Alcohol tolerance: An ecological parameter in the relative success of Drosophila melanogaster and Drosophila simulans

Laboratory experiments have shown D. melanogaster adults to be more tolerant to alcohol in the environment than D. simulans, with the females being more tolerant than the males of their species. Larval development on alcohol supplemented media also demonstrated an increased tolerance by D. melanogaster although the effect was not as clear cut as for the adult survival. Oviposition choice experiments demonstrated a marked rejection of alcohol impregnated laying sites by D. simulans when compared to standard medium sites. D. melanogaster showed a slight preference for alcohol supplemented sites.Collections in the maturation cellar of a vineyard produced, with the exception of a single D. simulans fly, entirely D. melanogaster adults while larvae and pupae from the cellar were also all D. melanogaster. Away from the alcohol resource, outside the cellar, both species were collected with D. simulans being the more common. However, the outside distribution of the two species was affected by alcohol fumes during vintage, as was the distribution of the sexes of D. melanogaster, with the more tolerant species or sex being closer to the source. The field results were thus in agreement with the laboratory predictions that D. melanogaster is better able to utilize an alcohol resource than D. simulans.

Solar-Climate Relationships in the Post-Pleistocene

The most conspicuous climatic aberration of the past two millennia was the temperature decline and glacial advance of the A.D. 1550 to 1900 period. This temperature decline has been correlated with an interval of lower solar activity and there is evidence from both the post-Pleistocene glacial record and from oxygen-18 analysis that such an interval han recurred at cyclic periods of around 2400 to 2600 years.

Competition between Species: Frequency Dependence

Whether two species competing for the same limited resources can stably coexist has been subject to controversy for several decades. The relative fitnesses of two species of Drosophila under competition in laboratory populations are shown to be inversely related to the relative frequencies of these species. This frequency-dependent fitness leads to a stable coexistence of the two species in spite of their competition for limited resources.

Snail populations, beech litter production, and the role of snails in litter decomposition

The population densities of snails living in beech litter were studied form March 1968 to April 1969. Litter production over one year was measured and the role of snails in litter disappearance assessed.Snails were extracted from litter using a modified Vágvölgyi (1952) flotation method, extraction efficiencies being 84%. The mean annual population density of the twenty-one species of snail recorded on the main sampling site was estimated at 489/m². Carychium tridentatum was the most numerous species, with a mean density of 200/m². Acanthinula aculeata, Punctum pygmaeum and Vitrea contracta also had fairly high mean densities. The mean annual biomass was 699 mg dry wt./m² or 278 mg ash-free dry wt./m². Hygromia striolata and Oxychilus cellarius/alliarius were the most important species in terms of biomass on the main site. Within the limits of accuracy imposed by the sampling regime the population densities of four out of five of the species (C. tridentatum, A. aculeata, V. contracta, Retinella pura) studied remained unchanged throughout the year, whereas P. pygmaeum had a significantly higher autumn population. C. tridentatum populations were highly aggregated at all times of the year, most markedly so in June. Other species were aggregated at certain times of the year only. Samples taken from other sites showed total population densities of snails ranging from 185-1082 snails/m².A total tree litter production of 652 g/m²/annum was recorded of which 584g/m²/annum was of beech material. 72% fell in the October-December period. 58% of the beech litter-fall was leaves, 5.2% bud-scales, 27% fruits and 10% twigs and bark. Summation of appropriate field layer peak standing crops amounted to 23.3 g/m². This was considered as potential litter and was equivalent to 3.4% of the total litter input. The litter standing on the woodland floor in Septermber 1968 was 2,700 g/m², hence, assuming a steady state, litter turnover time was estimated as 4.5 years.It was calculated that the total snail population ingested 0.35-0.43% of the annual litter input, of which 49% was assimilated. The role of the individual species is examined in relation to concepts of "key species" in ecosystem functioning. The possible role of slugs in decomposition processes is also discussed.

Food, feeding rates and assimilation in woodland snails

Analyses of the faeces of seven species of woodland, litterdwelling snails (Marpessa laminata, Clausilia bidentata, Oxychilus cellarius, O. alliarius, Discus rotundatus, Arianta arbustorum and Hygromia striolata), showed that all feed predominently on higher plant material, be it living or dead. H. striolata and A. arbustorum took more chlorophyll-containing plant material than the other species, D. rotundatus had a significant amount of fungus in its faeces, while the faeces of O. cellarius and O. alliarius contained significant amounts of animal material.The consumption and assimilation of a variety of foods by molluscs was studied in the laboratory using an ash-ratio technique, which had been shown to give similar results to those obtained by the standard gravimetric technique. The assimilation efficiency of the molluscs was found to be temperature independent, but ingestion rates and absolute assimilation rates were temperature dependent. The assimilation efficiency of D. rotundatus on living plant material (three field layer species) was 44.8±4.43% that of H. striolata (Urtica dioica) was 52.4±8.78% while O. cellarius and H. aspersa (on Lactuca sativa) had assimilation efficiencies of 70.2±4.40% and 53.50±6.04% respectively. The results fall within the range shown by other invertebrate groups. The assimilation efficiency of D. rotundatus on leaf litter (a mean of 49.1±1.88% on five litter types) was higher than that shown by other invertebrates, probably due to the presence of gut polysaccharidases. The assimilation on dead earthworm as animal material (86.9±2.53% with O. alliarius and 78.6±6.73% with D. rotundatus) was in the range of true carnivores. Consumption rates were more variable; Urtica dioica, amongst living material, was eaten in greatest quantity; Acer pseudoplatanus, Castanea sativa and Quercus robur litter were eaten in greater quantity than Fagus sylvatica and Carpinus betulus. Consumption was examined in terms of percentage body weight.

Environmental Temperatures of Tertiary Penguins

Marine paleotemperatures, determined by oxygen isotope measurement, show that Australasian Tertiary penguins, including giant forms, lived in warm to tropical environments. Evolution from smaller species also occurred in warm environments. Mid-Tertiary fluctuations of sea temperature were controlled by alternating uplift and erosion of "Tasmantis," an unstable meridional landmass occupying and extending beyond the present position of New Zealand.

STRUCTURE AND REPRODUCTION OF THE ALGAL SYMBIONTS OF HYDRA VIRIDIS(1)

The algal symbionts of Hydra viridis are found within vacuoles of the gastrodermal digestive cells of the host. Electron microscopy reveals that the symbionts possess cell walls, and that their reproductive cycle follows the general pattern of free-living Chlorella. Nuclear and chloroplast divisions arc followed by formation of new cell walls, the Golgi apparatus being quite active during cell wall synthesis. Autospores are released when the parent wall ruptures. The autospores are then usually segregated into separate animal vacuoles. Remnants of the ruptured parent wall persist in the vacuoles for an indefinite period. The ruptured parent walls curl at the breakage clefts, forming double-layered scroll-like structures. The fate of these wall remnants has not been firmly established. Long-term starvation of the animals does not result in a detectable change in the structure of the symbionts, and they continue to divide and to store carbohydrate as starch grains.

Apomixis: seasonal and population differences in a grass

Changes in incidence of apomictic and sexual embryo sacs were detected in Dichanthium aristatum in an experimental population at six stations covering 27 degrees of south latitude, and during the flowering season in a wild population. Differences were associated with photoperiods prevailing during development of inflorescences. Response to length of day was quantitative, differing in the two strains.

Ecological dosimetry: radiation levels influenced by plant growth

The feasibility of using lithium-7-fluoride thermoluminescent dosimeters under field conditions for natural radiation at levels of 5 milliroentgens is demonstrated. Radiation dosages in tree trunks increased threefold from winter to spring and summer. This increase is attributed to the gamma radiation field resulting from relatively high levels of potassium-40 and other radionuclides present in the foliage and branches during the growing season.