Ocean Acidification Amplifies the Olfactory Response to 2-Phenylethylamine: Altered Cue Reception as a Mechanistic Pathway?

Hermit crabs as model species for investigating the behavioural responses to pollution

Human impacts on the environment affect organisms at all levels of biological organisation and ultimately can change their phenotype. Over time, phenotypic change may arise due to selection but individual phenotypes are also subject to change via genotype × environment interactions. In animals, behaviour is the most flexible aspect of phenotype, and hence the most liable to change across environmental gradients including exposure to pollution. Here we review current knowledge on the impacts of pollution, broadly defined to include the release of substances, energy, and the effects of carbon emissions, on the behaviour of a highly studied group, the globally distributed hermit crabs. We first show how their obligate association with empty gastropod shells underpins their use as model organisms for the study of resource-assessment, contest, and risk-coping behaviours. Intense study of hermit crabs has advanced our understanding of how animals use information, and we discuss the ways in which pollutants can disrupt the cognitive processes involved. We then highlight current studies of hermit crabs, which paint a clear picture of behavioural changes due to multiple pollutants. Impacts on behaviour vary across pollutants and entire suites of behaviours can be influenced by a single pollutant, with the potential for interactive and cascade effects. Hermit crabs offer the opportunity for detailed behavioural analysis, including application of the repeated measures animal-personality framework, and they are highly amenable to experimental manipulations. As such, we show how they now provide a model system for studying the impacts of pollution on behaviour, yielding insights broadly applicable across animal diversity.

Invited review - the effects of anthropogenic abiotic stressors on the sensory systems of fishes

Climate change is a growing global issue with many countries and institutions declaring a climate state of emergency. Excess CO₂ from anthropogenic sources and changes in land use practices are contributing to many detrimental changes, including increased global temperatures, ocean acidification and hypoxic zones along coastal habitats. All senses are important for aquatic animals, as it is how they can perceive and respond to their environment. Some of these environmental challenges have been shown to impair their sensory systems, including the olfactory, visual, and auditory systems. While most of the research is focused on how ocean acidification affects olfaction, there is also evidence that it negatively affects vision and hearing. The effects that temperature and hypoxia have on the senses have also been investigated, but to a much lesser extent in comparison to ocean acidification. This review assembles the known information on how these anthropogenic challenges affect the sensory systems of fishes, but also highlights what gaps in knowledge remain with suggestions for immediate action. Olfaction, vision, otolith, pH, freshwater, seawater, marine, central nervous system, electrophysiology, mechanism.

Becoming nose-blind-Climate change impacts on chemical communication

Chemical communication via infochemicals plays a pivotal role in ecological interactions, allowing organisms to sense their environment, locate predators, food, habitats, or mates. A growing number of studies suggest that climate change-associated stressors can modify these chemically mediated interactions, causing info-disruption that scales up to the ecosystem level. However, our understanding of the underlying mechanisms is scarce. Evidenced by a range of examples, we illustrate in this opinion piece that climate change affects different realms in similar patterns, from molecular to ecosystem-wide levels. We assess the importance of different stressors for terrestrial, freshwater, and marine ecosystems and propose a systematic approach to address highlighted knowledge gaps and cross-disciplinary research avenues.

Acidification can directly affect olfaction in marine organisms

In the past decade, many studies have investigated the effects of low pH/high CO2 as a proxy for ocean acidification on olfactory-mediated behaviours of marine organisms. The effects of ocean acidification on the behaviour of fish vary from very large to none at all, and most of the maladaptive behaviours observed have been attributed to changes in acid-base regulation, leading to changes in ion distribution over neural membranes, and consequently affecting the functioning of gamma-aminobutyric acid-mediated (GABAergic) neurotransmission. Here, we highlight a possible additional mechanism by which ocean acidification might directly affect olfaction in marine fish and invertebrates. We propose that a decrease in pH can directly affect the protonation, and thereby, 3D conformation and charge distribution of odorants and/or their receptors in the olfactory organs of aquatic animals. This can sometimes enhance signalling, but most of the time the affinity of odorants for their receptors is reduced in high CO2/low pH; therefore, the activity of olfactory receptor neurons decreases as measured using electrophysiology. The reduced signal reception would translate into reduced activation of the olfactory bulb neurons, which are responsible for processing olfactory information in the brain. Over longer exposures of days to weeks, changes in gene expression in the olfactory receptors and olfactory bulb neurons cause these neurons to become less active, exacerbating the problem. A change in olfactory system functioning leads to inappropriate behavioural responses to odorants. We discuss gaps in the literature and suggest some changes to experimental design in order to improve our understanding of the underlying mechanisms and their effects on the associated behaviours to resolve some current controversy in the field regarding the extent of the effects of ocean acidification on marine fish.