Nged morphs, which are in charge of long range dispersion, clonal forms are able to react in a very short time using alternative escape behaviors for short range dispersion. Some aphids indeed leave their host plant and begin to explore their close environment to find fresh resources and to immediately settle new colonies [3,4] The release of volatile compounds, such as the alarm pheromone secreted by aphids in the presence of predators, also triggers various reactions such as the withdrawal of the stylet from the plant, or the walking or dropping off the host plant [5]. This high behavioral plasticity makes them good candidates to explore the molecular basis of such a phenomenon. Nevertheless, almost nothing is known of the physiological and genetic mechanisms controlling polyphenism and individual behavior in aphids [6,7].A natural polymorphism in the foraging gene (for), that encodes a cGMP-dependent protein kinase (PKG), has been shown to be Title Loaded From File associated to behavioral plasticity in several insect species [8]. In the fruit fly Drosophila melanogaster, larvae and adults of the rover phenotype have larger moving trails in the presence of food compared to sitters [9,10]. Higher levels of for expression and PKG activity are observed in the heads of the rover allelic variants [11]. The for gene was then suggested to play a role in the behavioral plasticity in response to food deprivation [12]. In the honeybee Apis mellifera, higher levels of expression of the for gene (Amfor) and PKG activities were detected in foragers compared to nurses [13]. A subsequent study evidenced an Amfor expression peak during the period of transition from nurse to forager, and suggested that in normal conditions the honeybee foraging behavior is at least partly due to a trigger-effect of Amfor [14]. The Amfor expression was thus strongly associated with tasks Title Loaded From File performed outside the hive and suggested to affect the division of labor by modulating phototaxis [15,16]. A differential expression of the for gene homologues has also been reported in other social insects although a negative correlation was initially observed between the PKG activity level and foraging activities. In the common wasp Vespula vulgaris, bumblebees and the some red harvester ants in the genus Pogonomyrmex, which all display progression of worker tasks during their lifespan, known as age-related polyethism, lower for mRNAThe Pea Aphid foraging Genelevels were detected in foraging workers than in nest workers [17?19]. Nevertheless, Ingram et al. [20] recently highlighted a more complex expression pattern of the for gene in the harvester ant foragers : for expression changes in the course of the day consistently with the task-specific circadian rhythm observed in this species. A similar fluctuation of the for expression level has been observed in honeybee over the time [14]. A more precise and systematic study of the for gene expression combined with a meticulous analysis of behavioral traits is likely the best approach to understand the mechanisms by which for modulates the insect behavior. The recent sequencing of the pea aphid Acyrthosiphon pisum genome and its subsequent automated annotation [21] has provided an appreciable tool to characterize the for gene in a clonal species displaying high behavioral plasticity. In this study, we first cloned the cDNAs of the pea aphid foraging gene orthologue Apfor. We then analyzed their expression patterns across parthenogenetic developmental stages, m.Nged morphs, which are in charge of long range dispersion, clonal forms are able to react in a very short time using alternative escape behaviors for short range dispersion. Some aphids indeed leave their host plant and begin to explore their close environment to find fresh resources and to immediately settle new colonies [3,4] The release of volatile compounds, such as the alarm pheromone secreted by aphids in the presence of predators, also triggers various reactions such as the withdrawal of the stylet from the plant, or the walking or dropping off the host plant [5]. This high behavioral plasticity makes them good candidates to explore the molecular basis of such a phenomenon. Nevertheless, almost nothing is known of the physiological and genetic mechanisms controlling polyphenism and individual behavior in aphids [6,7].A natural polymorphism in the foraging gene (for), that encodes a cGMP-dependent protein kinase (PKG), has been shown to be associated to behavioral plasticity in several insect species [8]. In the fruit fly Drosophila melanogaster, larvae and adults of the rover phenotype have larger moving trails in the presence of food compared to sitters [9,10]. Higher levels of for expression and PKG activity are observed in the heads of the rover allelic variants [11]. The for gene was then suggested to play a role in the behavioral plasticity in response to food deprivation [12]. In the honeybee Apis mellifera, higher levels of expression of the for gene (Amfor) and PKG activities were detected in foragers compared to nurses [13]. A subsequent study evidenced an Amfor expression peak during the period of transition from nurse to forager, and suggested that in normal conditions the honeybee foraging behavior is at least partly due to a trigger-effect of Amfor [14]. The Amfor expression was thus strongly associated with tasks performed outside the hive and suggested to affect the division of labor by modulating phototaxis [15,16]. A differential expression of the for gene homologues has also been reported in other social insects although a negative correlation was initially observed between the PKG activity level and foraging activities. In the common wasp Vespula vulgaris, bumblebees and the some red harvester ants in the genus Pogonomyrmex, which all display progression of worker tasks during their lifespan, known as age-related polyethism, lower for mRNAThe Pea Aphid foraging Genelevels were detected in foraging workers than in nest workers [17?19]. Nevertheless, Ingram et al. [20] recently highlighted a more complex expression pattern of the for gene in the harvester ant foragers : for expression changes in the course of the day consistently with the task-specific circadian rhythm observed in this species. A similar fluctuation of the for expression level has been observed in honeybee over the time [14]. A more precise and systematic study of the for gene expression combined with a meticulous analysis of behavioral traits is likely the best approach to understand the mechanisms by which for modulates the insect behavior. The recent sequencing of the pea aphid Acyrthosiphon pisum genome and its subsequent automated annotation [21] has provided an appreciable tool to characterize the for gene in a clonal species displaying high behavioral plasticity. In this study, we first cloned the cDNAs of the pea aphid foraging gene orthologue Apfor. We then analyzed their expression patterns across parthenogenetic developmental stages, m.
