The Effect of Group Size on the Interplay between Dominance and Reproduction in Bombus terrestris

Social insects provide good model systems for testing trade-offs in decision-making because of their marked reproductive skew and the dilemma workers face when to reproduce. Attaining reproductive skew requires energy investment in aggression or fertility signaling, creating a trade-off between reproduction and dominance. This may be density-dependent because the cost of achieving dominance may be higher in larger groups. We investigated the effect of group-size in B. terrestris queenless workers on two major reproduction-dominance correlates: between-worker aggression, and pheromone production, aiming at mimicking decision-making during the transition of worker behavior from cooperation and sterility to aggressive reproductive competition in whole colonies. Despite the competition, reproductive division of labor in colonies can be maintained even during this phase through the production of a sterility signal by sterile workers that has an appeasement effect on dominant nestmates. Worker-worker aggression, ovary activation, and production of sterility-appeasement signals may therefore constitute components of a trade-off affecting worker reproduction decisions. By constructing queenless groups of different size and measuring how this affected the parameters above, we found that in all groups aggression was not evenly distributed with the α-worker performing most of the aggressive acts. Moreover, aggression by the α-worker increased proportionally with group-size. However, while in small groups the α-worker monopolized reproduction, in larger groups several workers shared reproduction, creating two worker groups: reproductives and helpers. It appears that despite the increase of aggression, this was evidently not sufficient for the α-worker to monopolize reproduction. If we compare the α-worker to the queen in full-sized colonies it can be hypothesized that worker reproduction in B. terrestris colonies starts due to a gradual increase in the worker population and the queen's inability to physically inhibit worker oviposition. This may shift the trade-off between cost and benefit of worker reproduction and trigger the competition phase

Caste Specific Pheromone-Related Gene Expression in Honeybee Mandibular Glands

Dissertação de mestrado em Biocinética, apresentada à Faculdade de Ciências do Desporto e Educação Física da Universidade de CoimbraO presente trabalho teve como principal objetivo determinar a influência dos valores da curva força-velocidade dos flexores e extensores do joelho no remate de futebol. Foram avaliados sete atletas amadores de futebol (25,1 ± 1,97 anos), os quais foram submetidos a dois tipos de testes. Sendo o primeiro cinemático, através da filmagem de execução de um remate de futebol. Posteriomente, foi feita uma análise no programa kinovea, para determinar a velocidade de saida de bola, variáveis temporais e comportamento angular. Para a recolha dos dados isocinéticos foi utilizado um dinamómetro (Biodex Multijoint System 3 Pro 2) para cálculo da força máxima do membro inferior dos sujeitos. Na análise cinemática do futebol a variável velocidade máxima do joelho foi a que obteve maior correlação com a velocidade de saída de bola (r=0.96; P≤0.001). As variáveis, Distância do pé à bola e a Percentagem da posição do centro de gravidade obtiveram valores de correlação significativos (r=0.81 e r= 0.83; P≤ 0.01) correspondentemente. Por fim, as variáveis, ângulo da cintura pélvica e deslocamento angular do joelho em extensão, também mostraram correlações significativas (r=0.76 e r=0.70; P≤0.05) com a velocidade de saída de bola. Na correlação entre variáveis cinemáticas do remate de futebol com os testes isocinéticos, constatou-se que das três variáveis analisadas, os resultados das diferenças dos valores dos torques máximos em todas as velocidades de teste e o valor dos ângulos nos torques máximos obtiveram maior número de correlações significativas (ambas com 12 correlações cada para P≤0.05), já os valores dos torques máximos apenas obtiveram quatro correlações significativas para P≤0.05. Concluindo, a variável cinemática mais importante para o remate de futebol é a velocidade máxima do joelho, sendo que só é possível a sua análise a partir da utilização de novas tecnologias no treino. Relativamente aos testes isocinéticos, verificamos que a aplicação da curva força-velocidade nos testes isocinéticos apresenta mais informações do que os valores dos torques máximos. Palavras-chave: Futebol; Análise Cinemática; Testes Isocinéticos; Curva Força-Velocidade. iv Abstract The purpose of this study was to establish the values which influence the force-velocity curve of flexors and knee extensors on the soccer kick. Our subjects were seven amateur soccer players (25.1 ± 1.97 years), who underwent two types of tests. Therefore, the first Kinematic test was the avaluation of the soccer kick and maximal instep kicking with the preferred leg. Afterwards, an analysis on Kinovea program was made in order to calculate the ball speed, the angular behavior, and temporal variables. For the collection of data we used isokinetic dynamometers ((Biodex System 3 Pro Multijoint 2) to calculate the maximum strength of the lower member of the subjects. In kinematics football analysis, the variable maximum knee speed, was the one with the highest correlation with the ball speed (r = 0.96; P≤0.001). The variables, distance from the ball to the foot and the percentage of the center of gravity position obtained significant correlation (r = 0.81 and r = 0.83; P ≤ 0.01) correspondingly. Finally, the variables angle of the pelvis and the knee angular movement in extension, also showed a significant correlation (r = 0.76 and r = 0.70; P≤0.05) with the ball speed. As far as the correlation between kinematic variables football kicking with the isokinetic testing is concerned, it was found that the three variables in study, which were the results of the differences of the values of the maximum torque in all test speed and the value of the angles the maximum torques obtained more significant correlations (both with 12 correlations for each P≤0.05), since the values of the maximum torques only had four significant correlations for p≤0.05. In conclusion, the most important kinematics variable for the football kick is the maximum speed of the knee, and it is only possible to analyse by using new technologies in training. For isokinetic tests, we found that the application of the force-velocity curve in isokinetic tests gave us more information than the values of the maximum torque

Interspecific displacement mechanisms by the invasive little fire ant Wasmannia auropunctata

Abstract Competition between invasive species and native ones in the new environment was found to be significant and to affect both animal and plant species. Invasive ants are notorious for displacing local ant species through competition. Competitive displacement of native species can occur through interference and or resource competition. However, for invasive ants, little is known about the relative importance of competitive displacement. We studied competitive interactions of the little fire ant, Wasmannia auropunctata, one of the most destructive invasive ant species, with two other ant species, Monomorium subopacum and Pheidole teneriffana. We compared the species' foraging behavior and studied their aggressive interactions around food baits for the short (2 h) and long (21 days) term in the laboratory. Surprisingly we found that in short term experiments W. auropunctata had the poorest foraging abilities of the three species studied: it took the workers the longest to locate the bait and retrieve it; in addition they retrieved the lowest amount of food. When both W. auropunctata and M. subopacum were foraging the same bait, in the short term competition experiment, W. auropunctata workers did not defend the bait, and ceased foraging when encountered with competition. The long-term experiments revealed that W. auropunctata had the advantage in aggressive interactions over time; they eliminated seven of nine M. subopacum's nests while consuming some of the workers and brood. According to our laboratory studies, W. auropunctata cannot be considered an extirpator species, unless it has a substantial numerical advantage, in contrast with previous assumptions. Otherwise it may behave as an insinuator species, i.e. the workers do not initiate aggression and by staying undetected they can continue foraging adjacent to dominant species

Queen-produced volatiles change dynamically during reproductive swarming and are associated with changes in honey bee (Apis mellifera) worker behavior

International audienceAbstractDuring colony fission, honey bee workers are exquisitely sensitive to the presence of their queen in airborne swarms and bivouacs and will abandon swarming if she is absent. However, it is not known whether swarming queens produce a chemical bouquet that is distinct from non-swarming queens, containing either unique chemicals or altered proportions of chemicals. We found that queens emitted higher quantities and greater numbers of unique volatiles at liftoff than they did prior to swarming or in clustered bivouacs, and swarming workers tended to be attracted to these liftoff volatile blends. Pentadecane and heptadecane were collected most frequently and emitted in significantly higher quantities by queens at liftoff; these compounds have been described as pheromone components in other social insects, but not yet in honey bees. Our results suggest that volatile emission by queens is more dynamic than previously thought and that changes in their chemical signals may play a role in regulating the behavior of swarming workers

Cataglyphis desert ants: a good model for evolutionary biology in Darwin¿s anniversary year¿A review

Cataglyphis ants comprise one of the most characteristic groups of insects in arid regions around the Mediterranean basin and have been intensively studied over the last 30 years. These ants are central-place foragers and scavengers, single-prey loaders that have become a model for insect navigation using sophisticated visual orientation, having lost pheromone orientation. They are highly heat-tolerant ants that forage close to their critical thermal limit during the hottest hours of the day, with their long-chain cuticular hydrocarbons protecting them from desiccation. This is exemplified in two Cataglyphis species, each of which developed different mechanisms for counteracting extreme heat when foraging: polymorphism of workers vs. physiological and behavioral adaptations. Several species in this genus have also become a model for studying nestmate recognition mechanisms. The role of cuticular hydrocarbons and the postpharyngeal gland as a reservoir of hydrocarbons in nestmate recognition was initially discovered mainly in Cataglyphis, including the first experimental demonstration of the Gestalt model of nestmate recognition. These ants possess very acute discrimination capacities, down to individual recognition. Such fine discrimination is seemingly used by ants that rescue from ant-lion traps only those individuals that are their nestmates. Two main reproductive strategies are exhibited by species of this genus: some reproduce classically, by independent colony foundation following nuptial flight, whereas others reproduce by colony fission. Limited dispersion increases competition for access to resources, and local resource competition has been demonstrated. Multiple mating, which had been considered to be rare in ants, has also been reported in all species studied. Finally, the most important discovery in recent years with regard to reproduction strategies in Cataglyphis is probably the occurrence of thelytokous parthenogenesis in both workers and queens. In Cataglyphis cursor, queens are able to produce new queens by thelytoky, a phenomenon that was later found in four other ant species. This ability does not exist in any other Cataglyphis species, attesting to the great variety of reproductive strategies in this genus.Peer Reviewe

Recognition of caste and mating status maintains monogyny in the ant Aphaenogaster senilis

n ants dispersing through colony fission, queens mate near their natal nest and found a new society with the help of workers. This allows potential future queens to challenge the mother queen’s reproductive monopoly. Conflicts might be resolved if the mated queen signals her presence and the workers control the developmental fate of the diploid larvae (whether they develop to worker or queen). In this study we sought to determine whether, in the fission-performing ant Aphaenogaster senilis, conflicts between queens for control of the colony are resolved by the resident queen signalling her mating status. Virgin queens were less effective than newly mated queens in inhibiting queen rearing. Moreover, potential challenger queens were recognized and heavily aggressed independent of mating status. Chemical analyses showed that mating status was associated with changes in cuticular hydrocarbon and poison gland composition, but not in Dufour’s gland composition. Cuticular dimethylalkanes were identified as potential constituents that signal both caste (present in queens only) and mating status (mated queens have higher amounts). We hypothesised that pheromone emission by virgin queens did not reach the threshold needed to fully inhibit larval development into queens but was sufficiently high to stimulate overt aggression by mated queens. These findings provide evidence for the complexity of chemical communication in social insects, in which a small number of signals may have a variety of effects, depending on the context.Peer reviewe

Neural Mechanisms and Information Processing in Recognition Systems

Nestmate recognition is a hallmark of social insects. It is based on the match/mismatch of an identity signal carried by members of the society with that of the perceiving individual. While the behavioral response, amicable or aggressive, is very clear, the neural systems underlying recognition are not fully understood. Here we contrast two alternative hypotheses for the neural mechanisms that are responsible for the perception and information processing in recognition. We focus on recognition via chemical signals, as the common modality in social insects. The first, classical, hypothesis states that upon perception of recognition cues by the sensory system the information is passed as is to the antennal lobes and to higher brain centers where the information is deciphered and compared to a neural template. Match or mismatch information is then transferred to some behavior-generating centers where the appropriate response is elicited. An alternative hypothesis, that of “pre-filter mechanism”, posits that the decision as to whether to pass on the information to the central nervous system takes place in the peripheral sensory system. We suggest that, through sensory adaptation, only alien signals are passed on to the brain, specifically to an “aggressive-behavior-switching center”, where the response is generated if the signal is above a certain threshold

Queen-signal modulation of worker pheromonal composition in honeybees

Worker sterility in honeybees is neither absolute nor irreversible. Whether under queen or worker control, it is likely to be mediated by pheromones. Queen-specific pheromones are not exclusive to queens; workers with activated ovaries also produce them. The association between ovarian activation and queen-like pheromone occurrence suggests the latter as providing a reliable signal of reproductive ability. In this study we investigated the effect of queen pheromones on ovary development and occurrence of queen-like esters in workers' Dufour's gland. Workers separated from the queenright compartment by a double mesh behaved like queenless workers, activating their ovaries and expressing a queen-like Dufour's gland secretion, confirming that the pheromones regulating both systems are non-volatile. Workers with developed ovaries produced significantly more secretion than sterile workers, which we attribute primarily to increased ester production. Workers separated from the queenright compartment by a single mesh displayed a delayed ovarian development, which we attribute to interrupted transfer of the non-volatile pheromone between compartments. We suggest that worker expression of queen-like characters reflects a queen-worker arms race; and that Dufour's gland secretion may provide a reliable signal for ovarian activation. The associative nature between ovary development and Dufour's gland ester production remains elusive. © 2004 The Royal Society.Peer Reviewe