Cuticular hydrocarbons correlated with reproductive status in a queenless ant (original) (raw)
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Cuticular hydrocarbons provide reliable cues of fertility in the ant Gnamptogenys striatula
2006
Abstract In ca. 150 species of queenless ants, a specialized queen caste is rare or absent, and mated workers take over the role of the queen in some or all of the colonies. Previously, it has been shown that reproduction in queenless ants is regulated by a combination of dominance behavior and chemical fertility signaling. It is unknown, however, whether chemical signals alone can sufficiently regulate reproduction.
PLOS ONE
In insect societies, chemical communication plays an important role in colony reproduction and individual social status. Many studies have indicated that cuticular hydrocarbons (CHCs) are the main chemical compounds encoding reproductive status. However, these studies have largely focused on queenless or monogynous species whose workers are capable of egg laying and have mainly explored the mechanisms underlying queen-worker or worker-worker reproductive conflicts. Less is known about what occurs in highly polygynous ant species with permanently sterile workers. Here, we used the Argentine ant as a model to examine the role of CHCs in communicating reproductive information in such insect societies. The Argentine ant is unicolonial, highly polygynous, and polydomous. We identified several CHCs whose presence and levels were correlated with queen age, reproductive status, and fertility. Our results also provide new insights into queen executions in the Argentine ant, a distinctive feature displayed by this species in its introduced range. Each spring, just before new sexuals appear, workers eliminate up to 90% of the mated queens in their colonies. We discovered that queens that survived execution had different CHC profiles from queens present before and during execution. More specifically, levels of some CHCs were higher in the survivors, suggesting that workers could eliminate queens based on their chemical profiles. In addition, queen CHC profiles differed based on season and species range (native vs. introduced). Overall, the results of this study provide new evidence that CHCs serve as queen signals and do more than just regulate worker reproduction.
Sex, age and ovarian activity affect cuticular hydrocarbons in Diacamma ceylonense, a queenless ant
Journal of Insect Physiology, 2001
In the queenless ant, Diacamma ceylonense, the cuticular hydrocarbons (C25-C35) of nestmate workers vary in their proportions according to age and fertility. Newly eclosed adults ('callows') initially have the same cuticular profile, but with time this changes to that typical of foragers. In contrast, workers that begin to produce eggs develop a different cuticular profile. Several substances (n-C29 and some methyl C25 and C27) discriminate these different social categories (callows, foragers and egg-layers). In Diacamma ceylonense, inter-colony variation of the cuticular hydrocarbons was much lower than intra-colony variation. We also found qualitative differences between the sexes, with males having a clearly different profile with much more alkanes. We discuss these results in the context of physiological models of the relation between ovarian activity and the synthesis of cuticular hydrocarbons. Variations in cuticular profile are a reliable reflection of ovarian activity, and could be used by ants as a fertility signal.
Hierarchical perception of fertility signals and nestmate recognition cues in two dolichoderine ants
Behavioral Ecology and Sociobiology, 2009
In social insects, queens are likely to “honestly” inform their nestmates of their presence and fertility status through pheromonal communication. Cuticular hydrocarbons (CHCs) have been reported to be effective nestmate discriminators and strongly suspected to act as fertility signals, at least in some species. The use of the same chemical bouquet (i.e., the CHC profile) to convey two fundamentally different
Animal Behaviour
In social groups, competition often gives rise to conflicts, which are regulated through a variety of mechanisms. In several social insect species, the conflict for male production that takes place between workers after queen loss, is regulated through the establishment of a reproductive hierarchy. A recent study of Neoponera apicalis showed that workers differ in their fertility levels in the presence of the queen and proposed that such idiosyncratic differences might influence access to the top of the hierarchy after queen loss. In this study, we therefore sought to characterize the influence of the initial heterogeneity in ovarian development and its chemical
Fertility signalling and reproductive skew in queenless ants
Animal behaviour, 2004
Social insects often show an extreme reproductive skew. In queenless ants, colonies consist of morphologically identical workers that can all potentially reproduce sexually. Similarly to that in social vertebrates, aggression in these ants functions to select the reproductive(s). We investigated the mechanisms underlying reproductive skew in the monogynous queenless ant Streblognathus peetersi. Behavioural observations of disturbed hierarchies were integrated with physiological measures of fertility (vitellogenin titre in the haemolymph) and chemical analysis of cuticular hydrocarbons, which are putative fertility pheromones. This multifaceted approach revealed that the colony reproductive is determined as a result of aggression between high-ranking workers, but once an alpha is established, chemical signalling is enough to maintain reproductive skew. As already reported in several species of ants and also in a social wasp, egg layers have distinct profiles of cuticular hydrocarbons compared with infertile workers. Importantly, 'high rankers' who are unable to lay eggs also have a specific cuticular profile; this is consistent with their intermediate state of fertility indicated by vitellogenin levels. Rather than just ovarian activity, the cuticular hydrocarbon profile thus reveals the individual hormonal state that underlies reproductive activity. We compare the fertility signal in queenless ants with the 'badge of status' reported in various birds. We discuss the evolutionary stability of this communication system and give special emphasis to ecological constraints and the high degree of intracolonial relatedness typical of social insects.
Egg marking in the facultatively queenless ant Gnamptogenys striatula: The source and mechanism
Journal of Insect Physiology, 2008
Conflicts over reproductive division of labour are common in social insects. These conflicts are often resolved via antagonistic actions that are mediated by chemical cues. Dominant egg layers and their eggs can be recognized by a specific yet similar cuticular hydrocarbon profile. In the facultatively queenless ant Gnamptogenys striatula, a worker's cuticular hydrocarbon profile signals its fertility and this determines its position in the reproductive division of labour. How eggs acquire the same hydrocarbon profile is as yet unclear. Here, we search for glandular sources of egg hydrocarbons and identify the putative mechanism of egg marking. We found that eggs carry the same hydrocarbons as the cuticle of fertile workers, and that these hydrocarbons also occur in the ovaries and the haemolymph. None of the studied glands (Dufour, venom, labial and mandibular gland) contained these hydrocarbons. Our results indicate that hydrocarbons are deposited on eggs while still in the ovaries. The low hydrocarbon concentration in the ovaries, however, suggests they are produced elsewhere and transported through the haemolymph. We also found that fertile workers regularly deposit new hydrocarbons on eggs by rubbing laid eggs with a hairy structure on the abdominal tip from which a non-polar substance is secreted. r
Egg marking in the queen-less ant Gnamptogenys striatula: the source and mechanism.
Conflicts over reproductive division of labour are common in social insects. These conflicts are often resolved via antagonistic actions that are mediated by chemical cues. Dominant egg layers and their eggs can be recognized by a specific yet similar cuticular hydrocarbon profile. In the facultatively queenless ant Gnamptogenys striatula, a worker's cuticular hydrocarbon profile signals its fertility and this determines its position in the reproductive division of labour. How eggs acquire the same hydrocarbon profile is as yet unclear. Here, we search for glandular sources of egg hydrocarbons and identify the putative mechanism of egg marking. We found that eggs carry the same hydrocarbons as the cuticle of fertile workers, and that these hydrocarbons also occur in the ovaries and the haemolymph. None of the studied glands (Dufour, venom, labial and mandibular gland) contained these hydrocarbons. Our results indicate that hydrocarbons are deposited on eggs while still in the ovaries. The low hydrocarbon concentration in the ovaries, however, suggests they are produced elsewhere and transported through the haemolymph. We also found that fertile workers regularly deposit new hydrocarbons on eggs by rubbing laid eggs with a hairy structure on the abdominal tip from which a non-polar substance is secreted. r
Fertility Signaling and Partitioning of Reproduction in the Ant Neoponera apicalis
Journal of Chemical Ecology, 2015
All individuals in social insect colonies benefit from being informed about the presence and fertility state of reproducers. This allows the established reproductive individuals to maintain their reproductive monopoly without the need for physical control, and the non-reproductive individuals to make appropriate reproductive choices. Here, we studied whether fertility signaling is responsible for the partitioning of reproduction in the ant Neoponera apicalis. This species forms small colonies from one single-mated queen, with workers establishing reproductive hierarchies when hopelessly queenless. Previous studies identified putative fertility signals, particularly the hydrocarbon 13-methylpentacosane (13-MeC 25 ), and have shown that precise status discrimination based on these signals could be involved in the regulation of reproductive activities. Here, we extend these findings and reveal that all individuals, be they queens or workers, differ in their cuticular hydrocarbon profile according to fertility state. Proportions of 13-MeC 25 were a strong predictor of an individual's ovarian activity, and could, thus, advertise the established reproducer(s) in both queenright and queenless conditions. Furthermore, this compound might play a key role in the establishment of the reproductive hierarchy, since workers with low fertility at the onset of hierarchy formation already have relatively high amounts of 13-MeC 25 . Dyadic encounters showed that individuals with experimentally increased amounts of 13-MeC 25 triggered less agonistic interactions from top rankers, in accord with them Badvertisingĥ igher status. Thus, these bioassays supported the use of 13-MeC 25 by competing ants. This simple recognition system potentially allows permanent regulation of partitioning of reproduction in this species.
Journal of Chemical Ecology, 2011
Split sex ratio theory predicts that when kin structure varies among colonies of social insects, in order to maximize the inclusive fitness, colonies with relatively high sister-sister relatedness should specialize in producing reproductive females, whereas in those with relatively low sister-sister relatedness workers should bias their sex ratio towards males. However, in order to achieve this, workers need to be able to reliably assess the type of colony in which they live. The information on colony kin structure may be encoded in cuticular hydrocarbons (CHCs), assuming that genetic variability translates accurately into chemical variability. However, in genetically heterogeneous colonies, too accurate information may encourage the pursuit of individual interests through nepotistic behavior and reduce colony efficiency or cause social disruption. In this study, we estimated how well variability of CHC recognition cues reflects colony kin structure in the ant Formica exsecta. Our results show that CHC variability does not covary with kin structure or the overall genetic diversity of the colony, and that patrilines and matrilines can have distinct CHC profiles in some but not all colonies. However, within-colony relatedness remains the key determinant of colony sex ratios. Based on our results, CHC variability cannot serve as accurate information on withincolony relatedness, kin structure, or full-sib affiliation, nor do workers seem to use colony CHC variability as a proxy for sex-ratio adjustment. The use of this type of information thus could lead workers to make mistakes, and it remains unclear how colonies of Formica exsecta adjust offspring sex ratio to their optimal value.