Roosts as information centres: social learning of food preferences in bats

Cheerful tails: Delving into positive emotional contagion

This review delves into the phenomenon of positive emotional contagion (PEC) in rodents, an area that remains relatively understudied compared to the well-explored realm of negative emotions such as fear or pain. Rodents exhibit clear preferences for individuals expressing positive emotions over neutral counterparts, underscoring the importance of detecting and responding to positive emotional signals from others. We thoroughly examine the adaptive function of PEC, highlighting its pivotal role in social learning and environmental adaptation. The developmental aspect of the ability to interpret positive emotions is explored, intricately linked to maternal care and social interactions, with oxytocin playing a central role in these processes. We discuss the potential involvement of the reward system and draw attention to persisting gaps in our understanding of the neural mechanisms governing PEC. Presenting a comprehensive overview of the existing literature, we focus on food-related protocols such as the Social Transmission of Food Preferences paradigm and tickling behaviour. Our review emphasizes the pressing need for further research to address lingering questions and advance our comprehension of positive emotional contagion.

Socioecological drivers of injuries in female and male rhesus macaques (Macaca mulatta)

Competition over access to resources, such as food and mates, is believed to be one of the major costs associated with group living. Two socioecological factors suggested to predict the intensity of competition are group size and the relative abundance of sexually active individuals. However, empirical evidence linking these factors to injuries and survival costs is scarce. Here, we leveraged 10 years of data from free-ranging rhesus macaques where injuries inflicted by conspecifics are associated with a high mortality risk. We tested if group size and adult sex ratio predicted the occurrence of injuries and used data on physical aggression to contextualise these results. We found that males were less likely to be injured when living in larger groups, potentially due to advantages in intergroup encounters. Females, instead, had higher injury risk when living in larger groups but this was not explained by within-group aggression among females. Further, male-biased sex ratios predicted a weak increase in injury risk in females and were positively related to male-female aggression, indicating that male coercion during mating competition may be a cause of injuries in females. Overall, our results provide insights into sex differences in the fitness-related costs of competition and empirical evidence for long-standing predictions on the evolution of group living.

Social information facilitates learning about novel food sources in adult flower-visiting bats

Incorporating novel food sources into their diet is crucial for animals in changing environments. Although the utilization of novel food sources can be learned individually, learning socially from experienced conspecifics may facilitate this task and enable a transmission of foraging-related innovations across a population. In anthropogenically modified habitats, bats (Mammalia: Chiroptera) frequently adapt their feeding strategy to novel food sources, and corresponding social learning processes have been experimentally demonstrated in frugivorous and animalivorous species. However, comparable experiments are lacking for nectarivorous flower-visiting bats, even though their utilization of novel food sources in anthropogenically altered habitats is often observed and even discussed as the reason why bats are able to live in some areas. In the present study, we investigated whether adult flower-visiting bats may benefit from social information when learning about a novel food source. We conducted a demonstrator-observer dyad with wild Pallas' long-tongued bats (Glossophaga soricina; Phyllostomidae: Glossophaginae) and hypothesized that naïve individuals would learn to exploit a novel food source faster when accompanied by an experienced demonstrator bat. Our results support this hypothesis and demonstrate flower-visiting bats to be capable of using social information to expand their dietary repertoire.

Interaction time with conspecifics induces food preference or aversion in the wild Algerian mouse

The social transmission of a novel food preference can avoid unnecessary costs arising from tasting nonedible foods. This type of social learning has been demonstrated in laboratory rats and mice. However, among wild animals, there may be several constraints that make it less effective. Using wild Algerian mice (Mus spretus) tested in the laboratory, we demonstrate that a preference for a novel food can be transmitted between Observer and Demonstrator individuals and that it is maintained for at least 30 days. However, only half of the Observers acquired a preference for the same food as the Demonstrators, and only when the duration of oronasal investigation was above a certain threshold (≥122 s); below this threshold (<122 s), Observers acquired a preference for the alternative food offered, which was maintained for a shorter time. Sex, size, and identity of individuals did not influence the transmission of social information. The results show that different interaction times will result in animals copying or avoiding the food choices of others. This suggests that the transmission of social information among wild animals is complex and probably influenced by many factors (e.g., dominance, familiarity, and health condition), ultimately conditioning the type of interaction between individuals and its outcome. Testing wild animals and the ecological and social constraints they face is, therefore, an important step in our understanding of how effectively social information is transmitted in nature.

Continuous low-intensity predation by owls (Strix aluco) on bats (Nyctalus lasiopterus) in Spain and the potential effect on bat colony stability

Owls prey on bats, but information on owl predation is scarce, its impact on bat mortality is unclear, and reports on behavioural responses, including roost-switching and fission-fusion behaviour, are equivocal. To study the link between owl predation and anti-predator behaviour in bats, we evaluated seven months of video recordings at roosts and the behaviour of 51 passive integrated transponder (PIT)-tagged bats and bats without tags in a geographically isolated colony of greater noctule bats (Nyctalus lasiopterus) in Spain. We found the tawny owl Strix aluco to almost continuously hunt N. lasiopterus, from perches and on the wing, well after the bats emerged at dusk and when they returned to their roosts. We recorded 39 unsuccessful and three successful attacks. Nonetheless, we found no evidence that owl predation modifies bat behaviour. While the bats constituted only a very small proportion of the owls' diet, owl predation accounted for an estimated 30-40% of bat mortality, which may have a significant impact on small, local or isolated bat populations, in particular, and thereby shape regional bat distributions. We hypothesize that low roost availability may also affect the bats' potential response to predation, which could lead to natural predation having an excessive impact on bat populations.

A conceptual framework to predict social information use based on food ephemerality and individual resource requirements

Environmental variability poses a range of challenges to foraging animals trying to meet their energetic needs. Where food patches are unpredictable but shareable, animals can use social information to locate patches more efficiently or reliably. However, resource unpredictability can be heterogeneous and complex. The behavioural strategies animals employ to exploit such resources also vary, particularly if, when, and where animals use available social information. We reviewed the literature on social information use by foraging animals and developed a novel framework that integrates four elements - (1) food resource persistence; (2) the relative value of social information use; (3) behavioural context (opportunistic or coordinated); and (4) location of social information use - to predict and characterize four strategies of social information use - (1) local enhancement; (2) group facilitation; (3) following; and (4) recruitment. We validated our framework by systematically reviewing the growing empirical literature on social foraging in bats, an ideal model taxon because they exhibit extreme diversity in ecological niche and experience low predation risk while foraging but function at high energy expenditures, which selects for efficient foraging behaviours. Our framework's predictions agreed with the observed natural behaviour of bats and identified key knowledge gaps for future studies. Recent advancements in technology, methods, and analysis will facilitate additional studies in bats and other taxa to further test the framework and our conception of the ecological and evolutionary forces driving social information use. Understanding the links between food distribution, social information use, and foraging behaviour will help elucidate social interactions, group structure, and the evolution of sociality for species across the animal kingdom.

Demographic characteristics shape patterns of dawn swarming during roost switching in tree-dwelling Daubenton's bat

Frequent roost switching in fission–fusion societies of tree-dwelling bats is closely associated with swarming behaviour entailing ritualised night-time displays around the roost tree and/or at the roost entrance to signal its actual location, particularly immediately prior to sunrise. However, effects of demographic characteristics of individuals in this social behaviour remain unanswered. Using passive integrated transponders (PIT) and automatic readers, we recorded swarming activity of members of a Daubenton’s bat (Myotis daubentonii) maternity colony in the vicinity of their roosts. In total, 59,622 activity events of 281 PIT-tagged individuals were recorded on ten monitored roosts during three summer seasons. We found a gradual increase of swarming activity from midnight to sunrise in old adult females, whereas young females and juveniles primarily swarmed later at dawn. We attribute this difference to the learning status of younger bats, which are not yet able to perform a defined pattern of swarming activity, whereas older bats likely take a more active role in signalling the position of the roost. Old males exhibited the least swarming activity at maternity roosts, which mostly occurred between crepuscular periods, presumably due to their solitary lives. A negative correlation between genetic distance and swarming activity suggests an important role of kinship in the formation of the maternity colony as well as group cohesion during roost switching.

Sensory and Cognitive Ecology of Bats

We see stunning morphological diversity across the animal world. Less conspicuous but equally fascinating are the sensory and cognitive adaptations that determine animals’ interactions with their environments and each other. We discuss the development of the fields of sensory and cognitive ecology and the importance of integrating these fields to understand the evolution of adaptive behaviors. Bats, with their extraordinarily high ecological diversity, are ideal animals for this purpose. An explosion in recent research allows for better understanding of the molecular, genetic, neural, and behavioral bases for sensory ecology and cognition in bats. We give examples of studies that illuminate connections between sensory and cognitive features of information filtering, evolutionary trade-offs in sensory and cognitive processing, and multimodal sensing and integration. By investigating the selective pressures underlying information acquisition, processing, and use in bats, we aim to illuminate patterns and processes driving sensory and cognitive evolution.

Mixed-species groups in bats: non-random roost associations and roost selection in neotropical understory bats

BACKGROUND

Mixed-species groups in animals have been shown to confer antipredator, foraging and other benefits to their members that may provide selective advantages. In most cases, however, it is unclear whether functional benefits are a principal driver of heterospecific groups, or whether groups simply result from simultaneous exploitation of common resources. Mixed-species groups that form independently of environmental conditions may, however, evidence direct benefits of species associations. Bats are among the most gregarious mammals, with sometimes thousands of individuals of various species roosting communally. Despite numerous potential functional benefits of such mixed-species roosting groups, interspecific attraction has never been shown. To explore alternative explanations for mixed-species roosting, we studied roost selection in a speciose neotropical understory bat community in lowland rainforest in Costa Rica. Long term roost data were recorded over 10 years in a total of 133 roosts comprising both natural roosts and structurally uniform artificial roosts. We modelled bat roost occupancy and abundance in each roost type and in forest and pasture habitats to quantify the effects of roost- and environmental variability.

RESULTS

We found that bat species presence in natural roosts is predictable from habitat and structural roost parameters, but that the presence and abundance of other bat species further modifies roost choice. One third of the 12 study species were found to actively associate with selected other bat species in roosts (e.g. Glossophaga commissarisi with Carollia sowelli). Other species did not engage in communal roosting, which in some cases indicates a role for negative interspecific interactions, such as roost competition.

CONCLUSIONS

Mixed-species roosting may provide thermoregulatory benefits, reduce intraspecific competition and promote interspecific information transfer, and hence some heterospecific associations may be selected for in bats. Overall, our study contributes to an improved understanding of the array of factors that shape diverse tropical bat communities and drive the dynamics of heterospecific grouping in mammals more generally.

Selective Gene Loss of Visual and Olfactory Guanylyl Cyclase Genes Following the Two Rounds of Vertebrate-Specific Whole-Genome Duplications

Photoreceptors convey visual information and come in two flavors; dim-light and bright-light dedicated rod and cones. Both cell types feature highly specialized phototransduction cascades that convert photonic energy into intracellular signals. Although a substantial amount of phototransduction gene ohnologs are expressed either in rods or cones, visual guanylyl cyclases (GCs) involved in the calcium (Ca²⁺) dependent feedback regulation of phototransduction are neither rod nor cone specific. The co-existence of visual GCs in both photoreceptor types suggests that specialization of these ohnologs occurred despite their overlapping expression.

Here, we analyze gene retention and inactivation patterns of vertebrate visual and closely related olfactory GCs following two rounds (2R) of vertebrate-specific whole-genome duplication events (2R WGD). Although eutherians generally use two visual and one olfactory GC, independent inactivation occurred in some lineages. Sauropsids (birds, lizards, snakes, turtles, and crocodiles) generally have only one visual GC (GC-E). Additionally, turtles (testodes) also lost the olfactory GC (GC-D). Pseudogenization in mammals occurred in specific species/families likely according to functional needs (i.e., many species with reduced vision only have GC-E). Likewise, some species not relying on scent marks lack GC-D, the olfactory GC enzyme. Interestingly, in the case of fish, no species can be found with fewer than three (two visual and one olfactory) genes and the teleost-specific 3R WGD can increase this number to up to five. This suggests that vision in fish now requires at least two visual GCs.

Olfactory learning and memory in the greater short-nosed fruit bat Cynopterus sphinx: the influence of conspecifics distress calls

This study was designed to test whether Cynopterus sphinx distress calls influence olfactory learning and memory in conspecifics. Bats were exposed to distress calls/playbacks (PBs) of distress calls/modified calls and were then trained to novel odors. Bats exposed to distress calls/PBs made significantly fewer feeding attempts and bouts of PBs exposed to modified calls, which significantly induced the expression of c-Fos in the caudomedial neostriatum (NCM) and the amygdala compared to bats exposed to modified calls and trained controls. However, the expression of c-Fos in the hippocampus was not significantly different between the experimental groups. Further, protein phosphatase-1 (PP-1) expression was significantly lower, and the expression levels of E1A homologue of CREB-binding protein (CBP) (P300), brain-derived neurotrophic factor (BDNF) and its tyrosine kinase B1 (TrkB1) receptor were significantly higher in the hippocampus of control/bats exposed to modified calls compared to distress calls/PBs of distress call-exposed bats. Exposure to the call possibly alters the reciprocal interaction between the amygdala and the hippocampus, accordingly regulating the expression levels of PP1, P300 and BDNF and its receptor TrkB1 following training to the novel odor. Thus, the learning and memory consolidation processes were disrupted and showed fewer feeding attempts and bouts. This model may be helpful for understanding the contributions of stressful social communications to human disorders.

Better together? How intergroup associations affect energy balance and feeding behavior in wild bonobos

Abstract

When the benefits of interacting with out-group members exceed the associated costs, social groups may be expected to be tolerant towards each other. However, in many species exhibiting intergroup tolerance, the nature of benefits gained from intergroup encounters remains unclear. We investigated the potential costs and benefits associated with intergroup associations in bonobos, a species with varying degrees of intergroup tolerance, by testing whether these associations conferred energetic benefits to participants under different socioecological contexts and whether the consequences of these associations substantially differed from within-group competition. We used measures of socioecological factors (fruit abundance and group size), feeding and ranging behaviors, and a physiological marker of energy balance (urinary c-peptide of insulin) collected over a 19-month period from two neighboring wild communities in the Kokolopori Bonobo Reserve, Democratic Republic of the Congo. We found that intergroup associations were not related to individuals’ energy balance, but they were related to variations in individuals’ ranging and feeding behavior. Specifically, bonobos traveled longer distances, visited larger fruit patches, and increased the time spent feeding on fruits on days they associated with the neighboring group. These adaptations in feeding behavior may be strategies to offset the energetic costs of increased travel distances. In the absence of obvious energetic benefits and with clear strategies employed to offset energetic costs, it is likely that intergroup associations in bonobos provide benefits unrelated to energy acquisition, such as social benefits. Our study sheds light on the potential incentives promoting social networks to extend beyond and across groups in a tolerant species.

Significance statement

Intergroup encounters can be energetically costly due to increased competition over resources. Yet, some species associate with out-group individuals for extended periods of time when the benefits of participating in these associations exceed the potential costs. Bonobos, a species exhibiting intergroup tolerance, modified their feeding behavior during intergroup associations by feeding on larger fruit patches and increasing their time spent feeding on fruits, likely to offset energetic costs of increased travel distances. As results, individuals’ energy balance was not related with intergroup associations. The employment of such strategies in addition to the absence of clear energetic benefits suggests that intergroup associations in bonobos provide social rather than ecological benefits.

Social structure and relatedness in the fringe-lipped bat (Trachops cirrhosus)

General insights into the causes and effects of social structure can be gained from comparative analyses across socially and ecologically diverse taxa, such as bats, but long-term data are lacking for most species. In the neotropical fringe-lipped bat, Trachops cirrhosus, social transmission of foraging behaviour is clearly demonstrated in captivity, yet its social structure in the wild remains unclear. Here, we used microsatellite-based estimates of relatedness and records of 157 individually marked adults from 106 roost captures over 6 years, to infer whether male and female T. cirrhosus have preferred co-roosting associations and whether such associations were influenced by relatedness. Using a null model that controlled for year and roosting location, we found that both male and female T. cirrhosus have preferred roosting partners, but that only females demonstrate kin-biased association. Most roosting groups (67%) contained multiple females with one or two reproductive males. Relatedness patterns and recapture records corroborate genetic evidence for female philopatry and male dispersal. Our study adds to growing evidence that many bats demonstrate preferred roosting associations, which has the potential to influence social information transfer.

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.

Beyond the group: how food, mates, and group size influence intergroup encounters in wild bonobos

In social-living animals, interactions between groups are frequently agonistic, but they can also be tolerant and even cooperative. Intergroup tolerance and cooperation are regarded as a crucial step in the formation of highly structured multilevel societies. Behavioral ecological theory suggests that intergroup tolerance and cooperation can emerge either when the costs of hostility outweigh the benefits of exclusive resource access or when both groups gain fitness benefits through their interactions. However, the factors promoting intergroup tolerance are still unclear due to the paucity of data on intergroup interactions in tolerant species. Here, we examine how social and ecological factors affect the onset and termination of intercommunity encounters in two neighboring communities of wild bonobos, a species exhibiting flexible patterns of intergroup interactions, at Kokolopori Bonobo Reserve, Democratic Republic of the Congo. We recorded the timing and location of intercommunity encounters and measured fruit abundance and distribution, groups’ social characteristics, and space-use dynamics over a 19-month period. We found that intercommunity tolerance was facilitated by a decrease in feeding competition, with high fruit abundance increasing the likelihood of communities to encounter, and high clumpiness of fruit patches increasing the probability to terminate encounters likely due to increased contest. In addition, the possibility for extra-community mating, as well as the potential benefits of more efficient foraging in less familiar areas, reduced the probability that the communities terminated encounters. By investigating the factors involved in shaping relationships across groups, this study contributes to our understanding of how animal sociality can extend beyond the group level.

Maternal mouth-to-mouth feeding behaviour in flower-visiting bats, but no experimental evidence for transmitted dietary preferences

In addition to breast milk, several mammals feed their offspring with primary food items. This provisioning can offer both energetic and informational benefits: young might use parentally provided food as a source of nutrients, but also as a valuable option to socially learn about adults' food. For bats, there are only very few and partially anecdotal reports of adults feeding their pups with primary food, and there is also a lack of information about social learning processes during ontogeny. In the present study, we provide experimental evidence that lactating flower-visiting bats (Glossophaga soricina) provide regurgitated nectar via mouth-to-mouth feeding behaviour to their pups. After licking at their mothers' slightly opened mouth, pups defecated a marker substance that was exclusively available in the mothers' nectar diet. We additionally investigated associated informational benefits by testing for a social transmission of dietary preferences. We experimentally induced a dietary preference for specifically flavoured nectars to mothers with non-volant pups. Subsequently, after pups became volant, we tested their dietary preferences in a choice experiment. However, we found no experimental evidence that pups adopted the preferences of their mothers.

Odour discrimination learning in the Indian greater short-nosed fruit bat (Cynopterus sphinx): differential expression of Egr-1, C-fos and PP-1 in the olfactory bulb, amygdala and hippocampus

Activity-dependent expression of immediate-early genes (IEGs) is induced by exposure to odour. The present study was designed to investigate whether there is differential expression of IEGs (Egr-1, C-fos) in the brain region mediating olfactory memory in the Indian greater short-nosed fruit bat, Cynopterus sphinx We assumed that differential expression of IEGs in different brain regions may orchestrate a preference odour (PO) and aversive odour (AO) memory in C. sphinx We used preferred (0.8% w/w cinnamon powder) and aversive (0.4% w/v citral) odour substances, with freshly prepared chopped apple, to assess the behavioural response and induction of IEGs in the olfactory bulb, hippocampus and amygdala. After experiencing PO and AO, the bats initially responded to both, later only engaging in feeding bouts in response to the PO food. The expression pattern of EGR-1 and c-Fos in the olfactory bulb, hippocampus and amygdala was similar at different time points (15, 30 and 60 min) following the response to PO, but was different for AO. The response to AO elevated the level of c-Fos expression within 30 min and reduced it at 60 min in both the olfactory bulb and the hippocampus, as opposed to the continuous increase noted in the amygdala. In addition, we tested whether an epigenetic mechanism involving protein phosphatase-1 (PP-1) acts on IEG expression. The observed PP-1 expression and the level of unmethylated/methylated promoter revealed that C-fos expression is possibly controlled by odour-mediated regulation of PP-1. These results in turn imply that the differential expression of C-fos in the hippocampus and amygdala may contribute to olfactory learning and memory in C. sphinx.

MiR-132 regulated olfactory bulb proteins linked to olfactory learning in greater short-nosed fruit bat Cynopterus sphinx

Earlier, we showed that micro RNA-132 (miR-132) regulate the immediate early genes (IEGs) in the olfactory bulb (OB) of fruit bat Cynopterus sphinx during olfactory learning. This study was designed to examine whether the miR-132 regulate other proteins in OB during olfactory learning. To test this, miR-132 anti-sense oligodeoxynucleotide (AS-ODN) was delivered to the OB and then trained to novel odor. The 2-dimensional gel electrophoresis analysis showed that inhibition of miR-132 altered olfactory training induced expression of 321 proteins. Further, liquid chromatography-mass spectrometry (LC-MS/MS) analysis reveals the identity of differently expressed proteins such as phosphoribosyl transferase domain containing protein (PRTFDC 1), Sorting nexin-8 (SNX8), Creatine kinase B-type (CKB) and Annexin A11 (ANX A11). Among them PRTFDC 1 showing 189 matching peptides with highest sequence coverage (67.0%) and protein-protein interaction analysis showed that PRTFDC 1 is a homolog of hypoxanthine phosphoribosyltransferase-1 (HPRT-1). Subsequent immunohistochemical analysis (IHC) showed that inhibition of miR-132 down-regulated HPRT expression in OB of C. sphinx. In addition, western blot analysis depicts that HPRT, serotonin transporter (SERT), N-methyl-d-asparate (NMDA) receptors (2A,B) were down-regulated, but not altered in OB of non-sense oligodeoxynucleotide (NS-ODN) infused groups. These analyses suggest that miR-132 regulates the process of olfactory learning and memory formation through SERT and NMDA receptors signalling, which is possibly associated with the PRTFDC1-HPRT interaction.

Social communication in bats

Bats represent one of the most diverse mammalian orders, not only in terms of species numbers, but also in their ecology and life histories. Many species are known to use ephemeral and/or unpredictable resources that require substantial investment to find and defend, and also engage in social interactions, thus requiring significant levels of social coordination. To accomplish these tasks, bats must be able to communicate; there is now substantial evidence that demonstrates the complexity of bat communication and the varied ways in which bats solve some of the problems associated with their unique life histories. However, while the study of communication in bats is rapidly growing, it still lags behind other taxa. Here we provide a comprehensive overview of communication in bats, from the reasons why they communicate to the diversity and application of different signal modalities. The most widespread form of communication is the transmission of a signaller's characteristics, such as species identity, sex, individual identity, group membership, social status and body condition, and because many species of bats can rely little on vision due to their nocturnal lifestyles, it is assumed that sound and olfaction are particularly important signalling modes. For example, research suggests that secretions from specialized glands, often in combination with urine and saliva, are responsible for species recognition in several species. These olfactory signals may also convey information about sex and colony membership. Olfaction may be used in combination with sound, particularly in species that emit constant frequency (CF) echolocation calls, to recognize conspecifics from heterospecifics, yet their simple structure and high frequency do not allow much information of individual identity to be conveyed over long distances. By contrast, social calls may encode a larger number of cues of individual identity, and their lower frequencies increase their range of detection. Social calls are also known to deter predators, repel competitors from foraging patches, attract group mates to roost sites, coordinate foraging activities, and are used during courtship. In addition to sound, visual displays such as wing flapping or hovering may be used during courtship, and swarming around roost sites may serve as a visual cue of roost location. However, visual communication in bats still remains a poorly studied signal modality. Finally, the most common form of tactile communication known in bats is social grooming, which may be used to signal reproductive condition, but also to facilitate and strengthen cooperative interactions. Overall, this review demonstrates the rapid advances made in the study of bat social communication during recent years, and also identifies topics that require further study, particularly those that may allow us to understand adaptation to rapidly changing environmental conditions.

Bats without borders: Predators learn novel prey cues from other predatory species

Learning from others allows individuals to adapt rapidly to environmental change. Although conspecifics tend to be reliable models, heterospecifics with similar resource requirements may be suitable surrogates when conspecifics are few or unfamiliar with recent changes in resource availability. We tested whether Trachops cirrhosus, a gleaning bat that localizes prey using their mating calls, can learn about novel prey from conspecifics and the sympatric bat Lophostoma silvicolum. Specifically, we compared the rate for naïve T. cirrhosus to learn an unfamiliar tone from either a trained conspecific or heterospecific alone through trial and error or through social facilitation. T. cirrhosus learned this novel cue from L. silvicolum as quickly as from conspecifics. This is the first demonstration of social learning of a novel acoustic cue in bats and suggests that heterospecific learning may occur in nature. We propose that auditory-based social learning may help bats learn about unfamiliar prey and facilitate their adaptive radiation.

Persistent producer-scrounger relationships in bats

Social foraging theory suggests that group-living animals gain from persistent social bonds, which lead to increased tolerance in competitive foraging and information sharing. Bats are among the most social mammals, often living in colonies of tens to thousands of individuals for dozens of years, yet little is known about their social foraging dynamics. We observed three captive bat colonies for over a year, quantifying >13,000 social foraging interactions. We found that individuals consistently used one of two foraging strategies, either producing (collecting) food themselves or scrounging it directly from the mouth of other individuals. Individual foraging types were consistent over at least 16 months except during the lactation period when females shifted toward producing. Scroungers intentionally selected whom to interact with when socially foraging, thus generating persistent nonrandom social relationships with two to three specific producers. These persistent producer-scrounger relationships seem to reduce aggression over time. Finally, scrounging was highly correlated with vigilance, and we hypothesize that vigilant-prone individuals turn to scrounging in the wild to mitigate the risk of landing on a potentially unsafe fruit tree. We find the bat colony to be a rich and dynamic social system, which can serve as a model to study the role that social foraging plays in the evolution of mammalian sociality. Our results highlight the importance of considering individual tendencies when exploring social behavior patterns of group-living animals. These tendencies further emphasize the necessity of studying social networks over time.

Are migratory behaviours of bats socially transmitted?

To migrate, animals rely on endogenous, genetically inherited programmes, or socially transmitted information about routes and behaviours, or a combination of the two. In long-lived animals with extended parental care, as in bats, migration tends to be socially transmitted rather than endogenous. For a young bat to learn migration via social transmission, they would need to follow an experienced individual, most likely one roosting nearby. Therefore, we predicted that bats travelling together originate from the same place. It is also likely that young bats would follow their mothers or other kin, so we predicted that bats travelling together are more closely related to each other than bats not travelling together. To test our predictions, we used microsatellite genotypes and stable isotope values of δ (13)C, δ (15)N and δ (2)H to analyse the relatedness and geographical origins of migrating hoary bats (Lasiurus cinereus/Aeorestes cinereus (Baird et al. 2015 J. Mammal. 96, 1255-1274 (doi:10.1093/jmammal/gyv135)); n = 133) and silver-haired bats (Lasionycteris noctivagans; n = 87) killed at wind turbines over two consecutive autumn migrations. Contrary to our predictions, there was no evidence that related dyads of hoary bats or silver-haired bats were killed on the same night more frequently than expected by chance, or that the number of days between the fatalities of dyad members was influenced by relatedness or latitude of origin. Our data suggest that these bats do not socially transmit migration routes and behaviours among close kin.

Learning where to feed: the use of social information in flower-visiting Pallas' long-tongued bats (Glossophaga soricina)

Social learning is a widespread phenomenon among vertebrates that influences various patterns of behaviour and is often reported with respect to foraging behaviour. The use of social information by foraging bats was documented in insectivorous, carnivorous and frugivorous species, but there are little data whether flower-visiting nectarivorous bats (Phyllostomidae: Glossophaginae) can acquire information about food from other individuals. In this study, we conducted an experiment with a demonstrator-observer paradigm to investigate whether flower-visiting Pallas' long-tongued bats (Glossophaga soricina) are able to socially learn novel flower positions via observation of, or interaction with, knowledgeable conspecifics. The results demonstrate that flower-visiting G. soricina are able to use social information for the location of novel flower positions and can thereby reduce energy-costly search efforts. This social transmission is explainable as a result of local enhancement; learning bats might rely on both visual and echo-acoustical perception and are likely to eavesdrop on auditory cues that are emitted by feeding conspecifics. We additionally tested the spatial memory capacity of former demonstrator bats when retrieving a learned flower position, and the results indicate that flower-visiting bats remember a learned flower position after several weeks.

Information use in colonial living

Despite the fact that many animals live in groups, there is still no clear consensus about the ecological or evolutionary mechanisms underlying colonial living. Recently, research has suggested that colonies may be important as sources of social information. The ready availability of information from conspecifics allows animals to make better decisions about avoiding predators, reducing brood parasitism, migratory phenology, mate choice, habitat choice and foraging. These choices can play a large part in the development and maintenance of colonies. Here we review the types of information provided by colonial animals and examine the different ways in which decision-making in colonies can be enhanced by social information. We discuss what roles information might take in the evolution, formation and maintenance of colonies. In the process, we illustrate that information use permeates all aspects of colonial living.

Niche-specific cognitive strategies: object memory interferes with spatial memory in the predatory bat Myotis nattereri

Related species with different diets are predicted to rely on different cognitive strategies: those best suited for locating available and appropriate foods. Here we tested two predictions of the niche-specific cognitive strategies hypothesis in bats, which suggests that predatory species should rely more on object memory than on spatial memory for finding food and that the opposite is true of frugivorous and nectivorous species. Specifically, we predicted that: (1) predatory bats would readily learn to associate shapes with palatable prey and (2) once bats had made such associations, these would interfere with their subsequent learning of a spatial memory task. We trained free-flying Myotis nattereri to approach palatable and unpalatable insect prey suspended below polystyrene objects. Experimentally naïve bats learned to associate different objects with palatable and unpalatable prey but performed no better than chance in a subsequent spatial memory experiment. Because experimental sequence was predicted to be of consequence, we introduced a second group of bats first to the spatial memory experiment. These bats learned to associate prey position with palatability. Control trials indicated that bats made their decisions based on information acquired through echolocation. Previous studies have shown that bat species that eat mainly nectar and fruit rely heavily on spatial memory, reflecting the relative consistency of distribution of fruit and nectar compared with insects. Our results support the niche-specific cognitive strategies hypothesis and suggest that for gleaning and clutter-resistant aerial hawking bats, learning to associate shape with food interferes with subsequent spatial memory learning.

When to approach novel prey cues? Social learning strategies in frog-eating bats

Animals can use different sources of information when making decisions. Foraging animals often have access to both self-acquired and socially acquired information about prey. The fringe-lipped bat, Trachops cirrhosus, hunts frogs by approaching the calls that frogs produce to attract mates. We examined how the reliability of self-acquired prey cues affects social learning of novel prey cues. We trained bats to associate an artificial acoustic cue (mobile phone ringtone) with food rewards. Bats were assigned to treatments in which the trained cue was either an unreliable indicator of reward (rewarded 50% of the presentations) or a reliable indicator (rewarded 100% of the presentations), and they were exposed to a conspecific tutor foraging on a reliable (rewarded 100%) novel cue or to the novel cue with no tutor. Bats whose trained cue was unreliable and who had a tutor were significantly more likely to preferentially approach the novel cue when compared with bats whose trained cue was reliable, and to bats that had no tutor. Reliability of self-acquired prey cues therefore affects social learning of novel prey cues by frog-eating bats. Examining when animals use social information to learn about novel prey is key to understanding the social transmission of foraging innovations.

Social learning within and across species: information transfer in mouse-eared bats

Social learning describes information transfer between individuals through observation or direct interaction. Bats can live and forage in large groups, sometimes comprising several species, and are thus well suited for investigations of both intraspecific and interspecific information transfer. Although social learning has been documented within several bat species, it has not been shown to occur between species. Furthermore, it is not fully understood what level of interaction between individuals is necessary for social learning in bats. We address these questions by comparing the efficiency of observation versus interaction in intraspecific social learning and by considering interspecific social learning in sympatric bat species. Observers learned from demonstrators to identify food sources using a light cue. We show that intraspecific social learning exists in the greater mouse-eared bat (Myotis myotis (Borkhausen, 1797)) and that direct interaction with a demonstrator more efficiently leads to information transfer than observational learning alone. We also found evidence for interspecific information transfer from M. myotis to the lesser mouse-eared bat (Myotis oxygnathus Monticelli, 1885). Additionally, we opportunistically retested one individual that we recaptured from the wild 1 year after initial learning and found long-term memory of the trained association. Our study adds to the understanding of learning, information transfer, and long-term memory in wild-living animals.

Social learning and traditions in animals: evidence, definitions, and relationship to human culture

The number of publications concerned with social learning in nonhuman animals has expanded dramatically in recent decades. In this article, recent literature addressing three issues that have been of particular concern to those with both an interest in social learning and a background in experimental psychology are reviewed: (1) the definition as well as (2) empirical investigation of the numerous behavioral processes that support social learning in animals, and (3) the relationship of the 'traditions' seen in animals to the 'culture' that is so important in shaping the development of behavioral repertoires in humans. WIREs Cogn Sci 2012 doi: 10.1002/wcs.1196 For further resources related to this article, please visit the WIREs website.

Egr-1 antisense oligodeoxynucleotide administration into the olfactory bulb impairs olfactory learning in the greater short-nosed fruit bat Cynopterus sphinx

Postsynaptic densities (PSDs) contain proteins that regulate synaptic transmission. We examined two important examples of these, calcium/calmodulin-dependent protein kinase II (CaMKII) and PSD-95, in regard to the functional role of early growth response gene-1 (egr-1) in regulation of olfactory learning in the greater short-nosed fruit bat Cynopterus sphinx (family Pteropodidae). To test whether activation of egr-1 in the olfactory bulb (OB) is required for olfactory memory of these bats, bilaterally canulated individuals were infused with antisense (AS) or non-sense (NS)-oligodeoxynucleotides (ODN) of egr-1, or with phosphate buffer saline (PBS), 2h before the olfactory training. Our results showed that behavioral training significantly up-regulates immediate early gene (IEG) EGR-1 and key synaptic proteins Synaptotagmin-1(SYT-1), CaMKII and PSD-95, and phosphorylation of CaMKII in the OB at the protein level per se. Subsequently, we observed that egr-1 antisense-ODN infusion in the OB impaired olfactory memory and down regulates the expression of CaMKII and PSD-95, and the phosphorylation of CaMKII but not SYT-1. In contrast, NS-ODN or PBS had no effect on the expression of the PSDs CaMKII or PSD-95, or on the phosphorylation of CaMKII. When the egr-1 NS-ODN was infused in the OB after training for the novel odor there was no effect on olfactory memory. These findings suggest that egr-1 control the activation of CaMKII and PSD-95 during the process of olfactory memory formation.

Social Learning of a Novel Foraging Task by Big Brown Bats (Eptesicus fuscus)

Acquiring information via observation of others can be an efficient way to respond to changing situations or learn skills, particularly for inexperienced individuals. Many bat species are gregarious, yet few studies have investigated their capacity for learning from conspecifics. We tested whether big brown bats (Eptesicus fuscus) can learn a novel foraging task by interacting with knowledgeable conspecifics. In experimental trials 11 naïve bats (7 juveniles, 4 adults) interacted freely with trained bats that were capturing tethered mealworms, while in control trials 11 naïve bats (7 juveniles, 4 adults) flew with untrained bats. Naïve bats were then assessed for their ability to capture tethered mealworms. While no bat in the control group learned the task, a significant number of experimental bats, including juveniles with little or no experience foraging, showed evidence of learning. Eighty-two per cent of experimental bats and 27% of control bats directed feeding buzzes (echolocation calls associated with prey capture) at the mealworm. Furthermore, seven experimental bats (64%) showed evidence of learning by attacking and/or capturing the mealworm, while no bat in the control group attacked or captured the prey. Analyses of high-speed stereo video recordings revealed increased interaction with demonstrators among bats attacking or capturing the mealworm. At the time they displayed evidence of learning, bats flew closer together during feeding buzzes than during other portions of trials. Our results demonstrate that social interaction with experienced bats, and listening to feeding buzzes in particular, may play an integral role in development of foraging skills in bats.

Role of olfactory bulb serotonin in olfactory learning in the greater short-nosed fruit bat, Cynopterus sphinx (Chiroptera: Pteropodidae)

The role of olfactory bulb (OB) serotonin [5-hydroxytryptamine (5-HT)] in olfactory learning and memory was tested in the greater short-nosed fruit bat, Cynopterus sphinx (family Pteropodidae). Graded concentrations (25, 40, and 60microg) of 5,7-dihydroxytryptamine (5,7-DHT) or saline were injected into the OB of bats one day before training to the novel odor. In a behavioral test, 5,7-DHT (60microg) injected bats made significantly fewer feeding attempts and bouts when compared to saline-injected bats during learning and in the memory test. Subsequent biochemical analysis showed that 5-HT level was effectively depleted in the OB of 5,7-DHT injected bats. To test odor-induced 5-HT mediated changes in 5-HT receptors and second messenger cascade in the OB, we examined the expression of 5-HT receptors and mitogen-activated protein kinase (MAPK)/Erk cascade after training to the novel odor. We found that odor stimulation up-regulated the expression of 5-HT(1A) receptor, Erk1 and Creb1 mRNA, and phosphorylation of ERK1 and CREB1. Odor stimulation failed to induce expression in 5-HT-depleted bats, which is similar to control bats and significantly low compared to saline-treated bats. Together these data revealed that the level of 5-HT in the OB may regulate olfactory learning and memory in C. sphinx through Erk and CREB.

Flower bats (Glossophaga soricina) and fruit bats (Carollia perspicillata) rely on spatial cues over shapes and scents when relocating food

Background

Natural selection can shape specific cognitive abilities and the extent to which a given species relies on various cues when learning associations between stimuli and rewards. Because the flower bat Glossophaga soricina feeds primarily on nectar, and the locations of nectar-producing flowers remain constant, G. soricina might be predisposed to learn to associate food with locations. Indeed, G. soricina has been observed to rely far more heavily on spatial cues than on shape cues when relocating food, and to learn poorly when shape alone provides a reliable cue to the presence of food.

Methodology/Principal Findings

Here we determined whether G. soricina would learn to use scent cues as indicators of the presence of food when such cues were also available. Nectar-producing plants fed upon by G. soricina often produce distinct, intense odors. We therefore expected G. soricina to relocate food sources using scent cues, particularly the flower-produced compound, dimethyl disulfide, which is attractive even to G. soricina with no previous experience of it. We also compared the learning of associations between cues and food sources by G. soricina with that of a related fruit-eating bat, Carollia perspicillata. We found that (1) G. soricina did not learn to associate scent cues, including dimethyl disulfide, with feeding sites when the previously rewarded spatial cues were also available, and (2) both the fruit-eating C. perspicillata and the flower-feeding G. soricina were significantly more reliant on spatial cues than associated sensory cues for relocating food.

Conclusions/Significance

These findings, taken together with past results, provide evidence of a powerful, experience-independent predilection of both species to rely on spatial cues when attempting to relocate food.