Evolutionary ecology of facultative paedomorphosis in newts and salamanders

Facultative paedomorphosis is an environmentally induced polymorphism that results in the coexistence of mature, gilled, and fully aquatic paedomorphic adults and transformed, terrestrial, metamorphic adults in the same population. This polymorphism has been of interest to scientists for decades because it occurs in a large number of caudate amphibian taxa as well as in a large diversity of habitats. Numerous experimental and observational studies have been conducted to explain the proximate and ultimate factors affecting these heterochronic variants in natural populations. The production of each alternative phenotype is based on a genotypexenvironment interaction and research suggests that differences in the environment can produce paedomorphs through several ontogenetic pathways. No single advantage accounts for the maintenance of this polymorphism. Rather, the interplay of different costs and benefits explains the success of the polyphenism across variable environments. Facultative paedomorphosis allows individuals to cope with habitat variation, to take advantage of environmental heterogeneity in the presence of open niches, and to increase their fitness. This process is expected to constitute a first step towards speciation events, and is also an example of biodiversity at the intraspecific level. The facultative paedomorphosis system is thus ripe for future studies encompassing ecology, evolution, behaviour, endocrinology, physiology, and conservation biology. Few other systems have been broad enough to provide varied research opportunities on topics as diverse as phenotypic plasticity, speciation, mating behaviour, and hormonal regulation of morphology. Further research on facultative paedomorphosis will provide needed insight into these and other important questions facing biologists.     

Phototrophic sulfur bacteria and sulfate-reducing bacteria causing red waters in a shallow brackish coastal lagoon (Prévost Lagoon, France)

Abstract In the shallow lagoon of Prévost (43°30'N, 3°54'E; French Mediterranean coast), red waters occurring periodically during warm summers are a consequence of a succession of ecological events beginning in the early spring with a bloom of algae ( Ulva lactuca ). In summer 1977, a red water was analyzed; in the early summer, the water turned anoxic and became rich in sulfide which originated from sulfate reduction in the first 10 cm of the sediment. Numbers of both phototrophic and sulfate-reducing bacteria (SRB) increased during spring and summer, and the genera in the prevailing populations did not change: Thiocapsa (80%) among the phototrophic bacteria and Desulfovibrio and Desulfobacter among the SRB. They were also dominant during the period of red waters. A few Chromatium and Thiocystis species were also identified. During red water periods, these bacteria grew very actively, removing all the sulfide produced by SRB, and accumulated in the whole water column. Consequently, the sulfate level increased to 5 mmol·1⁻¹ higher than the theoretical sulfate level calculated from salinity, showing the active oxidation of sulfide by phototrophic bacteria. After the dystrophic crisis, oxic conditions were reestablished and the phototrophic bacterial biomass was partly grazed by zoobenthos organisms which densely populated the sediment surface.     

Sulfur disproportionating microbial communities in a dynamic,microoxic-sulfidic karst system

Biogeochemical sulfur cycling in sulfidic karst systems is largely driven by abiotic and biological sulfide oxidation, but the fate of elemental sulfur (S⁰) that accumulates in these systems is not well understood. The Frasassi Cave system (Italy) is intersected by a sulfidic aquifer that mixes with small quantities of oxygen-rich meteoric water, creating Proterozoic-like conditions and supporting a prolific ecosystem driven by sulfur-based chemolithoautotrophy. To better understand the cycling of S⁰ in this environment, we examined the geochemistry and microbiology of sediments underlying widespread sulfide-oxidizing mats dominated by Beggiatoa. Sediment populations were dominated by uncultivated relatives of sulfur cycling chemolithoautotrophs related to Sulfurovum, Halothiobacillus, Thiofaba, Thiovirga, Thiobacillus, and Desulfocapsa, as well as diverse uncultivated anaerobic heterotrophs affiliated with Bacteroidota, Anaerolineaceae, Lentimicrobiaceae, and Prolixibacteraceae. Desulfocapsa and Sulfurovum populations accounted for 12%–26% of sediment 16S rRNA amplicon sequences and were closely related to isolates which carry out autotrophic S⁰ disproportionation in pure culture. Gibbs energy (∆G_r) calculations revealed that S⁰ disproportionation under in situ conditions is energy yielding. Microsensor profiles through the mat-sediment interface showed that Beggiatoa mats consume dissolved sulfide and oxygen, but a net increase in acidity was only observed in the sediments below. Together, these findings suggest that disproportionation is an important sink for S⁰ generated by microbial sulfide oxidation in this oxygen-limited system and may contribute to the weathering of carbonate rocks and sediments in sulfur-rich environments.     

Survival of sulfate-reducing bacteria after oxygen stress, and growth in sulfate-free oxygen-sulfide gradients

Abstract The survival after oxygen stress was studied with eight species of sulfate-reducing bacteria. In the absence of sulfide all species tolerated 6 min of aeration without loss of viability. Even after 3 h of aeration the viability of four species ( Desulfovibrio vulgaris, D. desulfuricans, D. salexigens and Desulfobacter postgatei ) was not impaired. Four other species were sensitive to 3 h of aeration: the surviving fractions of Desulfotomaculum ruminis, D. nigrificans and Desulfococcus multivorans were about 1%, that of Desulfotomaculum orientis about 0.01%. Formation of spores resulted in oxygen resistance of D. orientis . Reducing agents did not protect the vegetative cells of this strain against oxygen toxicity. In contrast, sulfhydryl group-containing agents increased the oxygen sensitivity considerably.
Growth of sulfate- and sulfur-reducing bacteria in oxygen-sulfide gradients in agar tubes was studied. In the gradients these strictly anaerobic bacteria revealed oxygen-dependent growth in sulfate- and sulfur-free medium. Three sulfate-reducing bacteria that could not use thiosulfate or sulfur as electron acceptor failed to grow in oxygen-sulfide gradients. Obviously, not directly molecular oxygen, but oxidation products of sulfide, such as thiosulfate or sulfur, were used as electron acceptors and were continuously regenerated in a cycling process from sulfide by autoxidation. The conceivable ecological significance of a short sulfur cycle driven by autoxidation of sulfide is discussed.     

水蔗草兼性无融合生殖的季节变化

对广州地区水蔗草在不同季节的无融合生殖胚囊和有性生殖胚囊频率进行了研究。结果表明:无融合生殖胚囊和有性生殖胚囊的频率在不同季节差异十分显著。两年中,无融合生殖胚囊出现的频率分别在冬季和夏季最高。     

The meiofaunal community structure of a Mediterranean lagoon (Gialova lagoon, Ionian Sea)

The higher taxonomic structure of a meiofaunal community was investigated in an Eastern Mediterranean lagoon (Gialova lagoon, Ionian Sea). Seven stations were sampled on a seasonal basis during 1995–1996. Stations within the lagoon were found to support a maximum of 14 meiofaunal taxa with densities ranging from 17 to over 2000 individuals per 10 cm². Nematodes were not always the most abundant taxa, although they dominated about half of the total 28 samples. Uni- and multivariate analyses were employed to study the community structure. The distribution pattern of the meiofaunal community varied both across the lagoon and over the seasons. On the basis of the spatial differences a meiofaunal coenocline, correlated with the degree of isolation, was observed, composed of mainly two zones: one defined by the area close to the marine channel and the other the more isolated area in the inner lagoon. Meiofaunal distribution pattern was not clearly correlated to one environmental variable, but rather to many, and spatial and seasonal effects could be seen. Received: 2 March 1999 / Received in revised form: 6 December 1999 / Accepted: 9 December 1999     

Composition, structure and distribution of the ichthyoplankton in a Mediterranean coastal lagoon

The species composition and assemblage structure of the ichthyoplankton from the Mar Menor Lagoon in south‐east Spain are given. The fish larvae were sorted from zooplankton samples collected at 20 stations with a plankton net (50 cm mouth diameter and 500 μm mesh) during 36 surveys between February and December 1997. A total of 39 575 fish larvae representing 14 families, 22 genera and 36 species were identified. Gobiidae was the most dominant family (77·0%) followed by Blenniidae (19·4%) and Atherinidae (1·3%). The most abundant species were Gobius niger and Gobius paganellus , which accounted for 42·7 and 19·3% of the total respectively. These species were followed in order of relative abundance by Pomatoschistus marmoratus (13·9%), Parablennius pilicornis (9·4%), Lipophrys pavo (7·7%), Atherina boyeri (1·3%) and Parablennius tentacularis (1·3%). The high species diversity (2·0–2·8 bits individual⁻¹ for the annual diversity spectra at each sampling station) reflected a diverse assemblage of species. The main commercial species in the lagoon (Sparidae and Mugilidae) were poorly represented among the ichthyoplankton and they probably enter the lagoon on the bottom as recruits. Chlorophyll a concentration in the water column was the main factor explaining the seasonal variation in larval abundance. Spatial distribution of larvae was related to hydrographical circulation patterns in the lagoon and the movement of marine‐spawned larvae through the channels connecting the lagoon with the Mediterranean Sea.     

Microbiological and environmental variables involved in the sulfide buffering capacity along a eutrophication gradient in a coastal lagoon (Bassin d'Arcachon,France)

Microbiological and environmental variables involved in the removal of free sulfide were studied along an eutrophication transect in the Bassin d'Arcachon (France). At four sites, analyses were carried out on reduced sulfur compounds, iron species and total numbers of viable sulfur bacteria (sulfide-producing bacteria, colorless sulfur bacteria and purple sulfur bacteria). In addition, the chemical buffering capacity towards free sulfide and the potential microbiological sulfide oxidation rates were determined.In the ecosystem, no free sulfide occurs in the top layers of the sediment at all four sites, despite a high nutrient load and hence favourable conditions for sulfide-producing bacteria. The explanation of this apparent discrepancy was shown to be the high biological sulfide oxidizing capacity in combination with a high chemical buffering capacity.The data presented illustrate that the buffering capacity of sediments towards free sulfide is the combined result of the chemical and biological processes. The ratio between these were found to depend on the degree of eutrophication. It was shown that the chemical buffering capacity towards sulfide is severely overestimated when based on the pool of chemically reactive iron, a more realistic value is obtained by estimating the total amount of sulfide that can be added before free sulfide can be detected. A clear difference was observed between the numbers of colorless sulfur bacteria and the activity of the entire population. For a proper quantification of the sulfide buffering capacity of sediments, it is essential to estimate the concentration of iron and sulfur compounds that actually can react with sulfide, as well as to analyze the activities of sulfide-oxidizing microbes.     

Salinity and nutrients in a tropical coastal lagoon with groundwater discharges to the Gulf of Mexico

This study described the nutrient dynamics in a tropical coastal lagoon that is affected by the infiltration of cold nutrient-rich groundwater. The spatial and time variation of physicochemical characteristics (e.g., temperature, salinity, oxygen) and nutrients (e.g., nitrate, ammonium, soluble reactive silicate, soluble reactive phosphorus) are depicted and show changes with respect to weather conditions. The lagoon shows a permanent salinity gradient from the inner zone (14–19). Nitrate and soluble reactive silicate (SRSi) are inversely correlated with salinity. Soluble phosphorus (SRP) shows highest levels in the inner zone during winter months (>9 µM). Ammonium shows two high peaks, one in the rainy season (15 µM) and the other during winter (11 µM). The intensity and quality of rainfall influences the nitrate and SRSi inputs, while biological activity influences the SRP and ammonium levels.     

Zooplankton variability related to environmental changes in a eutrophic coastal lagoon in the Po Delta

Zooplankton variability in a lagoon of the Po Delta, the Sacca di Goro, was studied in relation to changes in its hydrodynamic and hydrological features. From 1987 to 1992 the lagoon was affected each summer by severe anoxia due to the decomposition of dense and widespread beds of Ulva rigida. In August 1992 a canal was opened through the sand bank closing off the lagoon from the sea in order to improve the water circulation. This hydraulic intervention led to significant environmental changes in the lagoon: during the two subsequent years the summer dystrophic crises were brief and less severe, due to a sharp decrease in the Ulva cover. At the same time a clear increase in phytoplankton biomass values was observed. Following the opening of the channel, the most remarkable change in zooplankton was a significant density increase of calanoids, particularly of Acartia tonsa.     

Evolutionary genetics of a defensive facultative symbiont of insects: exchange of toxin-encoding bacteriophage

The facultative endosymbiont of aphids, Hamiltonella defensa , kills parasitoid wasp larvae, allowing aphid hosts to survive and reproduce. This protection may depend on toxins that are encoded by the genomes of H. defensa and of its bacteriophage (APSE). Strains of H. defensa vary in degree of protection conferred upon Acyrthosiphon pisum (pea aphid). Although H. defensa is known to undergo some horizontal transmission among aphid maternal lineages, divergence, recombination, and population structure in H. defensa and APSE have not been characterized. We performed a multilocus sequence analysis of 10 bacterial and five phage loci for strains isolated from A. pisum and other aphid species. The H. defensa chromosome was found to be largely clonal, allowing us to generate a well-resolved H. defensa strain phylogeny. In contrast, APSE chromosomes undergo recombination and numerous H. defensa strains have probably lost the phage. Within a set of H. defensa strains that are indistinguishable on the basis of chromosomal genes or restriction digests of chromosomal fragments, loss of APSE is associated with decreased protection, strongly suggesting that APSE-encoded genes contribute to the defensive phenotype. Thus, homologous recombination of APSE genes and sexual transmission of symbionts and phage are likely factors influencing the exchange of ecologically important genes among symbionts. Although H. defensa has been lost, transferred and gained within A. pisum , one subclade of H. defensa appears to be universal within a subclade of the aphid genus Uroleucon , suggesting a transition from facultative, horizontal transmission to strictly vertical inheritance.     

Alterations in surfaces and textures of minerals during the bacterial leaching of a complex sulfide ore

Abstract

The purpose of the work was to characterize changes in surface textures of minerals during the biological leaching of a complex sulfide ore. The ore contained pyrrhotite (Fe_I__xS), pyrite (FeS₂), sphalerite (ZnS), pentlandite [(Ni,Fe,Co)₉S₈], and chalcopyrite (CuFeS₂). Several mixed cultures were initially screened using the ore material as the sole substrate. Shake flask leaching experiments showed no major differences among test cultures, which were all derived by enrichment techniques using environmental samples collected from a mine site. Leached pyrrhotite surfaces were invariably surrounded by a dark rim of elemental S. A reaction zone was also associated with leached sphalerite grains. Chemical analyses of leach solutions indicated that the relative ranking of biological leaching of the sulfide minerals was Zn > Ni > Co > Cu. Microscopic observations were in keeping with this rankin     

专一营养与兼性甲烷氧化菌降解氯代烃的研究现状、动力学分析及展望

生物修复技术被认为是氯代烃类污染物处理处置的最有效途径之一,而甲烷氧化菌在该领域表现出较大的应用潜力。近期研究发现,突破了仅能利用单碳化合物的局限,兼性甲烷氧化菌能够利用多种底物降解氯代烃,这一独特的新陈代谢特性,使其在污染物生物处置领域逐渐受到关注。结合本课题组研究成果,对甲烷氧化菌降解氯代烃进行了全面总结,主要包括:分析了不同菌株(纯菌株和混合菌株)对不同氯代烃的降解效果;比较了不同类型甲烷单加氧酶在不同底物体系中的活性表达和催化特性;总结了模型菌株甲基弯菌Methylosinus trichosporium OB3b降解氯代烃的动力学特性;概述了兼性甲烷氧化菌株降解氯代烃的特性及其应用潜力;最后讨论了甲烷氧化菌降解氯代烃存在的问题及未来发展方向。     

Environmental distribution and abundance of the facultative methanotroph Methylocella

Methylocella spp. are facultative methanotrophs, which are able to grow not only on methane but also on multicarbon substrates such as acetate, pyruvate or malate. Methylocella spp. were previously thought to be restricted to acidic soils such as peatlands, in which they may have a key role in methane oxidation. There is little information on the abundance and distribution of Methylocella spp. in the environment. New primers were designed, and a real-time quantitative PCR method was developed and validated targeting Methylocella mmoX (encoding the α-subunit of the soluble methane monooxygenase) that allowed the quantification of Methylocella spp. in environmental samples. We also developed and validated specific PCR assays, which target 16S rRNA genes of known Methylocella spp. These were used to investigate the distribution of Methylocella spp. in a variety of environmental samples. It was revealed that Methylocella species are widely distributed in nature and not restricted to acidic environments.     

On the changing ecology of Venice lagoon

The amplexial morphology of representative species from all anostracan families is described. Males of the Polyartemiidae and Artemiidae amplex the female's brood pouch. Males of all other families amplex the female's body between the brood pouch and the last pair of legs: a region referred to herein as the `amplexial groove.' The amplexial groove in females of Streptocephalus, Thamnocephalus, Dendrocephalus, Branchinella, and the Branchipodidae is unornamented and females are not separable among the species. Females in the genus Parartemia and the families Chirocephalidae and Linderiellidae have morphological characters within their amplexial region that complement the ornamentation of the male's second antennae, creating a `lock and key' fit unique to each species.     

The effect of stratification and seasonal variability on the profile of an anaerobic swine waste treatment lagoon

In this study, the characterization of an anaerobic swine waste treatment lagoon from a farrowing operation (approximately 2000 sows) was carried out to examine the dynamics of the system due to stratification and seasonal variability. Swine waste samples were taken at different depths with a pulley system equipped with a special sampler that allows for sampling exclusively at certain depth. Chemicals and microbial dynamics were monitored throughout a one-year-period. Results showed that nutrient (C, N, P, S) concentrations varied according to stratified lagoon layers and season. Trace minerals (Al, Ca, Fe, and Mg), on the other hand, appeared to be affected more by stratification than seasonal variability. Molecular analysis also showed that microbial community structure appeared to be affected by the stratification and seasonal variability. Based on these data, it is important to consider the effect of stratification and seasonal variability in managing these open lagoons.     

The distribution of phosphate in sediments and its relation with eutrophication of a Mediterranean coastal lagoon

A major problem of the Mediterranean coastal lagoons is an excessive input of nutrients (i.e. N and P), causing eutrophic conditions in summer. The sediments of these lagoons can serve as a reservoir by fixing phosphate, or as a source when this phosphate is released under certain conditions. Knowledge of nutrient sources and fluxes is needed if coastal lagoons are to be protected against eutrophication. Therefore, we have evaluated the total pool of phosphate in the lagoon sediments, and the quantity of phosphate which may be released.Sediment profiles have been analysed at two stations of the Lagune de Thau both in and outside the oyster-bank zone. A sequential fractionation, using chelating agents was performed to extract the inorganic (iron and calcium bound phosphate) and the organic phosphate fractions. A statistical analysis of the data set has revealed several significant factors which explain the fluctuations of the concentrations of each phosphate fraction. These factors are: the time of year (seasons), the depth (5 cm layers of sediment), and the site (station).A spatial and a temporal variation of the concentration of Tot-P was found. The largest variation between the two different zones appeared only in the first five cm of sediment. There is only a slight seasonal variation in the amount of phosphate at other depths at the two different zones. Season and station are the factors which control the variations in distribution of phosphate fractions. The spatial and temporal variations of the iron and calcium bound phosphate are explained by the redox potential and pH in the top layer of the sediment.Abbreviations In principle the general abbreviations are used (see page vi). Futhermore Fe(OOH)-P= Ferric hydroxide bound phosphate - CaCO₃-P= Calcium carbonate bound phosphate - ASOP= Acid soluble organic phosphate - ROP= Residual organic phosphate     

Sulfide oxidation under chemolithoautotrophic denitrifying conditions

Chemolithoautotrophic denitrifying microorganisms oxidize reduced inorganic sulfur compounds coupled to the reduction of nitrate as an electron acceptor. These denitrifiers can be applied to the removal of nitrogen and/or sulfur contamination from wastewater, groundwater, and gaseous streams. This study investigated the physiology and kinetics of chemolithotrophic denitrification by an enrichment culture utilizing hydrogen sulfide, elemental sulfur, or thiosulfate as electron donor. Complete oxidation of sulfide to sulfate was observed when nitrate was supplemented at concentrations equal or exceeding the stoichiometric requirement. In contrast, sulfide was only partially oxidized to elemental sulfur when nitrate concentrations were limiting. Sulfide was found to inhibit chemolithotrophic sulfoxidation, decreasing rates by approximately 21-fold when the sulfide concentration increased from 2.5 to 10.0 mM, respectively. Addition of low levels of acetate (0.5 mM) enhanced denitrification and sulfate formation, suggesting that acetate was utilized as a carbon source by chemolithotrophic denitrifiers. The results of this study indicate the potential of chemolithotrophic denitrification for the removal of hydrogen sulfide. The sulfide/nitrate ratio can be used to control the fate of sulfide oxidation to either elemental sulfur or sulfate.     

The consequences of facultative sex in a prey adapting to predation

A species reproductive mode, along with its associated costs and benefits, can play a significant role in its evolution and survival. Facultative sexuality, being able to reproduce both sexually and asexually, has been deemed evolutionary favourable as the benefits of either mode may be fully realized. In fact, many studies have focused on identifying the benefits of sex and/or the forces selecting for increased rates of sex using facultative sexual species. The costs of either mode, however, can also have a profound impact on a population's evolutionary trajectory. Here, we used experimental evolution and fitness assays to investigate the consequences of facultative sexuality in prey adapting to predation. Specifically, we compared the adaptive response of algal prey populations exposed to constant rotifer predation and which had alternating cycles of asexual and sexual reproduction where sexual episodes were either facultative (sexual and asexual progeny simultaneously propagated) or obligate (only sexual progeny propagated). We found that prey populations with facultative sexual episodes reached a lower final relative fitness and suffered a greater trade‐off in traits under selection, that is defence and competitive ability, as compared to prey populations with obligate sexual episodes. Our results suggest that costs associated with sexual reproduction (germination time) and asexual reproduction (selection interference) were amplified in the facultative sexual prey populations, leading to a reduction in the net advantage of sexuality. Additionally, we found evidence that the cost of sex was reduced in the obligate sexual prey populations because increased selection for sex was observed via the spontaneous production of sexual cells. These results show that certain costs associated with facultative sexuality can affect an organism's evolutionary trajectory.