Time-course RNASeq of Camponotus floridanus forager and nurse ant brains indicate links between plasticity in the biological clock and behavioral division of labor

Background Circadian clocks allow organisms to anticipate daily fluctuations in their environment by driving rhythms in physiology and behavior. Inter-organismal differences in daily rhythms, called chronotypes, exist and can shift with age. In ants, age, caste-related behavior and chronotype appear to be linked. Brood-tending nurse ants are usually younger individuals and show “around-the-clock” activity. With age or in the absence of brood, nurses transition into foraging ants that show daily rhythms in activity. Ants can adaptively shift between these behavioral castes and caste-associated chronotypes depending on social context. We investigated how changes in daily gene expression could be contributing to such behavioral plasticity in Camponotus floridanus carpenter ants by combining time-course behavioral assays and RNA-Sequencing of forager and nurse brains. Results We found that nurse brains have three times fewer 24 h oscillating genes than foragers. However, several hundred genes that oscillated every 24 h in forager brains showed robust 8 h oscillations in nurses, including the core clock genes Period and Shaggy. These differentially rhythmic genes consisted of several components of the circadian entrainment and output pathway, including genes said to be involved in regulating insect locomotory behavior. We also found that Vitellogenin, known to regulate division of labor in social insects, showed robust 24 h oscillations in nurse brains but not in foragers. Finally, we found significant overlap between genes differentially expressed between the two ant castes and genes that show ultradian rhythms in daily expression. Conclusion This study provides a first look at the chronobiological differences in gene expression between forager and nurse ant brains. This endeavor allowed us to identify a putative molecular mechanism underlying plastic timekeeping: several components of the ant circadian clock and its output can seemingly oscillate at different harmonics of the circadian rhythm. We propose that such chronobiological plasticity has evolved to allow for distinct regulatory networks that underlie behavioral castes, while supporting swift caste transitions in response to colony demands. Behavioral division of labor is common among social insects. The links between chronobiological and behavioral plasticity that we found in C. floridanus, thus, likely represent a more general phenomenon that warrants further investigation.

Defense in Social Insects: Diversity, Division of Labor, and Evolution

All social insects defend their colony from predators, parasites, and pathogens. In Oster and Wilson's classic work, they posed one of the key paradoxes about defense in social insects: Given the universal necessity of defense, why then is there so much diversity in mechanisms? Ecological factors undoubtedly are important: Predation and usurpation have imposed strong selection on eusocial insects, and active defense by colonies is a ubiquitous feature of all social insects. The description of diverse insect groups with castes of sterile workers whose main duty is defense has broadened the purview of social evolution in insects, in particular with respect to caste and behavior. Defense is one of the central axes along which we can begin to organize and understand sociality in insects. With the establishment of social insect models such as the honey bee, new discoveries are emerging regarding the endocrine, neural, and gene regulatory mechanisms underlying defense in social insects. The mechanisms underlying morphological and behavioral defense traits may be shared across diverse groups, providing opportunities for identifying both conserved and novel mechanisms at work. Emerging themes highlight the context dependency of and interaction between factors that regulate defense in social insects.

Assessment of Feeding Behavior of the Zoo-Housed Lesser Anteater (Tamandua tetradactyla) and Nutritional Values of Natural Prey

Very little information is available to zoo managers on the nutritional preferences of the lesser anteater, a highly specialized predator. By studying lesser anteater feeding behavior, we expect to contribute to improved management decisions and individual welfare experiences. We studied the response of zoo-housed lesser anteaters (n = 7) to feeders with live ants (Acromyrmex lundi) and termites (Cortaritermes fulviceps), and we also evaluated the nutritional values of these prey. We individually evaluated each lesser anteater (3 sessions), recording activities by camera. We ground insect samples into a coarse meal and evaluated in vitro biochemical parameters (humidity, lipids proteins, ash, and carbohydrates). Lesser anteaters spent more time with termites than with ants and consumed more termites. Ant meal presented a higher protein and lipid content than termite meal (35.28 ± 0.18% vs. 18.19 ± 0.34% and 16.95 ± 0.13% vs. 6.54 ± 0.31%, respectively), and carbohydrate digestibility was higher in termites. These findings indicate an association between the level of insect consumption and nutritional and digestibility values. This is the first exploration of lesser anteater responses to the presence of social insects in feeders and may serve to guide the study of food preferences in captivity.

Substantial variability in morphological scaling among bumblebee colonies

Differences in organ scaling among individuals may play an important role in determining behavioural variation. In social insects, there are well-documented intraspecific differences in colony behaviour, but the extent that organ scaling differs within and between colonies remains unclear. Using 12 different colonies of the bumblebee Bombus terrestris , we aim to address this knowledge gap by measuring the scaling relationships between three different organs (compound eyes, wings and antennae) and body size in workers . Though colonies were exposed to different rearing temperatures, this environmental variability did not explain the differences of the scaling relationships. Two colonies had differences in wing versus antenna slopes, three colonies showed differences in wing versus eye slopes and a single colony has differences between eye versus antenna slopes. There are also differences in antennae scaling slopes between three different colonies, and we present evidence for putative trade-offs in morphological investment. We discuss the utility of having variable scaling among colonies and the implication for understanding variability in colony fitness and behaviour.

Perilaku Pemilihan Makanan dan Pengenalan Anggota Koloni pada Semut Rangrang Oecophylla smaragdina

Weaver ants Oecophylla smaragdina are social insects that recognize nestmates using pheromone. This study analyzes the feeding behavior and nestmate recognition of weaver ants in the urban area of three different islands (Sumatra: Baturaja; Java: Banyuwangi; Papua: Sorong). The free ants were placed in the arena composed of chicken meat, sugar, bananas as the baits. Ten trapped ants were also located in the arena to explore the nestmate recognition between the free and the trapped ants. Five types of behaviors, i.e., approach, stalking, communication, competition, and agonistic, were recorded in 6 days. Food preferences were indicated by the number of conduct towards the feeding sites, and nestmate recognition was indicated by approaching the trapped nestmate. The results showed that the percentage of the approach behavior of free ants was the highest in the three islands but had no significant difference between Sumatra and Java and between Java and Sorong (p-value >0.05). However, the study showed significant differences for the other four behaviors observed. As predicted, the percentage of chicken meat foraged by the ants was the highest due to the carnivorous behavior. The free ants showed the nestmate recognition to the trapped ants in all behavior, except competition.

Identification of functional residues using machine learning provides insights into the evolution of odorant receptor gene families in solitary and social insects

The gene family of insect odorant receptors (ORs) has greatly expanded in the course of evolution. ORs allow insects to detect volatile chemicals and therefore play an important role in social interactions, the detection of enemies and preys, and during foraging. The sequences of several thousand ORs are known, but their specific function or ligands have been identified only for very few of them. To advance the functional characterization of ORs, we compiled, curated and aligned the sequences of 3,902 ORs from 21 insect species. We identified the amino acid positions that best predict the response to ligands using machine learning on sets of functionally characterized proteins from the fly Drosophila melanogaster, the mosquito Anopheles gambiae and the ant Harpegnathos saltator. We studied the conservation of these predicted relevant residues across all OR subfamilies and show that the subfamilies that expanded strongly in social insects exhibit high levels of conservation in their binding sites. This indicates that ORs of social insect families are typically finely tuned and exhibit a sensitivity to very similar odorants. Our novel approach provides a powerful tool to use functional information from a limited number of genes to investigate the functional evolution of large gene families.

Histone acetylation regulates the expression of genes involved in worker reproduction in the ant Temnothorax rugatulus

Background In insect societies, queens monopolize reproduction while workers perform tasks such as brood care or foraging. Queen loss leads to ovary development and lifespan extension in workers of many ant species. However, the underlying molecular mechanisms of this phenotypic plasticity remain unclear. Recent studies highlight the importance of epigenetics in regulating plastic traits in social insects. Thus, we investigated the role of histone acetylation in regulating worker reproduction in the ant Temnothorax rugatulus. We removed queens from their colonies to induce worker fecundity, and either fed workers with chemical inhibitors of histone acetylation (C646), deacetylation (TSA), or the solvent (DMSO) as control. We monitored worker number for six weeks after which we assessed ovary development and sequenced fat body mRNA. Results Workers survived better in queenless colonies. They also developed their ovaries after queen removal in control colonies as expected, but not in colonies treated with the chemical inhibitors. Both inhibitors affected gene expression, although the inhibition of histone acetylation using C646 altered the expression of more genes with immunity, fecundity, and longevity functionalities. Interestingly, these C646-treated workers shared many upregulated genes with infertile workers from queenright colonies. We also identified one gene with antioxidant properties commonly downregulated in infertile workers from queenright colonies and both C646 and TSA-treated workers from queenless colonies. Conclusion Our results suggest that histone acetylation is involved in the molecular regulation of worker reproduction, and thus point to an important role of histone modifications in modulating phenotypic plasticity of life history traits in social insects.

The lose-to-win strategy of the weak: intraspecific parasitism via egg abduction in a termite

Predation by larger conspecifics poses a major threat to small juveniles in many animal species. However, in social insects, raids perpetrated by large colonies may provide smaller colonies with opportunities for parasitization. Herein, in the termite Reticulitermes speratus , we demonstrate that small incipient colonies parasitize large mature colonies through egg abduction when attacked by raiding conspecifics. We observed that the eggs of incipient colonies were brought into raiding colonies while their parents were killed during the attack. In this species, unmated females found new colonies with female–female (FF) cooperation, in addition to the typical monogamous colony foundation. Interestingly, the abducted eggs of FF pairs developed into nymphs (reproductive caste) in the raiding colonies, whereas the eggs of male–female (MF) pairs developed into workers (non-reproductive caste). Parthenogenetic eggs are known to be developmentally predisposed to becoming female reproductives owing to genomic imprinting in termites. This study demonstrates that the plundering of small colonies by larger conspecific colonies not only results in the extinction of the weaker colonies, but also serves as a strategy that incipient colonies use to obtain the reproductive position in large colonies by stealth. The results elucidate the diversity and complexity of inter-colonial interactions in social insects.

RFID Technology Serving Honey Bee Research: A Comprehensive Description of a 32-Antenna System to Study Honey Bee and Queen Behavior

The fields of electronics and information technology have witnessed rapid development during the last decades, providing significant technical support to the field of biological sciences. Radio-Frequency Identification (RFID) technology has been used to automate the monitoring of animal location and behaviors in a wide range of vertebrate and invertebrate species, including social insects such as ants and honey bees (Apis mellifera L.) This technology relies on electromagnetic fields to identify and track transponders attached to objects automatically. Implementing new technologies to serve research purposes could be time-consuming and require technical expertise from entomologists and researchers. Herein, we present a detailed description on how to harness RFID technology to serve honey bee research effectively. We describe how to build and operate a 32-antenna RFID system used to monitor various honey bee behaviors such as foraging, robbing, queen and drone mating, which can be used in other social insects as well. Preliminary data related to queen nuptial flights were obtained using this unit and presented in this study. Virgin queens labeled with ~5mg transponders performed multiple (1-4) nuptial/orientation flights a day (9 am to 5 pm) ranging from 8 to 145 seconds each. Contrary to virgin queens, no hive exit was recorded for mated-queens. At full capacity, this unit can monitor up to 32 honey bee colonies concurrently and is self-sustained by a solar panel to work in remote areas. All materials, hardware and software needed to build and operate this unit are detailed in this study, offering researchers and beekeepers a practical solution and a comprehensive source of information enabling the implementation of RFID technology in their research perspective.