Body Size and the Neural, Cognitive and Sensory Basis of Sociality in Bees

Body size is a universal property affecting biological structure and function, from cell metabolism to animal behavior. The nervous system, the physical generator of behavior, is also affected by variations in body size; hence potentially affecting the way animals perceive, interpret and react to the environment. When animals join to form groups, such individual differences become part of the structure of the society, even determining social roles. Here, I explore the association between body size, behavior and social organization in honeybees and bumblebees. Focusing on bumblebees, I explore the link between body size, brain allometry and learning and memory performance, within the context of task specialization. I show that body size goes along with brain size and with learning and memory performance, and that foraging experience affects such cognitive and neural features. Next, I explore the association between body size and foraging task specialization in honeybees. Previous evidence showed a link between specialization on pollen or nectar foraging and sensory sensitivity, further associating sensitivity to the quality and/or quantity of resource exploited. I hypothesize that, as in solitary bees, larger body size is associated with higher sensory sensitivity. I test this hypothesis by comparing body size and the quality and quantity of the resource exploited by wild Africanized and European honeybees. I show that nectar foragers are smaller and have fewer olfactory sensilla, which might underlie their lower sensitivity to odors. Also, larger bees collect more pollen (within pollen foragers) and more dilute nectar (within nectar foragers). To further test this `size hypothesis', I compare strains of bees selected to store large ("high strain") or small ("low strain") amounts of pollen surplus. As these strains differ in sensory sensitivity, I predict that the more sensitive high strain bees are larger and have more sensory sensilla. I show that high strain bees are generally bigger, but have fewer sensory sensilla than low strain bees. These results show that in bees, body size is associated with an individual's sensory, neural and cognitive features, further suggesting that body size plays a more important role in the organization of bee societies than generally assumed.Embargo: Release after 7/29/201

Sobre liliputienses y brobdingnagianos: de bacterias a ballenas azules

Size is one of the most conspicuous properties of anything occurring in the living or inanimate world. We see around us small and large living and non-living entities; our universe is enormous and size even characterizes our immaterial images of gods and thoughts. We obviously assign those differences in size by comparison, according with the perception of our own size. But, are those differences in size relevant in the natural world? Does size really matter? These questions are far from trivial and are shared by scientific disciplines as diverse as ecology, evolutionary biology, neurobiology and developmental biology, among others

Migración, orientación y navegación: brújulas magnéticas en insectos

The use of magnetic information for orientation and navigation is a widespread phenomenon in animals. In contrast to our knowledge of navigational systems in vertebrates, our understanding of the mechanisms underlying the insect magnetic perception and use of the information is at an early stage. Some insects use magnetic information for simple body alignment or homing. There is also some evidence that insects might use the Earth’s magnetic field to orient during long-distance migrations. In most known cases, insects use a polarity compass, orienting by the North–South axis of the Earth’s magnetic field. However, recent studies have also pointed to a role for magnetic inclination in insect orientation. Also, magnetic information is coupled with other navigation compasses or cues, such as the sun or significant landmarks. The use of traditional insect models will be critical to increasing our knowledge of the proximal mechanisms. Nevertheless, the study of new species is necessary for the solution of specific questions regarding perception, processing, and use of magnetic information in insects. In this article, our current knowledge on the use of magnetic information for orientation and navigation in insects is broadly reviewed, from the nature of the magnetic compass to the diversity of its uses. Important directions for future research are also discussed

Toma de decisiones y aprendizaje asociativo del color en abejorros (Bombus impatiens)

In honeybees, the conditioning of the proboscis extension response (PER) has provided a powerful tool to explore the mechanisms underlying olfactory learning and memory. Unfortunately, PER conditioning does not work well for visual stimuli in intact honeybees, and performance is improved only after antennal amputation, thus limiting the analysis of visual learning and multimodal integration. Here, we study visual learning using the PER protocol in harnessed bumblebees, which exhibit high levels of odor learning under restrained conditions. We trained bumblebees in a differential task in which two colors differed in their rewarding values. We recorded learning performance as well as response latency and accuracy

La escala metabólica en insectos apoya las predicciones del modelo WBE

La asociación funcional entre el tamaño corporal y la tasa metabólica (BS-MR) es una de las cuestiones más intrigantes de la fisiología ecológica. En general, se observa un exponente de escala promedio de 3/4 en los taxones de animales y plantas. El valor numérico de 3/4 se predice teóricamente bajo la versión optimizada del modelo de red de suministro de recursos vasculares de West, Brown y Enquist. Sin embargo, recientemente se ha propuesto que los insectos expresen un exponente de escala numéricamente diferente y, por lo tanto, se ha rechazado la aplicación del modelo de red WBE a los insectos. Aquí, volvemos a analizar si tal variación está respaldada por una desviación global en todos lostaxones de insectos a nivel de orden y familia para evaluar si taxones específicos influyen en la escala metabólica de los insectos.The functional association between body size and metabolic rate (BS–MR) is one of the most intriguing issues in ecological physiology. An average scaling exponent of 3/4 is broadly observed across animal and plant taxa. The numerical value of 3/4 is theoretically predicted under the optimized version of West, Brown, and Enquist's vascular resource supply network model. Insects, however, have recently been proposed to express a numerically different scaling exponent and thus application of the WBE network model to insects has been rejected. Here, we re-analyze whether such variation is indeed supported by a global deviation across all insect taxa at the order and family levels to assess if specific taxa influence insect metabolic scaling. We show that a previous reported deviation is largely due to the effect of a single insect family (Termitidae)

Alometría sensorial, especialización de tareas de forrajeo y explotación de recursos en abejas

Insect societies are important models for evolutionary biology and sociobiology. The complexity of some eusocial insect societies appears to arise from self-organized task allocation and group cohesion. One of the best-supported models explaining self-organized task allocation in social insects is the response threshold model, which predicts specialization due to inter-individual variability in sensitivity to task-associated stimuli. The model explains foraging task specialization among honeybee workers, but the factors underlying the differences in individual sensitivity remain elusive. Here, we propose that in honeybees, sensory sensitivity correlates with individual differences in the number of sensory structures, as it does in solitary species. Examining European and Africanized honeybees, we introduce and test the hypothesis that body size and/or sensory allometry is associated with foraging task preferences and resource exploitation. We focus on common morphological measures and on the size and number of structures associated with olfactory sensitivity. We show that the number of olfactory sensilla is greater in pollen and water foragers, which are known to exhibit higher sensory sensitivity, compared to nectar foragers. These differences are independent of the distribution of size within a colony. Our data also suggest that body mass and number of olfactory sensilla correlate with the concentration of nectar gathered by workers, and with the size of pollen loads they carry. We conclude that sensory allometry, but not necessarily body size, is associated with resource exploitation in honeybees and that the differences in number of sensilla may underlie the observed differences in sensitivity between bees specialized on water, pollen and nectar collection

Aprendiendo del aprendizaje y la memoria en abejorros

The difficulty to simultaneously record neural activity and behavior presents a considerable limitation for studying mechanisms of insect learning and memory. The challenge is finding a model suitable for the use of behavioral paradigms under the restrained conditions necessary for neural recording. In honey-bees, Pavlovian conditioning relying on the proboscis extension reflex (PER) has been used with great success to study different aspects of insect cognition. However, it is desirable to combine the advantages of the PER with a more robust model that allows simultaneous electrical or optical recording of neural activity. Here, we briefly discuss the potential use of bumblebees as models for the study of learning and memory under restrained conditions. We base our arguments on the well-known cognitive abilities of bumblebees, their social organization and phylogenetic proximity to honeybees, our recent success using Pavlovian conditioning to study learning in two bumblebee species, and on the recently demonstrated robustness of bumblebees under conditions suitable for electrophysiological recording

Brain Allometry and Neural Plasticity in the Bumblebee Bombus occidentalis

Brain plasticity is a common phenomenon across animals and in many cases it is associated with behavioral transitions. In social insects, such as bees, wasps and ants, plasticity in a particular brain compartment involved in multisensory integration (the mushroom body) has been associated with transitions between tasks differing in cognitive demands. However, in most of these cases, transitions between tasks are age-related, requiring the experimental manipulation of the age structure in the studied colonies to distinguish age and experience-dependent effects. To better understand the interplay between brain plasticity and behavioral performance it would therefore be advantageous to study species whose division of labor is not age-dependent. Here, we focus on brain plasticity in the bumblebee Bombus occidentalis, in which division of labor is strongly affected by the individual's body size instead of age. We show that, like in vertebrates, body size strongly correlates with brain size. We also show that foraging experience, but not age, significantly correlates with the increase in the size of the mushroom body, and in particular one of its components, the medial calyx. Our results support previous findings from other social insects suggesting that the mushroom body plays a key role in experience-based decision making. We also discuss the use of bumblebees as models to analyze neural plasticity and the association between brain size and behavioral performance