size may have resulted from adaptations to different altitudes and may be important for the process of incipient speciation because body size differences could contribute to premating reproductive isolation.     

The contributions of evolutionary divergence and phenotypic plasticity to geographic variation in the western fence lizard,Sceloporus occidentalis

Local genetic adaptation and phenotypic plasticity are two mechanisms that can have marked effects on the morphology, performance, and behaviour of animals, producing geographic variation among populations. However, few studies have examined how these mechanisms interact during ontogeny to shape organismal phenotypes. We incubated eggs of the western fence lizard, Sceloporus occidentalis, from four populations (representing two latitudes and altitudes) in either a warm or cool environment in the laboratory. We then raised the hatchlings under common laboratory conditions, measured morphological and performance traits until 5 weeks of age, and compared juvenile morphology with that of field‐caught adults from each population. The results obtained indicate that some phenotypic traits that contribute to performance (body size, hindlimb length, head shape) were relatively canalized in juveniles and differed among populations in a way that was consistent with adults from their population of origin. However, other traits (forelimb length, inter‐limb length, mass, tail length), showed significant effects of incubation temperature, and this environmentally induced variation persisted throughout the experiment. Although selection pressure may be stronger for traits that are integral to survival, developmental effects might still have a lasting impact on traits less important to organismal fitness. We discuss the results obtained in the present study the context of the life history of these animals. © 2010 The Linnean Society of London, Biological Journal of the Linnean Society, 2010, 99 , 84–98.     

Mesosternal bristle number in a cosmopolitan drosophilid: an X-linked variable trait independent of sternopleural bristles

Mesosternal (MS) bristles in Drosophila are a pair of machrochaetae found at the sternal end of the sternopleural (STP) microchaetae, and are thought to be invariable. In a closely related drosophilid genus, Zaprionus, their number is four and, in contrast to Drosophila, they show interspecific and intraspecific variability. The genetic basis of MS bristle number variability was studied in Z. indianus, the only cosmopolitan species of the genus. The trait responded rapidly to selection and two lines were obtained, one lacking any bristles (0-0) and the other bearing the normal phenotype (2-2). Other symmetrical phenotypes, (1-1) and (3-3), could also be selected for, but with lesser success. By contrast, STP bristle number did not vary significantly between the two lines (0-0) and (2-2), revealing its genetic independence from MS bristle number. Reciprocal crosses between these two lines showed that MS bristle number is mainly influenced by a major gene on the X chromosome (i.e. F₁ males always resembled their mothers) with codominant expression (i.e. heterozygous F₁ females harboured an average phenotype of 2 bristles). However, trait penetrance was incomplete and backcrosses revealed that this variability was partly due to genetic modifiers, most likely autosomal. The canalization of MS bristle number was investigated under different temperatures, and the increased appearance of abnormal phenotypes mainly occurred at extreme temperatures. There was a bias, however, towards bristle loss, as shown by a liability (developmental map) analysis. Finally, when ancestral and introduced populations were compared, the latter were far less stable, suggesting that genetic bottlenecks may perturb the MS bristle number canalization system. MS bristle number, thus, appears to be an excellent model for investigating developmental canalization at both the quantitative and the molecular level.     

Adaptation of intestinal cell membrane enzymes to low temperatures in the Antarctic teleost Pagothenia bernacchii

The enzymatic activity (expressed as milliunits per milligram total proteins) of three intestinal brush-border membrane enzymes, leucine aminopeptidase, alkaline phosphatase and maltase, measured over a range of temperatures between 1.5 and 37 °C, has been found to be much higher in the Antarctic fish Pagothenia bernacchii than in the temperate fish Anguilla anguilla. To explain this experimental observation the apparent Michaelis-Menten constant, the maximal velocity, the activation energy values and the thermal stability of these three enzymes were measured. The apparent Michaelis-Menten constant values of leucine amino peptidase and alkaline phosphatase were different in the intestine mucosal homogenate of the two fish at each measured temperature (from a minimum of 2.5 to a maximum of 37 °C). However, the values found at 2.5 °C for the Antarctic species and 15 °C for the eel where comparable. Furthermore, its value was unchanged in eel intestine apical membranes, both in the presence and without enzyme lipid microenvironment. While the maximal enzymatic activities of the leucine aminopeptidase and maltase did not decrease without their enzyme lipid microenvironment, produced by treatment with Triton X-100, the impairment of alkaline phosphatase maximal activity cannot be significantly differentiated from a non-specific inhibitory effect of the detergent. The activation energy values of leucine amino peptidase, alkaline phosphatase and maltase were lower in the Antarctic fish (11.7, 5.6 and 11.8 kcal·mol^-1, respectively) than in the eel (13.6, 7.6 and 13.1 kcal·mol^-1, respectively). The thermal stability of alkaline phosphatase and maltase is different in Pagothenia bernacchii and Anguilla anguilla intestinal homogenate.Abbreviations BBM brush border membrane - E _a activation energy - EGTA ethyleneglycol-bis-(-amino ethylether)N, N-tetraacetic acid - HEPES 2-[4-(2-hydroxyethyl)-1-piperazinyl]-ethane sulphonic acid - Km_app apparent Michaelis-Menten constant - PMSF phenylmethyl-sulphonyl fluoride - TRIS TRIS (hydroxymethyl)-aminomethane     

Abdominal pigmentation and growth temperature in Indian Drosophila melanogaster: Evidence for genotype-environment interaction

Phenotypic variability for abdominal pigmentation in females of an Indian natural population ofDrosophila melanogaster was studied using isofemale lines and by rearing the larvae and pupae at 4 different temperatures ranging from 20–30°C. The dark pigmented area was found to increase in all the three segments when the growth temperature decreases. A significant positive correlation was detected for the occurrence of dark pigmentation in the 5th and 6th segments in each growth temperature but for other comparisons the correlation was not regular. Analysis of variance (ANOVA) was carried out both for individual segments over different growth temperatures and also for each temperature over the three abdominal segments and in all cases found to be statistically significant. The results are quite different from the earlier observation in FrenchDrosophila melanogaster and suggest that genes controlling pigmentation are temperature dependent; temperature could affect post-transitional events involved in pigmentation. The present findings also clearly indicate that significant genotype-environment interaction exists, responsible for the production of desired phenotype at the opportune moment during the life span of a species.     

Phenotypic plasticity to light intensity in Arabidopsis thaliana: invariance of reaction norms and phenotypic integration

Phenotypic plasticity (the pattern of response of organisms to changes in environmental conditions) and phenotypic integration (the pattern of character correlations) are important components of our understanding of the evolution of complex phenotypes. Most studies published so far in this area have been conducted within populations with the express aim of predicting future response to evolutionary forces. However, among-population differentiation for plasticity and trait correlations are important indicators of recent past events that have shaped the currently observable phenotypes. We investigated variation in the reaction norms of several traits in a large number of accessions of Arabidopsis thaliana exposed to different levels of light quantity as well as the environmental lability of the corresponding across-population character variance–covariance matrix. Our results show that there is an astounding degree of inter-population variation for character means and very little variation for plasticity, in agreement with the idea that A. thaliana is a light-specialist often occurring in open, disturbed habitats. However, this plant also shows patterns of plasticity that are predicted to be adaptive based on functional ecological considerations, such as an increase in either specific leaf area or leaf number (but not both) under low light. We also demonstrate that the set of character correlations in A. thaliana is extremely stable to changes in light availability, contrary to previous findings in the same species when different environmental factors were considered. Several processes that might have been responsible for the observed patterns are discussed as a prelude to follow-up research on these problems.     

林业有害植物金钟藤新枝在海南的月生长动态

【背景】近20多年来,金钟藤在海南和广东异常快速生长,对生物多样性和林业生产破坏严重。观测金钟藤的月生长动态,了解其在海南的生长量,能够为金钟藤的合理防治提供参考。【方法】采用定点定时观测法,对海南3个市县3种不同生境的金钟藤新枝的月生长量进行测定。【结果】金钟藤在海南全年可生长,一新枝月平均生长134 cm,全年累计平均生长1607 cm。金钟藤全年有2个生长高峰期,分别在4月和9月,其中4月平均生长206 cm,9月187 cm。金钟藤在11月生长量最小,平均生长86 cm。金钟藤在1—9月生长较快,一新枝累计平均生长1326 cm,占全年生长量的82.5%;在10月至12月生长缓慢,一新枝累计平均生长281 cm,占全年生长量的17.5%。不同生境之间的金钟藤生长有极显著差异,月平均生长量从高到低顺序为定安188 cm白沙131 cm五指山83 cm。金钟藤种子在3—7月均可萌发,花果期在4—7月。在海南月平均温度17~28℃、月平均降雨量28~396 mm的自然环境范围内,金钟藤的生长量与温度和降雨量没有显著相关性。【结论与意义】金钟藤在海南光照充足的生境里快速生长扩散,月平均生长量高达188 cm,其生长与生境、海拔和植被密切相关。     

Electrophoretic Mobility of Amylase in Drosophilids Indicates Adaptation to Ecological Diversity

Understanding the significance of electrophoretic variation is of interest for both ecological and evolutionary genetics. Although there has been a very active neutralist–selectionist debate about the patterns of electrophoretic variation in natural populations, it is only recently that charged amino acids have been shown to be important in enzyme adaptation. In this study we carried out a broad electrophoretic survey of amylase variation in 150 species of Drosophilids. The distribution of amylase electromorphs was found to be correlated with the geographical origin of the flies. Generally the faster migrating variants are found in warmer temperatures. There is also a correlation with the feeding habits of the species, in particular, fungus feeders consistently showed a deviating pattern of electrophoretic mobility. These correlations between ecological diversity and electrophoretic patterns indicate that at least some of the changes in charged amino acids are adaptive, and result from selection to cope with specific environments.     

Variability of Wing Size and Shape in Three Populations of a Recent Brazilian Invader, Zaprionus indianus (Diptera: Drosophilidae), from Different Habitats

Zaprionus indianus (Diptera: Drosophilidae) is an African species that was introduced in Brazil near the end of the 1990’s decade. To evaluate the adaptive potential of morphological traits in natural populations of this recently introduced species, we have investigated wing size and shape variation at Rio de Janeiro populations only two years after the first record of Z. indianus in Brazil. Significant genetic differences among populations from three distinct ecological habitats were detected. The heritability and evolvability estimates show that, even with the population bottleneck that should have occurred during the invasion event, an appreciable amount of additive genetic variation for wing size and shape was retained. Our results also indicated a greater influence of environmental variation on wing size than on wing shape. The importance of quantitative genetic variability and plasticity in the successful establishment and dispersal of Z. indianus in the Brazilian territory is then discussed.     

入侵性杂草皱匕果芥在中国的适生区预测及分析

[目的]对入侵性杂草皱匕果芥在我国的适生区进行预测,为入侵风险评估和损失预测提供数据支撑,同时为控制预案制定提供科学依据。[方法]先用ENMTools和SPSS分别对分布数据和环境变量进行筛选,再调用R程序包Kuenm校准MaxEnt模型确定最优参数设置,然后使用MaxEnt和ArcMap对皱匕果芥在中国的适生区进行预测,并将已公布的进境粮食指定监管场地、进口粮食加工企业地理位置与皱匕果芥在中国的适生区进行匹配分析。[结果]最冷月份最低温度、温度季节变化标准差和最冷季度降水量是对MaxEnt模型拟合重要性排名前3位的环境变量,最冷月份最低温度可能是影响皱匕果芥发生分布的最重要的自然因素;皱匕果芥在中国的中度适生区占中国陆地总面积的15.13%,主要集中在秦岭-淮河以南、龙门山-大凉山以东的亚热带季风气候区域;高度适生区占中国陆地总面积的1.67%,主要形成川渝、湖北-湖南和长三角3个中心。在皱匕果芥的中、高度适生区分布有901个进口粮食加工企业和57个进境粮食指定监管场地。[结论]皱匕果芥的中、高度适生区内存在我国粮棉等作物的重要产区,一旦该杂草大面积发生,将给我国粮棉等作物种植造成非常不利的影响。进口粮食的国际贸易是皱匕果芥入侵中国的主要途径,应当加强对进口粮食接卸、运输、加工等高风险区域和环节的监管力度,并积极实施外来入侵杂草的监测和调查,确保做到早发现、早防除,防止进一步扩散和危害。     

Climate change affects timing and size of populations of an invasive cyanobacterium in temperate regions

Cylindrospermopsis raciborskii, an invasive freshwater cyanobacterium, originated from the tropics but has spread to temperate zones over the last few decades. Its northernmost populations in Europe occur in North German lakes. How such dramatic changes in its biogeography are possible and how its population dynamics in the newly invaded habitats are regulated are still unexplained. We therefore conducted a long-term (1993–2005) study of two German lakes to elucidate the mechanisms behind C. raciborskii population dynamics and to identify the abiotic constraints on its development. Our data revealed that pelagic populations of C. raciborskii thrived for three months during the summer, contributing up to 23% of the total cyanobacteria biovolume. Population sizes varied greatly between years without exhibiting any distinct long-term trends. In the annual lifecycle, C. raciborskii filaments emerged in the pelagic habitat when the temperature rose above 15–17 °C. At that time, mean photosynthetically active radiation in the mixed water column (I _mix) overstepped its maximum. Rates of population net increase were highest at the beginning of the season (0.15–0.28 day⁻¹), declined continuously over time, and were significantly positively correlated with I _mix. This indicates that the onset of the pelagic population is temperature-mediated and that I _mix controls its growth. Since I _mix peaks before the population onset, the time of germination is of crucial importance for successful development. To test this hypothesis, we designed a model to simulate pelagic population size, starting at different dates in the annual cycle. Moving the population onset forward by 30 days resulted in a doubling of the population size. We therefore conclude that an earlier rise in water temperature associated with climate change has promoted the spread of C. raciborskii to the temperate zone. Earlier warming permits earlier germination, thereby shifting the pelagic populations to a phase with higher I _mix, which advances growth and the population establishment.