Hormonal correlates of reproductive status in the queenless ponerine ant, Streblognathus peetersi (original) (raw)
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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.
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.
Cuticular hydrocarbons correlated with reproductive status in a queenless ant
Proceedings of The Royal Society B: Biological Sciences, 1999
Reproductive division of labour is regulated behaviourally in social insects lacking morphologically specialized castes. The directional nature of dominance interactions shows that recognition occurs, but little is known about its basis. In the queenless ant Dinoponera quadriceps, the top worker in the hierarchy (`alpha') mates and produces o¡spring in each colony, while other workers remain virgin. Dominant ants frequently rub one antenna of subordinates against their own cuticle, and alpha and infertile nest-mates consistently di¡er in their relative proportions of the cuticular hydrocarbon 9-hentriacontene (9-C 31 ). The second-ranking`beta' occasionally lays unfertilized eggs and we show that she has less 9-C 31 than the alpha but more than infertile workers. To investigate further the link between 9-C 31 and ovarian activity, we experimentally removed alpha workers (n 11 individuals) and used solid-phase microextraction (SPME) with gas chromatography to measure changes in 9-C 31 on live beta workers which attained alpha status. The proportion of 9-C 31 on the replacement alpha increased signi¢cantly after six weeks, in parallel with her gain in fecundity. We discuss whether 9-C 31 provides honest information about egglaying ability, enabling ants to recognize the di¡erent classes of nest-mates involved in reproductive con£icts. Such fertility cues could reliably underpin the antagonistic interactions occurring in insect societies.
Ethology, 2010
We test two hypotheses about regulation of the reproductive division of labour in the permanently queenless ponerine ant, Diacamma sp., from Japan. All workers emerge with gemmae (tiny innervated thoracic appendages), but only one individual keeps them in each colony, and she is the only mated reproductive worker (gamergate). The gemmae of all other workers are mutilated by the gamergate soon after their emergence, and they can never mate. In the presence of gamergate, mutilated workers have inactive ovaries and do not behave aggressively. Two possible consequences of mutilation are: 1. olfactory sigiial-a pheromone inhibiting the oogenesis of mutilated workers is no longer released by the gemmae; and 2. endocrine degeneration of its afferent neuronal connections interferes reproductive physiology of a gamergate. Gemmae of gamergates were coated with shellac (to prevent pheromone emission) or removed, and over three weeks we studied any changes in ovarian activity of the gamergates as well as nestmate workers. Coating of geminae did not elicit worker oviposition, suggesting that gemmae pheromones do not have a regulatory function. Experimental mutilation of gamergates resulted in a slight increase in both the frequency of dominance interactions and the ovarian activity of mutilated workers, but this effect was much lower than in colonies where the gamergate was removed. This contrasts with the immediate change in the behaviour (aggressive to timid) of newly emerged workers following mutilation.
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
Regulation of reproduction in a queenless ant: aggression, pheromones and reduction in conflict
Proceedings. Biological sciences / The Royal Society, 2002
In the monogynous queenless ant Diacamma ceylonense, the future reproductive (future gamergate) is very aggressive towards infertile workers during the first days of her adult life. Overt aggression disappears at about three weeks, when the future gamergate begins to lay male-destined eggs and is ready to mate. Over the same period, her cuticular hydrocarbon profile alters, changing from a chemical signature similar to that of a sterile worker towards that of a gamergate. In nature, these behavioural and chemical changes will coincide with a reduction in conflict within the nest: faced with a virgin future gamergate, infertile workers have an interest in producing male-destined eggs; however, once the gamergate produces female eggs, they have an interest in rearing her offspring. This demonstration of a shift from physical inhibition to chemical signalling is interpreted in terms of sociogenetic theory, the role of cuticular hydrocarbons as an indicator of fertility in insects and t...
Juvenile Hormone in Adult Eusocial Hymenoptera: Gonadotropin and Behavioral Pacemaker
Archives of Insect Biochemistry and Physiology, 1997
Studies on the role of juvenile hormone (JH) in adult social Hymenoptera have focused on the regulation of two fundamental aspects of colony organization: reproductive division of labor between queens and workers and age-related division of labor among workers. JH acts as a gonadotropin in the primitively eusocial wasp and bumble bee species studied, and may also play this role in the advanced eusocial fire ants. However, there is no evidence that JH acts as a traditional gonadotropin in the advanced eusocial honey bee or in the few other ant species that have recently begun to be studied. The role of JH in agerelated division of labor has been most thoroughly examined in honey bees. Results of these studies demonstrate that JH acts as a “behavioral pacemaker,” influencing how fast a worker grows up and makes the transition from nest activities to foraging. Hypotheses concerning the evolutionary relationship between the two functions of JH in adult eusocial Hymenoptera are discussed.
Dominance hierarchy and reproductive conflicts among subordinates in a monogynous queenless ant
Behavioral Ecology, 1999
In insect societies lacking morphologically specialized breeders and helpers, reproduction is often restricted to behaviorally dominant individuals. Such societies occur in about 100 species of ants that have secondarily lost the queen caste. All females, who are morphologically workers, can potentially mate and lay eggs but only a few do so, and we demonstrate in Dinoponera quadriceps that this is regulated by a dominance hierarchy. Six types of agonistic interactions allowed the ranking of 5-10 workers in the hierarchy (n ϭ 15 colonies). In particular, alpha and beta had characteristic behavioral profiles and were easily recognized. Only alpha mated, and workers ranking beta to delta sometimes produced unfertilized, male-destined eggs. Natural replacements (n ϭ 19) and experimental removals (n ϭ 15) of alpha demonstrated that beta was the individual most likely to replace alpha, although gamma and more rarely delta sometimes did, and we discuss the conflict that occurs among high-ranking individuals over who should replace alpha. After such replacements, the new alpha behaved more aggressively than the overthrown alpha. Newly emerged workers tended to reach high ranks and displaced older high-ranking individuals down the hierarchy. Lowranking subordinates often prevented high-ranking individuals from replacing alpha by biting and holding their appendages (worker policing), which is consistent with the pattern of relatedness associated with monogyny and monandry in D. quadriceps. We investigated the relative importance of chemical communication and dominance interactions to regulate reproduction. Alpha, beta, and sterile workers have different signatures of cuticular hydrocarbons, and these may provide honest information which underpins worker policing by low-ranking individuals.