Colonies of the clonal ant Cerapachys biroi undergo stereotypic reproductive cycles made of two c... more Colonies of the clonal ant Cerapachys biroi undergo stereotypic reproductive cycles made of two constantly alternating phases. In the reproductive phase, eggs are collectively laid while pupae of the previous generation complete their development, whereas in the foraging phase, larvae feed on prey items provided by foraging workers and there is no reproductive activity until the onset of pupation. In a previous study, we showed that colonies of C. biroi are subject to a strict regulation of reproduction, with larval cues inhibiting ovarian activation in fertile adults. 4 Nonetheless, some individuals seem to lack sensitivity to these cues and fail to synchronize to the colony-level reproductive cycle. Those individuals are executed during their first foraging phase as reproductively mature individuals, when they exhibit for the first time their unusual physiology (i.e., reproductive activation during a non-reproductive phase). Interestingly, almost all the executed individuals belong to a worker subcaste specialized in reproduction (highly reproductive individuals, or HRIs, which have four to six ovarioles, lay up to eight eggs per cycle and do not engage in foraging; in contrast, low reproductive individuals or LRIs, which have two ovarioles, lay up to two eggs during few cycles and then become sterile foragers). Aggressed HRIs show
Dominance hierarchies allow group-living animals to regulate the partitioning of reproduction, bu... more Dominance hierarchies allow group-living animals to regulate the partitioning of reproduction, but the recognition systems underlying dominance interactions remain equivocal. Individual recognition, a cognitively complex recognition system, is often posited as an important mechanism for the regulation of linear dominance hierarchies because of its high level of precision. However, providing it actually allows a fine-scale discrimination of the individuals' statuses, status discrimination may offer an alternative, simpler, recognition system allowing the same level of precision while saving the memoryrelated costs associated with individual recognition. With the aim of disentangling the cognitive mechanisms underlying the formation and maintenance of hierarchies, we here studied the withingroup recognition systems in the ant Neoponera apicalis, where orphaned workers compete over male parentage in a linear hierarchical structure. Overall, we found that status discrimination abilities were in fact sufficient for the establishment and stabilization of linear hierarchies. The observed level of accuracy allowed fine-scale discrimination of all top rankers' hierarchical status, and thus translated into a functional individual discrimination of all competing workers at the top of the hierarchy. Low-ranking workers did not exhibit such fine-scale status discrimination. We moreover showed that a putative signal of fertility, 13-methylpentacosane, precisely labelled the workers' position in the hierarchy, thereby providing the recognition cue likely to explain the individuals' discrimination abilities. This signal could therefore play a key role in the regulation of the reproductive conflict in this species. In contrast with the traditional view, our study shows the implication of a cognitively simple but equivalently efficient recognition system during the emergence and stabilization of a linear dominance hierarchy. Ó
Proceedings of the Royal Society B: Biological Sciences, 2013
Restricted reproduction is traditionally posited as the defining feature of eusocial insect worke... more Restricted reproduction is traditionally posited as the defining feature of eusocial insect workers. The discovery of worker reproduction in foreign colonies challenges this view and suggests that workers' potential to pursue selfish interests may be higher than previously believed. However, whether such reproductive behaviour truly relies on a reproductive decision is still unknown. Workers' reproductive decisions thus need to be investigated to assess the extent of workers' reproductive options. Here, we show in the bumblebee Bombus terrestris that drifting is a distinct strategy by which fertile workers circumvent competition in their nest and reproduce in foreign colonies. By monitoring workers' movements between colonies, we show that drifting is a remarkably dynamic behaviour, widely expressed by both fertile and infertile workers. We demonstrate that a high fertility is, however, central in determining the propensity of workers to enter foreign colonies as well as their subsequent reproduction in host colonies. Moreover, our study shows that the drifting of fertile workers reflects complex decision-making processes associated with in-nest reproductive competition. This novel finding therefore adds to our modern conception of cooperation by showing the previously overlooked importance of alternative strategies which enable workers to assert their reproductive interests.
Background: The impact of social parasites on their hosts' fitness is a strong selective pressure... more Background: The impact of social parasites on their hosts' fitness is a strong selective pressure that can lead to the evolution of adapted defence strategies. Guarding the nest to prevent the intrusion of parasites is a widespread response of host species. If absolute rejection of strangers provides the best protection against parasites, more fine-tuned strategies can prove more adaptive. Guarding is indeed costly and not all strangers constitute a real threat. That is particularly true for worker reproductive parasitism in social insects since only a fraction of non-nestmate visitors, the fertile ones, can readily engage in parasitic reproduction. Guards should thus be more restrictive towards fertile than sterile non-nestmate workers. We here tested this hypothesis by examining the reaction of nest-entrance guards towards nestmate and non-nestmate workers with varying fertility levels in the bumble bee Bombus terrestris. Because social recognition in social insects mainly relies on cuticular lipids (CLs), chemical analysis was also conducted to examine whether workers' CLs could convey the relevant information upon which guards could base their decision. We thus aimed to determine whether an adapted defensive strategy to worker reproductive parasitism has evolved in B. terrestris colonies. Results: Chemical analysis revealed that the cuticular chemical profiles of workers encode information about both their colony membership and their current fertility, therefore providing potential recognition cues for a suitable adjustment of the guards' defensive decisions. We found that guards were similarly tolerant towards sterile non-nestmate workers than towards nestmate workers. However, as predicted, guards responded more aggressively towards fertile non-nestmates. Conclusion: Our results show that B. terrestris guards discriminate non-nestmates that differ in their reproductive potential and respond more strongly to the individuals that are a greatest threat for the colony. Cuticular hydrocarbons are the probable cues underlying the specific recognition of reproductive parasites, with the specific profile of highly fertile bees eliciting the agonistic response when combined with non-colony membership information. Our study therefore provides a first piece of empirical evidence supporting the hypothesis that an adapted defensive strategy against worker reproductive parasitism exists in B. terrestris colonies.
Colonies of the clonal ant Cerapachys biroi undergo stereotypic reproductive cycles made of two c... more Colonies of the clonal ant Cerapachys biroi undergo stereotypic reproductive cycles made of two constantly alternating phases. In the reproductive phase, eggs are collectively laid while pupae of the previous generation complete their development, whereas in the foraging phase, larvae feed on prey items provided by foraging workers and there is no reproductive activity until the onset of pupation. In a previous study, we showed that colonies of C. biroi are subject to a strict regulation of reproduction, with larval cues inhibiting ovarian activation in fertile adults. 4 Nonetheless, some individuals seem to lack sensitivity to these cues and fail to synchronize to the colony-level reproductive cycle. Those individuals are executed during their first foraging phase as reproductively mature individuals, when they exhibit for the first time their unusual physiology (i.e., reproductive activation during a non-reproductive phase). Interestingly, almost all the executed individuals belong to a worker subcaste specialized in reproduction (highly reproductive individuals, or HRIs, which have four to six ovarioles, lay up to eight eggs per cycle and do not engage in foraging; in contrast, low reproductive individuals or LRIs, which have two ovarioles, lay up to two eggs during few cycles and then become sterile foragers). Aggressed HRIs show
Dominance hierarchies allow group-living animals to regulate the partitioning of reproduction, bu... more Dominance hierarchies allow group-living animals to regulate the partitioning of reproduction, but the recognition systems underlying dominance interactions remain equivocal. Individual recognition, a cognitively complex recognition system, is often posited as an important mechanism for the regulation of linear dominance hierarchies because of its high level of precision. However, providing it actually allows a fine-scale discrimination of the individuals' statuses, status discrimination may offer an alternative, simpler, recognition system allowing the same level of precision while saving the memoryrelated costs associated with individual recognition. With the aim of disentangling the cognitive mechanisms underlying the formation and maintenance of hierarchies, we here studied the withingroup recognition systems in the ant Neoponera apicalis, where orphaned workers compete over male parentage in a linear hierarchical structure. Overall, we found that status discrimination abilities were in fact sufficient for the establishment and stabilization of linear hierarchies. The observed level of accuracy allowed fine-scale discrimination of all top rankers' hierarchical status, and thus translated into a functional individual discrimination of all competing workers at the top of the hierarchy. Low-ranking workers did not exhibit such fine-scale status discrimination. We moreover showed that a putative signal of fertility, 13-methylpentacosane, precisely labelled the workers' position in the hierarchy, thereby providing the recognition cue likely to explain the individuals' discrimination abilities. This signal could therefore play a key role in the regulation of the reproductive conflict in this species. In contrast with the traditional view, our study shows the implication of a cognitively simple but equivalently efficient recognition system during the emergence and stabilization of a linear dominance hierarchy. Ó
Proceedings of the Royal Society B: Biological Sciences, 2013
Restricted reproduction is traditionally posited as the defining feature of eusocial insect worke... more Restricted reproduction is traditionally posited as the defining feature of eusocial insect workers. The discovery of worker reproduction in foreign colonies challenges this view and suggests that workers' potential to pursue selfish interests may be higher than previously believed. However, whether such reproductive behaviour truly relies on a reproductive decision is still unknown. Workers' reproductive decisions thus need to be investigated to assess the extent of workers' reproductive options. Here, we show in the bumblebee Bombus terrestris that drifting is a distinct strategy by which fertile workers circumvent competition in their nest and reproduce in foreign colonies. By monitoring workers' movements between colonies, we show that drifting is a remarkably dynamic behaviour, widely expressed by both fertile and infertile workers. We demonstrate that a high fertility is, however, central in determining the propensity of workers to enter foreign colonies as well as their subsequent reproduction in host colonies. Moreover, our study shows that the drifting of fertile workers reflects complex decision-making processes associated with in-nest reproductive competition. This novel finding therefore adds to our modern conception of cooperation by showing the previously overlooked importance of alternative strategies which enable workers to assert their reproductive interests.
Background: The impact of social parasites on their hosts' fitness is a strong selective pressure... more Background: The impact of social parasites on their hosts' fitness is a strong selective pressure that can lead to the evolution of adapted defence strategies. Guarding the nest to prevent the intrusion of parasites is a widespread response of host species. If absolute rejection of strangers provides the best protection against parasites, more fine-tuned strategies can prove more adaptive. Guarding is indeed costly and not all strangers constitute a real threat. That is particularly true for worker reproductive parasitism in social insects since only a fraction of non-nestmate visitors, the fertile ones, can readily engage in parasitic reproduction. Guards should thus be more restrictive towards fertile than sterile non-nestmate workers. We here tested this hypothesis by examining the reaction of nest-entrance guards towards nestmate and non-nestmate workers with varying fertility levels in the bumble bee Bombus terrestris. Because social recognition in social insects mainly relies on cuticular lipids (CLs), chemical analysis was also conducted to examine whether workers' CLs could convey the relevant information upon which guards could base their decision. We thus aimed to determine whether an adapted defensive strategy to worker reproductive parasitism has evolved in B. terrestris colonies. Results: Chemical analysis revealed that the cuticular chemical profiles of workers encode information about both their colony membership and their current fertility, therefore providing potential recognition cues for a suitable adjustment of the guards' defensive decisions. We found that guards were similarly tolerant towards sterile non-nestmate workers than towards nestmate workers. However, as predicted, guards responded more aggressively towards fertile non-nestmates. Conclusion: Our results show that B. terrestris guards discriminate non-nestmates that differ in their reproductive potential and respond more strongly to the individuals that are a greatest threat for the colony. Cuticular hydrocarbons are the probable cues underlying the specific recognition of reproductive parasites, with the specific profile of highly fertile bees eliciting the agonistic response when combined with non-colony membership information. Our study therefore provides a first piece of empirical evidence supporting the hypothesis that an adapted defensive strategy against worker reproductive parasitism exists in B. terrestris colonies.
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Papers by Pierre Blacher