Identification and characterization of the cellular targets of sex-peptide mediating the post mating switch in female Drosophila melanogaster

Um angemessenes Verhalten zu generieren muss das Nervensystem Informationen über die Umgebung mit Informationen über den internen Zustand des Tieres verrechnen. Drosophila melanogaster Weibchen ändern ihr Verhalten nach der Paarung grundlegend. Während sich Jungfrauen mit Männchen paaren weisen Weibchen diese nach der Paarung zurück. Diese Verhaltensänderung wird duch ein Polypeptid, das sogenannte Sex-peptid (SP) ausgelöst, welches während der Paarung vom Männchen zum Weibchen übertragen wird. SP aktiviert einen spezifischen Rezeptor, den sogenannten Sex-peptid Rezeptor (SPR), welcher in vielen Zellen des Nervensystems und der weiblichen Sexualorgane exprimiert wird. Hier zeigen wir, dass SPR in einer kleinen Anzahl interner sensorischer Nervenzellen, die den Uterus und Ovidukt innervieren und ins zentrale Nervensystem projezieren, gebraucht wird, um die Verhaltensänderung auszulösen. Diese Nervenzellen exprimieren sowohl fruitless, welches in Nervenzellen, die für Paarungsverhalten wichtig sind, exprimiert wird, als auch pickpocket, welches in proprioceptiven Nerven exprimiert wird. Wir zeigen, dass Expression von SPR in diesen Neuronen sowohl nötig als auch ausreichend ist, um die Verhaltensänderung nach der Paarung auszulösen. Diese Neurone stellen daher einen Zugang zu einem Neuronalen Schaltkreis dar, der Informationen über die Umgebung mit internen Informationen über den Zustand des Tieres verrechnet, um angemessene Verhaltensweisen auszulösen.To generate an appropriate behavioral output the nervous system has to integrate information about the outside world as well as the internal state of the animal. Drosophila melanogaster females show a striking switch in their reproductive behavior after mating. When presented with the exact same sensory cues virgin females will accept males for copulation whereas the same female will reject male advances after she was mated. This switch in reproductive behavior is triggered by a small peptide, the Sex peptide (SP), transferred from the male to the female during mating. SP activates a specific receptor, the Sex-peptide-receptor (SPR), which is broadly expressed in the female’s nervous system and reproductive tract. Here, we pinpoint the action of SPR to a small subset of internal sensory neurons that innervate the female uterus and oviduct and that project to the central nervous system. These neurons express both fruitless, a marker of neurons implicated in sex-specific behaviors, and pickpocket, a marker for proprioceptive neurons. We show that SPR expression in these neurons is both required and sufficient to orchestrate the switch in reproductive behavior. These neurons therefore offer an entry point into a neuronal circuit that integrates information about the outside world with the internal state of the animal to produce appropriate behavioral actions

Evidence for positive selection in the gene fruitless in Anastrepha fruit flies

<p>Abstract</p> <p>Background</p> <p>Many genes involved in the sex determining cascade have indicated signals of positive selection and rapid evolution across different species. Even though <it>fruitless </it>is an important gene involved mostly in several aspects of male courtship behavior, the few studies so far have explained its high rates of evolution by relaxed selective constraints. This would indicate that a large portion of this gene has evolved neutrally, contrary to what has been observed for other genes in the sex cascade.</p> <p>Results</p> <p>Here we test whether the <it>fruitless </it>gene has evolved neutrally or under positive selection in species of <it>Anastrepha </it>(Tephritidae: Diptera) using two different approaches, a long-term evolutionary analysis and a populational genetic data analysis. The first analysis was performed by using sequences of three species of <it>Anastrepha </it>and sequences from several species of <it>Drosophila </it>using the ratio of nonsynonymous to synonymous rates of evolution in PAML, which revealed that the <it>fru </it>region here studied has evolved by positive selection. Using Bayes Empirical Bayes we estimated that 16 sites located in the connecting region of the <it>fruitless </it>gene were evolving under positive selection. We also investigated for signs of this positive selection using populational data from 50 specimens from three species of <it>Anastrepha </it>from different localities in Brazil. The use of standard tests of selection and a new test that compares patterns of differential survival between synonymous and nonsynonymous in evolutionary time also provide evidence of positive selection across species and of a selective sweep for one of the species investigated.</p> <p>Conclusions</p> <p>Our data indicate that the high diversification of <it>fru </it>connecting region in <it>Anastrepha </it>flies is due at least in part to positive selection, not merely as a consequence of relaxed selective constraint. These conclusions are based not only on the comparison of distantly related taxa that show long-term divergence time, but also on recently diverged lineages and suggest that episodes of adaptive evolution in <it>fru </it>may be related to sexual selection and/or conflict related to its involvement in male courtship behavior.</p

Ascending SAG neurons control sexual receptivity of Drosophila females

Mating induces pronounced changes in female reproductive behavior, typically including a dramatic reduction in sexual receptivity. In Drosophila, post-mating behavioral changes are triggered by sex peptide (SP), a male seminal fluid peptide that acts via a receptor (SPR) expressed in sensory neurons (SPSNs) of the female reproductive tract. Here, we identify second-order neurons that mediate the behavioral changes induced by SP. These SAG neurons receive synaptic input from SPSNs in the abdominal ganglion and project to the dorsal protocerebrum. Silencing SAG neurons renders virgin females unreceptive, whereas activating them increases the receptivity of females that have already mated. Physiological experiments demonstrate that SP down-regulates the excitability of the SPSNs, and hence their input onto SAG neurons. These data thus provide a physiological correlate of mating status in the female central nervous system and a key entry point into the brain circuits that control sexual receptivity