Brood Care Research Articles

Social immunity behaviour among ants infected by specialist and generalist fungi.

Social insects are distinguished by their lifestyle of living in groups with division of labour, cooperative brood care, and reproduction limited to a few colony members. Social insects often build large colonies with remarkable densities of highly related individuals and this can lead to an increased pathogen pressure. Our review focuses on interactions of ants with two important taxonomic groups of fungi infecting ants: Hypocreales (Ascomycota) and Entomophthorales (Entomophthoromycotina), and their different infection strategies, including host manipulation for optimal spore dispersal in the specialised ant pathogens. In social insects such as ants, resistance to pathogens is present at the colony level, with social immunity in addition to the individual resistance. We describe how ants use both organizational and behavioural defence strategies to combat fungal pathogens, with emphasis on highly specialised fungi from the genera Ophiocordyceps and Pandora.

RNA editing is abundant and correlates with task performance in a social bumblebee

Colonies of the bumblebee Bombus terrestris are characterized by wide phenotypic variability among genetically similar full-sister workers, suggesting a major role for epigenetic processes. Here, we report a high level of ADAR-mediated RNA editing in the bumblebee, despite the lack of an ADAR1-homolog. We identify 1.15 million unique genomic sites, and 164 recoding sites residing in 100 protein coding genes, including ion channels, transporters, and receptors predicted to affect brain function and behavior. Some edited sites are similarly edited in other insects, cephalopods and even mammals. The global editing level of protein coding and non-coding transcripts weakly correlates with task performance (brood care vs. foraging), but not affected by dominance rank or juvenile hormone known to influence physiology and behavior. Taken together, our findings show that brain editing levels are high in naturally behaving bees, and may be regulated by relatively short-term effects associated with brood care or foraging activities.

Parental incubation exchange in a territorial bird species involves sex-specific signalling

BackgroundEffective communication between sexual partners is essential for successful reproduction. Avian parents with biparental incubation need to know how to negotiate, when and who will incubate, and how to harmonize partner exchange at the nest. Although considerable effort has been dedicated to studies of incubation rhythms, few studies have investigated how behavioural signals serve to tighten cooperation between parents. Moreover, existing studies are almost exclusively restricted to species in which long distances between incubating and non-incubating parents prevent continuous communication during incubation. Thus, the most frequently described parental exchange system is a simple model characterized by the return of the non-incubating parent to the nest itself. Here, we propose more complex parental exchange behaviour in the Northern Lapwing (Vanellus vanellus), a territorial species capable of continuous partner communication during incubation and with a highly variable male contribution to incubation.ResultsNorthern Lapwing females regularly vocalized shortly before departing from the nest, while males mostly left the nest quietly. Responsiveness of the male to female vocalization, perhaps in combination with her flying away from the nest, helped to synchronize incubation care by increasing the probability of exchange, and also by shortening the exchange gaps. In contrast, a male-to-female exchange gap most often occurred after the male quietly flew away from the nest. The frequency of female vocal signalling was not correlated with the male incubation effort on a between-nest scale, but the highest probability of a female-to-male exchange occurred after vocal signalling by females with the most nest-attentive males. Conversely, lowered effort by females to vocalize in the night was accompanied by lower willingness of males to incubate.ConclusionsOur results suggest that (1) that the incubating parent can communicate with the non-incubating partner using sex-specific behavioural signals, and this helps to synchronize parental exchange on the nest, (2) this signalling may combine acoustic and visual cues, and (3) the efficiency of this signalling might influence the overall nest attendance. The presumption that the repertoire of behavioural signals during reproduction will be much more complex in territorial species that are capable of continuous communication between the partners during the incubation period should be further tested.

Ants in isolation: obstacles to testing worker responses to task stimuli outside of the colony context

In social insects, division of labor is commonly thought to be driven by differences among workers in their sensitivity, or response thresholds, to task-related stimuli. Despite the wide use of this mechanism throughout social insect research, actual empirical evidence for these thresholds is comparatively scarce. Here, we attempt to fill this empirical gap by testing individual task stimulus response thresholds, their consistency over time, and their relation to behavior in Temnothorax rugatulus ants. We also explored morphological differences in the antenna as one potential neural mechanism generating differences in sensitivity, and thus response threshold variation, across workers. Ants were exposed to different amounts of hungry brood, fungal spores, or sugar— stimuli that appear to drive brood care, grooming, and foraging behavior, respectively. Our measures of response thresholds were not repeatable across two trials for any of the three tested stimuli. In addition, responses to different stimulus intensities (possible response thresholds) were not associated with worker task allocation in the colony with the exception of brood care, in which case the results directly contradicted what the response threshold hypothesis predicts. Workers from different task groups also did not differ in their latency to respond to these stimuli or in the duration of their response. Sensilla density varied across workers but did not predict our measures of response thresholds to any of the tested stimuli. Though this is not what the response threshold hypothesis would have predicted, it is possible that testing ants in isolation may not accurately reflect their behavior in the colony, or that sensitivity to a task stimulus, alone, is not sufficient for driving division of labor. We suggest approaches to testing response thresholds that incorporate the roles of social context and competing task stimuli.

Compensatory and additive helper effects in the cooperatively breeding Seychelles warbler (Acrocephalus sechellensis).

In cooperatively breeding species, care provided by helpers may affect the dominant breeders’ investment trade‐offs between current and future reproduction. By negatively compensating for such additional care, breeders can reduce costs of reproduction and improve their own chances of survival. Alternatively, helper care can be additive to that of dominants, increasing the fledging fitness of the current brood. However, the influence helpers have on brood care may be affected by group size and territory quality. Therefore, the impact of helping needs to be disentangled from other factors determining offspring investment before conclusive inferences about the effect of help on additive and compensatory care can be made. We used 20 years of provisioning data to investigate the effect of helping on provisioning rates in the facultative cooperatively breeding Seychelles warbler Acrocephalus sechellensis. Our extensive dataset allowed us to statistically disentangle the effects of helper presence, living in larger groups and different food availability. We show compensatory and additive care (i.e., partial compensation) in response to helper provisioning. Helpers lightened the provisioning load of the dominant male and female and increased total provisioning to nestlings. This was irrespective of group size or territory quality (food availability). Moreover, our results illustrate sex‐specific variation in parental care over the course of the breeding event. We discriminate between temporal variation, group size, and territory quality processes affecting cooperative care and as such, gain further insight into the importance of these factors to the evolutionary maintenance of helping behavior.

Immunosenescence in honey bees (Apis mellifera L.) is caused by intrinsic senescence and behavioral physiology.

Young honey bee workers (0 to 2-3 weeks old) perform tasks inside the colony, including brood care (nursing), whereas older workers undergo foraging tasks during the next 3-4 weeks, when an intrinsic senescence program culminates in worker death. We hypothesized that foragers are less able to react to immune system stimulation than nurse bees and that this difference is due to an inefficient immune response in foragers. To test this hypothesis, we used an experimental design that allowed us to uncouple chronological age and behavior status (nursing/foraging). Worker bees from a normal age demography colony (where workers naturally transit from nursing to foraging tasks as they age) and of a single-cohort colony setup (composed of same-aged workers performing nursing or foraging tasks) were tested for survival and capability of activation of the immune system after bacterial injection. Expression of an antimicrobial peptide gene, defensin-1 (def-1), was used to assess immune system activation. We then checked whether the immune response includes changes in the expression of aging- and behavior-related genes, specifically vitellogenin (vg), juvenile hormone esterase (jhe), and insulin-like peptide-1 (ilp-1). We found a significant difference in survival rate between bees of different ages but carrying out the same tasks. Our results thus indicate that the bees' immune response is negatively affected by intrinsic senescence. Additionally, independent of age, foragers had a shorter lifespan than nurses after bacterial infection, although both were able to induce def-1 transcription. In the normal age demography colony, the immune system activation resulted in a reduction in the expression of vg, jhe and ilp-1 genes in foragers, but not in the nurse bees, demonstrating that age and behavior are both important influences on the bees' immune response. By disentangling the effects of age and behavior in the single-cohort colony, we found that vg, jhe and ilp-1 response to immune system stimulation was independent of behavior. Younger bees were able to mount a stronger immune response than older bees, thus highlighting age as an important factor for immunity. Taken together, our results provide new insights into how age and behavior affect the honey bee's immune response.

In a relationship: sister species in mixed colonies, with a description of new Chikunia species (Theridiidae)

Abstract Group-living behaviour is rare in spiders but has evolved repeatedly, yielding several species, some showing cooperation among close kin, and others living in colonies where each female builds its own web and is territorial. The most frequent origins of group living are seen in the cobweb spiders (Theridiidae) that commonly build three-dimensional webs and show extensive maternal care, both putatively pre-adaptive traits to spider sociality. A very unusual behaviour was recently discovered in the theridiid genus Chikunia, where two distinct but related species occur in mixed-species colonies with potentially indiscriminate brood care. These mixed colonies consist of Chikunia nigra and a newly discovered species. Here, we describe the new species, Chikunia bilde sp. nov., and summarize the unique biology of this species pair. We also place the origin of mixed-species group living in a phylogenetic context, firmly confirming the placement of Chikunia within the clade (lost colulus clade) previously characterized as containing a concentration of independent origins of group living. The two Chikunia studied here are sister species, representing a rare case of close genetic and behavioural interspecific relationship. We conclude that the loss of aggression that accompanies group living and social behaviour in cobweb spiders might help to explain the origin of mixed-species colonies.

First field evidence for alloparental egg care in cooperatively breeding fish

AbstractHelping behaviour in cooperative breeders has been intensively studied in many animal taxa, including arthropods, birds and mammals. In these highly social systems, helpers typically engage in brood care and the protection of dependent young. Such helping systems also exist in cooperatively breeding cichlid species of Lake Tanganyika. However, breeding in these species happens in clefts, narrow holes or shelters underneath stones. Therefore, direct brood care by breeders and helpers has thus far only been observed under artificial laboratory conditions. Under natural conditions, brood care behaviour has been estimated indirectly by determining the time spent in the breeding chamber, or by the number of visits to the breeding chamber. The reliability of such substitutes needs to be validated, for instance, by demonstrating alloparental egg care of helpers through direct observations in nature. Here, we describe direct egg care by a male helper of the cooperatively breeding cichlid Neolamprologus savoryi in the field. The helper inspected and cleaned the eggs and defended them against predators. By reconstructing the genetic relatedness using microsatellite markers, we show that the helper was the son of the breeding male, but unrelated to the breeding female. The genetic mother of the helper was defending a different territory next to the one where the helper showed alloparental egg care. This indicates that the helper had dispersed inside the male territory to assist another female to care for his half‐siblings. These results demonstrate alloparental egg care without reproductive share in a fish species under natural conditions, underlining that helping behaviour in cooperatively breeding fish has a strong non‐self‐serving component.

Challenging the safety and efficiency of homeopathy: Ignatia amara as an example, ants as models

Homeopathic treatments are considered by the vast majority of the scientific community as non-effective, apart from a well-documented placebo effect. Nevertheless, some experimental results raise questions about their efficiency, and numerous practitioners still consider homeopathy as an efficient alternative treatment instead of usual pharmaceutical drugs. Homeopathy is thus nowadays debated among the general public, practitioners and medical schools, and is still used by many patients in search for “natural” treatments. It is therefore relevant to bring information to feed this debate and to investigate the efficiency and safety of homeopathic drugs. We examined on ants, used as biological models, the effects of a homeopathic drug, Ignatia amara, advocated to ease symptoms of stress. We tested the effects of thus drug on ant’s ethological and physiological traits (1) under normal condition, then (2) under a stressing situation. We found that (1) this drug was not without adverse effects but slightly impacted some ants’ traits; (2) this drug could reduce the adverse effects caused by the stressing situation. It nearly fully restored the ants’ locomotion, orientation ability, audacity, tactile perception, brood caring, social relationship, escaping behavior, cognition, and slightly the memory. No adaptation and no habituation to the effects of Ignatia amara occurred, and no dependence on its consumption developed. The causes and mechanisms of these effects remain unknown to us, but our results support the hypothesis that, in some given cases, for some specific health problems, and using adequate product(s) and dose(s), a homeopathic treatment based on Ignata amara extracts could help patients to recover from stress symptoms.

Exposure and reactivity of the preterm infant to noise in the incubator.

To evaluate preterm infants' exposure and reactions to intense noise during incubator care. An observational and prospective study was performed in the intermediary care unit of a hospital in Ribeirão Preto (SP). Thirty-five preterm infants participated in the first stage of the study (measuring noise) and 20 in the second (analysis of responses to intense noise). Noise was measured for two hours using a dosimeter, and the responses were video recorded by three cameras connected to a computer. The preterm infants' responses to an Lmax higher than 65 decibels were analyzed. Every preterm infant presented Leq above the limit recommended by international organizations, and more than half of the babies had a mean Leq above the limit permitted by the Brazilian standard. Regarding the babies' responses to the intense noise, the majority of them showed blink reflex, startle reflex, facial mimics, changed bodily activities or changed sleep and wake state, all with statistically significant differences. The sound levels measured were intense. The noises that preterm infants are exposed to while being cared for in incubators constitute a stressor event. Sudden, intense noises change their behavioral state and causes reflexive and bodily responses, facial manifestations and changes in their sleep and wake state.

Common brain changes associated with increased activity in the forced swim test induced by drugs with different mechanisms of action

The set of ancient lakes on Sulawesi, Indonesia, represents a unique global hotspot of aquatic biodiversity. These lakes have been recognized widely because of their high number of endemic species with specialized and distinctive morphological characters, life history and ecological adaptations. An interesting case of unusual life history involving brood care exists in the planorbid limpets of the genus Protancylus, which live exclusively as epizoans on the endemic pachychilid gastropod Tylomelania. We aimed to unravel the evolutionary and phylogeographical patterns of Protancylus from the Malili lakes and Lake Poso using two mitochondrial markers in an integrated framework that includes morphological, life-history and ecological data. At least three species of Protancylus evolved allopatrically, with a newly recognized species occurring in lakes Matano and Mahalona. All species are characterized by low morphological variation, shared life-history traits including a unique reproduction strategy. Our genetic data indicates that a drift-based geographic speciation mode correlates with the present distribution pattern. The initial diversification significantly predates the ages of the respective lakes and the lineages of Protancylus are significantly older than their corresponding Tylomelania ‘hosts’. The deep split between P. pileolus of Lake Poso and the populations in the Malili lakes is remarkable and hints to a very early separation in a time frame when Sulawesi reached its current composition. As colonization and onset of diversification is strikingly different in Tylomelania and the epizoic Protancylus, co-evolutionary components in this association can be excluded and both evolved largely independently. We discuss and compare our findings to other invertebrate assemblages in the ancient lakes of Sulawesi.

Division of labor in honey bees is associated with transcriptional regulatory plasticity in the brain.

Studies in evolutionary and developmental biology show that relationships between transcription factors (TFs) and their target genes can be altered to result in novel regulatory relationships that generate phenotypic plasticity. We hypothesized that context-dependent shifts in the nervous system associated with behavior may also be linked to changes in TF-target relationships over physiological time scales. We tested this hypothesis using honey bee (Apis mellifera) division of labor as a model system by performing bioinformatic analyses of previously published brain transcriptomic profiles together with new RNAi and behavioral experiments. The bioinformatic analyses identified five TFs that exhibited strong signatures of regulatory plasticity as a function of division of labor. RNAi targeting of one of these TFs (broad complex) and a related TF that did not exhibit plasticity (fushi tarazu transcription factor 1) was administered in conjunction with automated analyses of foraging behavior in the field, laboratory assays of aggression and brood care behavior, and endocrine treatments. The results showed that changes in the regulatory relationships of these TFs were associated with behavioral state, social context and endocrine state. These findings provide the first empirical evidence that TF-target relationships in the brain are altered in conjunction with behavior and social context. They also suggest that one mechanism for this plasticity involves pleiotropic TFs high up in regulatory hierarchies producing behavior-specific transcriptional responses by activating different downstream TFs to induce discrete context-dependent transcriptional cascades. These findings provide new insights into the dynamic nature of the transcriptional regulatory architecture underlying behavior in the brain.

A pheromone that coordinates parental care is evolutionary conserved among burying beetles (Silphidae: Nicrophorus)

Pheromones regulating mating behavior are diverse in structure and typically show high species specificity. However, depending on their information content they can also be quite conserved across species. Here, we demonstrate that methyl geranate, an anti-aphrodisiac produced during brood care, is a conserved volatile organic compound within the genus Nicrophorus (burying beetles). Burying beetles are well known for their elaborate biparental care. They reproduce on small vertebrate carcasses and typically it is a pair of beetles, a male and a female, which cooperate in feeding and defending their young. During the intensive period of parental care, female Nicrophorus vespilloides have been shown to emit a volatile substance, methyl geranate, which acts as an anti-aphrodisiac and deters males from copulating. Methyl geranate is biosynthetically linked to juvenile hormone III, a hormone mediating a temporary infertility in this species. By investigating volatile emission of seven geographically and phylogenetically distinct burying beetle species, we provide evidence that methyl geranate is a conserved substance released by parenting adults throughout the genus. We, furthermore, show that there is high quantitative variation (1) between species, which can partly be explained by species differences in body size and (2) within species, which can be attributed to sex differences and individual brood size differences. Moreover, we demonstrate that a species of the genus Ptomascopus, which is closely related to Nicrophorus, but shows no elaborate post-hatching parental behavior, emits only trace amounts of methyl geranate during breeding. Our results, therefore, suggest that the synthesis of an anti-aphrodisiac was an important step in the evolution of concerted parental care in burying beetles. However, behavioral experiments are needed to further corroborate our hypothesis.

Appeasing their hosts: a novel strategy for parasite brood

Brood and social parasites exploit the parental care of their host and often integrate into host colonies using different strategies at different moments during their life cycle. In social wasps, the obligate social parasite Polistes atrimandibularis, using chemical mimicry and chemical insignificance, avoids detection by its host, Polistes biglumis, which has an efficient nestmate recognition system. Enslaved host foundresses accept and care for parasite brood as if it were their own. This observation raises the following question: how exactly do parasite brood escape detection and increase host acceptance? Here, we compared the cuticular chemical signatures of parasite brood and host brood. Their signatures differed in composition: parasite larvae and pupae had particularly high levels of alkenes (notably 9-nonacosene), which were absent in host larvae and pupae. Given this result, we tested the effect of 9-nonacosene on host foundresses, and documented that they reduced their aggression. Our findings address a novel integration strategy for social parasite brood as they suggest that the hydrocarbon serves as an appeasement substance and promotes host tolerance of parasite larvae and pupae, which are chemically disparate from host larvae and pupae.

Rapid adaptation in phoretic mite development time

Strong ecological selection can erode genetic variation and render populations unable to deal with changes in ecological conditions. In the adaptation of the phoretic mite Poecilochirus carabi to its host, the burying beetle Nicrophorus vespilloides, the timing of reproduction is crucial. Safe mite development is only possible during the beetles’ brood care; mites that develop too slowly will have virtually zero fitness. If the strong specialisation in development time leaves no room for standing genetic variation to remain, changes in beetle brood care are disastrous. Beetle brood care depends on temperature and is thus vulnerable to changing climate. Accidental host switches to another beetle species with shorter brood care would also have negative effects on the mites. Only sufficient standing genetic variation could allow mismatched mite lines to survive and adapt. To test whether such rapid adaptation is possible in principle, we artificially selected on mite generation time. We were able to speed up, but not to slow down, mite development. We conclude that there is enough standing genetic variation in development time to allow P. carabi to quickly adapt to new host species or climate conditions, which could potentially lead to the evolution of new mite species.

High level of extrapair fertilization in individual Tibetan azure‐winged magpies and their adaptive responses

Extrapair fertilizations (EPFs) occur widely in socially monogamous birds and result in mixed parentage in the brood. The response of an individual to these EPFs of its social mate remains poorly investigated in terms of parental care for the mixed brood. We addressed this question in a cooperatively‐breeding corvid, the azure‐winged magpie Cyanopica cyana. Parentage analysis indicated that 45% of females and 37% of males engaged in EPFs. There were 49% of cooperative groups and 36% of bi‐parental nests with extrapair paternity (EPP) offspring, and 22% of cooperative groups and 19% of bi‐parental nests with extrapair maternity (EPM) offspring. Based on the identity of offspring, we classified adults into four types: EPP offspring fathers/mothers, EPM offspring fathers/mothers, cuckolded males/females, and faithful males/females. A comparison of provisioning rates among all four types of breeders showed that 1) EPM offspring fathers had the highest provisioning rate; 2) cuckolded males did not reduce parental care, compared to faithful males and EPP offspring fathers; and 3) females of different types did not differ in their provisioning rates. Our findings suggest that a combination of frequent opportunities, low costs of cuckoldry, and the benefits of establishing a cooperative neighbourhood can explain why EPFs occur frequently in the Tibetan population of azure‐winged magpie.

Glyphosate affects the larval development of honey bees depending on the susceptibility of colonies.

As the main agricultural insect pollinator, the honey bee (Apis mellifera) is exposed to a number of agrochemicals, including glyphosate (GLY), the most widely used herbicide. Actually, GLY has been detected in honey and bee pollen baskets. However, its impact on the honey bee brood is poorly explored. Therefore, we assessed the effects of GLY on larval development under chronic exposure during in vitro rearing. Even though this procedure does not account for social compensatory mechanisms such as brood care by adult workers, it allows us to control the herbicide dose, homogenize nutrition and minimize environmental stress. Our results show that brood fed with food containing GLY traces (1.25–5.0 mg per litre of food) had a higher proportion of larvae with delayed moulting and reduced weight. Our assessment also indicates a non-monotonic dose-response and variability in the effects among colonies. Differences in genetic diversity could explain the variation in susceptibility to GLY. Accordingly, the transcription of immune/detoxifying genes in the guts of larvae exposed to GLY was variably regulated among the colonies studied. Consequently, under laboratory conditions, the response of honey bees to GLY indicates that it is a stressor that affects larval development depending on individual and colony susceptibility.

Phenotypic correlation between queen and worker brood care supports the role of maternal care in the evolution of eusociality.

Cooperative brood care by siblings, a defining feature of eusociality, is hypothesized to be evolutionarily derived from maternal care via shifts in the timing of the expression of genes underlying maternal care. If sibling and maternal care share a genetic basis, the two behaviors are expected to be genetically and phenotypically correlated. We tested this prediction in the black garden ant Lasius niger by quantifying the brood retrieval rate of queens and their first and later generation worker offspring. Brood retrieval rate of queens was positively phenotypically correlated with the brood retrieval rate of first generation but not with later generation workers. The difference between first and later generation workers could be due to the stronger similarity in care behavior provided by queens and first generation workers compared to later generations. Furthermore, we found that queen retrieval rate was positively correlated with colony productivity, suggesting that natural selection is acting on maternal care. Overall, our results support the idea of a shared genetic basis between maternal and sibling care as well as queen and worker traits more generally, which has implications for the role of intercaste correlations in the evolution of queen and worker traits and eusociality.

Clonal raider ant brain transcriptomics identifies candidate molecular mechanisms for reproductive division of labor

BackgroundDivision of labor between reproductive queens and workers that perform brood care is a hallmark of insect societies. However, studies of the molecular basis of this fundamental dichotomy are limited by the fact that the caste of an individual cannot typically be experimentally manipulated at the adult stage. Here we take advantage of the unique biology of the clonal raider ant, Ooceraea biroi, to study brain gene expression dynamics during experimentally induced transitions between reproductive and brood care behavior.ResultsIntroducing larvae that inhibit reproduction and induce brood care behavior causes much faster changes in adult gene expression than removing larvae. In addition, the general patterns of gene expression differ depending on whether ants transition from reproduction to brood care or vice versa, indicating that gene expression changes between phases are cyclic rather than pendular. Finally, we identify genes that could play upstream roles in regulating reproduction and behavior because they show large and early expression changes in one or both transitions.ConclusionsOur analyses reveal that the nature and timing of gene expression changes differ substantially depending on the direction of the transition, and identify a suite of promising candidate molecular regulators of reproductive division of labor that can now be characterized further in both social and solitary animal models. This study contributes to understanding the molecular regulation of reproduction and behavior, as well as the organization and evolution of insect societies.

Brain activation patterns following a cooperation opportunity in a highly social cichlid fish

In highly social species, individuals frequently face opportunities to cooperate. The molecular and neural mechanisms that integrate internal and external information prior to cooperative responses are not well understood. Using expression levels of egr-1, a genomic marker of neural activity, we quantified the neural response to an alloparental-care opportunity in a cooperatively breeding fish, a component of cooperative behaviour, across brain regions and time. In this species, alloparental care and submission are considered alternative strategies to appease dominants. We therefore investigated whether brood care and defence as well as submissive displays were associated with egr-1 expression. Finally, we predicted potential targets of the egr-1 transcription factor in the cichlid genome. This target prediction suggested that egr-1 regulates the expression of transcription factors involved in nervous system development, which could be implicated in social memory formation associated with cooperation. Egr-1 expression levels differed between test and control individuals and across time. Compared to a control, individuals experiencing the cooperation opportunity expressed less egr-1 in two brain regions, the cerebellum and the telencephalon. This down-regulation was independent of their behavioural reaction, i.e. whether they cooperated or not. However, within the subset of test individuals, egr-1 expression increased as a function of the amount of submissive behaviours, but not of cooperative behaviours, in the hypothalamus and potentially the telencephalon. These regions host structures that play a role in social decision-making; suggesting that egr-1 might be a suitable proxy for neural activation due to the social interaction component of the cooperation opportunity, rather than the actual alloparental care component.