Eusocial insects organize themselves into behavioral castes whose regulation has been proposed to involve epigenetic processes, including histone modification. In the carpenter ant Camponotus floridanus, morphologically distinct worker castes called minors and majors exhibit pronounced differences in foraging and scouting behaviors. We found that these behaviors are regulated by histone acetylation likely catalyzed by the conserved acetyltransferase CBP. Transcriptome and chromatin analysis in brains of scouting minors fed pharmacological inhibitors of CBP and histone deacetylases (HDACs) revealed hundreds of genes linked to hyperacetylated regions targeted by CBP. Majors rarely forage, but injection of a HDAC inhibitor or small interfering RNAs against the HDAC Rpd3 into young major brains induced and sustained foraging in a CBP-dependent manner. Our results suggest that behavioral plasticity in animals may be regulated in an epigenetic manner via histone modification.
The sophisticated organization of eusocial insect societies is largely based on the regulation of complex behaviors by hydrocarbon pheromones present on the cuticle. We used electrophysiology to investigate the detection of cuticular hydrocarbons (CHCs) by female-specific olfactory sensilla basiconica on the antenna of Camponotus floridanus ants through the utilization of one of the largest family of odorant receptors characterized so far in insects. These sensilla, each of which contains multiple olfactory receptor neurons, are differentially sensitive to CHCs and allow them to be classified into three broad groups that collectively detect every hydrocarbon tested, including queen and worker-enriched CHCs. This broad-spectrum sensitivity is conserved in a related species, Camponotus laevigatus, allowing these ants to detect CHCs from both nestmates and non-nestmates. Behavioral assays demonstrate that these ants are excellent at discriminating CHCs detected by the antenna, including enantiomers of a candidate queen pheromone that regulates the reproductive division of labor.
Mature colonies of many social insect species exhibit division of labor (DOL) where individual workers specialize in doing only a subset of the multiple tasks needed to maintain homeostasis. In newly initiated ant colonies, however, the first workers (called nanitics) are few in number and much smaller in size than those in mature colonies. This limited workforce must perform most of the tasks of mature colonies, but it is unknown if they also exhibit DOL. In this study, we tracked several inside-nest and outside-nest behaviors of nanitics in incipient Pogonomyrmex rugosus colonies. DOL arises in these colonies, whereby the relatively oldest workers (even if only by a few hours) are biased towards foraging, while younger nanitics concentrate on brood care. The addition of new nanitics shifts behavior in the oldest individual away from brood care but does not immediately increases its foraging. Conversely, nanitics left alone due to mortality of nest-mates forage more, but do not reduce brood care. The results suggest P. rugosus nanitics follow an age-related task specialization pattern that is broadly similar to mature colonies. The nanitic life stage may be, however, unique for ants in how fine-grained the DOL is in terms of absolute age differences and flexibility for task switching. Significance statementThe ecological success of ants is thought to be facilitated by workers dividing their labor across tasks. Commonplace in mature colonies is that individuals will perform safer, within-nest tasks such as brood care when young, and shift as they age towards riskier, outside-nest tasks such as foraging. Because many do the same task, the death of any single worker has minimal effect. We show, for the first time, a similar age-related, task specialization pattern also occurs in newly founded colonies. In this earliest life, history stage workers are small and few in number, precluding the massive task redundancy that characterizes mature colonies. Nevertheless, a division of labor correlating with relative age differences arises even when workers differ in age by only a few hours. This supports the hypothesis that a similar developmental pathway for task allocation in worker behavior occurs at all stages in colony life history.
The invasive success of the exotic Argentine ant [Linepithema humile (Mayr)] is often closely tied to year‐round availability of water sources. Previous studies suggest that the location of such water sources can strongly influence activity patterns of colonies and may be a key predictor of building infestations. We studied activity patterns of Argentine ants in relation to water and food resources in two open‐air structures (aviaries). In one series of manipulations, ant activity inside the aviaries was significantly reduced with the placement of numerous water sources around the outside. Inside activity increased again when the outside water sources were removed. A second series of manipulations involved the placement of water sources at targeted locations outside of the structures. Ant activity inside the aviaries consistently shifted significantly closer to these targeted sites. The results suggest that providing a reliable water source to Argentine ant colonies exterior to buildings can be a non‐chemical method of integrated pest management for reducing ant infestations. Independent of our manipulations, L. humile activity levels predictably declined with time of day, but these changes were uncorrelated with observed surface temperatures. In fact, activity was often noted at surface temperatures higher than those that cause worker mortality under laboratory conditions. This suggests that L. humile exhibits a consistent temperature‐independent circadian activity pattern of reduced foraging in afternoons relative to mornings.
Ants exhibit a size-associated colony founding trait that is characterized by the degree to which foundresses rely on internal reserves to raise their first brood of workers (claustrality). The reliance on stored reserves is positively correlated with degree of claustrality (claustral [ facultative [ semi-claustral) and is variable across species of Pogonomyrmex harvester ants. Three species of harvester ant foundresses that differ in degree of claustrality were observed initiating nests under laboratory conditions over 2 years. P. rugosus is fully claustral, P. salinus is facultative, and P. californicus is semi-claustral. Across species, degree of claustrality was positively associated with mean digging rate and nest depth over the first 3 days of nest initiation, total nest depth, and degree of nest closure. Branching and abundance of peripheral nodes were higher in semi-claustral and facultative nests than in claustral nests. The facultative species dug for the longest time and achieved the greatest tunnel length. Within each species, there were trends associating mass with digging rate, but these were not consistent in all species. There were no intraspecific trends of mass with nest depth. Also within species, a foundress's mass did not affect her tendency to open or close her nest. These results reveal degree of claustrality is correlated across species with several nest initiation characteristics that together may represent different colony founding syndromes.
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