The Effect of Deleterious Concentrations of Mercury on the Photosynthesis and Growth of Chlorella pyrenoidosa

The effect of mercury ions on the photosynthesis and growth of Chlorella pyrenoidosa in a balanced medium has been studied and compared with the effect of copper. In many ways Hg treated algae behave like algae treated with Cu in concentrations of the same molarity, but important deviations occur. Hg acts at a lower and in a more narrow range of concentrations than does Cu due to a more specific binding. The depressing effect of Hg is not counteracted by other cations such as potassium and sodium, and iron has only a slight effect. Cell division is stopped after Hg addition and there is no accumulation of assimilation products. On the contrary the cells become pale yellow. Preliminary studies indicate a light-independent leakage in the cytoplasmatic membrane leading to an outflow of potassium ions. This is the primary action of both Hg and Cu poisoning, but the leakage does not seem to be correlated with the decrease of photosynthesis. After a lapse of time — dependent on the mercury/cell concentration ratio — a detoxication takes place probably due to the binding of Hg to “insensitive sites” in the cells. Probable mechanisms for the action of Hg on photosynthesis and growth are discussed.     

Provinces, communities, and the proposed nektobenthic habit of Ordovician conodontophorids

Ordovician conodontophorid distribution, paleogeography, paleoclimate, and global tectonics strongly support the existence of one biogeographic conodontophorid province, largely restricted to equatorial regions and characterized by raised salinity and temperature. This Midcontinent Province is recognized in North America, Australia, and Siberia. The same data indicate that in other areas the North Atlantic Province represents a normal-marine, virtually cosmopolitan fauna. In both provinces, communities are recognized that show a lateral segregation, strongly indicating that the majority of Ordovician conodontophorids were benthic or nektobenthic. The only Ordovician pelagic forms we recognize are the simple cone genera that either lack, or have a simple, symmetry transition series. It appears possible to correlate certain evolutionary changes in the conodont apparatus with changes in preferred habitat.     

Paleontological patterns

Review of Smith, A. B. 1994: Symstematics and the Fossil Record: Documenting Evolutionary Patterns. 223 pp. Blackwell Scienfific Publications, Oxford     

Zooplankton grazing on [methyl-3H]thymidine-labeIled natural particle assemblages: determination of filtering rates and food selectivity

SUMMARY. 1. The grazing of [methyl-³H]thymidine-labelled bacteria by zooplankton was studied in Lake Norrviken. Sweden.
2. Animals did not ingest bacteria attached to large colonies of the cyanobacterium Microcystis wesenbergii Kom. but small aggregates of hacteria and free bacteria were readily consumed.
3. Diaphanosoma brachyurum (Liévin). Daphnia cucullata Sars. and Daphnia galeata Sars grazed free bacteria more quickly than aggregates, but Endiaptomus gracilis (Sars), Chydorus sphaericus Müll. and Bosmi- na coregoni s.l. Baird grazed the aggregates more readily.
4. Filtering rate determinations varied from LA to 123 μl ind. ⁻¹h ^{− 1}for various species.     

Supernumerary teeth in Lynx lynx and the irreversibility of evolution

Supernumerary dental elements have been reported in Lynx lynx by several authors. These features have been given different evolutionary interpretations by different commentators. I note here that, since these features are absent in the plesiomorphic sister-groups of L. lynx , they represent a true evolutionary reversal. If they were simply a retention of an evolutionarily older phenotype, we should expect to see them developed in at least one plesiomorphic sister-group. Such development of a previously hidden character can occur if it is genetically linked to features selected for, until it becomes phenotypically expressed, whereupon selection can act on the character itself. Since Dollo's law, which is the theoretical issue behind the present discussion, is not a law, but a rule, and, like all rules based on probabilities, we should expect to find exceptions in the fossil record. Such exceptions are not rare, but few are as spectacular as the present one, in which the redeveloped feature is at least phenotypically identical with one which has been lost in the Felidae since the Miocene.     

Studies of fossil hyaenas: the genera Thalassictis Gervais ex Nordmann, Palhyaena Gervais, Hyaenictitherium Kretzoi, Lycyaena Hensel and Palinhyaena Qiu, Huang & Guo

Samples of the Chinese upper Mioeene hyaenids Thalassictis wongii (Zdansky), Thalassictis hyaenoides (Zdansky) and Palinhyaena reperta Qiu, Huang & Guo are analysed and characterized statistically. The generic and specific designations above are considered correct. Using these samples as a basis, the taxonomic status of similar forms from Eurasia is evaluated. Lycyaena is considered a subgenus of Thalassictis and includes the species T. (L.) dubia (Zdansky), T. (L.) chaeretis (Gaudry), T. (L.) macrostoma (Lydekker), and T. (L.) crusafonti (Kurtén). 'Lycyaena' proava Pilgrim and 'L.' chinjiensis Pilgrim are removed from this subgenus. The type specimen of Palhyaena hipparionum (Gervais) is missing and cannot be determined to genus on the basis of published information. Most other forms are referred to Thalassictis (Thalassictis) , except 'Ictitherium' sivalense Lydekker, which is considered to be closely related to Palinhyaena .     

Monophily and pollination mechanisms in Angraecum arachnites Schltr. (Orchidaceae) in a guild of long-tongued hawk-moths (Sphingidae) in Madagascar

Anthecological relations between a long-spurred angraecoid orchid and pollinating Sphingidae are documented for the first time. In a primary forest on the Central Plateau of Madagascar Angraecum arachnites Schltr. was found to be pollinated by and adapted to a single species of hawk-moth, Panogena lingens (Butler), despite abundance of many concurrent Sphingidae of which several were also long-tongued. Furthermore, P. lingens was dimorphic in the length and breadth of its proboscis and only the morph with the longest and most slender proboscis was recorded to pollinate A. arachnites . Exclusive and precise adaptation to the latter morph of P. lingens existed in floral morphology and probably in other characteristics such as flowering phenology and chemical signalling. Several concurrently flowering orchid species were sharing P. lingens as a pollinator resource. The monophily in A. arachnites is interpreted as a result of a refined long-term specialization developed within an archaic evolutionary relationship in a relatively stable environment. The extraordinary number and diversity of long-spurred Orchidaceae in Madagascar appears to be a direct coevolutionary consequence of an Old-World-unique diversity of long-tongued archaic Sphingidae that has persisted in this isolated land.