Genetic diversity promotes homeostasis in insect colonies

Dynamics of Information Flow and Task Allocation of Social Insect Colonies: Impacts of Spatial Interactions and Task Switching

Models of social interaction dynamics have been powerful tools for understanding the efficiency of information spread and the robustness of task allocation in social insect colonies. How workers spatially distribute within the colony, or spatial heterogeneity degree (SHD), plays a vital role in contact dynamics, influencing information spread and task allocation. We used agent-based models to explore factors affecting spatial heterogeneity and information flow, including the number of task groups, variation in spatial arrangements, and levels of task switching, to study: (1) the impact of multiple task groups on SHD, contact dynamics, and information spread, and (2) the impact of task switching on SHD and contact dynamics. Both models show a strong linear relationship between the dynamics of SHD and contact dynamics, which exists for different initial conditions. The multiple-task-group model without task switching reveals the impacts of the number and spatial arrangements of task locations on information transmission. The task-switching model allows task-switching with a probability through contact between individuals. The model indicates that the task-switching mechanism enables a dynamical state of task-related spatial fidelity at the individual level. This spatial fidelity can assist the colony in redistributing their workforce, with consequent effects on the dynamics of spatial heterogeneity degree. The spatial fidelity of a task group is the proportion of workers who perform that task and have preferential walking styles toward their task location. Our analysis shows that the task switching rate between two tasks is an exponentially decreasing function of the spatial fidelity and contact rate. Higher spatial fidelity leads to more agents aggregating to task location, reducing contact between groups, thus making task switching more difficult. Our results provide important insights into the mechanisms that generate spatial heterogeneity and deepen our understanding of how spatial heterogeneity impacts task allocation, social interaction, and information spread.

Metabolic scaling as an emergent outcome of variation in metabolic rate

The allometric scaling of metabolic rate and what drives it are major questions in biology with a long history. Since the metabolic rate at any level of biological organization is an emergent property of its lower-level constituents, it is an outcome of the intrinsic heterogeneity among these units and the interactions among them. However, the influence of lower-level heterogeneity on system-level metabolic rate is difficult to investigate, given the tightly integrated body plan of unitary organisms. In this context, social insects such as honeybees can serve as important model systems because unlike unitary organisms, these superorganisms can be taken apart and reassembled in different configurations to study metabolic rate and its various drivers at different levels of organization. This commentary discusses the background of such an approach and how combining it with artificial selection to generate heterogeneity in metabolic rate with an analytical framework to parse out the different mechanisms that contribute to the effects of heterogeneity can contribute to the various models of metabolic scaling. Finally, the absence of the typical allometric scaling relationship among different species of honeybees is discussed as an important prospect for deciphering the role of top-down ecological factors on metabolic scaling. This article is part of the theme issue 'The evolutionary significance of variation in metabolic rates'.

Why do Hymenopteran workers drift to non-natal groups? Generalized reciprocity and the maximization of group and parental success

Eusocial Hymenoptera are often characterized by having facultatively or obligately sterile worker castes. However, findings across an increasing number of species are that some workers are non-natal-they have 'drifted' away from where they were born and raised. Moreover, drifters are often indistinguishable from natal workers in the work and benefits provided to joined groups. This seems an evolutionary paradox of providing benefits to potentially unrelated individuals over close kin. Rather than being mistakes, drifting is proposed to be adaptive if joiners either gain inclusive fitness by preferentially moving to other kin groups or through generalized reciprocity in which exchanging workers across groups raises group-level genetic diversity and creates social heterosis. It is unclear, however, if reciprocity is unlikely because of a susceptibility to cheating. In resolving this question, a series of evolutionary simulations show: (1) Reciprocity can persist under a range of genetic assumptions and scenarios of cheating, (2) cheating almost always evolves, but can be expressed in a variety of ways that are not always predictable, (3) the inclusive fitness hypothesis is equally or more susceptible to cheating. Moreover, existing data in Hymenoptera (although not extensive) are more consistent with generalized reciprocity. This supports a hypothesis that drifting, as a phenomenon, may more often reflect maximization of group and parental fitness rather than fitness gains for the individual drifters.

Social Learning versus Individual Learning in the Division of Labour

Division of labour, or the differentiation of the individuals in a collective across tasks, is a fundamental aspect of social organisations, such as social insect colonies. It allows for efficient resource use and improves the chances of survival for the entire collective. The emergence of large inactive groups of individuals in insect colonies sometimes referred to as laziness, has been a puzzling and hotly debated division-of-labour phenomenon in recent years that is counter to the intuitive notion of effectiveness. It has previously been shown that inactivity can be explained as a by-product of social learning without the need to invoke an adaptive function. While highlighting an interesting and important possibility, this explanation is limited because it is not yet clear whether the relevant aspects of colony life are governed by social learning. In this paper, we explore the two fundamental types of behavioural adaptation that can lead to a division of labour, individual learning and social learning. We find that inactivity can just as well emerge from individual learning alone. We compare the behavioural dynamics in various environmental settings under the social and individual learning assumptions, respectively. We present individual-based simulations backed up by analytic theory, focusing on adaptive dynamics for the social paradigm and cross-learning for the individual paradigm. We find that individual learning can induce the same behavioural patterns previously observed for social learning. This is important for the study of the collective behaviour of social insects because individual learning is a firmly established paradigm of behaviour learning in their colonies. Beyond the study of inactivity, in particular, the insight that both modes of learning can lead to the same patterns of behaviour opens new pathways to approach the study of emergent patterns of collective behaviour from a more generalised perspective.

Invasion potential of hornets (Hymenoptera: Vespidae: Vespa spp.)

Hornets are large, predatory wasps that have the potential to alter biotic communities and harm honey bee colonies once established in non-native locations. Mated, diapausing females (gynes) can easily be transported to new habitats, where their behavioral flexibility allows them to found colonies using local food and nest materials. Of the 22 species in the genus Vespa, five species are now naturalized far from their endemic populations and another four have been detected either in nature or during inspections at borders of other countries. By far the most likely pathway of long-distance dispersal is the transport of gynes in transoceanic shipments of goods. Thereafter, natural dispersal of gynes in spring and accidental local transport by humans cause shorter-range expansions and contribute to the invasion process. Propagule pressure of hornets is unquantified, although it is likely low but unrelenting. The success of introduced populations is limited by low propagule size and the consequences of genetic founder effects, including the extinction vortex linked to single-locus, complementary sex determination of most hymenopterans. Invasion success is enhanced by climatic similarity between source locality and introduction site, as well as genetic diversity conferred by polyandry in some species. These and other factors that may have influenced the successful establishment of invasive populations of V. velutina, V. tropica, V. bicolor, V. orientalis, and V. crabro are discussed. The highly publicized detections of V. mandarinia in North America and research into its status provide a real-time example of an unfolding hornet invasion.

A key gene for the climatic adaptation of Apis cerana populations in China according to selective sweep analysis

BACKGROUND

Apis cerana is widely distributed in China and, prior to the introduction of western honeybees, was the only bee species kept in China. During the long-term natural evolutionary process, many unique phenotypic variations have occurred among A. cerana populations in different geographical regions under varied climates. Understanding the molecular genetic basis and the effects of climate change on the adaptive evolution of A. cerana can promote A. cerana conservation in face of climate change and allow for the effective utilization of its genetic resources.

RESULT

To investigate the genetic basis of phenotypic variations and the impact of climate change on adaptive evolution, A. cerana workers from 100 colonies located at similar geographical latitudes or longitudes were analyzed. Our results revealed an important relationship between climate types and the genetic variation of A. cerana in China, and a greater influence of latitude compared with longitude was observed. Upon selection and morphometry analyses combination for populations under different climate types, we identified a key gene RAPTOR, which was deeply involved in developmental processes and influenced the body size.

CONCLUSION

The selection of RAPTOR at the genomic level during adaptive evolution could allow A. cerana to actively regulate its metabolism, thereby fine-tuning body sizes in response to harsh conditions caused by climate change, such as food shortages and extreme temperatures, which may partially elucidate the size differences of A. cerana populations. This study provides crucial support for the molecular genetic basis of the expansion and evolution of naturally distributed honeybee populations.

Urban ecosystem drives genetic diversity in feral honey bee

Urbanization can change biodiversity in both directions, positive and negative, and despite the rising global trend of urban beekeeping, little is known about the impact of urbanization on the genetic diversity of honey bees. We investigate how urbanization affects the genetic variability of feral and managed honey bee colonies that are spread throughout the entire city, even in highly urban areas, through genetic analysis of 82 worker bees. We found convincing evidence of high genetic differentiation between these two groups. Additionally, by comparing city samples with 241 samples from 46 apiaries in rural parts of the country, variations in mitochondrial tRNAleu-cox2 intergenic region and microsatellite loci indicated that feral colonies have distinct patterns of genetic diversity. These results, with evidence that feral honey bees find niches within highly modified and human-dominated urban landscapes, lead us to conclude that urbanization is a driver of the genetic diversity of feral honey bees in the city.

Behavioral variation across the days and lives of honey bees

In honey bee colonies, workers generally change tasks with age (from brood care, to nest work, to foraging). While these trends are well established, our understanding of how individuals distribute tasks during a day, and how individuals differ in their lifetime behavioral trajectories, is limited. Here, we use automated tracking to obtain long-term data on 4,100+ bees tracked continuously at 3 Hz, across an entire summer, and use behavioral metrics to compare behavior at different timescales. Considering single days, we describe how bees differ in space use, detection, and movement. Analyzing the behavior exhibited across their entire lives, we find consistent inter-individual differences in the movement characteristics of individuals. Bees also differ in how quickly they transition through behavioral space to ultimately become foragers, with fast-transitioning bees living the shortest lives. Our analysis framework provides a quantitative approach to describe individual behavioral variation within a colony from single days to entire lifetimes.

Social Factors in Heat Survival: Multiqueen Desert Ant Colonies Have Higher and More Uniform Heat Tolerance

AbstractInvestigations of thermally adaptive behavioral phenotypes are critical for both understanding climate as a selective force and predicting global species distributions under climate change conditions. Cooperative nest founding is a common strategy in harsh environments for many species and can enhance growth and competitive advantage, but whether this social strategy has direct effects on thermal tolerance was previously unknown. We examined the effects of alternative social strategies on thermal tolerance in a facultatively polygynous (multiqueen) desert ant, Pogonomyrmex californicus, asking whether and how queen number affects worker thermal tolerances. We established and reared lab colonies with one to four queens, then quantified all colony member heat tolerances (maximum critical temperature [CT_max]). Workers from colonies with more queens had higher and less variant CT_max. Our findings resemble weak link patterns, in which colony group thermal performance is improved by reducing frequencies of the most temperature-vulnerable individuals. Using ambient temperatures from our collection site, we show that multiqueen colonies have thermal tolerance distributions that enable increased midday foraging in hot desert environments. Our results suggest advantages to polygyny under climate change scenarios and raise the question of whether improved thermal tolerance is a factor that has enabled the success of polygyne species in other climatically extreme environments.

Multi-queen breeding is associated with the origin of inquiline social parasitism in ants

Social parasites exploit the brood care behavior of their hosts to raise their own offspring. Social parasites are common among eusocial Hymenoptera and exhibit a wide range of distinct life history traits in ants, bees, and wasps. In ants, obligate inquiline social parasites are workerless (or nearly-so) species that engage in lifelong interactions with their hosts, taking advantage of the existing host worker forces to reproduce and exploit host colonies’ resources. Inquiline social parasites are phylogenetically diverse with approximately 100 known species that evolved at least 40 times independently in ants. Importantly, ant inquilines tend to be closely related to their hosts, an observation referred to as ‘Emery’s Rule’. Polygyny, the presence of multiple egg-laying queens, was repeatedly suggested to be associated with the origin of inquiline social parasitism, either by providing the opportunity for reproductive cheating, thereby facilitating the origin of social parasite species, and/or by making polygynous species more vulnerable to social parasitism via the acceptance of additional egg-laying queens in their colonies. Although the association between host polygyny and the evolution of social parasitism has been repeatedly discussed in the literature, it has not been statistically tested in a phylogenetic framework across the ants. Here, we conduct a meta-analysis of ant social structure and social parasitism, testing for an association between polygyny and inquiline social parasitism with a phylogenetic correction for independent evolutionary events. We find an imperfect but significant over-representation of polygynous species among hosts of inquiline social parasites, suggesting that while polygyny is not required for the maintenance of inquiline social parasitism, it (or factors associated with it) may favor the origin of socially parasitic behavior. Our results are consistent with an intra-specific origin model for the evolution of inquiline social parasites by sympatric speciation but cannot exclude the alternative, inter-specific allopatric speciation model. The diversity of social parasite behaviors and host colony structures further supports the notion that inquiline social parasites evolved in parallel across unrelated ant genera in the formicoid clade via independent evolutionary pathways.

Assisted dispersal and reproductive success in an ant species with matchmaking

Workers of the ant Cardiocondyla elegans drop female sexuals into the nest entrance of other colonies to promote outbreeding with unrelated, wingless males. Corroborating the results from previous years, we document that carrier and carried female sexuals are typically related and that the transfer initially occurs mostly from their joint natal colonies to unrelated colonies. Female sexuals mate multiply with up to seven genetically distinguishable males. Contrary to our expectation, the colony growth rate of multiple‐mated and outbred female sexuals was lower than that of inbred or single‐mated females, leading to the question of why female sexuals mate multiply at all. Despite the obvious costs, multiple mating might be a way for female sexuals to “pay rent” for hibernation in an alien nest. We argue that in addition to evade inbreeding depression from regular sibling mating over many generations, assisted dispersal might also be a strategy for minimizing the risk of losing all reproductive investment when nests are flooded in winter.

The ontogeny of selection on genetic diversity in harvester ants

Selection may favour traits throughout an individual's lifetime or at a particular life stage. In many species of social insects, established colonies that are more genetically diverse outperform less diverse colonies with respect to a variety of traits that contribute to fitness, but whether selection favours high diversity in small colonies is unknown. We tested the hypothesis that selection favours genetically diverse colonies during the juvenile period using a multi-year field experiment with the harvester ant, Pogonomyrmex occidentalis. We used controlled matings to generate colonies that varied in genetic diversity and transplanted them into the field. We monitored their survival for seven (the 2015 cohort, n = 149) and six (the 2016 cohort, n = 157) years. Genetically more diverse colonies had greater survival, resulting in significant viability selection. However, in both cohorts survival was not influenced by genetic diversity until colonies were three years old. We suggest that changes in their internal organization enabled colonies to use the benefits of multiple genotypes, and discuss possible mechanisms that can generate this pattern.

Population Structure and Genetic Diversity of Chinese Honeybee (Apis Cerana Cerana) in Central China

Central China has a rich terrain with a temperate monsoon climate and varied natural environments for the Chinese honeybee (Apis cerana cerana). However, little comprehensive research on population genetic diversity has been done in this area. A population survey of the structure and genetic diversity of Apis cerana cerana in this area is deeply needed for understanding adaptation to variable environments and providing more references for the protection of honeybee biodiversity. In this study, we present a dataset of 72 populations of Chinese honeybees collected from nine sites by whole genome sequencing in Central China. We obtained 2,790,214,878 clean reads with an average covering a depth of 22×. A total of 27,361,052 single nucleotide polymorphisms (SNPs) were obtained by mapping to the reference genome with an average mapping rate of 93.03%. Genetic evolution analysis was presented via the population structure and genetic diversity based on the datasets of SNPs. It showed that Apis cerana cerana in plains exhibited higher genetic diversity than in mountain areas. The mantel test between Apis cerana cerana groups revealed that some physical obstacles, especially the overurbanization of the plains, contributed to the differentiation. This study is conducive to elucidating the evolution of Apis cerana in different environments and provides a theoretical basis for investigating and protecting the Chinese honeybee.

Abundant small RNAs in the reproductive tissues and eggs of the honey bee, Apis mellifera

Background

Polyandrous social insects such as the honey bee are prime candidates for parental manipulation of gene expression in offspring. Although there is good evidence for parent-of-origin effects in honey bees the epigenetic mechanisms that underlie these effects remain a mystery. Small RNA molecules such as miRNAs, piRNAs and siRNAs play important roles in transgenerational epigenetic inheritance and in the regulation of gene expression during development.

Results

Here we present the first characterisation of small RNAs present in honey bee reproductive tissues: ovaries, spermatheca, semen, fertilised and unfertilised eggs, and testes. We show that semen contains fewer piRNAs relative to eggs and ovaries, and that piRNAs and miRNAs which map antisense to genes involved in DNA regulation and developmental processes are differentially expressed between tissues. tRNA fragments are highly abundant in semen and have a similar profile to those seen in the semen of other animals. Intriguingly we also find abundant piRNAs that target the sex determination locus, suggesting that piRNAs may play a role in honey bee sex determination.

Conclusions

We conclude that small RNAs may play a fundamental role in honey bee gametogenesis and reproduction and provide a plausible mechanism for parent-of-origin effects on gene expression and reproductive physiology.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12864-022-08478-9.

The Diversity Decline in Wild and Managed Honey Bee Populations Urges for an Integrated Conservation Approach

Many parts of the globe experience severe losses and fragmentation of habitats, affecting the self-sustainability of pollinator populations. A number of bee species coexist as wild and managed populations. Using honey bees as an example, we argue that several management practices in beekeeping threaten genetic diversity in both wild and managed populations, and drive population decline. Large-scale movement of hive stocks, introductions into new areas, breeding programs and trading of queens contribute to reducing genetic diversity, as recent research demonstrated for wild and managed honey bees within a few decades. Examples of the effects of domestication in other organisms show losses of both genetic diversity and fitness functions. Cases of natural selection and feralization resulted in maintenance of a higher genetic diversity, including in a Varroa destructor surviving population of honey bees. To protect the genetic diversity of honey bee populations, exchange between regions should be avoided. The proposed solution to selectively breed all local subspecies for a use in beekeeping would reduce the genetic diversity of each, and not address the value of the genetic diversity present in hybridized populations. The protection of Apis mellifera’s, Apis cerana’s and Apis koschevnikovi’s genetic diversities could be based on natural selection. In beekeeping, it implies to not selectively breed but to leave the choice of the next generation of queens to the colonies, as in nature. Wild populations surrounded by beekeeping activity could be preserved by allowing Darwinian beekeeping in a buffer zone between the wild and regular beekeeping area.

Decoupled evolution of mating biology and social structure in Acromyrmex leaf-cutting ants

Abstract

Insect societies vary greatly in their social structure, mating biology, and life history. Polygyny, the presence of multiple reproductive queens in a single colony, and polyandry, multiple mating by females, both increase the genetic variability in colonies of eusocial organisms, resulting in potential reproductive conflicts. The co-occurrence of polygyny and polyandry in a single species is rarely observed across eusocial insects, and these traits have been found to be negatively correlated in ants. Acromyrmex leaf-cutting ants are well-suited for investigating the evolution of complex mating strategies because both polygyny and polyandry co-occur in this genus. We used microsatellite markers and parentage inference in five South American Acromyrmex species to study how different selective pressures influence the evolution of polygyny and polyandry. We show that Acromyrmex species exhibit independent variation in mating biology and social structure, and polygyny and polyandry are not necessarily negatively correlated within genera. One species, Acromyrmex lobicornis, displays a significantly lower mating frequency compared to others, while another species, A. lundii, appears to have reverted to obligate monogyny. These variations appear to have a small impact on average intra-colonial relatedness, although the biological significance of such a small effect size is unclear. All species show significant reproductive skew between patrilines, but there was no significant difference in reproductive skew between any of the sampled species. We find that the evolution of social structure and mating biology appear to follow independent evolutionary trajectories in different species. Finally, we discuss the evolutionary implications that mating biology and social structure have on life history evolution in Acromyrmex leaf-cutting ants.

Significance statement

Many species of eusocial insects have colonies with multiple queens (polygyny), or queens mating with multiple males (polyandry). Both behaviors generate potentially beneficial genetic diversity in ant colonies as well as reproductive conflict. The co-occurrence of both polygyny and polyandry in a single species is only known from few ant species. Leaf-cutting ants have both multi-queen colonies and multiply mated queens, providing a well-suited system for studying the co-evolutionary dynamics between mating behavior and genetic diversity in colonies of eusocial insects. We used microsatellite markers to infer the socio-reproductive behavior in five South American leaf-cutter ant species. We found that variation in genetic diversity in colonies was directly associated with the mating frequencies of queens, but not with the number of queens in a colony. We suggest that multi-queen nesting and mating frequency evolve independently of one another, indicating that behavioral and ecological factors other than genetic diversity contribute to the evolution of complex mating behaviors in leaf-cutting ants.

Slow-Fast Cognitive Phenotypes and Their Significance for Social Behavior: What Can We Learn From Honeybees?

Cognitive variation is proposed to be the fundamental underlying factor that drives behavioral variation, yet it is still to be fully integrated with the observed variation at other phenotypic levels that has recently been unified under the common pace-of-life framework. This cognitive and the resulting behavioral diversity is especially significant in the context of a social group, the performance of which is a collective outcome of this diversity. In this review, we argue about the utility of classifying cognitive traits along a slow-fast continuum in the larger context of the pace-of-life framework. Using Tinbergen’s explanatory framework for different levels of analyses and drawing from the large body of knowledge about honeybee behavior, we discuss the observed interindividual variation in cognitive traits and slow-fast cognitive phenotypes from an adaptive, evolutionary, mechanistic and developmental perspective. We discuss the challenges in this endeavor and suggest possible next steps in terms of methodological, statistical and theoretical approaches to move the field forward for an integrative understanding of how slow-fast cognitive differences, by influencing collective behavior, impact social evolution.

Direct evidence for increased disease resistance in polyandrous broods exists only in eusocial Hymenoptera

Background

The ‘genetic diversity’ hypothesis posits that polyandry evolved as a mechanism to increase genetic diversity within broods. One extension of this hypothesis is the ‘genetic diversity for disease resistance’ hypothesis (GDDRH). Originally designed for eusocial Hymenoptera, GDDRH states that polyandry will evolve as an effect of lower parasite prevalence in genetically variable broods. However, this hypothesis has been broadly applied to several other taxa. It is unclear how much empirical evidence supports GDDRH specifically, especially outside eusocial Hymenoptera.

Results

This question was addressed by conducting a literature review and posteriorly conducting meta-analyses on the data available using Hedges’s g. The literature review found 10 direct and 32 indirect studies with both having a strong publication bias towards Hymenoptera. Two meta-analyses were conducted and both found increased polyandry (direct tests; n = 8, g = 0.2283, p =  < 0.0001) and genetic diversity generated by other mechanisms (indirect tests; n = 10, g = 0.21, p =  < 0.0001) reduced parasite load. A subsequent moderator analysis revealed that there were no differences among Orders, indicating there may be applicability outside of Hymenoptera. However, due to publication bias and low sample size we must exercise caution with these results.

Conclusion

Despite the fact that the GDDRH was developed for Hymenoptera, it is frequently applied to other taxa. This study highlights the low amount of direct evidence supporting GDDRH, particularly outside of eusocial Hymenoptera. It calls for future research to address species that have high dispersal rates and contain mixes of solitary and communal nesting.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12862-021-01925-3.

The Collective Behavior of Ant Groups Depends on Group Genotypic Composition

Recently, researchers have documented variation between groups in collective behavior. However, how genetic variation within and between groups contributes to population-level variation for collective behavior remains unclear. Understanding how genetic variation of group members relates to group-level phenotypes is evolutionarily important because there is increasing evidence that group-level behavioral variation influences fitness and that the genetic architecture of group-level traits can affect the evolutionary dynamics of traits. Social insects are ideal for studying the complex relationship between individual and group-level variation because they exhibit behavioral variation at multiple scales of organization. To explore how the genetic composition of groups affects collective behavior, we constructed groups of pharaoh ants (Monomorium pharaonis) from 33 genetically distinct colonies of known pedigree. The groups consisted of either all workers from the same single colony or workers from two genetically different colonies, and we assayed the exploration and aggression of the groups. We found that collective exploration, but not aggression, depended on the specific genotypic combination of group members, i.e., we found evidence for genotype-by-genotype epistasis for exploration. Group collective behavior did not depend on the pedigree relatedness between genotypes within groups. Overall, this study highlights that specific combinations of genotypes influence group-level phenotypes, emphasizing the importance of considering nonadditive effects of genotypic interactions between group members.

The benefits of being big and diverse: early colony survival in harvester ants

In sessile organisms such as plants and benthic invertebrates, founding propagules typically suffer extremely high rates of mortality due to both extrinsic and intrinsic factors. Many social insect species share similarities with these groups, but factors influencing early colony survival are relatively unstudied. We used a field experiment to measure the importance of environmental quality relative to intrinsic colony properties in the harvester ant, Pogonomyrmex occidentalis, by monitoring the survival of 584 experimental colonies. We measured survival of transplanted colonies over four months in each of three years (2014-2016) at a site in western Colorado. Colony survival was primarily determined by colony features. Multiple mating by the queen and larger colony size at the time of transplant increased survival, but queen size, maternal lineage and the composition of plant species in the vicinity of the colony did not. Food supplementation increased survival significantly when natural food was scarce, but was not consistently beneficial, in contrast to predictions. Our results emphasize the general importance of rapid growth and early attainment of large size in the survival of sessile species. However, attributes specific to ants that are a consequence of their sociality also strongly affected survival. Colonies with multiply-mated queens were more likely to survive over a wide range of circumstances, highlighting the importance of this trait even at the early stages of colony life.

Experimental increase of worker diversity benefits brood production in ants

BACKGROUND

The reproductive division of labor of eusocial insects, whereby one or several queens monopolize reproduction, evolved in a context of high genetic relatedness. However, many extant eusocial species have developed strategies that decrease genetic relatedness in their colonies, suggesting some benefits of the increased diversity. Multiple studies support this hypothesis by showing positive correlations between genetic diversity and colony fitness, as well as finding effects of experimental manipulations of diversity on colony performance. However, alternative explanations could account for most of these reports, and the benefits of diversity on performance in eusocial insects still await validation. In this study, we experimentally increased worker diversity in small colonies of the ant Lasius niger while controlling for typical confounding factors.

RESULTS

We found that experimental colonies composed of workers coming from three different source colonies produced more larvae and showed more variation in size compared to groups of workers coming from a single colony.

CONCLUSIONS

We propose that the benefits of increased diversity stemmed from an improved division of labor. Our study confirms that worker diversity enhances colony performance, thus providing a possible explanation for the evolution of multiply mated queens and multiple-queen colonies in many species of eusocial insects.

Social insect colonies are more likely to accept unrelated queens when they come with workers

Relatedness underlies the evolution of reproductive altruism, yet eusocial insect colonies occasionally accept unrelated reproductive queens. Why would workers living in colonies with related queens accept unrelated ones, when they do not gain indirect fitness through their reproduction? To understand this seemingly paradox, we investigated whether acceptance of unrelated queens by workers is an incidental phenomenon resulting from failure to recognize non-nestmate queens, or whether it is adaptively favored in contexts where cooperation is preferable to rejection. Our study system is the socially polymorphic Alpine silver ant, Formica selysi. Within populations, some colonies have a single queen, and others have multiple, sometimes unrelated, breeding queens. Social organization is determined by a supergene with two haplotypes. In a first experiment, we investigated whether the number of reproductive queens living in colonies affects the ability of workers at rejecting alien queens, as multiple matrilines within colonies could increase colony odor diversity and reduce workers’ recognition abilities. As workers rejected all alien queens, independently of the number of queens heading their colony, we then investigated whether their acceptance is flexible and favored in specific conditions. We found that workers frequently accepted alien queens when these queens came with a workforce. Our results show that workers flexibly adjust their acceptance of alien queens according to the situation. We discuss how this conditional acceptance of unrelated queens may be adaptive by providing benefits through increased colony size and/or genetic diversity, and by avoiding rejection costs linked to fighting.

Task syndromes: linking personality and task allocation in social animal groups

Studies of eusocial insects have extensively investigated two components of task allocation: how individuals distribute themselves among different tasks in a colony and how the distribution of labor changes to meet fluctuating task demand. While discrete age- and morphologically-based task allocation systems explain much of the social order in these colonies, the basis for task allocation in non-eusocial organisms and within eusocial castes remains unknown. Building from recent advances in the study of among-individual variation in behavior (i.e., animal personalities), we explore a potential mechanism by which individuality in behaviors unrelated to tasks can guide the developmental trajectories that lead to task specialization. We refer to the task-based behavioral syndrome that results from the correlation between the antecedent behavioral tendencies and task participation as a task syndrome. In this review, we present a framework that integrates concepts from a long history of task allocation research in eusocial organisms with recent findings from animal personality research to elucidate how task syndromes and resulting task allocation might manifest in animal groups. By drawing upon an extensive and diverse literature to evaluate the hypothesized framework, this review identifies future areas for study at the intersection of social behavior and animal personality.

Large body size variation is associated with low communication success in tandem running ants

Abstract

Diversity in animal groups is often assumed to increase group performance. In insect colonies, genetic, behavioural and morphological variation among workers can improve colony functioning and resilience. However, it has been hypothesized that during communication processes, differences between workers, e.g. in body size, could also have negative effects. Tandem running is a common recruitment strategy in ants and allows a leader to guide a nestmate follower to resources. A substantial proportion of tandem runs fail because leader and follower lose contact. Using the ant Temnothorax nylanderi as a model system, we tested the hypothesis that tandem running success is impaired if leader and follower differ in size. Indeed, we found that the success rate of tandem pairs drops considerably as size variation increases: tandem runs were unsuccessful when the leader–follower size difference exceeded 10%, whereas ~ 80% of tandem runs were successful when ants differed less than 5% in body length. Possible explanations are that size differences are linked to differences in walking speed or sensory perception. Ants did not choose partners of similar size, but extranidal workers were larger than intranidal workers, which could reduce recruitment mistakes because it reduced the chance that very large and very small ants perform tandem runs together. Our results suggest that phenotypic differences between interacting workers can have negative effects on the efficiency of communication processes. Whether phenotypic variation has positive or negative effects is likely to depend on the task and the phenotypic trait that shows variation.

Significance statement

Diversity is often assumed to increase colony performance in social insects. However, phenotypic differences among workers could also have negative effects, e.g. during communication. Tandem running is a common recruitment strategy in ants, but tandem runs often fail when ants lose contact. We used the ant Temnothorax nylanderi to test the hypothesis that body size differences between tandem leader and follower impair tandem communication. We show that the success rate of tandem pairs drops considerably as size variation increases, possibly because ants of varying size also differ in walking speed. Our study supports the hypothesis that phenotypic variation among workers might not always be beneficial and can negatively impact the efficiency of communication processes.

Sociogenetic Organization of the Red Honey Ant (Melophorus bagoti)

Kin selection and inclusive fitness are thought to be key factors explaining the reproductive altruism displayed by workers in eusocial insect species. However, when a colony's queen has mated with <2 males, workers may increase their fitness by producing their own male offspring. Conversely, when the queen has mated with ≥2 males, workers are expected to increase their inclusive fitness by eschewing the production of their sons and preventing other workers from reproducing as well. Here, we investigated sociogenetic structure and worker reproduction in the red honey ant, Melophorus bagoti. Morphometric analyses revealed that workers belong to one of two distinct subcastes: they are either majors or minors. Using DNA microsatellite markers, we showed that all the colonies had a single, multiple-mated queen and that there was no relationship between worker patriline and worker subcaste. Furthermore, we found that workers were producing males in the presence of the queen, which contrasts with the predictions of inclusive fitness theory. Although our results are based on a small sample, they can serve as the foundation for future research examining worker reproduction in M. bagoti.

Genome-wide patterns of differentiation within and among U.S. commercial honey bee stocks

BACKGROUND

The population genetics of U.S. honey bee stocks remain poorly characterized despite the agricultural importance of Apis mellifera as the major crop pollinator. Commercial and research-based breeding programs have made significant improvements of favorable genetic traits (e.g. production and disease resistance). The variety of bees produced by artificial selection provides an opportunity to characterize the genetic diversity and regions of the genome undergoing selection in commonly managed stocks.

RESULTS

Pooled sequencing of eight honey bee stocks found strong genetic similarity among six of the stocks. Two stocks, Pol-line and Hilo, showed significant differentiation likely due to their intense and largely closed breeding for resistance to the parasitic Varroa mite. Few variants were identified as being specific to any one stock, indicating potential admixture among the sequenced stocks. Juxtaposing the underlying genetic variation of stocks selected for disease- and parasite-resistance behavior, we identified genes and candidate regions putatively associated with resistance regulated by hygienic behavior.

CONCLUSION

This study provides important insights into the distinct genetic characteristics and population diversity of honey bee stocks used in the United States, and provides further evidence of high levels of admixture in commercially managed honey bee stocks. Furthermore, breeding efforts to enhance parasite resistance in honey bees may have created unique genetic profiles. Genomic regions of interest have been highlighted for potential future work related to developing genetic markers for selection of disease and parasite resistance traits. Due to the vast genomic similarities found among stocks in general, our findings suggest that additional data regarding gene expression, epigenetic and regulatory information are needed to more fully determine how stock phenotypic diversity is regulated.

Digging into the Genomic Past of Swiss Honey Bees by Whole-Genome Sequencing Museum Specimens

Historical specimens in museum collections provide opportunities to gain insights into the genomic past. For the Western honey bee, Apis mellifera L., this is particularly important because its populations are currently under threat worldwide and have experienced many changes in management and environment over the last century. Using Swiss Apis mellifera mellifera as a case study, our research provides important insights into the genetic diversity of native honey bees prior to the industrial-scale introductions and trade of non-native stocks during the 20th century—the onset of intensive commercial breeding and the decline of wild honey bees following the arrival of Varroa destructor. We sequenced whole-genomes of 22 honey bees from the Natural History Museum in Bern collected in Switzerland, including the oldest A. mellifera sample ever sequenced. We identify both, a historic and a recent migrant, natural or human-mediated, which corroborates with the population history of honey bees in Switzerland. Contrary to what we expected, we find no evidence for a significant genetic bottleneck in Swiss honey bees, and find that genetic diversity is not only maintained, but even slightly increased, most probably due to modern apicultural practices. Finally, we identify signals of selection between historic and modern honey bee populations associated with genes enriched in functions linked to xenobiotics, suggesting a possible selective pressure from the increasing use and diversity of chemicals used in agriculture and apiculture over the last century.

A National Survey of Managed Honey Bee Colony Winter Losses (Apis mellifera) in China (2013–2017)

Surveys of managed honey bee colony losses worldwide have become fundamental for engineering a sustainable and systematic approach to protect honey bees. Though China is a member of the world’s apiculture superpowers, the investigation of honey bee colony losses from Chinese government was not formally launched until recently. In this study, we investigated the colony winter losses of the western honey bee (Apis mellifera) of four consecutive years in 2013–2017 from 19 provinces in China, with a total of 2387 responding Chinese beekeepers (195 hobby beekeepers, 1789 side-line beekeepers, 403 commercial beekeepers) providing the records of overwintering mortality of honey bee colonies. The calculated colony losses were 8.7%, a relatively low mortality below the world average. There still exist considerable variations in total losses among provinces (ranging from 0.9% to 22.0%), years (ranging from 8.1% to 10.6%) and scales of apiaries (ranging from 7.5% to 10.0%). Furthermore, we deeply analyzed and estimated the effects of potential risk factors on the colonies’ winter losses, and speculated that the queen problems, the operation sizes and proportion of new queens are leading causes of the high honey bee colony mortality in China. More research and advanced technical methods are still required for correlation analysis and verification in future surveys of managed honey bee colony winter losses.

Polyandry and paternity affect disease resistance in eusocial wasps

Polyandry (multiple mating by females) is a central challenge for understanding the evolution of eusociality. Several hypotheses have been proposed to explain its observed benefits in eusocial Hymenoptera, one of which, the parasite–pathogen hypothesis (PPH), posits that high genotypic variance among workers for disease resistance prevents catastrophic colony collapse. We tested the PPH in the polyandrous wasp Vespula shidai. We infected isolated workers with the entomopathogenic fungus Beauveria bassiana and quantified their survival in the laboratory. Additionally, we conducted a paternity analysis of the workers using nine microsatellite loci to investigate the relationship between survival and the matriline and patriline membership of the workers. As predicted by the PPH, nestmate workers of different patrilines showed differential resistance to B. bassiana. We also demonstrated variation in virulence among strains of B. bassiana. Our results are the first to directly support the PPH in eusocial wasps and suggest that similar evolutionary pressures drove the convergent origin and maintenance of polyandry in ants, bees, and wasps.

Declining genetic diversity of European honeybees along the twentieth century

The European honeybee (Apis mellifera) is a key pollinator and has in the last decades suffered significant population decline. A combination of factors, including decrease in genetic diversity and introduction of Varroa mites, have been suggested to be responsible for these losses, but no definitive cause has yet been appointed. In Europe not only have wild colonies been severely affected, but managed hives have had a massive decline in numbers. To test the hypothesis that honeybees’ genetic diversity has decreased in the recent past, we used reduced representation genome sequencing of 40 historical honeybee specimens collected in Natural History collections across Europe and compared them to genomic data from 40 individuals from extant populations (collected post 2006). Our results are consistent with the existence of five evolutionary lineages as previously described, and show a decrease in genetic diversity between historical and extant individuals of the same lineage, as well as high levels of admixture in historical specimens. Our data confirm that a loss of genetic diversity has occurred during the last century, potentially increasing honeybees’ vulnerability to contemporary ecological and anthropogenic stressors.

A computational model of task allocation in social insects: ecology and interactions alone can drive specialisation

Social insects allocate their workforce in a decentralised fashion, addressing multiple tasks and responding effectively to environmental changes. This process is fundamental to their ecological success, but the mechanisms behind it are not well understood. While most models focus on internal and individual factors, empirical evidence highlights the importance of ecology and social interactions. To address this gap, we propose a game theoretical model of task allocation. Our main findings are twofold: Firstly, the specialisation emerging from self-organised task allocation can be largely determined by the ecology. Weakly specialised colonies in which all individuals perform more than one task emerge when foraging is cheap; in contrast, harsher environments with high foraging costs lead to strong specialisation in which each individual fully engages in a single task. Secondly, social interactions lead to important differences in dynamic environments. Colonies whose individuals rely on their own experience are predicted to be more flexible when dealing with change than colonies relying on social information. We also find that, counter to intuition, strongly specialised colonies may perform suboptimally, whereas the group performance of weakly specialised colonies approaches optimality. Our simulation results fully agree with the predictions of the mathematical model for the regions where the latter is analytically tractable. Our results are useful in framing relevant and important empirical questions, where ecology and interactions are key elements of hypotheses and predictions.

Population Genomics Provide Insights into the Evolution and Adaptation of the Eastern Honey Bee (Apis cerana)

The mechanisms by which organisms adapt to variable environments are a fundamental question in evolutionary biology and are important to protect important species in response to a changing climate. An interesting candidate to study this question is the honey bee Apis cerana, a keystone pollinator with a wide distribution throughout a large variety of climates, that exhibits rapid dispersal. Here, we resequenced the genome of 180 A. cerana individuals from 18 populations throughout China. Using a population genomics approach, we observed considerable genetic variation in A. cerana. Patterns of genetic differentiation indicate high divergence at the subspecies level, and physical barriers rather than distance are the driving force for population divergence. Estimations of divergence time suggested that the main branches diverged between 300 and 500 Ka. Analyses of the population history revealed a substantial influence of the Earth's climate on the effective population size of A. cerana, as increased population sizes were observed during warmer periods. Further analyses identified candidate genes under natural selection that are potentially related to honey bee cognition, temperature adaptation, and olfactory. Based on our results, A. cerana may have great potential in response to climate change. Our study provides fundamental knowledge of the evolution and adaptation of A. cerana.

Genetic Characterization of Exotic Commercial Honey Bee (Hymenoptera: Apidae) Populations in Thailand Reveals High Genetic Diversity and Low Population Substructure

Domestication of animal species is often associated with a reduction in genetic diversity. The honey bee, Apis mellifera Linnaeus, 1758, has been managed by beekeepers for millennia for both honey and wax production and for crop pollination. Here we use both microsatellite markers and sequence data from the mitochondrial COI gene to evaluate genetic variation of managed A. mellifera in Thailand, where the species is introduced. Microsatellite analysis revealed high average genetic diversity with expected heterozygosities ranging from 0.620 ± 0.184 to 0.734 ± 0.071 per locus per province. Observed heterozygosities were generally lower than those expected under Hardy-Weinberg equilibrium, both locally and across the population as a whole. Mitochondrial sequencing revealed that the frequency of two evolutionary linages (C-Eastern European and O-Middle Eastern) are similar to those observed in a previous survey 10 yr ago. Our results suggest that Thai beekeepers are managing their A. mellifera in ways that retain overall genetic diversity, but reduce genetic diversity between apiaries.

Population genomics and morphological features underlying the adaptive evolution of the eastern honey bee (Apis cerana)

Background

The adaptation of organisms to changing environments is self-evident, with the adaptive evolution of organisms to environmental changes being a fundamental problem in evolutionary biology. Bees can pollinate in various environments and climates and play important roles in maintaining the ecological balance of the earth.

Results

We performed an analysis of 462 Apis cerana (A. cerana) specimens from 31 populations in 11 regions and obtained 39 representative morphological features. We selected 8 A. cerana samples from each population and performed 2b-RAD simplified genome sequencing. A total of 11,506 high-quality single nucleotide polymorphism (SNP) loci were obtained. For these SNPs, the minor allele frequency (MAF) was > 1%, the average number of unique labels for each sample was 49,055, and the average depth was 72.61x. The ratios of the unique labels of all samples were 64.27–86.33%.

Conclusions

Using 39 morphological characteristics as the data set, we proposed a method for the rapid classification of A. cerana. Using genomics to assess population structure and genetic diversity, we found that A. cerana has a large genetic difference at the ecotype level. A comparison of A. cerana in North China revealed that some physical obstacles, especially the overurbanization of the plains, have isolated the populations of this species. We identified several migration events in North China and Central China. By comparing the differences in the environmental changes in different regions, we found that A. cerana has strong potential for climate change and provides a theoretical basis for investigating and protecting A. cerana.

Defining Pollinator Health: A Holistic Approach Based on Ecological, Genetic, and Physiological Factors

Evidence for global bee population declines has catalyzed a rapidly evolving area of research that aims to identify the causal factors and to effectively assess the status of pollinator populations. The term pollinator health emerged through efforts to understand causes of bee decline and colony losses, but it lacks a formal definition. In this review, we propose a definition for pollinator health and synthesize the available literature on the application of standardized biomarkers to assess health at the individual, colony, and population levels. We focus on biomarkers in honey bees, a model species, but extrapolate the potential application of these approaches to monitor the health status of wild bee populations. Biomarker-guided health measures can inform beekeeper management decisions, wild bee conservation efforts, and environmental policies. We conclude by addressing challenges to pollinator health from a One Health perspective that emphasizes the interplay between environmental quality and human, animal, and bee health.

Queen Execution, Diploid Males, and Selection For and Against Polyandry in the Brazilian Stingless Bee Scaptotrigona depilis

Female mating frequency varies. Determining the causes of this variation is an active research area. We tested the hypothesis that in stingless bees, Meliponini, single mating is due to the execution of queens that make a matched mating at the complementary sex determination locus and have diploid male offspring. We studied the Brazilian species Scaptotrigona depilis. We made up 70 test colonies so that 50% (single matched mating), 25% (double mating), 12.5% (quadruple mating), or 0% (single nonmatched mating) of the emerging brood were diploid males. Queen execution following diploid male emergence was equal and high in colonies producing 50% (77% executed) and 25% (75%) diploid males versus equal and low in colonies producing 12.5% (7%) and 0% (0%) diploid males. These results show that queens that mate with two males with similar paternity suffer an increased chance of being executed, which selects against double mating. However, double mating with unequal paternity (e.g., 25∶75), which occasionally occurs in S. depilis, is selectively neutral. Single mating and double mating with unequal paternity form one adaptive peak. The results show a second adaptive peak at quadruple mating. However, this is inaccessible via gradual evolutionary change in a selective landscape with reduced fitness at double mating.

Unique DNA Methylation Profiles Are Associated with cis-Variation in Honey Bees

DNA methylation is an important epigenetic modification that mediates diverse processes such as cellular differentiation, phenotypic plasticity, and genomic imprinting. Mounting evidence suggests that local DNA sequence variation can be associated with particular DNA methylation states, indicating that the interplay between genetic and epigenetic factors may contribute synergistically to the phenotypic complexity of organisms. Social insects such as ants, bees, and wasps have extensive phenotypic plasticity manifested in their different castes, and this plasticity has been associated with variation in DNA methylation. Yet, the influence of genetic variation on DNA methylation state remains mostly unknown. Here we examine the importance of sequence-specific methylation at the genome-wide level, using whole-genome bisulfite sequencing of the semen of individual honey bee males. We find that individual males harbor unique DNA methylation patterns in their semen, and that genes that are more variable at the epigenetic level are also more likely to be variable at the genetic level. DNA sequence variation can affect DNA methylation by modifying CG sites directly, but can also be associated with local variation in cis that is not CG-site specific. We show that covariation in sequence polymorphism and DNA methylation state contributes to the individual-specificity of epigenetic marks in social insects, which likely promotes their retention across generations, and their capacity to influence evolutionary adaptation.

Substantial Heritable Variation in Recombination Rate on Multiple Scales in Honeybees and Bumblebees

Meiotic recombination shuffles genetic variation and promotes correct segregation of chromosomes. Rates of recombination vary on several scales, both within genomes and between individuals, and this variation is affected by both genetic and environmental factors. Social insects have extremely high rates of recombination, although the evolutionary causes of this are not known. Here, we estimate rates of crossovers and gene conversions in 22 colonies of the honeybee, Apis mellifera, and 9 colonies of the bumblebee, Bombus terrestris, using direct sequencing of 299 haploid drone offspring. We confirm that both species have extremely elevated crossover rates, with higher rates measured in the highly eusocial honeybee than the primitively social bumblebee. There are also significant differences in recombination rate between subspecies of honeybee. There is substantial variation in genome-wide recombination rate between individuals of both A. mellifera and B. terrestris and the distribution of these rates overlap between species. A large proportion of interindividual variation in recombination rate is heritable, which indicates the presence of variation in trans-acting factors that influence recombination genome-wide. We infer that levels of crossover interference are significantly lower in honeybees compared to bumblebees, which may be one mechanism that contributes to higher recombination rates in honeybees. We also find a significant increase in recombination rate with distance from the centromere, mirrored by methylation differences. We detect a strong transmission bias due to GC-biased gene conversion associated with noncrossover gene conversions. Our results shed light on the mechanistic causes of extreme rates of recombination in social insects and the genetic architecture of recombination rate variation.

Conflict and major transitions - why we need true queens

In contrast to human societies, where kings and queens can be sources of conflict, we argue that the morphologically distinct queens of insect colonies are central to the minimization of conflict within their societies. Thus, the evolution of irreversible queen and worker castes represents a major transition in social evolution. Queens are selected to become better reproducers, and workers are selected to become better workers. The reproductive success of queens and workers are, therefore, inextricably linked. Workers achieve reproductive success by assisting the queen, whereas the queen needs her workers to provide her with the wherewithal to raise her brood. The tighter the mutual dependence, the lower conflict, and the larger insect societies can become. As the queen becomes a better breeder, workers are selected to become better at raising their siblings. Yet, nothing in nature is ever free of conflict and with the evolution of a true worker caste a new set of conflicts arises. Multiple mating by queens in particular opens the door to a new set of conflicts. Ironically, multiple mating can only evolve once within-colony conflict is reduced by evolving a true worker caste.

Within-individual behavioural variability and division of labour in social insects

Division of labour, whereby individuals divide the workload in a group, is a recurrent property of social living. The current conceptual framework for division of labour in social insects is provided by the response-threshold model. This model posits that the differences between individuals (i.e. between-individual variability) in responsiveness to task-associated stimuli is a key feature for task specialisation. The consistency of individual behaviours (i.e. within-individual variability) in task performance represents an additional but little-considered component driving robust patterns of division of labour. On the one hand, the presence of workers with a high level of within-individual variability presumably allows colonies to rapidly adapt to external fluctuations. On the other hand, a reduced degree of within-individual variability promotes a stricter specialisation in task performance, thereby limiting the costs of task switching. The ideal balance between flexibility and canalisation probably varies depending on the developmental stage of the colony to satisfy its changing needs. Here, I introduce the main sources of within-individual variability in behaviours in social insects and I review neural correlates accompanying the changes in behavioural flexibility. I propose the hypothesis that the positive scaling between group size and the intensity of task specialisation, a relationship consistently reported both within and between taxa, may rely on reduced within-individual variability via self-organised processes linked to the quality of brood care. Overall, I emphasise the need for a more comprehensive characterisation of the response dynamics of individuals to better understand the mechanisms shaping division of labour in social insects.

Comparative screening of endosymbiotic bacteria associated with the asexual and sexual lineages of the termite Glyptotermes nakajimai

Males provide opportunities both for sexual reproduction and for sex-based phenotypic differences within animal societies. In termites, the ubiquitous presence of both male and female workers and soldiers indicate that males play a critical role in colonies of these insects. However, we have recently reported all-female asexual societies in a lineage of the termite Glyptotermes nakajimai – a dramatic transition from mixed-sex to all-female asexual societies. It is known that female-producing parthenogenesis in insects can be induced by maternally inherited endosymbiotic bacteria, such as Wolbachia, Cardinium, and Rickettsia. Here, we screen for the presence of endosymbiotic bacteria in the asexual and sexual lineages of G. nakajimai. Our bacterial screening of the asexual lineage did not reveal any likely causal agents for parthenogenetic reproduction, whereas screening of the sexual lineage resulted in Wolbachia being detected. Our findings suggest that the asexuality in G. nakajimai is likely to be maintained without manipulation by endosymbiotic bacteria.

Genetic Diversity in the Progeny of Commercial Australian Queen Honey Bees (Hymenoptera: Apidae) Produced in Autumn and Early Spring

Honey bee [Apis mellifera L. (Hymenoptera: Apidae)] queens are polyandrous, mating with an average 12 males (drones). Polyandry has been shown to confer benefits to queens and the colonies they head, including avoidance of inviable brood that can arise via sex locus homozygosity, increased resilience to pests and pathogens, and increased survival and productivity, leading to improved colony-level fitness. Queens with an effective mating frequency (ke) greater than 7 are considered adequately mated, whereas queens that fall below this threshold head colonies that have increased likelihood of failure and may be less productive for beekeepers. We determined ke in queens produced in early Spring and Autumn by five Australian commercial queen producers to determine whether the queens they produced were suitably mated. Drone populations are low at these times of year, and therefore, there is an increased risk that queens would fall below the ke > 7 threshold. We found that 33.8% of Autumn-produced queens did not meet the threshold, whereas 93.8% of Spring queens were adequately mated. The number of colonies contributing drones to the mating pool was similarly high in both seasons, suggesting that although many colonies have drones, their numbers may be decreased in Autumn and management strategies may be required to boost drone numbers at this time. Finally, queens had similar levels of homozygosity to workers, and inbreeding coefficients were very low, suggesting that inbreeding is not a problem.

Caste-Specific Expression of Na+/K+-ATPase in the Asian Weaver Ant, Oecophylla smaragdina (Fabricius, 1775)

Social insect colonies adopt different levels of survival strategies and exhibit well-defined reproductive division of labour. Oecophylla smaragdina (Fabricius, 1775) has physiological and behavioral adaptations that enable them to forage at extreme environmental conditions and are lethal to most other insects. Ion homeostasis is the key process in an organism's survival mechanism. Among ion pumps, the ATP-dependent sodium-potassium ion pump is essential for maintaining the Na⁺ and K⁺ ionic balance and is well known as the primary consumer of energy. Oecophylla smaragdina plays pivotal role as a model among social insects for understanding ion homeostasis at the organization level of the castes. We have evaluated the expression and activity of Na⁺/K⁺-ATPase among various castes of O. smaragdina (worker subcastes, queen and male). Real-time PCR and immunoblotting analyses revealed the differential expression of Na⁺/K⁺-ATPase in the castes. Significantly higher expression of Na⁺/K⁺-ATPase mRNA and protein were observed in the minor workers, queen, major workers and males respectively. These results suggest that in the weaver ant colony, the castes might have variously adapted and evolved with a well-developed ion transport mechanism which allows them to perform allocated tasks within the nest and could be a key to their adaptive benefits towards division of labour.

Cytonuclear incongruences hamper species delimitation in the socially polymorphic desert ants of the Cataglyphis albicans group in Israel

Assessing whether behavioural, ecological or geographical factors trigger population divergence provides key insights into the biological processes driving speciation. Recent speciation in restricted geographic area without obvious ecological barriers prompts the question of the behavioural mechanisms underlying species divergence. In this context, we investigated phylogenetic relationships in the Cataglyphis albicans desert ant complex in Israel. We first determined accurate species delimitation using two mitochondrial and six nuclear genes, as well as 11 microsatellite markers to investigate cryptic species in this group, assessing reduction in gene flow between populations. We then investigated whether different species in this group exhibit distinct reproductive strategies, inferring social structure and queen-mating frequency in each species uncovered. Our findings highlight the presence of at least six distinct Cataglyphis albicans species in the restricted range of Israel; four of them co-occur in a 50 × 50 km area in North Negev, while two are endemic from there. However, our results reveal incongruences between nuclear and mitochondrial clustering, which complicate species identification and preclude the exclusive use of mtDNA to confidently delimit species in this group. Finally, we show that the different species of the C. albicans group in Israel exhibit quite similar reproductive strategies with most of them having colonies headed by a single queen mated with several males; colonies of one species were, however, headed by several queens. Overall, this weak variation across species thereby unlikely represents the main evolutionary force behind speciation of these sympatric species. We then discuss the potential evolutionary processes that underlie speciation in this group in the absence of clear geographical or ecological barriers.

Behavioral flexibility promotes collective consistency in a social insect

Deciphering the mechanisms that integrate individuals and their behavior into a functional unit is crucial for our understanding of collective behaviors. We here present empirical evidence for the impressive strength of social processes in this integration. We investigated collective temperature homeostasis in bumblebee (Bombus terrestris) colonies and found that bees are less likely to engage in thermoregulatory fanning and do so with less time investment when confronted with heat stress in a group setting than when facing the same challenge alone and that this down-regulation of individual stimulus-response behavior resulted in a consistent proportion of workers in a group engaged in the task of fanning. Furthermore, the bees that comprised the subset of fanning individuals changed from trial to trial and participation in the task was predominately unpredictable based on previous response behavior. Our results challenge basic assumptions in the most commonly used class of models for task allocation and contrast numerous collective behavior studies that emphasize the importance of fixed inter-individual variation for the functioning of animal groups. We demonstrate that bumblebee colonies maintain within-group behavioral heterogeneity and a consistent collective response pattern based on social responsiveness and behavioral flexibility at the individual level.