The implication of survival rates in natural populations of Drosophila: capture-recapture experiments on domestic species

Adult survival rates were estimated in field populations of domestic Drosophila species by means of multiple capture-recapture experiments. Micronized fluorescent dusts were used as marking agents and analysis used the Fisher-Ford model: the assumptions of this model are justified using evidence from this study and the literature. Survival rates were commonly 0.45-0.85 per day, suggesting that mean life expectancy for adult flies is from 1.3 to 6.2 days in natural populations. No consistent differences in survival between sexes or seasons were demonstrated. The implications of low natural survival rates are discussed.     

Speciation in sympatric species of land snails from the genus Trochulus (Gastropoda,Hygromiidae)

The identification and designation of land snail species in the genus Trochulus on the basis of shell characteristics are problematic because of their great phenotypic plasticity. Some genetic analyses have proved inconclusive, with much variation within populations and apparent gene flow among them. We examined this issue by morphometric and molecular approaches on the morphologically similar species T. coelomphala, T. hispidus and T. striolatus, co‐occurring in the Alpenvorland of Germany. While these species differed in shell and reproductive system morphology, there were forms that turned out intermediate in shell characters between T. coelomphala and T. hispidus but had genital morphology similar to T. coelomphala. Phylogenetic analysis, however, showed that these forms clustered neither with T. coelomphala nor T. hispidus but are sister to T. striolatus from the same region, which suggests that they evolved by way of sympatric speciation. Further, these analyses suggest that T. coelomphala diverged within T. hispidus; a crossing experiment indicated that they were interfertile. Expanding the study to include all available Trochulus sequences enabled us to infer evolutionary relationships between them and showed that T. hispidus is polyphyletic. Some Trochulus samples of one nominal species were grouped within others. The combination of phenotypic plasticity and possible mitochondrial DNA introgression illustrates the complex nature of evolutionary processes and the need for caution in the application of traditional taxonomic practice.     

New insigths on the metabolic diversity among the epibiotic microbial communitiy of the hydrothermal shrimp Rimicaris exoculata

The Rimicaris exoculata dominates the megafauna of some of the Mid Atlantic ridge hydrothermal vent sites. This species harbors a rich community of bacterial epibionts inside its gill chamber. Literature data indicate that a single 16S rRNA phylotype dominates this epibiotic community, and is assumed to be a sulfide-oxidizing bacteria. However attempts of cultivation were not successful and did not allow to confirm it. The aim of our study was to test the hypothesis of sulfide oxidation in the gill chamber, by a multidisciplinary approach, using in vivo experiments at in situ pressure in the presence of sulfide, microscopic observations and a molecular survey. Morphology of microorganisms, before and after treatment, was analyzed to test the effect of sulfide depletion and re-exposure. Our observations, as well as molecular data indicate a wider diversity than previously described for this shrimp's epibiotic community. We observed occurrence of bacterial intracellular sulfur- and iron-enriched granules and some methanotrophic-like bacteria cells for the first time. Genes that are characteristic of methane-oxidizing (pmoA) and sulfide-oxidizing (APS) bacteria were identified. These results suggest that three metabolic types (iron, sulfide and methane oxidation) may co-occur within the epibiont community associated with Rimicaris exoculata. As this shrimp colonizes chemically contrasted environments, the relative abundance of each metabolic type could vary according to the local availability of reduced compounds.     

Can separation along the temperature niche axis promote coexistence between native and invasive species?

Aim Western mosquitofish (Gambusia affinis) have been linked with the decline of native fish and amphibians throughout the world. Separation along the temperature niche axis may promote the long‐term coexistence of introduced western mosquitofish, with native species in temperate regions. Recent research has shown that western mosquitofish can reduce the recruitment of native least chub (Iothichthys phlegethontis) endemic to the Bonneville Basin. We tested the hypotheses that cold temperatures (≤ 15 °C in the summer, freezing winters) would: (1) reduce the aggressive and predatory effects of western mosquitofish on least chub, and (2) eliminate the overwinter survival and recruitment of western mosquitofish while having little effect on least chub recruitment. Location Bonneville Basin of Utah, USA. Methods We used short‐term tests in the laboratory at the level of individuals and manipulated temperature (warm, cold and seasonal treatments) in long‐term experiments using mesocosms at the population level. Results Cold temperatures (≤ 15 °C) reduced the aggression and predation of western mosquitofish on least chub at the level of individuals. At the population level, however, cool summers (≤ 15 °C) eliminated recruitment in both species because they required warm summers (c. 20–30 °C) to survive freezing winters. Although least chub had an overwinter advantage in survival (75% least chub, 45% western mosquitofish), it was overwhelmed by the rapid reproduction of western mosquitofish as temperatures increased in the summer. Main conclusions Studies at the level of populations are necessary to understand the ultimate effects of introduced species on native taxa. Separation along the temperature niche axis was not sufficient to promote coexistence between these species in habitats with warm summers (c. 30 °C). Although coexistence may be possible in habitats with cool summers (≤ 20 °C) and freezing winters, the ability of niche separation to promote long‐term coexistence between native and introduced species may ultimately depend on their respective rates of evolution. Long‐term coexistence may not be possible if introduced species can adapt to new environmental conditions faster than native species can evolve mechanisms to reduce their harmful effects.     

Whole-Ecosystem Experiments: Replication Versus Realism: The Need for Ecosystem-Scale Experiments

The results of bottle and mesocosm experiments were compared with those obtained in whole-ecosystem experiments at the Experimental Lakes Area. Unless they can be cleverly designed to mimic major ecosystem processes and community compositions, smaller-scale experiments often give highly replicable, but spurious, answers. Problems with appropriate scaling are difficult to deduce without direct comparisons with whole-ecosystem experiments. Reasons are many, but include inappropriate spatial scales to include whole communities, in particular predators and nocturnally active animals; temporal scales that are too short to assess accurately the response of slow-responding organisms and biogeochemical processes; and elimination of key littoral–pelagic and catchment–lake interactions. Identical studies of limnological processes in lakes of a large range of sizes reveals that scaling correction is also necessary when extrapolating from small lakes to large ones. Accurate management decisions cannot be made with confidence unless ecosystem scales are studied. Received 26 March 1998; accepted 14 May 1998.     

Experimental Research Examining How People Can Cope with Uncertainty Through Soft Haptic Sensations

Human beings are constantly surrounded by uncertainty and change. The question arises how people cope with such uncertainty. To date, most research has focused on the cognitive strategies people adopt to deal with uncertainty. However, especially when uncertainty is due to unpredictable societal events (e.g., economical crises, political revolutions, terrorism threats) of which one is unable to judge the impact on one’s future live, cognitive strategies (like seeking additional information) is likely to fail to combat uncertainty. Instead, the current paper discusses a method demonstrating that people might deal with uncertainty experientially through soft haptic sensations. More specifically, because touching something soft creates a feeling of comfort and security, people prefer objects with softer as compared to harder properties when feeling uncertain. Seeking for softness is a highly efficient and effective tool to deal with uncertainty as our hands are available at all times. This protocol describes a set of methods demonstrating 1) how environmental (un)certainty can be situationally activated with an experiential priming procedure, 2) that the quality of the softness experience (what type of softness and how it is experienced) matters and 3) how uncertainty can be reduced using different methods.     

Weak response of saltmarsh infauna to ecosystem-wide nutrient enrichment and fish predator reduction: A four-year study

We examined the effect of whole-ecosystem manipulations of predator removal and nutrient enrichment on saltmarsh macroinfauna in the Plum Island Estuary, Massachusetts. Nitrate and phosphate loading rates were increased 10× above background levels in experimental creeks, and we significantly reduced (by 60%) the abundance of the killifish, Fundulus heteroclitus, a key predator in this system. Two creek pairs were manipulated; Creek Pair 1 for three growing seasons and Creek Pair 2 for one. Infaunal responses were examined in four habitats along the inundation gradient: mudflat, creek wall, Spartina alterniflora, and S. patens habitats. Although benthic microalgae increased synergistically in our treatments, we detected no long-term, population-level numerical response by any taxon. Similarly, no long-term species diversity or community responses were observed. However, nutrient enrichment increased the population biomass of the polychaete Manayunkia aestuarina in the creek wall habitat and the oligochaete Cernosvitoviella immota in the S. alterniflora habitat. No numerical or biomass responses of infauna were detected in predator removal treatments although indirect effects associated with killifish reduction may have contributed to an ephemeral interaction between nutrient addition and predator reduction in S. patens habitat. Our data suggest that population and community responses between benthic microalgae and macroinfauna are not tightly coupled even though some species benefit from increased benthic algae biomass by achieving larger body size.     

Two criteria for the comparison of multiple arrangements of experiments and their use to answer the question: Is it better to compare p treatment groups with p controls or with a single control

In experimental situations examining the effectiveness of p(p>1) treatments by comparing treated groups and untreated controls the following question arose: Which experimental arrangement is more appropriate, an arrangement A₁ using for the p comparisons only one single control, or an arrangement A₂ using for every comparison another control. To answer this question two criteria are formulated. The first criterion takes into consideration the expected numbers of type I and type II errors, and the second criterion the probabilities of type I and of type II errors. According to the first criterion A₁ and A₂ do not differ, generally. According to the second criterion A₁ with the comparison of means of normal distributed variables is better than A₂. Pooling of all p controls is better than A₂ according to both criteria. A₁ is better also according to the often used experimentwise type I error rate. The formulated criteria have some analogy to those of MILLER (1966). It may be possible to use them not only for comparing experimental arrangements but also tests.