Dynamic shifts in social network structure and composition within a breeding hybrid population.

Mating behaviour and the timing of reproduction can inhibit genetic exchange between closely related species; however, these reproductive barriers are challenging to measure within natural populations. Social network analysis provides promising tools for studying the social context of hybridization, and the exchange of genetic variation, more generally. We test how social networks within a hybrid population of California Callipepla californica and Gambel's quail Callipepla gambelii change over discrete periods of a breeding season. We assess patterns of phenotypic and genotypic assortment, and ask whether altered associations between individuals (association rewiring), or changes to the composition of the population (individual turnover) drive network dynamics. We use genetic data to test whether social associations and relatedness between individuals correlate with patterns of parentage within the hybrid population. To achieve these aims, we combine RFID association data, phenotypic data and genomic measures with social network analyses. We adopt methods from the ecological network literature to quantify shifts in network structure and to partition changes into those due to individual turnover and association rewiring. We integrate genomic data into networks as node-level attributes (ancestry) and edges (relatedness, parentage) to test links between social and parentage networks. We show that rewiring of associations between individuals that persist across network periods, rather than individual turnover, drives the majority of the changes in network structure throughout the breeding season, and that the traits involved in phenotypic/genotypic assortment were highly dynamic over time. Social networks were randomly assorted based on genetic ancestry, suggesting weak behavioural reproductive isolation within this hybrid population. Finally, we show that the strength of associations within the social network, but not levels of genetic relatedness, predicts patterns of parentage. Social networks play an important role in population processes such as the transmission of disease and information, yet there has been less focus on how networks influence the exchange of genetic variation. By integrating analyses of social structure, phenotypic assortment and reproductive outcomes within a hybrid zone, we demonstrate the utility of social networks for analysing links between social context and gene flow within wild populations.

Effects of load mass and size on cooperative transport in ants over multiple transport challenges.

Some ant species cooperatively transport a wide range of extremely large, heavy food objects of various shapes and materials. While previous studies have examined how object mass and size affect the recruitment of additional workers, less is understood about how these attributes affect the rest of the transport process. Using artificial baits with independently varying mass and size, we reveal their effects on cooperative transport in Paratrechina longicornis across two transport challenges: movement initiation and obstacle navigation. As expected, object mass was tightly correlated with number of porters as workers adjust group size to the task. Mass affected performance similarly across the two challenges, with groups carrying heavy objects having lower performance. Yet, object size had differing effects depending on the challenge. While larger objects led to reduced performance during movement initiation - groups took longer to start moving these objects and had lower velocities - there was no evidence for this during obstacle navigation, and the opposite pattern was weakly supported. If a group struggles to start moving an object, it does not necessarily predict difficulty navigating around obstacles; groups should persist in trying to move 'difficult' objects, which may be easier to transport later in the process. Additionally, groups hitting obstacles were not substantially disrupted, and started moving again sooner than at the start, despite the nest direction being blocked. Paratrechina longicornis transport groups never failed, performing well at both challenges while carrying widely varying objects, and even transported a bait weighing 1900 times the mass of an individual.

Assessing Behavioral Associations in a Hybrid Zone through Social Network Analysis: Complex Assortative Behaviors Structure Associations in a Hybrid Quail Population.

Behavior can strongly influence rates and patterns of hybridization between animal populations and species. Yet few studies have examined reproductive behaviors in natural hybrid zones within the fine-scale social context in which they naturally occur. We use radio-frequency identification tags with social network analyses to test whether phenotypic similarity in plumage and mass correlate with social behavior throughout a breeding season in a California and Gambel's quail hybrid zone. We use a novel approach to partition phenotypic variation in a way that does not confound differences between sexes and species, and we illustrate the complex ways that phenotype and behavior structure the social environment, mating opportunities, and male-male associations. Associations within the admixed population were random with respect to species-specific plumage but showed strong patterns of assortment based on sexually dimorphic plumage, monomorphic plumage, and mass. Weak behavioral reproductive isolation in this admixed population may be the result of complex patterns of phenotypic assortment based on multiple traits rather than a lack of phenotypic discrimination. More generally, our results support the utility of social network analyses for analyzing behavioral factors affecting genetic exchange between populations and species.

Octopamine and tyramine modulate the thermoregulatory fanning response in honey bees (Apis mellifera).

Biogenic amines regulate the proximate mechanisms underlying most behavior, including those that contribute to the overall success of complex societies. For honey bees, one crucial set of behaviors contributing to the welfare of a colony is involved with nest thermoregulation. Worker honeybees cool the colony by performing a fanning behavior, the expression of which is largely influenced by response thresholds modulated by the social environment. Here, we examined how changes in biogenic amines affect this group-performed thermoregulatory fanning behavior in honeybees. Concentrations of two biogenic amines, octopamine and tyramine, are significantly lower in active fanners than in non-fanners, but there is no difference in dopamine and serotonin concentrations. Direct feeding of octopamine and tyramine induced a decrease in fanning responses, but only when both amines were included in the treatment. This is the first evidence that fanning behavior is influenced by these two biogenic amines, and this result is consistent with the typical role of these neurotransmitters in regulating locomotor activity in other insects. Individual variation in amine expression also provides a mechanistic link that helps to explain how this group behavior might be coordinated within a colony.

Collective strategy for obstacle navigation during cooperative transport by ants.

Group cohesion and consensus have primarily been studied in the context of discrete decisions, but some group tasks require making serial decisions that build on one another. We examine such collective problem solving by studying obstacle navigation during cooperative transport in ants. In cooperative transport, ants work together to move a large object back to their nest. We blocked cooperative transport groups of Paratrechina longicornis with obstacles of varying complexity, analyzing groups' trajectories to infer what kind of strategy the ants employed. Simple strategies require little information, but more challenging, robust strategies succeed with a wider range of obstacles. We found that transport groups use a stochastic strategy that leads to efficient navigation around simple obstacles, and still succeeds at difficult obstacles. While groups navigating obstacles preferentially move directly toward the nest, they change their behavior over time; the longer the ants are obstructed, the more likely they are to move away from the nest. This increases the chance of finding a path around the obstacle. Groups rapidly changed directions and rarely stalled during navigation, indicating that these ants maintain consensus even when the nest direction is blocked. Although some decisions were aided by the arrival of new ants, at many key points, direction changes were initiated within the group, with no apparent external cause. This ant species is highly effective at navigating complex environments, and implements a flexible strategy that works for both simple and more complex obstacles.

Consensus or Deadlock? Consequences of Simple Behavioral Rules for Coordination in Group Decisions.

Coordinated collective behaviors often emerge from simple rules governing the interactions of individuals in groups. We model mechanisms of coordination among ants during cooperative transport, a challenging task that requires a consensus on travel direction. Our goal is to determine whether groups following simple behavioral rules can reach a consensus using minimal information. Using deterministic and stochastic models, we investigate behavioral factors that affect coordination. We define and investigate three types of behavioral rules governing individual behavior that differ in the information available: individuals either 1) have no information, 2) can measure transport success, or 3) measure success while also knowing whether they are aligned with the majority. We find that groups break deadlocks only if individuals more readily give up when they are going against the majority, corresponding to rule type 3 -such groups are "informed." These behavioral rules succeed through positive and negative feedbacks that are implemented in our model via a single mechanism: individuals only need to measure the relative group sizes to make effective decisions. We also find that groups reach consensus more quickly if they have either a shared bias, high sensitivity to group behavior, or finely tuned persistence. Each of these is a potential adaptation for efficient cooperative transport. This flexibility makes the behavioral rules in the informed case relatively robust to deficiencies in the individuals' capabilities. While inspired by ants, our results are generalizable to other collective decisions with deadlocks, and demonstrate that groups of behaviorally simple individuals with no memory and extremely limited information can break symmetry and reach a consensus in a decision between two equal options.

Animal behavior: social recognition in crickets.

A recent study of social recognition in crickets shows that decorated cricket females use self-referenced recognition information in their choice of mates. This allows the polyandrous females to choose novel, diverse mates.

Colony-specific cuticular hydrocarbon profile in Formica argentea ants.

The cuticular hydrocarbons of the ant Formica argentea were identified by gas chromatography/mass spectrometry. Behavioral bioassays tested the role of each class of cuticular hydrocarbon in nestmate recognition, and statistical analyses looked for potential colony-specific signatures. The cuticular hydrocarbons of F. argentea consist of n-alkanes, alkenes, and methyl-branched alkanes. Behavioral bioassays demonstrated that changes in the alkene and methyl-branched alkane signature of F. argentea increased aggression, but changes in alkanes did not. Statistical analyses demonstrated that F. argentea workers present a colony-specific hydrocarbon profile based on their methyl-branched C(29) alkane signature. Using this signature alone, it is possible to group worker ants statistically by nest, suggesting that methyl-branched C(29) alkanes may be important in nestmate recognition for this species. These results support the idea that variation in positional isomers of cuticular hydrocarbons of the same carbon chain length may provide enough information for nestmate recognition. Although the addition of alkenes increased aggression in F. argentea, alkenes did not provide a colony-specific signature. This study reinforces the idea that investigators studying nestmate recognition should not examine cuticular hydrocarbon profiles as a whole but rather, should look for colony-specific signatures embedded in parts of the profile.

Use of flax oil to influence honey bee nestmate recognition.

Fatty acids, normally found in comb wax, have a strong influence on nestmate recognition in honey bees, Apis mellifera L. Previous work has shown that bees from different colonies, when treated with 16- or 18-carbon fatty acids, such as oleic, linoleic, or linolenic acids, are much less likely to fight than bees from two colonies when only one of the two is treated. Previous work also shows that the influence of comb wax on recognition has practical applications; transfer of empty comb between colonies, before merger of those colonies, reduces fighting among workers within the merged colony. Flax oil contains many of the same fatty acids as beeswax. Here, we tested the hypothesis that treatment of individual bees with flax oil affects nestmate recognition; the results proved to be consistent with this hypothesis and showed that treated bees from different colonies were less likely to fight than untreated bees. These results suggest that flax oil may be useful in facilitating colony mergers.

Eusocial evolution and the recognition systems in social insects.

Eusocial species, animals which live in colonies with a reproductive division of labor, typically have closed societies, in which colony members are allowed entry and nonmembers, including animals of the same species, are excluded. This implies an ability to discriminate colony members ("self") from nonmembers ("nonself"). We draw analogies between this type of discrimination and MHC-mediated cellular recognition in vertebrates. Recognition of membership in eusocial colonies is typically mediated by differences in the surface chemistry between members and nonmembers and we review studies which support this hypothesis. In rare instances, visual signals mediate recognition. We highlight the need for better understanding of which surface compounds actually mediate recognition and for further work on how differences between colony members and nonmembers are perceived.

Insulin Modifies Honeybee Worker Behavior.

The insulin signaling pathway has been hypothesized to play a key role in regulation of worker social insect behavior. We tested whether insulin treatment has direct effects on worker honeybee behavior in two contexts, sucrose response thresholds in winter bees and the progression to foraging by summer nurse bees. Treatment of winter worker bees with bovine insulin, used as a proxy for honeybee insulin, increased the bees' sucrose response threshold. Treatment of summer nurse bees with bovine insulin significantly decreased the age at which foraging was initiated. This work provides further insight into the role of endocrine controls in behavior of in honeybees and insects in general.

The thermal properties of beeswaxes: unexpected findings.

Standard melting point analyses only partially describe the thermal properties of eusocial beeswaxes. Differential scanning calorimetry (DSC) revealed that thermal phase changes in wax are initiated at substantially lower temperatures than visually observed melting points. Instead of a sharp, single endothermic peak at the published melting point of 64 degrees C, DSC analysis of Apis mellifera Linnaeus wax yielded a broad melting curve that showed the initiation of melting at approximately 40 degrees C. Although Apis beeswax retained a solid appearance at these temperatures, heat absorption and initiation of melting could affect the structural characteristics of the wax. Additionally, a more complete characterization of the thermal properties indicated that the onset of melting, melting range and heat of fusion of beeswaxes varied significantly among tribes of social bees (Bombini, Meliponini, Apini). Compared with other waxes examined, the relatively malleable wax of bumblebees (Bombini) had the lowest onset of melting and lowest heat of fusion but an intermediate melting temperature range. Stingless bee (Meliponini) wax was intermediate between bumblebee and honeybee wax (Apini) in heat of fusion, but had the highest onset of melting and the narrowest melting temperature range. The broad melting temperature range and high heat of fusion in the Apini may be associated with the use of wax comb as a free-hanging structural material, while the Bombini and Meliponini support their wax structures with exogenous materials.

A predictive distribution map for the giant tropical ant, Paraponera clavata.

Paraponera clavata (Fabricius 1775) (Formicidae: Paraponerinae) is a widely distributed Neotropical ant whose large size has attracted the attention of numerous collectors. Working from museum specimens, a georeferenced database of collection localities was developed. This database then served as the source for computer generated predictive distribution maps. Annual rainfall was the most important variable chosen by the computer model to predict the distribution of P. clavata, both on the scale of the neotropics and at a finer scale at the northern end its distribution in Costa Rica and Nicaragua. When the model was forced to use vegetation as the first predictive variable, the Neotropical model used temperature and rainfall variance as additional variables, while the Mesoamerican model used both climatic and soils variables. Overall, the modeling suggests that P. clavata is more sensitive to abiotic factors (rainfall, temperature, soils) than to biotic factors (vegetation type) in its distribution, although this conclusion comes with the caveat that the vegetation types used in the model are quite generalized. Predictive distribution mapping holds great promise for generating more precise representations of insect distributions, thereby allowing better tests of the extent of distribution overlaps and other community relationships.

Interspecific variation in beeswax as a biological construction material.

Beeswax is a multicomponent material used by bees in the genus Apis to house larvae and store honey and pollen. We characterized the mechanical properties of waxes from four honeybee species: Apis mellifera L., Apis andreniformis L., Apis dorsata L. and two subspecies of Apis cerana L. In order to isolate the material effects from the architectural properties of nest comb, we formed raw wax in to right, circular cylindrical samples, and compressed them in an electromechanical tensometer. From the resulting stress-strain curves, values for yield stress, yield strain, stress and strain at the proportional limit, stiffness, and resilience were obtained. Apis dorsata wax was stiffer and had a higher yield stress and stress at the proportional limit than all of the other waxes. The waxes of A. cerana and A. mellifera had intermediate strength and stiffness, and A. andreniformis wax was the least strong, stiff and resilient. All of the waxes had similar strain values at the proportional limit and yield point. The observed differences in wax mechanical properties correlate with the nesting ecology of these species. A. mellifera and A. cerana nest in cavities that protect the nest from environmental stresses, whereas the species with the strongest and stiffest wax, A. dorsata, constructs relatively heavy nests attached to branches of tall trees, exposing them to substantially greater mechanical forces. The wax of A. andreniformis was the least strong, stiff and resilient, and their nests have low masses relative to other species in the genus and, although not built in cavities, are constructed on lower, often shielded branches that can absorb the forces of wind and rain.

Mating frequency, within-colony relatedness and male production in a yellow jacket wasp, Dolichovespula arenaria.

We examined the mating frequencies of queens in a social wasp, Dolichovespula arenaria (Vespinae) using DNA microsatellites. Five of the seven colonies supported the hypothesis of single mating by queens. The other two colonies supported two and three matings, with effective paternity of 1.48 and 1.91. Mean worker relatedness was 0.77 +/- 0.09. In two of the four male-containing colonies, all were likely progeny of the queen. In the other two colonies workers produced 8 and 14% of the male wasps. Overall, 94.3% of the male wasps were likely progeny of the queen. These patterns are consistent with published studies of vespine wasps.

Defensive behavior of honey bees: organization, genetics, and comparisons with other bees.

One key advantage of eusociality is shared defense of the nest, brood, and stored food; nest defense plays an important role in the biology of eusocial bees. Recent studies on honey bees, Apis mellifera, have focused on the placement of defensive activity in the overall scheme of division of labor, showing that guard bees play a unique and important role in colony defense. Alarm pheromones function in integrating defensive responses; honey bee alarm pheromone is an excellent example of a multicomponent pheromonal blend. The genetic regulation of defensive behavior is now better understood from the mapping of quantitative trait loci (QTLs) associated with variation in defensiveness. Colony defense in other eusocial bees is less well understood, but enough information is available to provide interesting comparisons between A. mellifera and other species of Apis, as well as with allodapine, halictine, bombine, and meliponine bees. These comparative studies illustrate the wide variety of evolutionary solutions to problems in colony defense in the Apoidea.

Foraging energetics of the ant, Paraponera clavata.

The energy currencies used by foraging animals are expected to relate to the energy costs and benefits of resource collection. However, actual costs of foraging are rarely measured. We measured the ratio of energetic benefit relative to cost (B/C) during foraging for the giant tropical ant, Paraponera clavata. The B/C ratio was 3.9 for nectar-foragers and 67 for insect prey foragers. In contrast, the B/C ratio during foraging for seed harvester ants (Pogonomyrmex occidentalis) is over 1000, demonstrating that the B/C ratio can vary widely among ants. The B/C ratio was 300 times lower for nectar-foraging Paraponera than for the seed-harvesting Pogonomyrmex because of: (1) a 5-fold lower energetic benefit per trip, (2) a 10-fold greater cost due to longer foraging distances, and (3) a 6-fold greater energy cost per meter due to larger body size. For Paraponera daily colonial energy intake rates are similar to expeditures and may limit colony growth and reproduction. In contrast, for Pogonomyrmex energy intake rates are an order of magnitude higher than estimated costs, suggesting that Pogonomyrmex colonies are unlikely to be limited by short-term energy intake. We suggest that variation in individual B/C ratios may explain why the foraging behavior of Paraponera but not Pogonomyrmex appears sensitive to foraging costs.

Distance effects on resource profitability and recruitment in the giant tropical ant, Paraponera clavata.

We examine how cost and benefit components of resource profitability affect recruitment in the giant tropical ant, Paraponera clavata. To vary resource profitability, we changed the quantity of artificial nectar baits presented to foragers and the distance of nectar baits from the nest. Both distance to and amount of resource affected quantitative aspects of recruitment. At increased distances foragers were less likely to recruit, and fewer workers were recruited to the resource area. The amount of nectar affected the tendency of foragers to recruit, but had no effect on the number of ants recruited. Variation in resource distance was also associated with qualitative changes in recruitment strategy. Foragers at distant sites recruited from the canopy rather than from the nest, and often transferred nectar to other workers for transport to the nest. Nectar transfer and extra-nidal recruitment significantly reduced the time required for resource collection. It may also have increased the ability of workers to specialize in specific foraging tasks. A portion of the colony's foraging force specialized spatially by remaining in distant foraging areas without returning to the nest. The flexible recruitment system of P. clavata increases colonial net energetic gain rates by concentrating foraging effort on resources yielding the highest net energetic rewards, and increases the competitive abilities of individual colonies at resource sites by decreasing collection times.

Thievery, home ranges, and nestmate recognition inEctatomma ruidum.

Thievery of food items among colonies of a ponerine ant,Ectatomma ruidum was common; nonnestmates in colonies or near the colony entrances receive incoming food items and carry them to their own colony. In our study area 7 of 10 colonies were victimized by thief ants. Colonies have discrete home ranges and home range size is correlated with the number of workers in the colony. Worker ants discriminate nestmates from non-nestmates when non-nestmates are presented at colony entrances, but individuals from different colonies were not observed to engage in agonistic interactions away from nest entrances. Non-nestmates gain entrance to colonies when the entrance is unguarded. Many instances of non-nestmates being removed from colonies by residents were observed. The costs and benefits of theft under these circumstances are considered.