We compared the published cuticular hydrocarbon (CHC) profiles of 78 ant species across 5 subfamilies. Almost 1,000 CHCs have been described for these species, composing 187 distinct homologous series and ten hydrocarbon groups. In descending order of occurrence were: n-alkanes > monomethylalkanes > dimethylalkanes > alkenes > dienes>> trimethylalkanes>> methylalkenes > methylalkadienes > trienes > tetramethylalkanes. Odd chain lengths and positions of methyl or double bonds at odd carbon numbers were far more numerous than even chain-length compounds or bond positions. Although each species possess its own unique pattern of CHCs, we found no association between CHC profile and phylogeny. The production of the biosynthetically complex compounds (e.g., methyl branched dienes) by the most primitive living ant suggests that the basic genetic architecture required to produce the rich diversity of CHCs was already present prior to their adaptive radiation. Unlike the ubiquitous n-alkanes and monomethylalkanes, there is a huge diversity of species-specific dimethylalkanes that makes them likely candidates for species and nest-mate discrimination signals.

Distinguishing nest-mates from non-nest-mates underlies key animal behaviours, such as territoriality, altruism and the evolution of sociality. Despite its importance, there is very little empirical support for such a mechanism in nature. Here we provide data that the nest-mate recognition mechanism in an ant is based on a colony-specific Z9-alkene signature, proving that surface chemicals are indeed used in ant nest-mate recognition as was suggested 100 years ago. We investigated the cuticular hydrocarbon profiles of 10 Formica exsecta colonies that are composed almost entirely of a Z9-alkene and alkane component. Then we showed that worker aggression is only elicited by the Z9-alkene part. This was confirmed using synthetic Z9-alkene and alkane blends matched to the individual colony profiles of the two most different chemical colonies. In both colonies, only glass beads with 'nest-mate' alkene profiles received reduced aggression. Finally, changing the abundance of a single Z9-alkene on live ants was shown to significantly increase the aggression they received from nest-mates in all five colonies tested. Our data suggest that nest-mate discrimination in the social insects has evolved to rely upon highly sensitive responses to relatively few compounds.

Summary1. Prey species often possess defences (e.g. toxins) coupled with warning signals (i.e. aposematism). There is growing evidence that the expression of aposematic signals often varies within species and correlates with the strength of chemical defences. This has led to the speculation that such signals may be 'honest', with signal reliability ensured by the costliness of producing or maintaining aposematic traits. 2. We reared larval seven-spot ladybirds (Coccinella septempunctata) on a Low or High aphid diet and measured the effects on warning signal expression (elytral carotenoid pigmentation, conspicuousness, spot size), levels of defensive alkaloids (precoccinelline, coccinelline), and relationships between these traits. 3. High-diet individuals had greater total precoccinelline levels, and elytra carotenoid concentrations at adulthood which was detectable to a typical avian predator. However, larval diet did not significantly affect adult body mass or size, spot size or coccinelline levels. 4. Elytra carotenoid concentrations correlated positively with total precoccinelline levels in both diet groups and sexes. However, the relationship between elytra carotenoid concentrations and total levels of coccinelline depended on sex: in both diet groups, elytra carotenoids and coccinelline levels were positively correlated in females, but negatively correlated in males. Spot size and coccinelline levels correlated positively in Low-diet individuals, but negatively in High-diet individuals. 5. These results point to physiological linkages between components of aposematism, which are modulated by resource (i.e. food) availability and affect the honesty of signals. Developmental diet, but also sex, influenced the relationships between signals and toxin levels. Ladybirds are sexually size dimorphic, and thus in comparison with males, females may be more susceptible to resource limitation and more likely to be honest signallers.

A comparison of the cuticular hydrocarbon profiles of thirteen sympatric species of Formica ants from Finland, along with a subset of five species from the British Isles, was conducted. This permitted a comparison of the evolution of these profiles within a single genus and the stability of these profiles over large geographical and evolutionary distances. The study indicated that species-specific hydrocarbon profiles remained remarkably stable between Finland and the British Isles and were not influenced by ecological factors such as soil or vegetation types. This stability allowed candidate cuticular hydrocarbons or groups of hydrocarbons to be identified that may constitute species-specific recognition cues in these ants. In Formica, cuticular hydrocarbon composition has evolved down two distinct paths, either elevated production of Z-9-alkenes or the production of various dimethylalkanes. Evolution of hydrocarbons can be predicted for the other five Formica species for which the cuticular profiles are known. The Z-9-alkenes, dienes, and various distinctive combinations of dimethylalkanes can be used as unique species recognition cues in the Formica ants and this parallels the evolution of species-specific cuticular hydrocarbon composition in the Drosophila flies.

It is unclear why some species become successful invaders whilst others fail, and whether invasive success depends on pre-adaptations already present in the native range or on characters evolving de-novo after introduction. Ants are among the worst invasive pests, with Lasius neglectus and its rapid spread through Europe and Asia as the most recent example of a pest ant that may become a global problem. Here, we present the first integrated study on behavior, morphology, population genetics, chemical recognition and parasite load of L. neglectus and its non-invasive sister species L. turcicus. We find that L. neglectus expresses the same supercolonial syndrome as other invasive ants, a social system that is characterized by mating without dispersal and large networks of cooperating nests rather than smaller mutually hostile colonies. We conclude that the invasive success of L. neglectus relies on a combination of parasite-release following introduction and pre-adaptations in mating system, body-size, queen number and recognition efficiency that evolved long before introduction. Our results challenge the notion that supercolonial organization is an inevitable consequence of low genetic variation for chemical recognition cues in small invasive founder populations. We infer that low variation and limited volatility in cuticular hydrocarbon profiles already existed in the native range in combination with low dispersal and a highly viscous population structure. Human transport to relatively disturbed urban areas thus became the decisive factor to induce parasite release, a well established general promoter of invasiveness in non-social animals and plants, but understudied in invasive social insects.

Insect cuticular hydrocarbons (CHCs) are primarily antidesiccation agents, but they also play crucial roles in intra- and interspecific communication, especially among social Hymenoptera. The complex CHC profiles of social insects have often been compared among individuals, kin, nestmates, colonies, and species. In the ant Formica exsecta, only the (Z)-9-alkene part of the CHC profile encodes the nestmate signal. Here, we showed that the other major part of the CHC profile with n-alkane components is influenced strongly by the task a worker performs (foraging vs nonforaging). This part of the profile is independent of the nestmate signal. Therefore, the CHC profile of F. exsecta workers is composed of two independent parts: a colony-specific (Z)-9-alkene profile under genetic influence and an environmentally influenced task-related n-alkane profile. The dissociating of the CHC profile into two or more independent parts has implications for the analysis and interpretation of past and future CHC studies.

BackgroundThe invasive garden ant, Lasius neglectus, is the most recently detected pest ant and the first known invasive ant able to become established and thrive in the temperate regions of Eurasia. In this study, we aim to reconstruct the invasion history of this ant in Europe analysing 14 populations with three complementary approaches: genetic microsatellite analysis, chemical analysis of cuticular hydrocarbon profiles and behavioural observations of aggression behaviour. We evaluate the relative informative power of the three methodological approaches and estimate both the number of independent introduction events from a yet unknown native range somewhere in the Black Sea area, and the invasive potential of the existing introduced populations.ResultsThree clusters of genetically similar populations were detected, and all but one population had a similar chemical profile. Aggression between populations could be predicted from their genetic and chemical distance, and two major clusters of non-aggressive groups of populations were found. However, populations of L. neglectus did not separate into clear supercolonial associations, as is typical for other invasive ants.ConclusionThe three methodological approaches gave consistent and complementary results. All joint evidence supports the inference that the 14 introduced populations of L. neglectus in Europe likely arose from only very few independent introductions from the native range, and that new infestations were typically started through introductions from other invasive populations. This indicates that existing introduced populations have a very high invasive potential when the ants are inadvertently spread by human transport.

The possession of a colony identity is a fundamental property that underlies much animal behavior. In insect societies, it is widely accepted that nest-mate recognition cues are encoded within the cuticular hydrocarbons. Despite numerous studies over the past 30years, the identification of these nest-mate specific signatures is only just starting to occur. In this paper, we show two different methods by which nest-mate-specific signatures can be encoded within the hydrocarbon profile of two species of Formica ants. In F. exsecta, nest-mate-specific signatures rely on the distribution of chain lengths of a single type of hydrocarbon, various (Z)-9-alkenes, which are present in colony-specific proportions. In F. fusca, variation in nine different positional isomers of C(25)-dimethylalkanes is sufficient to produce unique colony profiles. By using this information alone, we correctly assigned 97 F. exsecta workers into their respective 20 colonies and 111 F. fusca workers into their respective 30 colonies. These two systems or variations of them may be expected to occur in many insect societies that have a strong colony identity.