Yamaguchi A et al. (2010), Sexually distinct development of vocal pathways...

XB-ART-41773

Dev Neurobiol 2010 Nov 01;7013:862-74. doi: 10.1002/dneu.20822.

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Sexually distinct development of vocal pathways in Xenopus laevis.

Yamaguchi A , Muñoz MM , Bose TO , Oberlander JG , Smith S .

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Deterministic rules, rather than experience, are thought to regulate the development of simple behaviors in vertebrates and invertebrates. We revisited this issue through examination of the sexually distinct vocalizations of African clawed frogs (Xenopus laevis), a reproductive behavior used by sexually mature males and females. We discovered that, as expected for simple behavior, female vocalizations develop through deterministic rules. The rare calls of juvenile females are indistinguishable from those of adult females. The vocal pathways of juvenile females, as measured by the contractile properties of the laryngeal muscles (the vocal muscles) and the laryngeal motoneuron somata (vocal motoneurons) size, are the developmental default and do not differentiate as they mature. Male Xenopus, in contrast, produce extensive vocalizations with rudimentary acoustic structure before reaching sexual maturity. Moreover, the functional properties of the vocal central pattern generator mature before muscle fibers and motoneuron size are fully masculinized. The results suggest that neuronal activity during development may be important in organizing the contractile properties of the muscle fibers in male, but not in female Xenopus.

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	Figure 1. Vocal development in male and female Xenopus. A–G: Normalized frequency histograms of instantaneous click rates obtained from adult females (A), juvenile females (B), juvenile males (all animals combined, C), Group I juvenile males (D), Group II juvenile males (E), Group III juvenile males (F), adult males (G). H–M: Sound spectrograms of calls recorded from an adult female (H), juvenile female (I), Group I juvenile male (J), Group II juvenile male (K), Group III juvenile male (L), and adult male (M).
	Figure 2. Body mass of juvenile males is a poor predictor of vocal maturity. Bivariate plots of maximum instantaneous click rates (top) and maximum sustained click rates (bottom) as a function of body mass. Note that there is no association between click rates and body mass. The range of body weight for each juvenile group is indicated with a horizontal bar with double arrows in the bottom.
	Figure 3. Sound spectrograms of advertisement calls produced by adult males and juvenile Group III males. Dotted line indicates the onset of fast trills. Arrows indicate the silent intervals found at the end of the fast trills in all juvenile males.
	Figure 4. Fictive advertisement calls produced by adult and juvenile male brains. Shaded boxes indicate fast trills in each call. Note that there are no silent intervals (see Fig. 3). In fictive advertisement calls of juvenile males.
	Figure 5. Contractile properties of adult and juvenile laryngeal muscles. A: Contractile force recorded from a laryngeal muscle in response to repetitive stimulation delivered to the laryngeal nerve. B: Slope to peak tension and half‐relaxation time were measured from the tension profile elicited in response to a single shock delivered to the nerve. C: Proportion of fused tension produced in response to stimuli delivered at 10, 30, 50, and 70 Hz by larynges obtained from adult females, juvenile females, juvenile males, and adult males. D, E: Cell plots of tension slope (D) and half relaxation time (E). Error bars indicate standard errors. Asterisks in C, D, and E indicate significant differences, and “n.s.” indicates not significant difference. [Color figure can be viewed in the online issue, which is available at wileyonlinelibrary.com.]
	Figure 6. Size of laryngeal motoneuron somata. A: Cell plots of somata size obtained from adult and juvenile males and females. Error bars indicate standard errors. B: Regression plot of mean somata volume as a function of body mass. Four groups of animals (adult and juvenile males and females) are color coded as in A. C: Bivariate plot showing the somata volume as a function of body mass. Color coding scheme is the same as in A. Adult males do not have small sized motoneurons, indicated by dotted line.

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