Finding a sexually receptive partner of the opposite sex is a challenge; one solution is to advertise. That advertising is usually the province of males has shaped scenarios for sexual selection, especially the ardent active male courting the passive but choosy female. Herein we consider an unusual case in which constraints on reproduction may have led to fertility advertisement by female frogs. When oviposition is imminent, female South African clawed frogs swim to an advertising male and produce an aphrodisiac call, rapping, that stimulates both male vocalization and approach. Males respond to rapping with a distinctive answer call. The rapping-answer interaction thus forms a duet between partners of a receptive pair.In most vertebrates, perhaps due to the greater investment of females in gametes and offspring (1), it is the male that competes for receptive conspecific females (2, 3). Many males find mates by advertising; prominent examples are mating leks and the songs of birds and frogs. This simple solution works well when the responding female can be identified by the signaling male. However, if the signaling environment is noisy or if population density is high, it may be difficult for the signaler to distinguish the responder. Under these conditions, we might expect a reciprocal signaling system involving both sexes. Herein we present evidence for a system of auditory recognition-receptive duets-in the South African clawed frog.We have studied male-female courtship vocalizations in Xenopus laevis, a member of a large genus of totally aquatic frogs from southern Africa (4). Xenopus inhabit murky ponds and mating occurs at night so that few if any visual cues are available to identify potential mates. Instead, it is believed that Xenopus, like other frogs (5), relies on auditory cues to broadcast receptivity and location. At the time we began our studies, two courtship vocalizations had been examined in this species. The advertisement or mating call (6) given only by sexually receptive males (7) is loud and prolonged with distinct fast and slow trill phases (7,8). Sexually receptive females display positive phonotaxis to tapes of advertisement calling (8). Ticking (6), given by sexually unreceptive females (9), is a quiet, slow, and monotonous trill (10) believed to function as a release call (6, 11).It has been assumed that male Xenopus find females by producing prolonged bouts of advertisement calling to which females are attracted; the male then clasps the nearest moving animal, releasing those that tick (12). The natural breeding conditions for Xenopus, high population density and low visibility, suggest that finding a mate may not be this simple. Unless the calling male could isolate himself from the rest of the group, clasping every animal in his vicinity would be disadvantageous; how then does he discriminate a responder?We have examined populations of Xenopus near Cape Town during the prolonged breeding season (about 6 months). Most (88%) adult males taken from these ponds were sexually rec...
Refinement of topographic maps during sensitive periods of development is a characteristic feature of diverse sensory and motor circuits in the nervous system. Within the neural system that controls vocal learning and behavior in zebra finches, axonal connections of the cortical nucleus lMAN demonstrate striking functional and morphological changes during vocal development in juvenile males. These circuits are uniquely important for song production during the sensitive period for vocal learning, and the overall size of these brain regions and their patterns of axonal connectivity undergo dramatic growth and regression during this time. Axonal connections to and from lMAN are topographically organized in adult males that have already learned song. We wondered whether the large-scale changes seen in lMAN circuitry during the time that vocal behavior is being learned and refined could be accompanied by the emergence of topographic mapping. However, results presented herein demonstrate that most of these song-control circuits show the same broad patterns of axonal connectivity between subregions of individual nuclei at the onset of song learning as seen in adult birds. Thus, coarse topographic organization is not dependent on the types of experience that are crucial for vocal learning. Furthermore, this maintenance of topographic organization throughout the period of song learning is clearly not achieved by maintenance of static axonal arbors. In fact, because the volumes of song-control nuclei are growing (or regressing), topography must be maintained by active remodeling of axonal arbors to adapt to the changes in overall size of postsynaptic targets. A salient exception to this pattern of conserved topography is the projection from lMAN to the motor cortical region RA: this pathway is diffusely organized at the onset of song learning but undergoes substantial refinement during early stages of song learning, suggesting that remodeling of axonal connections within this projection during the period of vocal learning may signify the production of increasingly refined vocal utterances.
3,4-Methylenedioxymethamphetamine (MDMA) is a psychoactive drug of abuse which is increasingly popular in human recreational drug use. In rats, the drug has been shown to stimulate locomotion while decreasing exploratory behavior. MDMA acts as an indirect agonist of serotonin (5-HT) receptors by inducing 5-HT release by a 5-HT reuptake transporter-dependent mechanism, although it is not known which 5-HT receptors are important for the behavioral effects of the drug. In order to examine the role of specific 5-HT receptors, we assessed the behavioral effects of MDMA on knockout mice lacking the 5-HT1B receptor. Knockout animals show a reduced locomotor response to MDMA, although delayed locomotor stimulation is present in these animals. This finding indicates that the locomotor effects of MDMA are dependent upon the 5-HT1B receptor, at least in part. In contrast, MDMA eliminates exploratory behavior in both normal and knockout mice, suggesting that the exploratory suppression induced by MDMA occurs through mechanisms other than activation of the 5-HT1B receptor. To confirm these findings, we tested the effects of MDMA on the locomotor and exploratory behavior of wild-type mice pretreated with GR 127935, a 5-HT1B/1D receptor antagonist. These mice had an attenuated locomotor response to MDMA, but still exhibited the drug-induced suppression of exploration.
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