The Interplay Between Scent Trails and Group-Mass Recruitment Systems in Ants

Large ant colonies invariably use effective scent trails to guide copious ant numbers to food sources. The success of mass recruitment hinges on the involvement of many colony members to lay powerful trails. However, many ant colonies start off as single queens. How do these same colonies forage efficiently when small, thereby overcoming the hurdles to grow large? In this paper, we study the case of combined group and mass recruitment displayed by some ant species. Using mathematical models, we explore to what extent early group recruitment may aid deployment of scent trails, making such trails available at much smaller colony sizes. We show that a competition between group and mass recruitment may cause oscillatory behaviour mediated by scent trails. This results in a further reduction of colony size to establish trails successfully.     

Recognition of Individuals from Mixed Colony by Formica sanguinea and Formica polyctena Ants

It was examined whether Formica polyctena and F. sanguinea ants from a mixed colony elicit higher levels of aggression of conspecific ants in comparison to ants from homospecific colonies. Individuals were confronted in an experimental arena and their behavior was recorded. It was found that F. polyctena workers behaved more aggressively toward ants from a mixed colony. This pattern, however, was not confirmed in F. sanguinea. Moreover, both species clearly discriminated between conspecific and allospecific ants from a mixed colony. It seems that as a result of social interactions both species exchanged cuticular hydrocarbons, which caused their recognition labels to adjust to some extent. Results of the present study support the idea that that F. sanguinea is able to form mixed colonies in which species-specific recognition cues are probably still retained.     

Differential Recruitment of Camponotus femoratus (Fabricius) Ants in Response to Ant Garden Herbivory

Although several studies have shown that ants can recognize chemical cues from their host plants in ant-plant systems, it is poorly demonstrated in ant gardens (AGs). In this interaction, ant species constantly interact with various epiphyte species. Therefore, it is possible to expect a convergence of chemical signals released by plants that could be acting to ensure that ants are able to recognize and defend epiphyte species frequently associated with AGs. In this study, it was hypothesized that ants recognize and differentiate among chemical stimuli released by AG epiphytes and non-AG epiphytes. We experimentally simulated leaf herbivore damage on three epiphyte species restricted to AGs and a locally abundant understory herb, Piper hispidum, in order to quantify the number of recruited Camponotus femoratus (Fabricius) defenders. When exposed to the AG epiphytes Peperomia macrostachya and Codonanthe uleana leaves, it was observed that the recruitment of C. femoratus workers was, on average, respectively 556% and 246% higher than control. However, the number of ants recruited by the AG epiphyte Markea longiflora or by the non-AG plant did not differ from paper pieces. This indicated that ants could discern between chemicals released by different plants, suggesting that ants can select better plants. These results can be explained by evolutionary process acting on both ants’ capability in discerning plants’ chemical compounds (innate attraction) or by ants’ learning based on the epiphyte frequency in AGs (individual experience). To disentangle an innate behavior, a product of classical coevolutionary process, from an ant’s learned behavior, is a complicated but important subject to understand in the evolution of ant-plant mutualisms.     

Trophallaxis Mediates Uniformity of Colony Odor in Cataglyphis iberica Ants (Hymenoptera, Formicidae)

We studied the effect of nestmate separation on trophallaxis in the polydomous ant Cataglyphis iberica. After dividing three colonies into two equivalent subgroups, one queenright and one queenless, we quantified the frequency of trophallaxis within each subgroup, between the workers from the two subgroups (mixed trophallaxis), and trophallaxis involving the queen. Observations of trophallaxis were conducted over four periods of time: for 2 weeks before the separation of the two subgroups, 8 weeks during separation, immediately after reunification, and 3 weeks following reunification. Subgroups were identically fed on the eve of each day of observation. Group separation induced an increase in mixed frequencies of trophallaxis just after reunification, after which trophallaxis returned to the initial level observed before separation. Previous results showed that group separation in C. iberica induces hydrocarbon profile divergence and that reunification restores this chemical modification. The current results seem to indicate that increased trophallaxis permits a uniform odor to be reestablished among previously separated ants. Trophallaxis involving the queen is infrequent and does not seem to be crucial in the process of odor exchange. Our data confirm that trophallaxis plays a key role in establishing the Gestalt colony odor, particularly among naturally separated satellite nests in a polydomous species like C. iberica.     

Colony Wide Behavioral Contexts of Stridulation in Imported Fire Ants (Solenopsis invicta Buren)

Red imported fire ants, Solenopsis invicta, possess stridulatory organs and stridulate in a variety of contexts. We used a stethoscope mounted microphone to study stridulation at the colony level in the context of emigration, disturbance, and excavation. In conjunction with preliminary observations of nest and foraging activities, our results suggest stridulation serves multiple functions in S. invicta. Stridulation was not significantly increased in colonies during responses to disturbance, and only marginally during colony emigration. Colonies involved in excavation, however, exhibited a significant increase in stridulatory activity. Four possible explanations for the function of stridulation in this context are discussed in relation to the stridulatory behavior of individuals, solitary wasps, and published literature on formicid stridulation.     

Conserved Microsatellites in Ants Enable Population Genetic and Colony Pedigree Studies across a Wide Range of Species

Broadly applicable polymorphic genetic markers are essential tools for population genetics, and different types of markers have been developed for this purpose. Microsatellites have been employed as particularly polymorphic markers for over 20 years. However, PCR primers for microsatellite loci are often not useful outside the species for which they were designed. This implies that a new set of loci has to be identified and primers developed for every new study species. To overcome this constraint, we identified 45 conserved microsatellite loci based on the eight currently available ant genomes and designed primers for PCR amplification. Among these loci, we chose 24 for in-depth study in six species covering six different ant subfamilies. On average, 11.16 of these 24 loci were polymorphic and in Hardy-Weinberg equilibrium in any given species. The average number of alleles for these polymorphic loci within single populations of the different species was 4.59. This set of genetic markers will thus be useful for population genetic and colony pedigree studies across a wide range of ant species, supplementing the markers available for previously studied species and greatly facilitating the study of the many ant species lacking genetic markers. Our study shows that it is possible to develop microsatellite loci that are both conserved over a broad range of taxa, yet polymorphic within species. This should encourage researchers to develop similar tools for other large taxonomic groups.     

Effect of Colony, Patch Distance, And Trajectory Sense on Movement Complexity in Foraging Ants

Animals display foraging trajectories when exploiting food patches. These displacements have been studied, particularly in organisms that forage from a central place. The complexity of a movement path may be analyzed by means of the fractal dimension, an index that estimates the tortuosity of a trajectory. In field experiments we studied the effect of trajectory sense, distance to the resource patch and colony on the movement complexity in a common ant of central Chile. We found that these factors and their interactions significantly affected the complexity of movement paths. We discuss whether mortality risk determines more linear trajectories when the resource patch is distant from the nest, and whether the information acquired from the environment by workers determines less complex return trips.     

Task Partitioning in Insect Societies. I. Effect of Colony Size on Queueing Delay and Colony Ergonomic Efficiency

The collection and handling of colony resources such as food, water, and nest construction material is often divided into subtasks in which the material is passed from one worker to another. This is known as task partitioning. When material is transferred directly from one individual to another, queueing delays frequently occur because individuals must sometimes wait for a transfer partner. A stochastic simulation model was written to study the effect of colony size on these delays. Queueing delay decreases roughly exponentially with colony size because stochastic fluctuations in the arrival of individuals are lower in larger colonies. These results support empirical studies of Polybia occidentalis and other theoretical studies of honeybees. The effect of the relative number of individuals in the two subtask groups was also studied. There is a unique optimal ratio of the number of workers associated with each of the subtasks that simultaneously minimizes mean queueing delay and maximizes colony nectar-processing rate. Deviations from this optimal ratio, for example, as a result of forager mortality or changes in nectar productivity that affect foraging trip duration, increase mean queueing delays greatly, especially in smaller colonies.     

Size Matters: Metastatic Cluster Size and Stromal Recruitment in the Establishment of Successful Prostate Cancer to Bone Metastases

Prostate cancer (PCa) impacts over 180,000 men every year in the USA alone, with 26,000 patients expected to succumb to the disease (cancer.gov). The primary cause of death is metastasis, with secondary lesions most commonly occurring in the skeleton. Prostate cancer to bone metastasis is an important, yet poorly understood, process that is difficult to explore with experimental techniques alone. To this end we have utilized a hybrid (discrete–continuum) cellular automaton model of normal bone matrix homeostasis that allowed us to investigate how metastatic PCa can disrupt the bone microenvironment. Our previously published results showed that PCa cells can recruit mesenchymal stem cells (MSCs) that give rise to bone-building osteoblasts. MSCs are also thought to be complicit in the establishment of successful bone metastases (Lu, in Mol Cancer Res 4(4):221–233, 2006). Here we have explored the aspects of early metastatic colonization and shown that the size of PCa clusters needs to be within a specific range to become successfully established: sufficiently large to maximize success, but not too large to risk failure through competition among cancer and stromal cells for scarce resources. Furthermore, we show that MSC recruitment can promote the establishment of a metastasis and compensate for relatively low numbers of PCa cells seeding the bone microenvironment. Combined, our results highlight the utility of biologically driven computational models that capture the complex and dynamic dialogue between cells during the initiation of active metastases.     

The Role of Colony Size on Tunnel Branching Morphogenesis in Ant Nests

Many ant species excavate nests that are made up of chambers and interconnecting tunnels. There is a general trend of an increase in nest complexity with increasing population size. This complexity reflects a higher ramification and anastomosis of tunnels that can be estimated by the meshedness coefficient of the tunnelling networks. It has long been observed that meshedness increases with colony size within and across species, but no explanation has been provided so far. Since colony size is a strong factor controlling collective digging, a high value of the meshedness could simply be a side effect of a larger number of workers. To test this hypothesis, we study the digging dynamics in different group size of ants Messor sancta. We build a model of collective digging that is calibrated from the experimental data. Model''s predictions successfully reproduce the topological properties of tunnelling networks observed in experiments, including the increase of the meshedness with group size. We then use the model to investigate situations in which collective digging progresses outward from a centre corresponding to the way tunnelling behaviour occurs in field conditions. Our model predicts that, when all other parameters are kept constant, an increase of the number of workers leads to a higher value of the meshedness and a transition from tree-like structures to highly meshed networks. Therefore we conclude that colony size is a key factor determining tunnelling network complexity in ant colonies.     

雄性菲菊头蝠夏季集群大小的变化及其影响因素

本研究以栖息于废弃防空洞的雄性菲菊头蝠(Rhinolophus pusillus)作为研究对象,探究其夏季集群大小变化及其潜在影响因素.应用红外热成像仪监测菲菊头蝠在6月到8月期间的集群大小.利用单因素方差分析和一般线性回归模型,检验菲菊头蝠集群大小的月变化及其与洞内微气候的关系.研究发现,菲菊头蝠集群大小从6月至8月...     

Record Dynamics in Ants

The success of social animals (including ourselves) can be attributed to efficiencies that arise from a division of labour. Many animal societies have a communal nest which certain individuals must leave to perform external tasks, for example foraging or patrolling. Staying at home to care for young or leaving to find food is one of the most fundamental divisions of labour. It is also often a choice between safety and danger. Here we explore the regulation of departures from ant nests. We consider the extreme situation in which no one returns and show experimentally that exiting decisions seem to be governed by fluctuating record signals and ant-ant interactions. A record signal is a new ‘high water mark’ in the history of a system. An ant exiting the nest only when the record signal reaches a level it has never perceived before could be a very effective mechanism to postpone, until the last possible moment, a potentially fatal decision. We also show that record dynamics may be involved in first exits by individually tagged ants even when their nest mates are allowed to re-enter the nest. So record dynamics may play a role in allocating individuals to tasks, both in emergencies and in everyday life. The dynamics of several complex but purely physical systems are also based on record signals but this is the first time they have been experimentally shown in a biological system.     

Ants and Habitat Specificity in Aphids

A number of rare butterflies are known to only utilise their host plant species when they grow in particular situations. Field data are presented showing that two rare species of aphid also only utilised their host plants when they grew in particular situations, namely near ant nests. The oak-feeding aphid Stomaphis quercus only occupied trees within 17 m of a Lasius fulignosus nest. The thyme-feeding aphid Aphis serpylli only occurred in a region of a Breckland grass heath where the sward contained a high density of Lasius niger nests, and then most commonly only in quadrats containing ant nests. The sward that was suitable for A. serpylli was generated by the action of farm traffic. It is concluded that ants indirectly impose habitat specificity on these aphids.     

The Effect of Diet and Opponent Size on Aggressive Interactions Involving Caribbean Crazy Ants (Nylanderia fulva)

Biotic interactions are often important in the establishment and spread of invasive species. In particular, competition between introduced and native species can strongly influence the distribution and spread of exotic species and in some cases competition among introduced species can be important. The Caribbean crazy ant, Nylanderia fulva, was recently introduced to the Gulf Coast of Texas, and appears to be spreading inland. It has been hypothesized that competition with the red imported fire ant, Solenopsis invicta, may be an important factor in the spread of crazy ants. We investigated the potential of interspecific competition among these two introduced ants by measuring interspecific aggression between Caribbean crazy ant workers and workers of Solenopsis invicta. Specifically, we examined the effect of body size and diet on individual-level aggressive interactions among crazy ant workers and fire ants. We found that differences in diet did not alter interactions between crazy ant workers from different nests, but carbohydrate level did play an important role in antagonistic interactions with fire ants: crazy ants on low sugar diets were more aggressive and less likely to be killed in aggressive encounters with fire ants. We found that large fire ants engaged in fewer fights with crazy ants than small fire ants, but fire ant size affected neither fire ant nor crazy ant mortality. Overall, crazy ants experienced higher mortality than fire ants after aggressive encounters. Our findings suggest that fire ant workers might outcompete crazy ant workers on an individual level, providing some biotic resistance to crazy ant range expansion. However, this resistance may be overcome by crazy ants that have a restricted sugar intake, which may occur when crazy ants are excluded from resources by fire ants.     

蚂蚁与蚁运植物的互惠共生关系

蚁运植物（myrmecochore)即指种子靠蚂蚁携带散布的植物。在长期的协同进化中,蚂蚁与蚁运植物形成了互惠共生关系。由于蚁运植物种子上附生有蚂蚁喜食的油质体,蚂蚁取食油质体后,将种子丢弃在蚁巢附近,从而使植物得以扩散。蚁运植物广布全世界,但主要分布在澳大利亚和南非。蚂蚁主要搬运草本植物和部分灌木植物的种子。对蚂蚁与蚁运植物互惠共生关系的研究表明：蚂蚁的搬运有利于保护和传播植物种子;蚁巢有利于种子萌发,出苗和建群;蚂蚁的搬运是影响某些温带森林群落结构的重要因素之一;蚂蚁与蚁运植物互惠共生对自然群落的恢复有重要作用。     

Recruitment Distance from the Nearest Reproductive Conspecific Increases with Tree Size in Tropical Premontane Wet Forests

Studies have shown that median distances of plants from the nearest reproductive conspecific (recruitment distance) shifts outward with increasing age or size class, and that plant spatial distribution changes over time in a predictable manner. However, observations and empirical evidence for such predictable changes are limited, and underlying mechanisms explaining such patterns for a wide range of individual sizes are not fully explored. In Costa Rican premontane wet forests, I empirically tested whether recruitment distance changes in a predictable manner with increasing size for five animal‐dispersed tree species by considering all post‐germination sizes. Specifically, I tested the Janzen–Connell hypothesis and the colonization hypothesis by considering distance, density, size, herbivory, biotic infection, and light availability simultaneously. Recruitment distance increased with increasing size (16–22 m) for the four non‐pioneer species, suggesting eventual regeneration success for seeds dispersed away from reproductive conspecifics. During the 2 years of this study, I found positive distance‐dependent survivorship and light availability were important for post‐seedling survivorship, in agreement with the Janzen–Connell hypothesis and the colonization hypothesis, respectively, but only for seedlings. However, seedlings did not escape aboveground herbivory or biotic infection better when the seeds were dispersed greater distances. Results highlight the importance of seed dispersal for successful regeneration, and suggest that changes in spatial distribution over time may be predictable in the vicinity of maternal trees for some non‐pioneer tree species.