Table 1.

Mean syllable number in the cross between the song races

Genotype	Monosyllabic	Mono × poly	Poly × mono	Polysyllabic
Mean syllable number	1	1.94	2.53	3.60
Standard deviation	—	0.02	0.02	0.03

Monosyllabic populations are monomorphic. The standard deviation estimates for the polysyllabic and hybrid genotypes are from a generalized linear model analysis. For the hybrids, the sample sizes are 840 chirps from 5 males of each genotype, and there are significant differences both among males within genotypes (F_8,830 = 113, P < 0.001) and between genotypes (F_1,830 = 577, P < 0.001 or F_1,8 = 77, P = 0.04 if the variance among males is used as the denominator mean square). The polysyllabic analysis involved around 1500 chirps from four males each of five families, and the estimate is for the variance of family means. There were significant differences among males within families (F_15,1478 = 85, P < 0.001; average SD within males = 0.06). Families did not differ if the variance among males was used as the denominator mean square (F_4,15 = 1.2, not significant).