Actions speak louder than words: the case for responsible scientific activism in an era of planetary emergency.

The world's understanding of the climate and ecological crises rests on science. However, scientists' conventional methods of engagement, such as producing ever more data and findings, writing papers and giving advice to governments, have not been sufficiently effective at persuading politicians to act on the climate and ecological emergency. To date, governments' decisions (such as continuing with vast subsidies for fossil fuels) clearly show that powerful vested interests have been much more influential than the amassed scientific knowledge and advice. We argue that in the face of this inaction, scientists can have the maximum amount of influence by lending their support to social movements pressing for action, joining as active participants and considering civil disobedience. Scientists seeking to halt continued environmental destruction also need to work through our institutions. Too many scientific organizations, from national academies of science to learned societies and universities, have not taken practical action on climate; for example, many still partner with fossil fuel and other compromised interests. We therefore also outline a vision for how scientists can reform our scientific institutions to become powerful agents for change.

Rapid evidence review to inform safe return to campus in the context of coronavirus disease 2019 (COVID-19).

Background: Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is transmitted predominantly through the air in crowded and unventilated indoor spaces among unvaccinated people. Universities and colleges are potential settings for its spread. Methods: An interdisciplinary team from public health, virology, and biology used narrative methods to summarise and synthesise evidence on key control measures, taking account of mode of transmission. Results: Evidence from a wide range of primary studies supports six measures.  Vaccinate (aim for > 90% coverage and make it easy to get a jab). Require masks indoors, especially in crowded settings. If everyone wears well-fitting cloth masks, source control will be high, but for maximum self-protection, respirator masks should be worn.  Masks should not be removed for speaking or singing. Space people out by physical distancing (but there is no "safe" distance because transmission risk varies with factors such as ventilation, activity levels and crowding), reducing class size (including offering blended learning), and cohorting (students remain in small groups with no cross-mixing). Clean indoor air using engineering controls-ventilation (while monitoring CO 2 levels), inbuilt filtration systems, or portable air cleaners fitted with high efficiency particulate air [HEPA] filters). Test asymptomatic staff and students using lateral flow tests, with tracing and isolating infectious cases when incidence of coronavirus disease 2019 (COVID-19) is high. Support clinically vulnerable people to work remotely. There is no direct evidence to support hand sanitising, fomite controls or temperature-taking. There is evidence that freestanding plastic screens, face visors and electronic air-cleaning systems are ineffective. Conclusions: The above six evidence-based measures should be combined into a multi-faceted strategy to maximise both student safety and the continuation of in-person and online education provision. Staff and students seeking to negotiate a safe working and learning environment should collect data (e.g. CO 2 levels, room occupancy) to inform conversations.

Pheromones: Stink Fights in Lemurs.

Some primates, in particular lemurs, have long been known to communicate by smell. However, no bona fide primate pheromones have been identified. A recent study of ring-tailed lemurs offers some - disputed - candidate molecules for a male pheromone.

Reproducible research into human chemical communication by cues and pheromones: learning from psychology's renaissance.

Despite the lack of evidence that the 'putative human pheromones' androstadienone and estratetraenol ever were pheromones, almost 60 studies have claimed 'significant' results. These are quite possibly false positives and can be best seen as potential examples of the 'reproducibility crisis', sadly common in the rest of the life and biomedical sciences, which has many instances of whole fields based on false positives. Experiments on the effects of olfactory cues on human behaviour are also at risk of false positives because they look for subtle effects but use small sample sizes. Research on human chemical communication, much of it falling within psychology, would benefit from vigorously adopting the proposals made by psychologists to enable better, more reliable science, with an emphasis on enhancing reproducibility. A key change is the adoption of study pre-registration and/or Registered Reports which will also reduce publication bias. As we are mammals, and chemical communication is important to other mammals, it is likely that chemical cues are important in our behaviour and that humans may have pheromones, but new approaches will be needed to reliably demonstrate them. This article is part of the Theo Murphy meeting issue 'Olfactory communication in humans'.

Pheromones.

The reality of invisible chemical signals, pheromones, between members of the same species was recognized long before they could be identified. Charles Darwin proposed that the breeding season sexual smells of male crocodiles, goats and other animals, too, could have evolved by sexual selection of the smelliest males through female choice. But it's not just sex. We now know that pheromones are used by species all across the animal kingdom, in every habitat, and in a wide range of biological contexts, from trail, alarm, and queen pheromones in social insects to the mammary pheromone produced by mother rabbits. Pheromones have provided fascinating examples of signal evolution. In some model organisms, such as moths, Drosophila, Caenorhabditis elegans, and Mus musculus, a complete signaling system can be genetically dissected, from the enzymes producing pheromones, perception by chemosensory receptors, through to the neural circuits processing the signals.

The search for human pheromones: the lost decades and the necessity of returning to first principles.

As humans are mammals, it is possible, perhaps even probable, that we have pheromones. However, there is no robust bioassay-led evidence for the widely published claims that four steroid molecules are human pheromones: androstenone, androstenol, androstadienone and estratetraenol. In the absence of sound reasons to test the molecules, positive results in studies need to be treated with scepticism as these are highly likely to be false positives. Common problems include small sample sizes, an overestimate of effect size (as no effect can be expected), positive publication bias and lack of replication. Instead, if we are to find human pheromones, we need to treat ourselves as if we were a newly discovered mammal, and use the rigorous methods already proven successful in pheromone research on other species. Establishing a pheromone relies on demonstration of an odour-mediated behavioural or physiological response, identification and synthesis of the bioactive molecule(s), followed by bioassay confirmation of activity. Likely sources include our sebaceous glands. Comparison of secretions from adult and pre-pubertal humans may highlight potential molecules involved in sexual behaviour. One of the most promising human pheromone leads is a nipple secretion from the areola glands produced by all lactating mothers, which stimulates suckling by any baby not just their own.

Pheromones and signature mixtures: defining species-wide signals and variable cues for identity in both invertebrates and vertebrates.

Pheromones have been found in species in almost every part of the animal kingdom, including mammals. Pheromones (a molecule or defined combination of molecules) are species-wide signals which elicit innate responses (though responses can be conditional on development as well as context, experience, and internal state). In contrast, signature mixtures, in invertebrates and vertebrates, are variable subsets of molecules of an animal's chemical profile which are learnt by other animals, allowing them to distinguish individuals or colonies. All signature mixtures, and almost all pheromones, whatever the size of molecules, are detected by olfaction (as defined by receptor families and glomerular processing), in mammals by the main olfactory system or vomeronasal system or both. There is convergence on a glomerular organization of olfaction. The processing of all signature mixtures, and most pheromones, is combinatorial across a number of glomeruli, even for some sex pheromones which appear to have 'labeled lines'. Narrowly specific pheromone receptors are found, but are not a prerequisite for a molecule to be a pheromone. A small minority of pheromones act directly on target tissues (allohormone pheromones) or are detected by non-glomerular chemoreceptors, such as taste. The proposed definitions for pheromone and signature mixture are based on the heuristic value of separating these kinds of chemical information. In contrast to a species-wide pheromone, there is no single signature mixture to find, as signature mixtures are a 'receiver-side' phenomenon and it is the differences in signature mixtures which allow animals to distinguish each other.

Are vectors able to learn about their hosts? A case study with Aedes aegypti mosquitoes.

The way in which vectors distribute themselves amongst their hosts has important epidemiological consequences. While the role played by active host choice is largely unquestioned, current knowledge relates mostly to the innate response of vectors towards stimuli signalling the presence or quality of their hosts. Many of those cues, however, can be unpredictable, and therefore prevent the incorporation of the appropriate response into the vector's behavioural repertoire unless some sort of associative learning is possible. We performed a wide range of laboratory experiments to test the learning abilities of the mosquito, Aedes aegypti. Mosquitoes were exposed to choice procedures in (1) an olfactomenter and (2) a 'visual arena'. Our goal was to determine whether the mosquitoes were able to associate unconditional stimuli (blood feeding, human breath, vibration and electrical shock) with particular odours (citral, carvone, citronella oil and eugenol) and visual patterns (horizontal or vertical black bars) to which they had been previously observed to be responsive. We found no evidence supporting the hypothesis that associative learning abilities are present in adult Ae. aegypti. We discuss the possibilities that the assays employed were either inappropriate or insufficient to detect associative learning, or that associative learning is not possible in this species.

Are vectors able to learn about their hosts? A case study with Aedes aegypti mosquitoes

The way in which vectors distribute themselves amongst their hosts has important epidemiological consequences. While the role played by active host choice is largely unquestioned, current knowledge relates mostly to the innate response of vectors towards stimuli signalling the presence or quality of their hosts. Many of those cues, however, can be unpredictable, and therefore prevent the incorporation of the appropriate response into the vector's behavioural repertoire unless some sort of associative learning is possible. We performed a wide range of laboratory experiments to test the learning abilities of the mosquito, Aedes aegypti. Mosquitoes were exposed to choice procedures in (1) an olfactomenter and (2) a 'visual arena'. Our goal was to determine whether the mosquitoes were able to associate unconditional stimuli (blood feeding, human breath, vibration and electrical shock) with particular odours (citral, carvone, citronella oil and eugenol) and visual patterns (horizontal or vertical black bars) to which they had been previously observed to be responsive. We found no evidence supporting the hypothesis that associative learning abilities are present in adult Ae. aegypti. We discuss the possibilities that the assays employed were either inappropriate or insufficient to detect associative learning, or that associative learning is not possible in this species