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Organismal traits may experience conflicting selection pressures if they fulfil different functions simultaneously. This can require trade‐offs between functions or alternatively functional separation between elements of the trait.An important multifunctional trait in insects is the cuticular hydrocarbon (CHC) layer. CHCs cover the body of nearly all insects, protect against desiccation and serve as a communication signal. In social insects like ants, they provide cues for nestmate recognition. To maintain their waterproofing function, insects have to adjust CHC composition to current temperatures. These changes might affect information content and interfere with communication, which would be especially detrimental in social insects.Here, we studied how acclimation affects nestmate recognition in two sister species of the ant genus Lasius. Colony fragments were exposed to three climate regimes. We analysed behaviour towards same and differently acclimated conspecifics, and determined which CHCs were related to acclimatory changes, colony differences and inter‐individual aggression.Differential acclimation led to higher aggression and chemical distances among former nestmates. We identified small CHC subsets, which only differed among colonies or among acclimation treatments. Moreover, few compounds sufficed to explain inter‐individual aggression, suggesting that ants do not use the entire CHC profile for nestmate recognition and that colony identity is encoded in a redundant way.Across individual CHCs, their contribution to colony differences and to differences among acclimatory treatments was negatively correlated, indicating that there is some degree of functional separation. However, CHC classes could not be clearly assigned to one or another function, indicating that the role of each CHC is idiosyncratic and may differ among species. Acclimatory effects and colony differences were more independent from each other in L. platythorax than in L. niger, indicating that functional separation can differ even among sister species.Our results show that CHC functions are more intertwined than previously assumed, suggesting that insects cannot optimise all functions independently. The main constraint might be the need to maintain a certain phase behaviour of the CHC layer, which depends on CHC composition and affects functionality. The need to separate functions might depend on species‐specific ecological and life‐history parameters.Read the free Plain Language Summary for this article on the Journal blog. [ABSTRACT FROM AUTHOR]

Queen pheromones, which signal the presence of a fertile queen and induce daughter workers to remain sterile, are considered to play a key role in regulating the reproductive division of labor of insect societies. Although queen pheromones were long thought to be highly taxon-specific, recent studies have shown that structurally related long-chain hydrocarbons act as conserved queen signals across several independently evolved lineages of social insects. These results imply that social insect queen pheromones are very ancient and likely derived from an ancestral signalling system that was already present in their common solitary ancestors. Based on these new insights, we here review the literature and speculate on what signal precursors social insect queen pheromones may have evolved from. Furthermore, we provide compelling evidence that these pheromones should best be seen as honest signals of fertility as opposed to suppressive agents that chemically sterilize the workers against their own best interests. [ABSTRACT FROM AUTHOR]

Caterpillars of the parasitic lycaenid butterfly are often adopted by host ants. It has been proposed that this adoption occurs because the caterpillars mimic the cuticular hydrocarbons of the host ant. This study aimed to examine whether caterpillars of the Japanese lycaenid butterfly Niphanda fusca induce adoption by mimicking their host ant Camponotus japonicus. Behavioral observations conducted in the laboratory showed that most second-instar caterpillars were not adopted, whereas most third-instar caterpillars were successfully adopted by host workers. A chemical comparison detected no characteristic differences in the cuticular hydrocarbon profiles between second- and third-instar caterpillars. However, morphological features of the caterpillars differed between the second and third instars; third-instar caterpillars developed exocrine glands (ant organs) such as tentacle organs and a dorsal nectary organ. These results suggest that multiple chemical signatures, not only cuticular hydrocarbons, may be important for invasion of the host ant nest. [ABSTRACT FROM AUTHOR]

Cuticular hydrocarbons (CHCs) are expressed on an insect's cuticle and are one of the major factors allowing insects to identify members of their own species, colony and gender. As a result of their species-specificity, CHCs are increasingly used to delimit species in addition to more conventional methods, such as morphology or genetic markers, and so play an important role in chemotaxonomy. Species vary in the type of CHCs that they produce, as well as in the relative quantities of shared compounds. This review summarizes not only how taxonomists may differentiate between species based on CHC profiles, but also the incentive for using CHC composition as taxonomic tool. Benefits regarding the identification of cryptic species and early signs of reproductive isolation are then discussed, giving examples from studies of taxonomy, behaviour and biosynthesis. For taxonomic characters to reliably indicate species boundaries, their limitations need to be known. Potential problems caused by environmental effects, intra-species variation in profiles and other technical issues are highlighted, and suggestions are made regarding their avoidance. It remains a challenge to determine the variation beyond which two species can be called independent; a problem shared by most methods of delimitation. Recently, there has been a shift towards using a combination of different taxonomic tools, both molecular and non-molecular, to test observed species differences. [ABSTRACT FROM AUTHOR]

Summary 1. Trade-offs between current and future resource allocation can select for elevated reproductive effort in individuals facing mortality. Males are predicted to benefit from increasing investment in costly sexually selected signals after experiencing an acute life span reduction, although few examples of such facultative terminal investment are known. 2. In the mealworm beetle, Tenebrio molitor, males' odours become more attractive to females following a life-threatening immune challenge. However, the pheromones involved are unknown, hindering further insight into the proximate mechanisms and ultimate consequences of terminal investment. 3. Using chemical and behavioural analyses, we show that the cuticular hydrocarbons (CHCs) of T. molitor are sexually dimorphic and are used by females to locate and select males. Moreover, both male CHCs and glandular pheromones were affected by experimental immune challenge in a fashion that made them more attractive to females. 4. The results suggest that males terminally invest in both short- and medium-range pheromones when they perceive reduced future survival. Moreover, the constitutive and inducible aspects of male and female CHC production are consistent with sex-specific selection on the signalling and defensive functions of CHCs. The implications of terminal investment for 'dishonest' signalling and the efficacy of sexual selection are discussed. [ABSTRACT FROM AUTHOR]

Discrimination between nestmates and non-nestmates in social insects is thought to rely on the pattern of cuticular hydrocarbons. We investigated the cuticular hydrocarbon profiles of 2 parapatric sibling ant species, Temnothorax nylanderi (Förster, 1850) and Temnothorax crassispinus (Karavaiev, 1926), and their hybrid. We found that although the profiles show considerable similarities, a discriminant analysis based on the relative peak areas of cuticular hydrocarbons separates the 3 taxa. The profiles of hybrids were not consistently intermediate between those of the paternal species, suggesting either non-additive interactions among the parental biosynthetic pathways or systematic differences in environment-derived odor cues. [ABSTRACT FROM AUTHOR]