The Mechanisms And Regulation Of Vocal Behavior In Male African Clawed Frogs, Xenopus Laevis

Vocal behavior is universal in anuran amphibians and plays a very important role in their reproduction. Although there is no consistent evidence, many researchers suggested that vocal behavior of anuran amphibians were closely related to the circulating levels of sexual hormones. In anurans, some studies showed that androgens have a significant effect on muscles of vocal organs as well as vocal motor neurons. In addition, it was demonstrated that the androgen receptor expressed in vocal control regions of the amphibian brains. Those suggested that androgens were very important in mediating vocal behavior, although the mechanisms have been unknown. Application of arginine vasotocin (AVT) increased largely levels of advertisement call and decreased release calls. Male and female African Clawed Frogs (Xenopus laevis) produce calls and engage in dueting in both silt-filled ponds and laboratory aquaria. Previous research has established that males produce different answer calls in response to receptive and non-receptive female calls. In the present study, in addition to male answer calls, male phonotropism behaviors were measured for the first time during playbacks of natural female rapping and ticking calls as well as synthetic stimuli consisting of ticking calls with 90 ms inter-click intervals (ICIs) and rapping calls with 250 ms ICIs. The expression of androgen receptor mRNA and immediate early gene in brain preoptic area (POA) were detected in male African clawed frogs with different calling amounts. The main results and conclusions we obtained are as follows:1. Males approach a loudspeaker significantly more often in response to rapping calls and remain longer in the proximity of the speaker. Moreover males produce answer calls more frequently in response to female rapping calls and produce few answer calls in response to female ticking calls. Synthetic ticking calls with 90 ms ICIs evoked an intermediate phonotaxis response while synthetic rapping calls with 250 ms ICIs evoked the same level of phonotaxy as natural ticking calls.2. Based on phylogenetic analysis, this paper reviewed the relationship between hormones including sex hormones and AVT, and vocal production and perception through all anuran species studied to date. We found that in anuran brains the AVT system related to vocal behaviors were very conservative while the sex hormone systems involved in vocal communication might be originated independently from varied taxa of anuran.3.The expressions of androgen receptor and egr1 gene mRNAs were found in neurons within the POA, a region considered as the first order nucleus in controlling anuran vocalizations. There may be relationships between expression of androgen receptor in POA and advertisement calls per minute, and between advertisement calls and egr1 evoked in POA.In conclusion, our results therefore support the hypothesis that the most important acoustic features of female communication signals in frogs are amplitude fluctuations and temporal modulation patterns and reveal that male tend to approach and visit a calling female who advertised sexual receptivity. Based on phylogenetic analysis, this paper reviewed the relationship between hormones including sex hormones and AVT, and vocal production and perception through all anuran species studied to date, proposing that the sex hormone systems involved in vocal communication might be originated independently from varied taxa of anuran. Furthermore, by using in situ hybridization, we can safely draw the conclusion that androgen play an extremely important role in vocal behavior through binding to its receptors that expressed strongly in the POA of the male X. laevis.