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71.
Heliozoa are ubiquitous, unicellular phagotrophs with slender radiating axopodia for trapping prey. We sequenced 18S rRNA genes from 35 cultured centrohelid heliozoa (18 studied by electron microscopy) and 28 environmental libraries (18 freshwater, 10 marine), yielding 97 new sequences, this exceeding described species. Phylogenetic analyses show two major groups and that ancestral centrohelids probably had inner plate-like tangential and distinct outer radial silica scales, the latter diverging early into contrasting scale types seen in extant Pterocystis/Choanocystis and Acanthocystis/Raphidiophryidae. Scales were lost at least thrice. Pterocystis is paraphyletic, as was the classical family Acanthocystidae; Heterophrys was polyphyletic. Using scale morphology and rRNA sequences, we establish new families Pterocystidae (Pterocystis, Raineriophrys, Chlamydaster), Marophryidae (type Marophrys (Heterophrys) marina gen. et comb. nov.) and Choanocystidae, new suborders Pterocystina (Pterocystidae, Choanocystidae, Heterophryidae) and Acanthocystina (Acanthocystidae, Raphidiophryidae, Marophryidae), and ten new Pterocystis, Acanthocystis and Choanocystis species. Most clades are exclusively freshwater or exclusively marine; evolutionary transitions between these habitats have been rare. 相似文献
72.
Common reed die-back is a widely investigated phenomenon in Central Europe, not frequently recorded in S-European areas and almost unknown in the Mediterranean Basin. Symptoms of reed decline recently observed in the Italian Peninsula provided the starting point for a detailed investigation on a reed population in one of the largest freshwater ecosystems in Central Italy. The analyses were conducted over two vegetative seasons in 19 plots at seven locations. A set of 13 morphologic and phenologic reed traits were screened, monitored and statistically analysed. The data indicated the presence of the reed die-back syndrome in a wet Mediterranean ecosystem and enabled us to highlight a set of usable traits to detect the condition of decline. Among them, the stem height and diameter, the number of nodes, the relative growth rate and the lateral root diameter resulted the most significant factors highlighting the declining condition. Some environmental characteristics of the reed stands were also taken into account. The period of submersion and the presence of standing litter emerged as important features of the stands, strictly related to the degree of decline in the population. The results draw attention to the risk, in southern Europe too, of the loss of an ecosystem which plays an important role in biodiversity conservation. 相似文献
73.
Cyanobacterial blooms and the production of cyanotoxins represent a serious global problem. Although the effects of a group of important cyanotoxins, microcystins (MCs), have been studied intensively in various organisms, little is known about the natural functions of these cyclic heptapeptides. MCs may have allelopathic effects. This paper summarizes the information from the studies that have investigated the effects of MCs on photoautotrophs in vitro and in vivo. Interactions with terrestrial plants, macrophytes, macroalgae, and planktonic microalgae are reported in detail with respect to the ecological relevancy of experimental conditions related to allelopathy. Our review shows that only a limited number of studies described harmful effects of MCs at concentrations that are typical for the environment. Consequently, the ability of MCs to act as general allelopathic compounds against photoautotrophs seems unlikely. However, further research is needed for definitive confirmation or rejection of the allelopathic hypothesis as well as, an explanation of the crucial question of MC function in the context of new information from evolutionary and molecular biology. 相似文献
74.
P. SPIERENBURG E.C.H.E.T. LUCASSEN A.F. LOTTER J.G.M. ROELOFS 《Freshwater Biology》2009,54(9):1819-1831
1. During the past century, isoetid vegetation types in softwater lakes have often been invaded by faster‐growing elodeids. In these C‐limited systems, this may be related to rising aquatic CO2 levels. 2. In a laboratory experiment we tested the growth response of two elodeid species, Myriophyllum alterniflorum and Callitriche hamulata, at four different CO2 levels, ranging from 20 to 230 μmol L−1. In addition, we tested the effect of the nutrient status of the sediment on the growth of C. hamulata at the different CO2 levels. 3. Shoot and root growth increased with rising CO2 availability. Irrespective of sediment type, growth was minimal to negative at the lowest CO2 treatment level, while becoming positive at CO2 levels around 40–50 μmol L−1. Substantial growth was only obtained when the macrophytes were growing on mesotrophic sediments. The plants reached close to maximal growth at CO2 levels of c. 100 μmol L−1. 4. Within this experiment, the growth of C. hamulata at CO2 levels above 90 μmol L−1 may have been limited by N and P availability in both sediment types. The growth rate of M. alterniflorum did not seem to be limited by N and P availability, most likely due to its much higher relative root production. 5. The experimental results show that neither M. alterniflorum nor C. hamulata is able to invade isoetid‐dominated softwater lakes at very low aquatic CO2 concentrations. However, if the sediments contain enough nutrients, a rise in aquatic CO2 could allow the invasion of elodeid species leading to the subsequent disappearance of slow‐growing isoetids. 相似文献
75.
Pillans RD Good JP Anderson WG Hazon N Franklin CE 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》2005,175(1):37-44
This study examined the osmoregulatory status of the euryhaline elasmobranch Carcharhinus leucas acclimated to freshwater (FW) and seawater (SW). Juvenile C. leucas captured in FW (3 mOsm l–1 kg–1) were acclimated to SW (980–1,000 mOsm l–1 kg–1) over 16 days. A FW group was maintained in captivity over a similar time period. In FW, bull sharks were hyper-osmotic regulators, having a plasma osmolarity of 595 mOsm l–1 kg–1. In SW, bull sharks had significantly higher plasma osmolarities (940 mOsm l–1 kg–1) than FW-acclimated animals and were slightly hypo-osmotic to the environment. Plasma Na+, Cl–, K+, Mg2+, Ca2+, urea and trimethylamine oxide (TMAO) concentrations were all significantly higher in bull sharks acclimated to SW, with urea and TMAO showing the greatest increase. Gill, rectal gland, kidney and intestinal tissue were taken from animals acclimated to FW and SW and analysed for maximal Na+/K+-ATPase activity. Na+/K+-ATPase activity in the gills and intestine was less than 1 mmol Pi mg–1 protein h–1 and there was no difference in activity between FW- and SW-acclimated animals. In contrast Na+/K+-ATPase activity in the rectal gland and kidney were significantly higher than gill and intestine and showed significant differences between the FW- and SW-acclimated groups. In FW and SW, rectal gland Na+/K+-ATPase activity was 5.6±0.8 and 9.2±0.6 mmol Pi mg–1 protein h–1, respectively. Na+/K+-ATPase activity in the kidney of FW and SW acclimated animals was 8.4±1.1 and 3.3±1.1 Pi mg–1 protein h–1, respectively. Thus juvenile bull sharks have the osmoregulatory plasticity to acclimate to SW; their preference for the upper reaches of rivers where salinity is low is therefore likely to be for predator avoidance and/or increased food abundance rather than because of a physiological constraint. 相似文献
76.
77.
Célio?Magalh?esEmail author Sérgio Luiz S.?Bueno Georgina?Bond-Buckup Wagner Cotroni?Valenti Humberto L. Melo da?Silva Fábio?Kiyohara Emerson C.?Mossolin Sérgio S.?Rocha 《Biodiversity and Conservation》2005,14(8):1929-1945
Based on recent surveys of the freshwater decapod fauna, distributional data of five exotic species of freshwater decapod crustaceans for the hydrographic basins of the state of São Paulo are presented, as part of a large initiative for a comprehensive survey of the state’s biodiversity (BIOTA-FAPESP Program). These species are the North American crayfish Procambarus clarkii (Girard) (Cambaridae), the crab Dilocarcinus pagei Stimpson (Trichodactylidae) from the Amazon and Paraguay/lower Paraná River Basins, and the palaemonid shrimps Macrobrachium rosenbergii (De Man), from the Indo-Pacific region, Macrobrachium amazonicum (Heller) and Macrobrachium jelskii (Miers), both from the Orinoco, Amazon and the Paraguay/lower Paraná River Basins. Possible modes by which their introduction might have occurred are commented upon and potential consequences are discussed. 相似文献
78.
Conservation of Freshwater Biodiversity: a Comparison of Different Area Selection Methods 总被引:2,自引:0,他引:2
Pedro?AbellánEmail author David?Sánchez-Fernández Josefa?Velasco Andrés?Millán 《Biodiversity and Conservation》2005,14(14):3457-3474
The biodiversity of freshwater systems is endangered, especially in Mediterranean semiarid areas such as the south east of
the Iberian Peninsula, whose rich and endemic biota is threatened by the development of surrounding land-crop irrigation.
For this reason, the prioritization of areas for biodiversity conservation is an urgent target. In this study we used data
records of water beetles from a province of the southeast of Spain for assessing priority areas for freshwater biodiversity
conservation. We compare the performance of various area-selection methods, ranging from scoring procedures to complementarity-based
algorithms, which are based on different criteria such as richness, rarity and vulnerability. The complementarity approaches
were more efficient than methods using scoring or richness and rarity hotspots for representing conservation targets in a
given number of areas and for identifying the minimum set of areas containing all species at least once. Within these, the
richness-based algorithm was more efficient than rarity-based algorithm. Crucial target habitats for aquatic biodiversity
conservation in the area studied are streams at medium altitude, hypersaline streams, and endorreic and karstic complexes. 相似文献
79.
Wendy R.?TownsendEmail author A.?Randall Borman Eduardo?Yiyoguaje Luis?Mendua 《Biodiversity and Conservation》2005,14(11):2743-2755
The Cofán Indians of Aguarico and Zábalo Rivers in Ecuador in 1990 began a turtle recuperation effort by raising turtle hatchlings
(Podocnemis expansa and P. unifilis) in small pools. To evaluate the effectiveness of this program, the Cofán developed and tested three methods to document
changes in the populations of turtles. The first method consisted of interviews with people from neighbouring communities
about their perceptions of changes in turtle abundance. The second method was a direct count of turtles observed along the
rivers from canoe. The third method was an indirect count, involving turtle nest censusing along community beaches. Two of
the methods yielded numerical, statistically positive turtle population trends. The turtle program has influenced the community's
perception of turtle conservation issues so that, instead of hunting the adults and eggs, they now protect them. The training
in record-keeping permits them to make a transparent history of the equitability of access to the turtle egg resource. The
Cofán monitoring experience strengthened their successful petition to the Ecuadorian government for the rights to manage their
territorial lands within the Cuyabeno Wildlife Reserve, and to receive protected area status and management rights to other
ancestral lands. The experience gained by the Zábalo monitors is now serving as a model for the design and implementation
of the park monitoring system of the newly-established Cofán Park Ranger Corps, which will be patrolling three Ecuadorian
Ecological Reserves which overlap Cofán inhabited areas. 相似文献
80.
The role of periphytes in the shift between macrophyte and phytoplankton dominated systems in a shallow, eutrophic lake (Lake Taihu, China) 总被引:1,自引:0,他引:1
Based on experiments of periphyte response to different trophic levels and their impact on macrophyte production, it was found
that the periphyte biomass increased with the nutrient concentrations. Increased trophic level and periphyte biomass resulted
in decreased macrophyte photosynthesis. It was suggested that the periphytes could cause resilience and hysteresis in the
system shifts between macrophyte and phytoplankton domination. Other factors, such as fish farming, storm induced waves and
mechanical destruction, and high water levels could be the perturbations during the system shifts, but these are not the key
factors. Instead, the nutrient loading and periphyte abundance could determine the shift in lake ecosystem between macrophyte
and phytoplankton domination. This finding could theoretically elucidate the mechanism of ecosystem shifts between macrophyte
and phytoplankton domination. 相似文献