Evolution of the mitochondrial DNA control region in the mbuna (Cichlidae) species flock of lake Malawi, East Africa

Considerable controversy has surrounded the application of mitochondrial DNA data to reconstruction of evolutionary relationships among the endemic cichlids of Lake Malawi. Central to this debate has been the issue of whether lineage sorting is complete, and thus whether these data actually reflect species phylogeny, or simply gene genealogy. Review of all mtDNA control region sequences available for members of one monophyletic subset of this species flock, the Malawi rockfishes, or mbuna, strongly indicates that lineage sorting is incomplete: Character-based analyses of these sequences reconstruct gene, not species, interrelationships. Analysis of the pattern of nucleotide substitutions differentiating these mtDNA alleles suggests that pyrimidine residues undergo transition substitutions more often than do purines. Estimation of the magnitude of derived sequence differentiation in light of the reconstructed gene genealogy suggests that the mbuna may be of considerably more recent vintage than previous molecular characterizations have indicated. Received: 6 April 1996 / Accepted: 3 March 1997     

The ecology of ruffe,Gymnocephalus cernuus (Pisces: Percidae) introduced to Mildevatn,western Norway

Synopsis Diet, habitat use, diel and seasonal activity and a number of population parameters were studied on ruffe,Gymnocephalus cernuus, introduced to Mildevatn, western Norway. This lake is sited outside the natural range of the ruffe and has a lower fish diversity and a different fish species composition than within its native range. From June through September the ruffe was planktivorous and mainly caught at 4 to 6 m depth in the benthic zone. At other times of year ruffe was feeding on zoobenthos and caught deeper in the benthic zone. Ruffe was mainly day active. Zooplankton feeding during summer is the clearest difference compared to ruffe populations living within its natural range. Presence of large zooplankton organisms available for ruffe is suggested as the main reason for the difference found in food choice. The availability of large zooplankton is probably due to community structure caused by a predator and lack of interspecific competition for zooplankton in the deeper parts of the lake. Piscivorous brown trout.Salmo trutta, restrict the habitat of threespined stickleback,Gasterosteus aculeatus, to the zone of littoral vegetation, allowing high densities of larger zooplankton species likeBythotrephes longimanus to be present in the lake. Brown trout is present only in the upper light and well oxygenated parts of the lake, leaving a refuge for the ruffe, where they can feed on the rich zooplankton community.     

POST-PLEISTOCENE DIATOM SUCCESSION IN DOUGLAS LAKE,MICHIGAN1,2

Analysis of fossil diatom assemblages recovered from a 12.2 m core reveals a series of distinct floristic associations. The associations present are correlated with sediment type and reflect successive stages in the development of the lake. A basal red clay sediment contains a planktonic association characteristic of large, proglacial lakes. At 10.0 m core depth, sediment type changes to fine sand containing a higher abundance of benthic species indicating reduction of water depth at the deposition site. Marl sediments begin at 9.7 m and contain an association characteristic of a small, shallow, oligotrophic lake. At 8.8 m the marl sequence is interrupted by highly organic sediment containing a eutrophic plankton association. From 8.5 to 7.6 m the sediment type grades from marl to organic, apparently reduced sediments and diatom associations present contain successively higher percentages of planktonic species associated with eutrophic habitats. By the 7.6 m level a eutrophic plankton association, similar to the modern flora, is established and remains remarkably constant to the surface of the section.     

A revision of the genus Labidochromis (Teleostei: Cichlidae) from Lake Malawi

The diagnosis of the genus Labidochromis is revised to include species with bicuspid outer teeth. Sixteen species, of which 13 are new, are described and illustrated and the validity of five others is discussed. The interrelationships between members of the genus and the relationship of the genus to other genera are discussed. No clearly defined sister group to the genus has been found either within or outside the Lake Malawi cichlid species flock. A key based on the coloration of known species is included.     

Reproductive patterns in seventeen species of warmwater fishes in a Missouri River reservoir

Synopsis The timing of ovarian maturation and spawning of 17 warmwater fish species in Lake Oahe (South and North Dakota) was estimated from changes in the mean ovary indices (ratios of ovary weight to fish length). The onset of vitellogenesis varied within species (up to 2 months). Maturation of the ova took from 7.5 to 10 months, depending on species. Annual variations in the mean date of peak spawning of individual species during 1964–1971 were usually less than a week. There was little overlap of the annual mean peak spawning dates of the 17 species, and an established sequence of spawning among species was shown. A relatively high incidence of atresia in the shovelnose sturgeon, northern pike, and carp indicated that these species had apparently not yet adapted to the altered and variable spawning conditions in this reservoir. Regularity of spawning would seem to provide the best chance for spawning success in variable environments such as Lake Oahe.     

Opposing effects of human peripheral blood lymphocytes on the growth of cultured leukemia cell lines

Natural killing of two human leukemia cell lines (K562 and Molt 4) in a soft-agar, clonagenic assay was shown to be the result of two opposite yet concurrent processes: target cell colony stimulation and inhibition. The stimulatory effect was demonstrable when the effector lymphocytes and target cells were separated in contiguous agar layers, suggesting mediation by a soluble factor. Similarly, stimulation occurred when the effector lymphocytes and target cells were combined at low effector-target cell ratios that do not favor direct cell contact. Target colony inhibition was found to be dominant when large E:T ratios were employed. Both target-effector binding and natural killing were significantly reduced in medium devoid of divalent cations.     

A limnological reconnaissance of Lake Tebenquiche,Salar de Atacama,Chile

A number of expeditions to the area of Salar de Atacama, Chile, 68° 15'W, 20° 30'S, have involved studies of the biological and chemical features of Lake Tebenquiche, situated in the interior of the salar. Chemically, Tebenquiche is hypersaline, with practically anoxic waters dominated by sodium and chloride ions but with high concentrations of sulphate also. The lake is surrounded and invaded by macrophytes, dominated by Scirpus olmeyi and Juncus, which provide organic material for the formation of bacterial mats. The fauna of limnetic crustaceans is almost exclusively of Artemia salina. The most important genera of bacteria are: Marinomonas, Halobacterium, Acinetobacter and the sulphur reductors Vibrio and Bacillus. The Cyanobacteria are represented exclusively by Oscillatoria.     

发展生态渔业,保护水域环境——朱湖水体生态农业初探

渔业是大农业的一环。在充分合理的利用好水体自然资源,大力发展水产品生产的同时,认真保护好水域生态环境,这不仅是渔业的问题,也完全符合环保这项基本国策。研究渔业生态,发展生态渔业也是当今水产养殖发展的主要方向。“水体生态农业”是依据生态学原理,生态     

Shoreline algal wash as a factor in reed decline in Lake Constance-Untersee

This paper assesses the chemical and mechanical impact of algal wash (Cladophora, Spirogyra, Chara) upon the lakeside reed belt (Phragmites australis) using field mapping methods, bioassays with Scenedesmus acutus in batch culture, and field experiments. Heavy mats of filamentous algae are correlated with a reduction in number of the outermost reed stalks. The water pressed from decaying heaps of Cladophora and Spirogyra reduced the growth rate of Scenedesmus significantly, but mats from Chara did not. It is assumed that the toxic substance is an organic compound. In field experiments the detrimental effect could not be clearly evidenced. The reasons for this are discussed. It is concluded that mechanical impact is of major importance.     

Trend,seasonality, cycle,and irregular fluctuations in primary productivity at Lake Tahoe,California-Nevada,USA

Primary productivity has been measured routinely at Lake Tahoe since 1967, and a number of mechanisms underlying variability in the productivity record have now been identified. A long-term trend due to nutrient loading dominates the series. Seasonality also is prominent, apparently controlled by direct physical factors unrelated to the trophic cascade. A 3-yr cycle has been detected and several possible mechanisms are considered. Irregular fluctuations also are present, caused in part by isolated events (a forest fire) and recurring but variable phenomena (spring mixing). Except possibly for the 3-yr cycle, the known sources of variability appear to operate bottom-up through direct physical and chemical effects on the phytoplankton.