Effects of acidification on olfactory-mediated behaviour in freshwater and marine ecosystems: a synthesis

For many aquatic organisms, olfactory-mediated behaviour is essential to the maintenance of numerous fitness-enhancing activities, including foraging, reproduction and predator avoidance. Studies in both freshwater and marine ecosystems have demonstrated significant impacts of anthropogenic acidification on olfactory abilities of fish and macroinvertebrates, leading to impaired behavioural responses, with potentially far-reaching consequences to population dynamics and community structure. Whereas the ecological impacts of impaired olfactory-mediated behaviour may be similar between freshwater and marine ecosystems, the underlying mechanisms are quite distinct. In acidified freshwater, molecular change to chemical cues along with reduced olfaction sensitivity appear to be the primary causes of olfactory-mediated behavioural impairment. By contrast, experiments simulating future ocean acidification suggest that interference of high CO₂ with brain neurotransmitter function is the primary cause for olfactory-mediated behavioural impairment in fish. Different physico-chemical characteristics between marine and freshwater systems are probably responsible for these distinct mechanisms of impairment, which, under globally rising CO₂ levels, may lead to strikingly different consequences to olfaction. While fluctuations in pH may occur in both freshwater and marine ecosystems, marine habitat will remain alkaline despite future ocean acidification caused by globally rising CO₂ levels. In this synthesis, we argue that ecosystem-specific mechanisms affecting olfaction need to be considered for effective management and conservation practices.     

Sum of fears among intraguild predators drives the survival of green sea turtle (Chelonia mydas) eggs

Ecologists have long theorized that apex predators stabilize trophic systems by exerting a net protective effect on the basal resource of a food web. Although experimental and observational studies have borne this out, it is not always clear what behavioural mechanisms among the trophically connected species are responsible for this stability. Fear of intraguild predation is commonly identified as one such mechanism in models and mesocosm studies, but empirical evidence in natural systems remains limited, as the complexity of many trophic systems renders detailed behavioural studies of species interactions challenging. Here, we combine long-term field observations of a trophic system in nature with experimental behavioural studies of how all the species in this system interact, in both pairs and groups. The results demonstrate how an abundant, sessile and palatable prey item (sea turtle eggs, Chelonia mydas) survives when faced by three potential predators that all readily eat eggs: an apex predator (the stink ratsnake, Elaphe carinata) and two mesopredators (the brown rat, Rattus norvegicus, and kukri snake, Oligodon formosanus). Our results detail how fear of intraguild predation, conspecific cannibalism, habitat structure and territorial behaviour among these species interact in a complex fashion that results in high egg survival.     

The relative importance of olfaction and vision in a diurnal and a nocturnal hawkmoth

Nectar-feeding animals can use vision and olfaction to find rewarding flowers and different species may give different weight to the two sensory modalities. We have studied how a diurnal or nocturnal lifestyle affects the weight given to vision and olfaction. We tested naïve hawkmoths of two species in a wind tunnel, presenting an odour source and a visual stimulus. Although the two species belong to the same subfamily of sphingids, the Macroglossinae, their behaviour was quite different. The nocturnal Deilephila elpenor responded preferably to the odour while the diurnal Macroglossum stellatarum strongly favoured the visual stimulus. Since a nocturnal lifestyle is ancestral for sphingids, the diurnal species, M. stellatarum, has evolved from nocturnal moths that primarily used olfaction. During bright daylight visual cues may have became more important than odour.     

Using physiology and behaviour to understand the responses of fish early life stages to toxicants

The use of early life stages of fishes (embryos and larvae) in toxicity testing has been in existence for a long time, generally utilizing endpoints such as morphological defects and mortality. Behavioural endpoints, however, may represent a more insightful evaluation of the ecological effects of toxicants. Indeed, recent years have seen a considerable increase in the use of behavioural measurements in early life stages reflecting a substantial rise in zebrafish Danio rerio early life‐stage toxicity testing and the development of automated behavioural monitoring systems. Current behavioural endpoints identified for early life stages in response to toxicant exposure include spontaneous activity, predator avoidance, capture of live food, shoaling ability and interaction with other individuals. Less frequently used endpoints include measurement of anxiogenic behaviours and cognitive ability, both of which are suggested here as future indicators of toxicant disruption. For many simple behavioural endpoints, there is still a need to link behavioural effects with ecological relevance; currently, only a limited number of studies have addressed this issue. Understanding the physiological mechanisms that underlie toxicant effects on behaviour so early in life has received far less attention, perhaps because physiological measurements can be difficult to carry out on individuals of this size. The most commonly established physiological links with behavioural disruption in early life stages are similar to those seen in juveniles and adults including sensory deprivation (olfaction, lateral line and vision), altered neurogenesis and neurotransmitter concentrations. This review highlights the importance of understanding the integrated behavioural and physiological response of early life stages to toxicants and identifies knowledge gaps which present exciting areas for future research.     

Improving odour assessment in LCA—the odour footprint

Purpose

Odour is an important aspect of systems for human and agricultural waste management and many technologies are developed with the sole purpose of reducing odour. Compared with greenhouse gas assessment and the assessment of toxicity, odour assessment has received little attention in the life cycle assessment (LCA) community. This article aims to redress this.

Methods

Firstly, a framework for the assessment of odour impacts in LCA was developed considering the classical LCA framework of emissions, midpoint and endpoint indicators. This suggested that an odour footprint midpoint indicator was worth striving for. An approach to calculating an areal indicator we call “odour footprint”, which considers the odour detection threshold, the diffusion rate and the kinetics of degradation of odourants, was implemented in MATLAB. We demonstrated the use of the characterisation factors we calculated in a case study based on odour removal technology applied to a pig barn.

Results and discussion

We produced a list of 33 linear characterisation factors based on hydrogen sulphide equivalents, analogous to the linear carbon dioxide equivalency factors in use in carbon footprinting, or the dichlorobenzene equivalency factors developed for assessment of toxic impacts in LCA. Like the latter, this odour footprint method does not take local populations and exposure pathway analysis into account—its intent is not to assess regulatory compliance or detailed design. The case study showed that despite the need for materials and energy, large factor reductions in odour footprint and eutrophication potential were achieved at the cost of a smaller factor increase in greenhouse emissions.

Conclusions

The odour footprint method is proposed as an improvement on the established midpoint method for odour assessment in LCA. Unlike it, the method presented here considers the persistence of odourants. Over time, we hope to increase the number of characterised odourants, enabling analysts to perform simple site-generic LCA on systems with odourant emissions.     

Behavioural variability of olfactory exploration of the pet dog in relation to human adults

Recent studies have underlined the importance of olfaction in the regulation of the relations between man and his pet dog. This study shows that the exploratory olfactory behavioural mechanisms of the pet dog in relation to the human adult differ according to whether the adult is known to the dog or not. This study also confirms the previous hypothesis concerning the functions of chemcial substances emitted by man in the man/animal relational systems. It would appear that olfaction enables the dog to apprehend information concerning the identity and emotional state of the human subject.     

RNA synthetic biology

RNA molecules play important and diverse regulatory roles in the cell by virtue of their interaction with other nucleic acids, proteins and small molecules. Inspired by this natural versatility, researchers have engineered RNA molecules with new biological functions. In the last two years efforts in synthetic biology have produced novel, synthetic RNA components capable of regulating gene expression in vivo largely in bacteria and yeast, setting the stage for scalable and programmable cellular behavior. Immediate challenges for this emerging field include determining how computational and directed-evolution techniques can be implemented to increase the complexity of engineered RNA systems, as well as determining how such systems can be broadly extended to mammalian systems. Further challenges include designing RNA molecules to be sensors of intracellular and environmental stimuli, probes to explore the behavior of biological networks and components of engineered cellular control systems.     

Bacterial olfaction

Sensing their environment is a crucial ability of all life forms. In higher eukaryotes the sensing of airborne volatile compounds, or olfaction, is well developed. In plants, slime moulds and yeast there is also compelling evidence that these organisms can smell their environment and respond accordingly. Here we show that bacteria are also capable of olfaction. Bacillus licheniformis was able to sense airborne volatile metabolites produced by neighbouring bacterial cultures and cells could respond to this chemical information in a coordinated way. When Bacillus licheniformis was grown in a microtitre plate adjacent to a bacterial culture of the same or a different species, growing in complex medium, biofilm formation and pigment production were elicited by volatile molecules. A weaker response occurred in increasingly distant wells. The emitted volatile molecule was identified as ammonia. These data demonstrate that B. licheniformis has evolved the ability collect information about its environment from the surrounding air and physiologically respond to it in a manner similar to olfaction. This is the first time that a behavioural response triggered by odorant molecules received through the gas phase is described in bacteria.     

Epidemiology of Mental Health Attendances at Emergency Departments: Systematic Review and Meta-Analysis

BackgroundThe characteristics of Emergency Department (ED) attendances due to mental or behavioural health disorders need to be described to enable appropriate development of services. We aimed to describe the epidemiology of mental health-related ED attendances within health care systems free at the point of access, including clinical reason for presentation, previous service use, and patient sociodemographic characteristics.MethodSystematic review and meta-analysis of observational studies describing ED attendances by patients with common mental health conditions.Findings18 studies from seven countries met eligibility criteria. Patients attending due to mental or behavioural health disorders accounted for 4% of ED attendances; a third were due to self-harm or suicidal ideation. 58.1% of attendees had a history of psychiatric illness and up to 58% were admitted. The majority of studies were single site and of low quality so results must be interpreted cautiously.ConclusionsPrevalence studies of mental health-related ED attendances are required to enable the development of services to meet specific needs.     

Taste Perception in Kallmann Syndrome,A Model of Congenital Anosmia

ObjectiveTo investigate taste, a component of flavor perception, using electrogustometry (EG) in patients with congenital anosmia associated with Kallmann syndrome (KS).MethodsFour patients with KS and 4 control subjects participated in this study. During the first phase of the investigation, the study subjects were administered the University of Pennsylvania Smell Identification Test. During the second phase of the study, EG testing of 2 regions on the anterior tongue tip was performed through an electrode.ResultsPatients with KS, as expected, scored in the anosmic range on the University of Pennsylvania Smell Identification Test, whereas the control group had a normal sense of smell. The difference in the olfaction scores was significant between the 2 study groups (P < 0.015). The result of taste assessment of patients with KS and control subjects with use of EG was not significantly different between the 2 study groups (P = 0.874).ConclusionThe current study demonstrates that patients with KS have a normal sense of taste, as determined by EG. This finding is consistent with the fact that the deficit in KS is purely olfactory. Because flavor perception is not a common complaint in patients with this condition, it may be postulated that persons with KS compensate for the absent sense of smell. Further studies need to be undertaken to explore how patients with KS compensate for the olfactory dysfunction, information that should contribute to the understanding of the interplay of the various components of flavor perception. (Endocr Pract. 2007;13:716-720)     

Can We Identify the Active Ingredients of Behaviour Change Interventions for Coronary Heart Disease Patients? A Systematic Review and Meta-Analysis

BackgroundThe main behaviour change intervention available for coronary heart disease (CHD) patients is cardiac rehabilitation. There is little recognition of what the active ingredients of behavioural interventions for CHD might be. Using a behaviour change technique (BCT) framework to code existing interventions may help to identify this. The objectives of this systematic review are to determine the effectiveness of CHD behaviour change interventions and how this may be explained by BCT content and structure.ConclusionsBehaviour change interventions for CHD patients appear to have a positive impact on a number of outcomes. Using an existing BCT taxonomy to code the interventions helped us to understand which were the most commonly used techniques, providing information and goal setting, but not the active components of these complex interventions.     

Disruptive physiology: olfaction and the microbiome–gut–brain axis

This review covers the field of olfaction and chemosensation of odorants and puts this information into the context of interactions between microbes and behaviour; the microbiome–gut–brain axis (MGBA). Recent emphasis has also been placed on the concept of the holobiome which states that no single aspect of an organism should be viewed separately and thus must include examination of their associated microbial populations and their influence. While it is known that the microbiome may be involved in the modulation of animal behaviour, there has been little systematized effort to incorporate into such studies the rapidly developing knowledge of the wide range of olfactory systems. The classical olfactory system is evolutionarily conserved in multiple taxa from insects through to fish, reptiles and mammals, and is represented by the largest gene families in vertebrates. Mice have over 1000 different olfactory receptors and humans about 400. They are distributed throughout the body and are even found in spermatozoa where they function in chemotaxis. Each olfactory receptor has the unique functional capability of high‐affinity binding to several different molecular ligands. These and other properties render the cataloguing of odorants (odorome) with specific actions a difficult task. Some ectopic olfactory receptors have been shown to have functional effects in the gut and kidney, highlighting the complexity of the systems engaged by odorants. However, there are, in addition to classical olfactory receptors, at least two other families of receptors involved in olfaction that are also widely found expressed on tissues in many different organs in addition to the nervous system and brain: the trace‐amine associated and formyl peptide receptors. Bacteria can make many if not most odorants and are responsible for recognition of species and relative relatedness, as well as predator presence, among many other examples. Activation of different combinations of olfactory receptors by bacterial products such as β‐phenylethylamine have been shown even to control expression of emotions such as fear and aggression. The number of examples of bacterial products and volatile odorants influencing brain function and behaviour is expanding rapidly. Since it is recognized that many different bacterial products and metabolites also function as social cues, and may themselves be directly or indirectly causative of behavioural change, it becomes ever more important to include olfaction into studies of the MGBA. Clearly there are broader implications for the involvement of olfaction in this rapidly evolving field. These include improvement in our understanding of the pathways engaged in various behaviours, and the identification of novel approaches and new targets in efforts to modulate behavioural changes.     

Internal representations of smell in the <Emphasis Type="Italic">Drosophila</Emphasis> brain

Recent advances in sensory neuroscience using Drosophila olfaction as a model system have revealed brain maps representing the external world. Once we understand how the brain’s built-in capability generates the internal olfactory maps, we can then elaborate how the brain computes and makes decision to elicit complex behaviors. Here, we review current progress in mapping Drosophila olfactory circuits and discuss their relationships with innate olfactory behaviors. Hui-Hao lin and Chih-Yung Lin contributed equally to this work.     

CO2-induced ocean acidification increases anxiety in Rockfish via alteration of GABAA receptor functioning

The average surface pH of the ocean is dropping at a rapid rate due to the dissolution of anthropogenic CO₂, raising concerns for marine life. Additionally, some coastal areas periodically experience upwelling of CO₂-enriched water with reduced pH. Previous research has demonstrated ocean acidification (OA)-induced changes in behavioural and sensory systems including olfaction, which is due to altered function of neural gamma-aminobutyric acid type A (GABA_A) receptors. Here, we used a camera-based tracking software system to examine whether OA-dependent changes in GABA_A receptors affect anxiety in juvenile Californian rockfish (Sebastes diploproa). Anxiety was estimated using behavioural tests that measure light/dark preference (scototaxis) and proximity to an object. After one week in OA conditions projected for the next century in the California shore (1125 ± 100 µatm, pH 7.75), anxiety was significantly increased relative to controls (483 ± 40 µatm CO₂, pH 8.1). The GABA_A-receptor agonist muscimol, but not the antagonist gabazine, caused a significant increase in anxiety consistent with altered Cl⁻ flux in OA-exposed fish. OA-exposed fish remained more anxious even after 7 days back in control seawater; however, they resumed their normal behaviour by day 12. These results show that OA could severely alter rockfish behaviour; however, this effect is reversible.     

Adaptation of the repellency response to DEET in Rhodnius prolixus

For many years it has been accepted that DEET interferes with the detection of odours from the host instead of having a repellent effect. However, recent work showed that DEET acts as an odorant molecule and elicits a behavioural response in the absence of other stimuli. Therefore, DEET must promote some phenomenon connected with the stimuli-sensory system interaction, such as a sensory adaptation, where the sensory system regulates its sensitivity to different stimuli intensities during continuous or repetitive exposure. In this work, we studied different aspects of the insect-DEET interaction through behavioural observations. Previous exposure of fifth instar Rhodnius prolixus nymphs to DEET decreased the behavioural response to this repellent. We observed a decrease in repellence after different times of continuous stimulation with DEET in a time-dependent manner. The response to DEET was recovered 10 min after exposure, when insects were continuously stimulated during 5 or 10 min; maximum repellence was recovered 20 min after exposure when insects were stimulated for 20 min. DEET produced a repellent effect when nymphs were exposed only to its vapours. These results suggest that exposure to DEET produces adaptation in R. prolixus nymphs, and that the behavioural response elicited by DEET occurs via olfaction when no other stimuli are present.     

Use of Olfaction During Prey Location by the Common Vampire Bat (Desmodus rotundus)1

The common vampire bat, Desmodus rotundus, feeds on mammalian blood and is a major agricultural pest in Latin America. One way to prevent bats from biting livestock is to understand how the bats locate the livestock. We confirmed the role of olfaction in foraging with a modified cafeteria trial. Bats significantly favored blood meals associated with scent (fur, feces) over meals lacking these olfactory cues. These results confirm earlier observations on the role of olfaction during prey location by this species, and have potential to facilitate eradication measures without extensive loss of other bat species.     

Vegetation change at high elevation: scale dependence and interactive effects on Niwot Ridge

Background: High-elevation mountain systems may be particularly responsive to climate change.

Aims: Here we investigate how changes along elevation gradients in mountain systems can aid in predicting vegetation distributional changes in time, focusing on how changing climatic controls affect meso-scale transitions at the lower and upper boundaries of alpine vegetation (with forest and subnival zones, respectively) as well as micro-scale transitions among plant communities within the alpine belt. We focus on climate-related drivers, particularly in relation to climate change, but also consider how species interactions, dispersal and responses to disturbance may influence plant responses to these abiotic drivers.

Results: Empirical observations and experimental studies indicate that changing climatic controls influence both meso-scale transitions at the upper and lower boundaries of alpine vegetation and micro-scale transitions among plant communities within tundra. Micro-scale heterogeneity appears to buffer response in many cases, while interactions between climate and other changes may often accelerate change.

Conclusions: Interactions with microtopography and larger edaphic gradients have the capacity to both facilitate rapid changes and reinforce stability, and that these interactions will affect the responsiveness of vegetation to climate change at different spatial scales.     

Suppression of adult cytogenesis in the rat brain leads to sex‐differentiated disruption of the HPA axis activity

ObjectivesThe action of stress hormones, mainly glucocorticoids, starts and coordinates the systemic response to stressful events. The HPA axis activity is predicated on information processing and modulation by upstream centres, such as the hippocampus where adult‐born neurons (hABN) have been reported to be an important component in the processing and integration of new information. Still, it remains unclear whether and how hABN regulates HPA axis activity and CORT production, particularly when considering sex differences.Materials and MethodsUsing both sexes of a transgenic rat model of cytogenesis ablation (GFAP‐Tk rat model), we examined the endocrinological and behavioural effects of disrupting the generation of new astrocytes and neurons within the hippocampal dentate gyrus (DG).ResultsOur results show that GFAP‐Tk male rats present a heightened acute stress response. In contrast, GFAP‐Tk female rats have increased corticosterone secretion at nadir, a heightened, yet delayed, response to an acute stress stimulus, accompanied by neuronal hypertrophy in the basal lateral amygdala and increased expression of the glucocorticoid receptors in the ventral DG.ConclusionsOur results reveal that hABN regulation of the HPA axis response is sex‐differentiated.