Catchment context and the bottom‐up regulation of the abundance of specialist semi‐aquatic weevils on water hyacinth

1. Bottom‐up regulation is prevalent in plant–herbivore interactions and is thought to be particularly important in the case of aquatic plants and their specialist insect herbivores. 2. Recently published mesocosm studies have shown that the abundance of specialist Neochetina weevils, N. bruchi and N. eichhorniae, on water hyacinth (Eichhornia crassipes) are principally under the influence of nutrients in plant tissues. 3. We examined historical patterns of the abundance of these species of semi‐aquatic weevils in two water bodies from catchments with significantly different nutrient loads in subtropical Australia to test the validity of the published conceptual model of bottom‐up regulation. 4. Our results revealed that these weevils are indeed under bottom‐up regulation under field conditions. However, the nature of this regulation appears to be influenced by the broader catchment context of the water hyacinth‐infested water body, with plant tissue nutrients influencing weevil abundance more in the catchment with lower nutrient run‐offs. 5. Our findings reaffirm the importance of bottom‐up regulation in plant–insect interactions, add to the growing evidence of indirect effects spanning terrestrial and aquatic ecosystems, and inform management of water hyacinth using these weevils as biocontrol agents.     

Phytoremediation of landfill leachate waste contaminants through floating bed technique using water hyacinth and water lettuce

Abstract

In the present study, the effectiveness of water hyacinth and water lettuce was tested for the phytoremediation of landfill leachate for the period of 15?days. Fifteen plastic containers were used in experimental setup where aquatic plants were fitted as a floating bed with the help of thermo-pole sheet. It was observed that both plants significantly (p?<?0.05/p?<?0.01/p?<?0.001) reduce the physicochemical parameters pH, TDS, BOD, COD and heavy metals like Zn, Pb, Fe, Cu and Ni from landfill leachate. Maximum reduction in these parameters was obtained at 50% and 75% landfill leachate treatment and their removal rate gradually increased from day 3 to day 15 of the experiment. The maximum removal rate for heavy metals such as for Zn (80–90%), Fe (83–87%) and Pb (76–84%) was attained by Eichhornia crassipes and Pistia stratiotes. Value of bioconcentration and translocation factor was less than 1 which indicates the low transport of heavy metals from roots to the above-ground parts of the plants. Both these plants accumulate heavy metals inside their body without showing much reduction in growth and showing tolerance to all the present metals. Therefore, results obtained from the study suggest that these aquatic plants are suitable candidate for the removal of pollution load from landfill leachate.     

Colonization of Coquillettidia linealis (Skuse) with reference to other Coquillettidia and Mansonia species

The immature stages of Coquillettidia and Mansonia mosquitoes are cryptic and spend the duration of their development attached to the tissues of subsurface aquatic plants. This obligatory association makes them difficult to collect and has precluded detailed investigation of the biology of Coquillettidia linealis, a species of significant pest and vector status in Australia, as well as other species in the genus Coquillettidia in Australia and elsewhere. This paper describes the first successful establishment and maintenance of a colony of Cq. linealis. Blood‐seeking wild adults were collected and induced to oviposit under laboratory conditions, where methods were developed to rear larval populations to adult maturity in a colony that was maintained through eight successive generations. Colonies of Coquillettidia xanthogaster and Coquillettidia sp. nr crassipes were also established and reared through at least six generations and five generations, respectively, while two species of Mansonia, Mansonia uniformis and Mansonia septempunctata, were also reared successfully for six and two generations, respectively.     

大水面放养水葫芦对富营养化湖泊水体可培养细菌群落结构的影响

【目的】了解大水面放养水葫芦对富营养化湖泊水体可培养细菌群落结构和多样性的影响。【方法】采用稀释平板法,分别对云南滇池紫根水葫芦放养区(ZW)、野生型普通水葫芦放养区(PW)、未放养水葫芦对照区(CK)水体中细菌进行分离,并对其16S r RNA序列进行分析。【结果】分别从ZW、PW、CK 3种水体分离得到54、49、40株菌落形态差异的细菌,Shannon-Wiener多样性指数分别为3.17、3.07、2.73,细菌数量分别为1.35×107、8.35×106、2.70×106 CFU/L。16S r RNA序列分析表明,ZW、PW、CK 3种水体可培养细菌主要包括变形菌门α亚群(Alphaproteobacteria,35.1%、32.4%和40%)、放线菌门(Actinobacteria,18.9%、32.4%和20%)、变形菌门β亚群(Betaproteobacteria,13.5%、5.9%和16.0%)、变形菌门γ亚群(Gammaproteobacteria,13.5%、14.6%和12.0%)、拟杆菌门(Bacteroidetes,13.5%、8.8%和8.0%)和厚壁菌门(Firmicutes,2.7%、5.9%和4.0%)。在属的水平上,3种水体仅有鞘氨醇盒菌属(Sphingopyxis)、红细菌属(Rhodobacter)、黄色杆菌属(Xanthobacter)、新鞘脂菌属(Novosphingobium)、鞘氨醇单胞菌属(Sphingomonas)、假单胞菌属(Pseudomonas)、微杆菌属(Microbacterium)、链霉菌属(Steptomyces)、黄杆菌属(Flavobacterium)、芽孢杆菌属(Bacillus)等10个属的细菌为共有菌属。【结论】大水面放养水葫芦提高了富营养化湖泊水体中可培养细菌的多样性,改变了细菌的群落结构。     

水葫芦根际细菌群落结构多样性分析

【目的】了解水葫芦根际细菌群落结构。【方法】运用末端限制性片段长度多态性(Terminal restriction fragment length polymorphism,T-RFLP)技术分析富营养化水体中水葫芦根际和水葫芦近、远水样的细菌群落特征及多样性,结合克隆文库技术和培养法分析根际的细菌种群类型。【结果】同一时期水葫芦根际细菌多样性(Shannon-Weiner指数H′或Simpson指数D)更高,水葫芦近水样次之,远水样最小。10月份的细菌多样性高于5月份的。通过水葫芦根际细菌的克隆文库可知变形杆菌门(Proteobacteria)是水葫芦根际细菌的主要类群,占总群体的65.1%,包括噬菌弧菌(Bacteriovorax sp.)、Dechloromonas sp.、Leptothrix sp.、红螺菌科(Rhodospirillaceae)、Rhodoferax sp.和红环菌科(Rhodocyclaceae)等。T-RFLP图谱显示159 bp为最大优势菌,247 bp为第二大优势菌,对照克隆文库及培养结果分析247 bp属于γ-Proteobacteria,159 bp为不动杆菌(Acinetobacter sp.)。【结论】水葫芦根际细菌的群落结构丰富,不同时段水葫芦根际细菌的丰度略有变化,主要类群为变形杆菌门。     

外源亚精胺对Hg2+胁迫下凤眼莲抗氧化系统的影响

通过Hoagland溶液培养实验,研究了外源亚精胺(Spd)(0.1 mmol?L-1)对Hg2+(0、10、20、30和40μmol?L-1)胁迫下凤眼莲叶片细胞内叶绿素、可溶性糖、可溶性蛋白含量及抗氧化系统的调节作用.结果显示,(1)随Hg2+处理浓度的升高,各处理凤眼莲叶片叶绿素a(Chl a)和叶绿素b(Chl b)含量均先升后降,并均在10μmol?L-1时达到最高值,但外源Spd处理组显著高于相应对照.(2)各处理凤眼莲叶片可溶性蛋白含量随Hg2+处理浓度的升高也呈先升后降趋势,而可溶性糖含量则呈持续上升趋势,但外源Spd处理亦明显高于相应对照.(3)随Hg2+处理浓度的升高,抗氧化物质AsA和GSH含量及抗氧化酶SOD、CAT、POD、APX及GR活性也均呈先升后降的变化趋势,而外源Spd处理植株的含量和活性均显著高于相应对照.(4)各处理凤眼莲叶片的H2O2、MDA含量及O2?-产生速率随Hg2+处理浓度的升高均持续上升,但在外源Spd处理后均比对照组下降.研究表明,Hg2+胁迫使凤眼莲生长受到严重伤害,外源Spd可大幅度地提高其抗氧化物质含量和保护酶活性,从而增强凤眼莲抗Hg2+胁迫的能力.     

Spatial distribution of aquatic birds in Anavilundawa Ramsar wetland sanctuary in Sri Lanka

Biotic and abiotic factors that influence the avian distribution in a dry zone wetland was investigated by studying the distribution of Asian Openbill (Anastomus oscitans), Cotton Pygmy-goose (Nettapus coromandelianus) and Pheasant-tailed Jacana (Hydrophasianus chirurgus) in Anavilundawa Ramsar sanctuary in Sri Lanka in 2006. Their distribution was recorded in Anavilundawa, Suruwila and Maiyawa reservoirs, their catchments and respective paddy fields, through line transects. The floral cover of surface water was recorded by floating quadrates. Water lily (Nymphea spp.) was the dominant flora in Anavilundawa reservoir, invasive water hyacinth (Eichhornia crassipes) in Suruwila reservoir and a native lotus (Nelumbo nucifera) in Maiyawa reservoir, respectively. Anavilundawa area had a higher distribution of birds than in the other two areas. Among the three species observed, Asian Openbill distribution was mainly restricted to Anavilundawa whereas Pheasant-tailed Jacana was present in all three areas. Nesting of Asian Openbill occurred only in Anavilundawa while nesting of Pheasant-tailed Jacana was only observed in Maiyawa. Among the three species recorded, Cotton Pygmy-goose numbers were the least. Asian Openbill preferred dead trees and trees with no leaves for nesting and perching over live trees. It is concluded that the spread of invasives such as Water hyacinth and Salvinia (Salvinia molesta) forming mats over surface water have reduced the abundance of habitat specialists like Cotton Pygmy-goose.     

Evolutionary pathways to self-fertilization in a tristylous plant species

Evolutionary transitions from outcrossing to selfing occur commonly in heterostylous genera. The morphological polymorphisms that characterize heterostyly provide opportunities for different pathways for selfing to evolve. Here, we investigate the origins and pathways by which selfing has evolved in tristylous Eichhornia paniculata by providing new evidence based on morphology, DNA sequences and genetic analysis. The primary pathway from outcrossing to selfing involves the stochastic loss of the short-styled morph (S-morph) from trimorphic populations, followed by the spread of selfing variants of the mid-styled morph (M-morph). However, the discovery of selfing variants of the long-styled morph (L-morph) in Central America indicates a secondary pathway and distinct origin for selfing. Comparisons of multi-locus nucleotide sequences from 27 populations sampled from throughout the geographical range suggest multiple transitions to selfing. Genetic analysis of selfing variants of the L- and M-morphs demonstrates recessive control of the loss of herkogamy, although the number of factors appears to differ between the forms. Early stages in the establishment of selfing involve developmental instability in the formation of flowers capable of autonomous self-pollination. The relatively simple genetic control of herkogamy reduction and frequent colonizing episodes may often create demographic conditions favouring transitions to selfing in E. paniculata .