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To optimize fitness when facing predation, animals perform threat-sensitive predator avoidance whereby they match the magnitude of the antipredator response to the severity of the perceived threat. Injury-released chemical alarm cues are a reliable indicator of predation risk in aquatic organisms, triggering overt antipredator responses upon detection by conspecifics. Animals with threat sensitivity typically have graded responses to increasing concentrations of these cues which plateau when a maximal response is reached, however, this is undocumented in crayfish. Furthermore, most research currently uses alarm cue exposures consisting of one crushed crayfish diluted in 100–400 mL of water, while it could be ecologically relevant for them to respond to lower concentrations, especially given that predation events can consist of bites or lacerations which would release less alarm cues. The quantity of cue administered into the tank (exposure concentration) is also highly variable, making experimental comparisons difficult. In our study, we collected crayfish alarm cues by rinsing five cut sites (to mimic laceration wounds) and diluting the cues in 100 mL to 100 L of water. Over two experiments, we determined the antipredator response of crayfish exposed to one of five alarm cue concentrations or a water control. During these trials, 20 mL of the cues were administered into 10 L of water, thereby standardizing the test subject’s exposure to the cues. While we failed to find evidence of graded responses, we discovered that alarm cues elicited overt antipredator behaviour when diluted in up to 10 L of water, but this response was lost when cues were diluted in 100 L. Furthermore, this study is the first to successfully use frozen-thawed alarm cues in crayfish. These findings can help direct future research, providing information on the ecologically relevant range of chemical cues and improving welfare by reducing lab-animal sacrifice.

The partial pressure of CO 2 in the oceans has increased rapidly over the past century, driving ocean acidification and raising concern for the stability of marine ecosystems 1 – 3 . Coral reef fishes are predicted to be especially susceptible to end-of-century ocean acidification on the basis of several high-profile papers 4 , 5 that have reported profound behavioural and sensory impairments—for example, complete attraction to the chemical cues of predators under conditions of ocean acidification. Here, we comprehensively and transparently show that—in contrast to previous studies—end-of-century ocean acidification levels have negligible effects on important behaviours of coral reef fishes, such as the avoidance of chemical cues from predators, fish activity levels and behavioural lateralization (left–right turning preference). Using data simulations, we additionally show that the large effect sizes and small within-group variances that have been reported in several previous studies are highly improbable. Together, our findings indicate that the reported effects of ocean acidification on the behaviour of coral reef fishes are not reproducible, suggesting that behavioural perturbations will not be a major consequence for coral reef fishes in high CO 2 oceans. In contrast to previous studies, analyses now show that ocean acidification does not perturb important behaviours—such as the avoidance of chemical cues from predators—of coral reef fishes.

Persistent neural activity in cortical, hippocampal, and motor networks has been described as mediating working memory for transiently encountered stimuli 1 , 2 . Internal emotional states, such as fear, also persist following exposure to an inciting stimulus 3 , but it is unclear whether slow neural dynamics are involved in this process. Neurons in the dorsomedial and central subdivisions of the ventromedial hypothalamus (VMHdm/c) that express the nuclear receptor protein NR5A1 (also known as SF1) are necessary for defensive responses to predators in mice 4 – 7 . Optogenetic activation of these neurons, referred to here as VMHdm SF1 neurons, elicits defensive behaviours that outlast stimulation 5 , 8 , which suggests the induction of a persistent internal state of fear or anxiety. Here we show that in response to naturalistic threatening stimuli, VMHdm SF1 neurons in mice exhibit activity that lasts for many tens of seconds. This persistent activity was correlated with, and required for, persistent defensive behaviour in an open-field assay, and depended on neurotransmitter release from VMHdm SF1 neurons. Stimulation and calcium imaging in acute slices showed that there is local excitatory connectivity between VMHdm SF1 neurons. Microendoscopic calcium imaging of VMHdm SF1 neurons revealed that persistent activity at the population level reflects heterogeneous dynamics among individual cells. Unexpectedly, distinct but overlapping VMHdm SF1 subpopulations were persistently activated by different modalities of threatening stimulus. Computational modelling suggests that neither recurrent excitation nor slow-acting neuromodulators alone can account for persistent activity that maintains stimulus identity. Our results show that stimulus-specific slow neural dynamics in the hypothalamus, on a time scale orders of magnitude longer than that of working memory in the cortex 9 , 10 , contribute to a persistent emotional state. Persistent neural activity in the mouse hypothalamus encodes aversive emotional states related to specific threatening stimuli.

The appropriate selection of passive and active defensive behaviors in threatening situations is essential for survival. Previous studies have shown that passive defensive responses depend on activity of the central nucleus of the amygdala (CeA), whereas active ones primarily rely on the nucleus accumbens (NAc). However, the mechanisms underlying flexible switching between these two types of responses remain unknown. Here we show in mice that the paraventricular thalamus (PVT) mediates the selection of defensive behaviors through its interaction with the CeA and the NAc. We show that the PVT–CeA pathway drives conditioned freezing responses, whereas the PVT–NAc pathway is inhibited during freezing and, instead, signals active avoidance events. Optogenetic manipulations revealed that activity in the PVT–CeA or PVT–NAc pathway biases behavior toward the selection of passive or active defensive responses, respectively. These findings provide evidence that the PVT mediates flexible switching between opposing defensive behaviors. Ma et al. show that the PVT biases the selection of passive and active defensive behaviors via mostly segregated projections to the CeA and the NAc. Their results update current views on the role of the midline thalamus in fear-related behaviors.

Many prey species rely on publicly available personal and social information regarding local predation threats to assess risks and make context-appropriate behavioral decisions. However, in sexually dimorphic species, males and females are expected to differ in the perceived costs and/or benefits associated with predator avoidance decisions. Recent studies suggest that male Trinidadian guppies (Poecilia reticulata) show reduced or absent responses to acute personal information cues, placing them at greater risk of predation relative to females. Our goal here was to test the hypothesis that adult (reproductively active) male guppies rely on social information to limit potential costs associated with their lack of response to risky personal cues. Adult male guppies were exposed to personal chemosensory cues (either conspecific alarm cues (AC), a novel odor, or a water control) in the presence of a shoal of three females inside a holding container that allowed the transmission of visual but not chemical cues. At the same time, we exposed females to either risk from AC or no risk, resulting in the display of a range of female behavior, from calm to alarmed, available as social information for males. Alarmed females caused male fright activity to increase and male interest in females to decrease, regardless of the personal cue treatment. These results indicate that male guppies rely more on female information regarding predation risk than their own personal information, probably to balance trade-offs between reproduction and predator avoidance.

Flight, an active fear response to imminent threat, is dependent on the rapid risk assessment of sensory information processed by the cortex. The thalamic reticular nucleus (TRN) filters information between the cortex and the thalamus, but whether it participates in the regulation of flight behavior remains largely unknown. Here, we report that activation of parvalbumin-expressing neurons in the limbic TRN, but not those in the sensory TRN, mediates flight. Glutamatergic inputs from the cingulate cortex (Cg) selectively activate the limbic TRN, which in turn inhibits the intermediodorsal thalamic nucleus (IMD). Activation of this Cg→limbic TRN→IMD circuit results in inhibition of the IMD and produces flight behavior. Conversely, removal of inhibition onto the IMD results in more freezing and less flight, suggesting that the IMD may function as a pro-freeze center. Overall, these findings reveal a novel corticothalamic circuit through the TRN that controls the flight response.Dong, Wang et al. uncover a circuit linking Glu+cingulate inputs→PV+ neurons in the limbic thalamic reticular nucleus→intermediodorsal thalamic nucleus, and show that this cortico-intrathalamic circuit is a component of the fear circuitry and controls flight behavior in mice.

Termites are eusocial insects that live in large colonies made up of queens, kings, workers, and soldiers. Queens and kings start new colonies and continually reproduce. Workers are responsible for many crucial roles, including colony husbandry, foraging, and nest construction. Soldiers are adapted for colony defense, usually with large heads and mandibles to ward off predators, but their defensive adaptations prevent them from caring for themselves or performing tasks within the nest. The soldiers of some termite species participate in foraging, either directly by scouting food sources and recruiting workers, or indirectly by influencing worker foraging behavior through their presence. Colonies of the Formosan subterranean termite maintain relatively large soldier proportions compared to termites in their invasive range, but the potential soldier influence on foraging workers has not yet been studied. Since the soldiers of other termite species can influence food exploration, we hypothesized that soldier presence also influences foraging behavior in this species. We compared the exploratory behavior of foraging groups of 100 workers and either 0, 2, 10, or 30 soldiers to determine whether soldier concentration influenced tunnel complexity, tunnel speed, food location, or food collection. In the context of this study, soldier presence did not influence worker foraging behavior, which suggests that workers of the Formosan subterranean termite can maintain foraging efficiency regardless of fluctuations in soldier presence. Termites are eusocial insects that live in organized colonies consisting of reproductives, workers, and soldiers. Soldiers are specialized for defense but are expensive to maintain, as they are incapable of husbandry and must be fed and groomed by workers. The soldiers of several species influence foraging behavior by acting as scouts that initiate foraging or by mediating worker behavioral plasticity during food exploration. These behaviors imply that soldiers may play a keystone role in termite colony function, apart from defense. Subterranean termite workers tunnel through soil in search of food while accompanied by varying proportions of soldiers, depending on the species and colony conditions. Previous studies have shown that soldiers accelerate worker exploratory tunneling behavior in two Reticulitermes species, the colonies of which contain fewer than 2% soldiers. This effect, however, is unknown in other subterranean species with different soldier proportions. In this study, we examined the influence of soldiers on exploratory foraging behavior in the Formosan subterranean termite, Coptotermes formosanus Shiraki, which is an economically devastating invasive species that maintains a relatively high soldier proportion (about 10%). When 100 foraging workers were grouped with 0, 2, 10, or 30 soldiers in two-dimensional foraging arenas, we found no significant effect of soldiers on the tunnel length, branch pattern, food source interception, or food collected within 96 h. These results suggest that C. formosanus colonies maintain food exploration efficiency regardless of soldier proportion variation.

Background Social insect colonies routinely face large vertebrate predators, against which they need to mount a collective defence. To do so, honeybees use an alarm pheromone that recruits nearby bees into mass stinging of the perceived threat. This alarm pheromone is carried directly on the stinger; hence, its concentration builds up during the course of the attack. We investigate how bees react to different alarm pheromone concentrations and how this evolved response pattern leads to better coordination at the group level. Results We first present a dose-response curve to the alarm pheromone, obtained experimentally. This data reveals two phases in the bees’ response: initially, bees become more likely to sting as the alarm pheromone concentration increases, but aggressiveness drops back when very high concentrations are reached. Second, we apply Projective Simulation to model each bee as an artificial learning agent that relies on the pheromone concentration to decide whether to sting or not. Individuals are rewarded based on the collective performance, thus emulating natural selection in these complex societies. By also modelling predators in a detailed way, we are able to identify the main selection pressures that shaped the response pattern observed experimentally. In particular, the likelihood to sting in the absence of alarm pheromone (starting point of the dose-response curve) is inversely related to the rate of false alarms, such that bees in environments with low predator density are less likely to waste efforts responding to irrelevant stimuli. This is compensated for by a steep increase in aggressiveness when the alarm pheromone concentration starts rising. The later decay in aggressiveness may be explained as a curbing mechanism preventing worker loss. Conclusions Our work provides a detailed understanding of alarm pheromone responses in honeybees and sheds light on the selection pressures that brought them about. In addition, it establishes our approach as a powerful tool to explore how selection based on a collective outcome shapes individual responses, which remains a challenging issue in the field of evolutionary biology.

Most animals must defend themselves in order to survive. Defensive behaviour includes detecting predators or intruders, avoiding them by staying low-key or escaping or deterring them away by means of aggressive behaviour, i.e., attacking them. Responses vary across insect species, ranging from individual responses to coordinated group attacks in group-living species. Among different modalities of sensory perception, insects predominantly use the sense of smell to detect predators, intruders, and other threats. Furthermore, social insects, such as honeybees and ants, communicate about danger by means of alarm pheromones. In this review, we focus on how olfaction is put to use by insects in defensive behaviour. We review the knowledge of how chemical signals such as the alarm pheromone are processed in the insect brain. We further discuss future studies for understanding defensive behaviour and the role of olfaction.

Many prey species rely on publicly available personal and social information regarding local predation threats to assess risks and make context-appropriate behavioral decisions. However, in sexually dimorphic species, males and females are expected to differ in the perceived costs and/or benefits associated with predator avoidance decisions. Recent studies suggest that male Trinidadian guppies (Poecilia reticulata) show reduced or absent responses to acute personal information cues, placing them at greater risk of predation relative to females. Our goal here was to test the hypothesis that adult (reproductively active) male guppies rely on social information to limit potential costs associated with their lack of response to risky personal cues. Adult male guppies were exposed to personal chemosensory cues (either conspecific alarm cues (AC), a novel odor, or a water control) in the presence of a shoal of three females inside a holding container that allowed the transmission of visual but not chemical cues. At the same time, we exposed females to either risk from AC or no risk, resulting in the display of a range of female behavior, from calm to alarmed, available as social information for males. Alarmed females caused male fright activity to increase and male interest in females to decrease, regardless of the personal cue treatment. These results indicate that male guppies rely more on female information regarding predation risk than their own personal information, probably to balance trade-offs between reproduction and predator avoidance.