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Inter-specific variation in the occurrence of individual recognition (IR) has mostly been examined in species that differ with respect to two critical conditions necessary for such ability: presence of complex social behaviours and sender’s distinctiveness. However, variation in IR when species share such conditions is lesser known. We tested for IR in the paper wasp Polistes versicolor and compared the results with published information on IR in Polistes fuscatus. Both species have a flexible nest-founding behaviour and form dominance hierarchies. Additionally, both have individually distinctive facial patterns. P. versicolor faces are highly variable, and they do not appear to be associated with individual quality, consistent with the role as cues in IR. However, the wasps did not discriminate between nestmates with familiar and unfamiliar faces. Besides, wasps did not discriminate between familiar and unfamiliar social partners. Familiar discrimination (discrimination of individuals based on prior social interactions) is considered the first stage toward IR; therefore, P. versicolor wasps, unlike P. fuscatus, lack the ability for IR. Our results suggest that the high variation in colour pattern may not be a good proxy for the occurrence of IR in paper wasps and that neutral variation may be an underestimated factor promoting phenotypic variability. High inter-individual phenotypic variability in primitively eusocial paper wasps has sometimes been considered to be a result of selection for efficient individual identity signalling, especially because senders may benefit from being individually recognised. P. versicolor paper wasp females have highly variable inter-individual facial patterns. However, we demonstrated that they lack individual recognition. After excluding some potentially confounding hypothesis, we conclude that selection for efficient individual identity signalling is not the only factor promoting phenotypic variability in paper wasps and that at least in some species, neutral variation may play a role.

In group-level recognition, discriminators use sensory information to distinguish group members and non-members. For example, entrance guards in eusocial insect colonies discriminate nestmates from intruders by comparing their odour with a template of the colony odour. Despite being a species-rich group of eusocial bees closely related to the honey bees, stingless bee nestmate recognition is a relatively little-studied area. We studied Frieseomelitta varia, a common Brazilian species of stingless bee known as marmelada. By measuring the rejection rates of nestmate and non-nestmate worker bees by guards, we were able to show that guards became significantly less accepting (from 91 to 46%) of nestmates that had acquired odour cues from non-nestmate workers; however, guards did not become significantly more accepting (from 31 to 42%) of non-nestmates that had acquired equivalent amounts of odour cues from the guard's nestmates. These data strongly suggest that guards use an "undesirableabsent" system in recognition, whereby incoming conspecific workers are only accepted if undesirable cues are absent, despite the presence of desirable cues. We suggest that an undesirableabsent system is adaptive because robbing by conspecifics may be an important selective factor in F. varia, which would lead to selection for a non-permissive acceptance strategy by guards.

Like many modular organisms, genetically distinct colonies of the hydrozoan Hydractinia symbiolongicarpus naturally fuse to produce chimeras. One of the principal cooperative benefits of fusion arises from the increased size of the resulting chimeric individual, which may enhance survivorship. However, fusion also promotes conflict through competition between cell lineages for representation in reproductive tissues. Previous studies on H. symbiologicarpus show that, consistent with kin selection theory, a highly polymorphic self/non-self recognition system limits fusion to close kin. However, these recognition systems are intrinsically subject to error. Conspecific acceptance threshold theory predicts that as the costs and benefits of making recognition errors change, or the frequencies of encounters between acceptable and unacceptable kin vary, the recognition system should respond. Specifically, as the benefits of acceptance decline or the frequency of encounters with unacceptable individuals increases, the acceptance threshold should become more restrictive. We tested this hypothesis by monitoring changes in the expression of fusion/rejection behaviors of H. symbiolongicarpus during colony establishment, a period of high mortality when the size-dependent benefits of fusion may be changing most rapidly, and the frequency of encounters with close kin declines. Across seven full-sib families, fusion frequencies between pairs of sibling colonies declined from 73% for 3-day-old colonies to 58% by day 12. This decline is consistent with optimal acceptance threshold theory. However, the period of maximum decline also corresponds to an interval during which the recognition effector mechanism becomes fully functional, suggesting that the shift to a more restrictive conspecific acceptance threshold may reflect an intrinsic constraint on recognition system maturation.