Jack-of-all-trades master of all? Snake vertebrae have a generalist inner organization

Snakes are a very speciose group of squamates that adapted to various habitats and ecological niches. Their ecological diversity is of particular interest and functional demands associated with their various styles of locomotion are expected to result in anatomical specializations. In order to explore the potential adaptation of snakes to their environment we here analyze variation in vertebral structure at the microanatomical level in species with different locomotor adaptations. Vertebrae, being a major element of the snake body, are expected to display adaptations to the physical constraints associated with the different locomotor modes and environments. Our results revealed a rather homogenous vertebral microanatomy in contrast to what has been observed for other squamates and amniotes more generally. We here suggest that the near-absence of microanatomical specializations in snake vertebrae might be correlated to their rather homogeneous overall morphology and reduced range of morphological diversity, as compared to lizards. Thus, snakes appear to retain a generalist inner morphology that allows them to move efficiently in different environments. Only a few ecologically highly specialized taxa appear to display some microanatomical specializations that remain to be studied in greater detail.     

Cryptic multiple hypotheses testing in linear models: overestimated effect sizes and the winner's curse

Fitting generalised linear models (GLMs) with more than one predictor has become the standard method of analysis in evolutionary and behavioural research. Often, GLMs are used for exploratory data analysis, where one starts with a complex full model including interaction terms and then simplifies by removing non-significant terms. While this approach can be useful, it is problematic if significant effects are interpreted as if they arose from a single a priori hypothesis test. This is because model selection involves cryptic multiple hypothesis testing, a fact that has only rarely been acknowledged or quantified. We show that the probability of finding at least one ‘significant’ effect is high, even if all null hypotheses are true (e.g. 40% when starting with four predictors and their two-way interactions). This probability is close to theoretical expectations when the sample size (N) is large relative to the number of predictors including interactions (k). In contrast, type I error rates strongly exceed even those expectations when model simplification is applied to models that are over-fitted before simplification (low N/k ratio). The increase in false-positive results arises primarily from an overestimation of effect sizes among significant predictors, leading to upward-biased effect sizes that often cannot be reproduced in follow-up studies (‘the winner's curse’). Despite having their own problems, full model tests and P value adjustments can be used as a guide to how frequently type I errors arise by sampling variation alone. We favour the presentation of full models, since they best reflect the range of predictors investigated and ensure a balanced representation also of non-significant results.     

Pigeon homing: sun compass use in the southern hemisphere

Although the sun compass of birds is based on learning the sun's arc during development, it was unclear whether birds can use the sun when its apparent movement is reversed, in particular, whether northern birds that have been introduced into the southern hemisphere can use the southern sun. To answer this question, clock-shift experiments were performed with local homing pigeons in Auckland, New Zealand (37°S). In three fast-shift tests and two slow-shift tests, the experimental birds showed deflections from the untreated controls that were the mirror images of those observed in the northern hemisphere. These results clearly show that homing pigeons in New Zealand use a sun compass that is adapted to the situation in the southern hemisphere. The learning processes establishing the compensation mechanisms thus appear to be free of constraints concerning the direction of the sun's movement. Differences from recent findings with migratory birds, where the direction of celestial rotation proved of crucial importance for establishing the migratory direction, are discussed: the differences may arise from the different orientation tasks, in particular, from the involvement of innate information in establishing the migratory direction. Received: 13 November 1997 / Accepted after revision: 28 February 1998     

Entwicklung und Anwendung von Pflanzenschutzmitteln: Wirtschaftliche Aspekte

The development of new active ingredients and formulations is increasingly influenced by costs and regulations in the frame of pesticide registration procedures. Lawmakers and administrators therefore take over more responsibility, not only for the subject of regulation, but also for fair and balanced rules which can be predicted in the long-term. There are, however, deficiencies in the choice of certain quality standards — like in the European drinking water directive — which are not risk-related and which are susceptible to giving misleading guidance. Testing requirements should be scrutinized for efficiency, i.e. whether the increase in knowledge and safety is in reasonable proportion to the invested resources.     

Free Energy Reduction by Molecular Interface Crossing: Novel Mechanism for the Transport of Material Across the Interface of Nanoscale Droplets Induced by Competing Intermolecular Forces for Application in Perfluorocarbon Blood Substitutes

 Perfluorocarbons (PFCs) are inert liquids which can dissolve – and release – approximately 50 times more oxygen than blood plasma. Oxygen carriers based on PFCs are easy to produce, free of biological components, and more rigorously sterilizable than blood. PFCs injected into the body are eliminated by expiration through the lungs. Before reaching the lungs, PFCs accumulate in storage organs such as liver and spleen. In these organs nanoscale PFC droplets reduce their free energy by unifying to microscopic drops, thus indirectly lowering the rate of their expiration. The model of free energy reduction by molecular interface crossing (FERMIC), a novel emulsion breaking mechanism derived from first principles as presented here, leads to a better understanding of the structure formation processes relevant in perfluorocarbons (PFCs) in vivo. Received: 11 November 1998 / Accepted in revised form: 18 February 1999     

Expositionsabschätzung mittels Modellrechnungen

Human exposure to polycyclic aromatic hydrocarbons (PAH) via daily liquid consumption (primarily through the intake of drinking water) is estimated using model calculations based on the indicator substance benzo(a)pyrene. The additional contribution to oral exposure by a consumption of solid nutrients, and by soil and dust ingestion, are evaluated using typical background conditions in Germany (conurbations of North-Rhine-Westphalia). A series of further scenarios is then applied to examine the influence of elevated PAH concentrations in the daily intake of liquid. The degree of PAH exposure via liquid only equals or exceeds the exposure via the solid fraction of the diet under very specific conditions. The contribution via liquid consumption to a total lifelong exposure of both BAP and PAH caused by dietary intake may be estimated as approximately 4 %. It increases to 56 % under a level equivalent to the Dutch intervention value for groundwater and reaches 90 % under a level equivalent to the WHO guideline for drinking water. Considering occupants who live on PAH contaminated garden allotments with private wells, the highest degree of exposure is caused by vegetables followed by house dust, then liquid diet and finally by soil. Finally, the model approach is used for evaluating the success of potential remedial treatments with respect to exposure reduction. In addition to the application of average values, conservative estimates of exposure in terms of 95 % values are set out in this publication based on sumulation methodologies.