Microclimatic origin of inhaled air affects olfactory navigation of homing pigeons

Earlier experiments led to the conclusion that homing pigeons are able to deduce positional information from atmospheric odours they perceive at the site of release. Here we show that this ability is significantly reduced, if the inhaled air does not originate from the free airspace in an open landscape but from a close-to-the-ground level of a forest or a maize field.     

The sun compass

Summary The sun compass was discovered by G. Kramer in caged birds showing migratory restlessness. Subsequent experiments with caged brids employing directional training and clock shifts, carried out by Hoffmann and by Schmidt-Koenig, showed that sun azimuth is used and sun altitude ignored. McDonald found the accuracy to be ±3^o–±5^o. According to Hoffmann and to Schmidt-Koenig, caged birds trained at medium northern latitudes were able to allow for the sun's apparent movement north of the arctic circle but not in equatorial and trans-equatorial latitudes.In homing experiments, and employing clock shifts, Schmidt-Koenig demonstrated that the sun compass is used by homing pigeons during initial orientation. This finding supports the existence of a map and compass navigational system. Pigeons living in equatorial latitudes utilize the sun compass even under the extreme solar conditions of equinox (Ranvaud, Schmidt-Koenig, Ganzhorn et al.). The use of the sun compass during zenith passage of the sun is being investigated.     

Pigeons homing: Some experiments for testing the olfactory hypothesis

Summary Homing experiments on Swiss pigeons show that the birds use olfactory cues for navigational purposes and that outward journey detours influence their initial orientation.This work was supported by the Consiglio Nazionale delle Ricerche and by the Swiss National Foundation for Scientific Research.     

Is there a space–time continuum in olfaction?

The coding of olfactory stimuli across a wide range of organisms may rely on fundamentally similar mechanisms in which a complement of specific odorant receptors on olfactory sensory neurons respond differentially to airborne chemicals to initiate the process by which specific odors are perceived. The question that we address in this review is the role of specific neurons in mediating this sensory system—an identity code—relative to the role that temporally specific responses across many neurons play in producing an olfactory perception—a temporal code. While information coded in specific neurons may be converted into a temporal code, it is also possible that temporal codes exist in the absence of response specificity for any particular neuron or subset of neurons. We review the data supporting these ideas, and we discuss the research perspectives that could help to reveal the mechanisms by which odorants become perceptions.     

The vomeronasal system

In addition to the main olfactory system, many vertebrates possess a vomeronasal system that conveys more specialized chemosensory information. Unlike the airborne, volatile stimuli detected by the main olfactory system, vomeronasal stimuli are typically proteins of the lipocalin family which bind small, volatile ligands. Despite the smaller number of vomeronasal receptor types, the projection patterns of the vomeronasal receptor neurons to multiple glomeruli in the accessory olfactory bulb appear to be more complicated than those of the main olfactory system. The vomeronasal system has a direct sub-neocortical projection to hypothalamic areas that mediates specific behavioural and hormonal responses to pheromonal stimuli. However, the integration and transmission of this information can be modulated by learning mechanisms. The aim of this article is to outline some of the functions of the vomeronasal system, and in particular to comment on recent advances in our understanding of how vomeronasal information is coded and processed.     

Multi-model ensembles in climate science: Mathematical structures and expert judgements

Projections of future climate change cannot rely on a single model. It has become common to rely on multiple simulations generated by Multi-Model Ensembles (MMEs), especially to quantify the uncertainty about what would constitute an adequate model structure. But, as Parker points out (2018), one of the remaining philosophically interesting questions is: “How can ensemble studies be designed so that they probe uncertainty in desired ways?” This paper offers two interpretations of what General Circulation Models (GCMs) are and how MMEs made of GCMs should be designed. In the first interpretation, models are combinations of modules and parameterisations; an MME is obtained by “plugging and playing” with interchangeable modules and parameterisations. In the second interpretation, models are aggregations of expert judgements that result from a history of epistemic decisions made by scientists about the choice of representations; an MME is a sampling of expert judgements from modelling teams. We argue that, while the two interpretations involve distinct domains from philosophy of science and social epistemology, they both could be used in a complementary manner in order to explore ways of designing better MMEs.     

Signaling in the Chemosensory Systems

The mammalian olfactory system has evolved complex mechanisms to detect a vast range of molecular cues. In rodents, the olfactory system comprises several distinct subsystems. Current interest has focused on the exact role that each of these subsystems plays in detecting molecular information and regulating chemosensory-dependent behaviors. Here, we summarize recent results showing that the mouse main and accessory olfactory systems detect, at least in part, overlapping sets of social chemosignals. These findings give rise to a model that involves parallel processing of the same molecular cues in both systems. Together with previous work, this model will lead to a better understanding of the general organization of chemical communication in mammals and give a new direction for future experiments.     

Sensory basis of bird orientation

Summary Sensory information which may be essential for the complex process of orientation of birds is described in this article. The use of vibrational, visual, chemical, olfactory, magnetic cues and their receptive mechanisms, as far as they are known, are explained. Special reference is given to the behavioral and physiological aspects of magnetic sensitivity.     

Sensory basis of bird orientation

Sensory information which may be essential for the complex process of orientation of birds is described in this article. The use of vibrational, visual, chemical, olfactory, magnetic cues and their receptive mechanisms, as far as they are known, are explained. Special reference is given to the behavioral and physiological aspects of magnetic sensitivity.     

On the ORigin of smell: odorant receptors in insects

Olfaction, the sense of smell, depends on large, divergent families of odorant receptors that detect odour stimuli in the nose and transform them into patterns of neuronal activity that are recognised in the brain. The olfactory circuits in mammals and insects display striking similarities in their sensory physiology and neuroanatomy, which has suggested that odours are perceived by a conserved mechanism. Here I review recent revelations of significant structural and functional differences between the Drosophila and mammalian odorant receptor proteins and discuss the implications for our understanding of the evolutionary and molecular biology of the insect odorant receptors. Received 23 March 2006; accepted 28 April 2006     

Electroencephalography of the olfactory bulb in relation to prespawn homing

Summary remarks It is evident that the bulbar EEG is a complex response which can be influenced by several methodological and stimulant variables. What EEG patterns tell us about actual behavior remains obscure. The bulbar EEG which is evoked by homestream water is not necessarily a reflection of olfactory memory. The evoked bulbar EEG also does not necessarily demonstrate the salmon has distinguished the home-water from another water in terms of migrational orientation. Despite lack of absolute specificity, a correlation between bulbar EEG and actual behavioral performance has been observed even though some non-home waters evoke responses similar to that of the home water. In general it has been found that the home water response can be distinguished from the response to other natural waters. Failure to obtain complete specificity may be due to a variety of variables which have been alluded to earlier in this section. Thus considering that the evoked EEG is a reflection of the integration of a diverse afferent input, further electrical and computer analyses may eventually permit the decoding of the EEG in terms of behavior. However, if the EEG proves to be more a quantitative rather than qualitative reflection of brain activity, relating EEG to behavior will prove to be of limited value. Since afferent responses in the olfactory bulb are influenced by impulses from higher brain centers, studies on centrifugal aspects during olfactory stimulation may be useful in gaining some qualitative understanding of the home water evoked EEG of the olfactory bulb.     

Initial orientation of homing pigeons: different sensitivity to altered magnetic fields in birds of different countries

Summary In experiments performed in Italy, altered magnetic fields were effective in biasing the initial orientation of Italian pigeons but not that of German pigeons raised in Italy, suggesting a genetic difference between the two bird stocks.We are grateful to Dr H. G. Wallraff who kindly supplied the German pigeons used in our experiments and gave useful suggestions.     

Galton's Quincunx: Probabilistic causation in developmental behavior genetics

In what sense are associations between particular markers and complex behaviors made by genome-wide association studies (GWAS) and related techniques discoveries of, or entries into the study of, the causes of those behaviors? In this paper, we argue that when applied to individuals, the kinds of probabilistic ‘causes’ of complex traits that GWAS-style studies can point towards do not provide the kind of causal information that is useful for generating explanations; they do not, in other words, point towards useful explanations of why particular individuals have the traits that they do. We develop an analogy centered around Galton's “Quincunx” machine; while each pin might be associated with outcomes of a certain sort, in any particular trial, that pin might be entirely bypassed even if the ball eventually comes to rest in the box most strongly associated with that pin. Indeed, in any particular trial, the actual outcome of a ball hitting a pin might be the opposite of what is usually expected. While we might find particular pins associated with outcomes in the aggregate, these associations will not provide causally relevant information for understanding individual outcomes. In a similar way, the complexities of development likely render impossible any moves from population-level statistical associations between genetic markers and complex behaviors to an understanding of the causal processes by which individuals come to have the traits that they in fact have.     

Hensen's node — The ’Organizer’ of the amniote embryo

Conclusion If the hundred years of study on theHensen's node — i.e. on gastrulation and early determination of the embryos of amniote vertebrates — teach anything, they teach in the first place how limited and fragmentary our knowledge is about one of the most central problems of the whole developmental biology. We know that the events in early amniote development — or early avian development, on which our data and ideas are nearly all based — in many ways resemble those in early Amphibian development, which is only slightly better understood, but we also know that direct extrapolations from anamniotes to amniotes cannot be made without proper reservations and without studying the amniote embryos themselves. And we have practically no idea of what is really going on in the cells of the blastoderm when they move, invaginate, induce or are induced, interact, become determined and begin their differentiation. We know that at the stages of gastrulation, the node, and indeed the whole blastoderm, is in a very labile state and can be regulated in many ways to produce a harmonious whole — or a monster — although we only understand very poorly the modes of this regulation. The progress made during the decades, and particularly in recent years, shows, however, that useful information is accumulating to produce a coherent picture, and there is no reason to be pessimistic.Dedicated to ProfessorEtienne Wolff on the occasion of his retirement.     

The role of orientation experiments in discovering mechanisms

Many types of experiments have been recognized in the literature. One important type we discuss in this article is the orientation experiment. While orientation experiments are like other types of experiments in that they are tests for causal relevance, they also have other qualities. One important (but not the only) goal of these experiments is to offer a rough, qualitative characterization of the mechanism responsible for a capacity of interest, effectively constraining future research. This makes them particularly useful during the early stages of investigation, when an explanandum-phenomenon has just been identified and several (often competing) hypotheses as to the qualitative character of the mechanism responsible for it are proposed. We illustrate our claims, and explicate a number of additional aims that orientation experiments can sometimes serve, by considering three case studies from different era's, namely the discovery of the mechanisms responsible for i) the capacity of eels to produce numbing sensations (17th and 18th century), ii) puerperal fever in Semmelweis' Vienna Maternity Hospital (19th century), and iii) the capacity of pigeons to home (20th century).     

Cooperative interactions between odorant-binding proteins of Anopheles gambiae

To understand olfactory discrimination in Anopheles gambiae, we made six purified recombinant OBPs and investigated their ligand-binding properties. All OBPs were expressed in bacteria with additional production of OBP47 in the yeast Kluveromyces lactis. Ligand-binding experiments, performed with a diverse set of organic compounds, revealed marked differences between the OBPs. Using the fluorescent probe N-phenyl-1-naphthylamine, we also measured the binding curves for binary mixtures of OBPs and obtained, in some cases, unexpected behaviour, which could only be explained by the OBPs forming heterodimers with binding characteristics different from those of the component proteins. This shows that OBPs in mosquitoes can form complexes with novel ligand specificities, thus amplifying the repertoire of OBPs and the number of semiochemicals that can be discriminated. Confirmation of the likely role of heterodimers was demonstrated by in situ hybridisation, suggesting that OBP1 and OBP4 are co-expressed in some antennal sensilla of A. gambiae.     

Neuronal plasticity and regeneration in the olfactory system of mammals: morphological and functional recovery following olfactory bulb deafferentation

The mammalian olfactory system has the unique property in the permanent turnover of the olfactory sensory neurons under normal conditions and following injury. This implies that the topographical map of the epithelium-to-bulb connections generated during ontogenesis has to be maintained despite neuron renewal in order to insure olfactory information processing. One way to investigate this issue has been to disrupt the peripheral connections and analyze how neural connections may be reestablished as well as how animals may perform in olfactory-mediated tasks. This review surveys the main data pertaining to both morphological and functional recoveries taking place in the peripheral olfactory system following olfactory bulb deafferentation. Conclusions from these studies are enlightened by recent data from molecular biology.     

What is mechanistic evidence,and why do we need it for evidence-based policy?

It has recently been argued that successful evidence-based policy should rely on two kinds of evidence: statistical and mechanistic. The former is held to be evidence that a policy brings about the desired outcome, and the latter concerns how it does so. Although agreeing with the spirit of this proposal, we argue that the underlying conception of mechanistic evidence as evidence that is different in kind from correlational, difference-making or statistical evidence, does not correctly capture the role that information about mechanisms should play in evidence-based policy. We offer an alternative account of mechanistic evidence as information concerning the causal pathway connecting the policy intervention to its outcome. Not only can this be analyzed as evidence of difference-making, it is also to be found at any level and is obtainable by a broad range of methods, both experimental and observational. Using behavioral policy as an illustration, we draw the implications of this revised understanding of mechanistic evidence for debates concerning policy extrapolation, evidence hierarchies, and evidence integration.     

Forecasting quality and information

It is assumed that demand for information that subjectively appears to be relevant for forecasting improves forecasting quality. To study this hypothesis a number of forecasting experiments were conducted. Fifty managers from the housing business, from banking, and from a research institution were asked to forecast interest rates, using a Delphi process. They communicated via a computer system, and, to support their judgements, they had access to a data bank that was stored in the same system. Their communication with the system was automatically recorded. Part of the data collected in these experiments is used to study the existence of a relationship between information activities and forecasting results. A weak positive relationship is found if non-linear functions are tested, where information demand is corrected by those data retrievals that seem to have resulted from an inability to handle the information system. For further research a more general, albeit less informative, Boolean model is suggested.     

Overcast tests with clock-shifted pigeons

In order to investigate the pigeon's compass mechanism, a series of overcast tests with clock-shifted birds were run at two familiar release sites. While controls were able to assume a correct homeward direction, the experimental birds' initial orientation cannot be explained either on the basis of a time-compensated sun compass or of a time-independent magnetic compass. Speculative explanations of our paradoxical results are attempted.