Food for Sex in Bats Revealed as Producer Males Reproduce with Scrounging Females

Hippocampal representation during collective spatial behaviour in bats

Social animals live and move through spaces shaped by the presence, motion and sensory cues of multiple other individuals1-6. Neural activity in the hippocampus is known to reflect spatial behaviour7-9 yet its study is lacking in such dynamic group settings, which are ubiquitous in natural environments. Here we studied hippocampal activity in groups of bats engaged in collective spatial behaviour. We find that, under spontaneous conditions, a robust spatial structure emerges at the group level whereby behaviour is anchored to specific locations, movement patterns and individual social preferences. Using wireless electrophysiological recordings from both stationary and flying bats, we find that many hippocampal neurons are tuned to key features of group dynamics. These include the presence or absence of a conspecific, but not typically of an object, at landing sites, shared spatial locations, individual identities and sensory signals that are broadcasted in the group setting. Finally, using wireless calcium imaging, we find that social responses are anatomically distributed and robustly represented at the population level. Combined, our findings reveal that hippocampal activity contains a rich representation of naturally emerging spatial behaviours in animal groups that could in turn support the complex feat of collective behaviour.

Male cooperation improves their own and kin-group productivity in a group-foraging spider

Cooperation should only evolve if the direct and/or indirect benefits exceed the costs. Hence, cooperators are expected to generate selective benefits for themselves and the kin-group while defectors will impose costs. The subsocial spider, Australomisidia ergandros, shows consistent cooperation and defection tactics while foraging. Cooperative individuals are consistently likely to share prey with other group members whereas defector spiders rarely share the prey they acquired. Here, we assess costs and benefits of cooperation, and the causal determinants behind cooperative and defective phenotypes. We constructed experimental kin-colonies of A. ergandros composed of pure cooperative or defector foragers and show that pure cooperative groups had higher hunting success as they acquired prey more quickly with greater joint participation than pure defector groups. Importantly, defectors suffered higher mortality than cooperators and lost considerable weight. A social network approach using subadult spiders revealed that foraging tactic is sex dependent with males cooperating more frequently than females. Our results provide a rare empirical demonstration of sex-specific male cooperation that confer individual and kin-group benefits.

Re-examining extreme sleep duration in bats: implications for sleep phylogeny, ecology, and function

Bats, quoted as sleeping for up to 20 h a day, are an often used example of extreme sleep duration amongst mammals. Given that duration has historically been one of the primary metrics featured in comparative studies of sleep, it is important that species specific sleep durations are well founded. Here, we re-examined the evidence for the characterization of bats as extreme sleepers and discuss whether it provides a useful representation of the sleep behavior of Chiroptera. Although there are a wealth of activity data to suggest that the diurnal cycle of bats is dominated by rest, estimates of sleep time generated from electrophysiological analyses suggest considerable interspecific variation, ranging from 83% to a more moderate 61% of the 24 h day spent asleep. Temperature-dependent changes in the duration and electroencephalographic profile of sleep suggest that bats represent a unique model for investigating the relationship between sleep and torpor. Further sources of intra-specific variation in sleep duration, including the impact of artificial laboratory environments and sleep intensity, remain unexplored. Future studies conducted in naturalistic environments, using larger sample sizes and relying on a pre-determined set of defining criteria will undoubtedly provide novel insights into sleep in bats and other species.

Cortical representation of group social communication in bats

Social interactions occur in group settings and are mediated by communication signals that are exchanged between individuals, often using vocalizations. The neural representation of group social communication remains largely unexplored. We conducted simultaneous wireless electrophysiological recordings from the frontal cortices of groups of Egyptian fruit bats engaged in both spontaneous and task-induced vocal interactions. We found that the activity of single neurons distinguished between vocalizations produced by self and by others, as well as among specific individuals. Coordinated neural activity among group members exhibited stable bidirectional interbrain correlation patterns specific to spontaneous communicative interactions. Tracking social and spatial arrangements within a group revealed a relationship between social preferences and intra- and interbrain activity patterns. Combined, these findings reveal a dedicated neural repertoire for group social communication within and across the brains of freely communicating groups of bats.

Fruit bats adjust their foraging strategies to urban environments to diversify their diet

Background

Urbanization is one of the most influential processes on our globe, putting a great number of species under threat. Some species learn to cope with urbanization, and a few even benefit from it, but we are only starting to understand how they do so. In this study, we GPS tracked Egyptian fruit bats from urban and rural populations to compare their movement and foraging in urban and rural environments. Because fruit trees are distributed differently in these two environments, with a higher diversity in urban environments, we hypothesized that foraging strategies will differ too.

Results

When foraging in urban environments, bats were much more exploratory than when foraging in rural environments, visiting more sites per hour and switching foraging sites more often on consecutive nights. By doing so, bats foraging in settlements diversified their diet in comparison to rural bats, as was also evident from their choice to often switch fruit species. Interestingly, the location of the roost did not dictate the foraging grounds, and we found that many bats choose to roost in the countryside but nightly commute to and forage in urban environments.

Conclusions

Bats are unique among small mammals in their ability to move far rapidly. Our study is an excellent example of how animals adjust to environmental changes, and it shows how such mobile mammals might exploit the new urban fragmented environment that is taking over our landscape.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12915-021-01060-x.

Sick bats stay home alone: fruit bats practice social distancing when faced with an immunological challenge

Along with its many advantages, social roosting imposes a major risk of pathogen transmission. How social animals reduce this risk is poorly documented. We used lipopolysaccharide challenge to imitate bacterial infection in both a captive and a free‐living colony of an extremely social, long‐lived mammal—the Egyptian fruit bat. We monitored behavioral and physiological responses using an arsenal of methods, including onboard GPS to track foraging, acceleration sensors to monitor movement, infrared video to record social behavior, and blood samples to measure immune markers. Sick‐like (immune‐challenged) bats exhibited an increased immune response, as well as classic illness symptoms, including fever, weight loss, anorexia, and lethargy. Notably, the bats also exhibited behaviors that would reduce pathogen transfer. They perched alone and appeared to voluntarily isolate themselves from the group by leaving the social cluster, which is extremely atypical for this species. The sick‐like individuals in the open colony ceased foraging outdoors for at least two nights, thus reducing transmission to neighboring colonies. Together, these sickness behaviors demonstrate a strong, integrative immune response that promotes recovery of infected individuals while reducing pathogen transmission inside and outside the roost, including spillover events to other species, such as humans.

Effect of group size on producer-scrounger strategies of Wistar rats

In a collective foraging situation, we assessed the distribution of search responses of Wistar rats relative to the size of the group. For both, small and large groups, the number of production opportunities per capita was equal. Foraging strategies were classified as either production (opening gates with food) or scrounging (following conspecifics). Small groups showed a higher proportion of producers than large groups and required less time to deplete the food. The proportion of producing and scrounging responses yields to equilibrium between their payoffs. Producing and scrounging were highly correlated with different prior responses. Also, the relative frequency of producing and scrounging associated activities correlated with the time spent consuming food procured by each activity. It is possible that a simple outcome-strategy feedback mechanism mediates the choice of prior activities and procurement responses.

Decision making in foraging bats

Foraging is a complex and cognitively demanding behavior. Although it is often regarded as a mundane task, foraging requires the continuous weighting and integration of many sources of information with varying levels of credence. Bats are extremely diverse in their ecology and behavior, and thus demonstrate a wide variety of foraging strategies. In this review, we examine the different factors influencing the decision process of bats during foraging. Technological developments of recent years will soon enable real-time tracking of environmental conditions, of the position and quality of food items, the location of conspecifics, and the bat's movement history. Monitoring these variables alongside the continuous movement of the bat will facilitate the testing of different decision-making theories such as the use of reinforcement learning in wild free ranging bats and other animals.