PHOTOSYNTHESIS AS A FUNCTION OF LIGHT INTENSITY AND OF TEMPERATURE WITH DIFFERENT CONCENTRATIONS OF CHLOROPHYLL

1. Photosynthesis reaches its maximum rate at about the same light intensity over the whole range of chlorophyll concentrations studied. 2. Over this range the process shows the same relationship to temperature. The value of the temperature characteristic decreases gradually as the temperature rises. 3. The rate of photosynthesis is more depressed by prussic acid the lower the chlorophyll concentration. 4. These results are interpreted as indicating that photosynthesis possibly involves an autocatalytic reaction, and that chlorophyll must play some part in the process in addition to its rôle in the absorption of light.     

Bacterial Iron Oxidation in Circumneutral Freshwater Habitats: Findings from the Field and the Laboratory

Lithotrophic Fe-oxidation at neutral pH is becoming recognized as an important microbial process. An overview of the microbial iron cycle is presented with an emphasis on the role of microbes that grow under microaerobic conditions at oxic-anoxic transition zones where Fe(II) is abundant. Examples of these environments from freshwater are considered. Contrary Creek is a spring-fed wetland in Virginia. Measurements over the course of a year showed that it had a consistent pH around 6, and Fe(II) concentrations ranged from 25 to 300 μ M, with the highest concentrations in the summer months. At all times abundant flocs of Fe-oxides composed principally of Lepthothrix ochracea sheaths were present. Based on observations at this site, and other sites, a model for microbial Fe mat formation is presented. A thermal site in Yellowstone National Park that had consistent circumneutral pH and high Fe(II) concentrations was also studied. This site did not have evidence for Fe-oxidizing bacteria, but was, instead, dominated by a cyanobacterial photosynthetic mat. Consideration is given to growth conditions for pure cultures of Fe-oxidizing bacteria (FeOB) in the laboratory. A novel method of growing FeOB on gradient plates was developed. This led to an increase of cell yields to 2 × 10⁸ cells/ml, which is nearly an order of magnitude greater than previous methods have yielded. Finally, speculation is made as to the potential for conditions on Mars that might have been conducive for microbial Fe-oxidation.     

Azteca Ants as Antiherbivore Agents of Tococa formicaria (Melastomataceae) in Brazilian Cerrado

Several ant species have been found associated with domatia of plant species of the genus Tococa (Melastomataceae). In the present study we investigated the relationships between Tococa formicaria Mart. and ants in the Cerrado (savanna-like vegetation) from central Brazil. We addressed questions about the utilisation of domatia by different ant species and their efficiency in reducing herbivory. We found 8 ant species in the domatia, with Azteca sp. 1 being present in 47.2% of the sampled individuals. The other species found were: Azteca sp. 2, Camponotus sp., Dolichoderus gr. diversus, Dolichoderus lutosus, Leptothorax sp., Oligomyrmex sp. and Linepithema sp. The dominance of Azteca sp. 1 was significantly higher in the larger individuals, with about 85% of individuals in the highest size class being occupied by this species. We performed experiments of attack to live baits (termites) on T. formicaria leaves and on leaves of control species (any other neighbouring plant species of similar size). The recruitment rates were significantly higher on T. formicaria leaves. We also showed that herbivory was significantly lower in T. formicaria individuals occupied by Azteca sp. 1 than in individuals occupied by other ant species. The results of this study may be considered as evidence to support the assumption of a mutualistic relationship through defence against herbivory between Azteca ants and T. formicaria.     

MEASUREMENTS OF THE METABOLISM OF TWO PROTOZOANS

1. The respiration of Amoeba proteus was measured. 10 c. mm. of cells were found to use about 1.6 mm.³ of oxygen per hour at 20°C. The respiratory quotient was found to be nearly unity. 2. No anaerobic metabolism was found for Amoeba. 3. The respiration of Blepharisma was found to be from 3 to 7 mm.³ oxygen per hour for 10 mm.³ cells. The respiratory quotient was about 1. 4. Blepharisma was shown to have a definite anaerobic metabolism. 80 mm.³ cells caused the evolution of 12.5 mm.³ carbon dioxide per hour at 20°C. in the presence of bicarbonate.     

Signatures of speciation? Distribution and diversity of Hypoplectrus (Teleostei: Serranidae) colour morphotypes

Aim To test historical and current influences on the distributions of sympatric colour morphotypes in the coral reef fish genus Hypoplectrus. Location The Caribbean and surrounding tropical waters. These areas cover the entire distribution of the genus. Methods A large and extensive database of Hypoplectrus sightings was used to establish the distribution of colour morphotypes and test a long‐standing hypothesis regarding their origin. First, we considered the evidence for the previously proposed ‘population centre’ hypothesis, which suggests that current morphotype distributions reflect past conditions where these colour forms evolved in allopatry. Using morphotype sighting data, the existence of clusters in occurrence and density was tested. Second, we examined whether the observed patterns of morphotype co‐occurrence deviate from random expectations using null model simulations, within subregions of the distribution of the genus, to infer ecological influences on distribution. Results There is considerable variation in morphotype distribution, with even widespread morphotypes showing geographical clustering. There is also little evidence to suggest past or current geographical isolation, with only one of the 11 morphotypes (Hypoplectrus chlorurus) showing a density distribution that is consistent with the population centre hypothesis. Null model analyses show that variation in local morphotype co‐occurrence is typically significantly lower than expected under random dispersal conditions. Main conclusions Our results strongly suggest that morphotype co‐occurrence is not random, but there is no evidence to suggest a past allopatric radiation in Hypoplectrus colour. Current distributions are likely to be driven by competitive interactions and/or habitat preferences. Our study highlights the value of the Hypoplectrus species complex as a system for the study of speciation in the marine environment, and implies that these closely related morphotypes have ecological relevance rather than being simple colour variants of a single polymorphic species.