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Genetic control of the hypothalamo‐pituitary axis and the effect of hybridization on sexual maturation ( Xiphophorus , Pisces, Poeciliidae)

1982; Wiley; Volume: 220; Issue: 3 Linguagem: Inglês

10.1002/jez.1402200305

1097-010X

Isaac Y. Bao, Klaus D. Kallman,

Genetic and Clinical Aspects of Sex Determination and Chromosomal Abnormalities

Abstract The onset of sexual maturity in fishes of the genus Xiphophorus depends upon a multiple allelic series at the P locus. X. helleri of genotype P h P h initiate sexual maturity at 10.4 weeks and X. maculatus of genotypes P 3 P 3 or P 4 P 4 at 8.7 or 20 weeks, respectively. Hybrids between the two species of genotype P h P h and possessing some autosomes of X. maculatus in homozygous condition exhibit precocious maturation at 5.3 weeks and are correspondingly small. P h P h hybrids of the backcross generations to X. helleri mature at the same age and size as X. helleri . The P 3 P h and P 4 P h backcross hybrids, however, exhibit greatly delayed maturation, and the delay becomes more severe as the number of X. helleri autosomes increases. The phenotype results from the interaction of the P locus with a system of regulatory genes. Both the P factors and the regulatory systems are species‐specific. Synthetic luteinizing hormone‐releasing hormone (LH‐RH) was effective in inducing proliferation and functional activity in the gonadotrops and ultimately sexual maturity in all genotypes, including P h P 3 hybrids. Whereas the response of different genotypes to gonadotropin was essentially the same, their response to LH‐RH was significantly different. A positive correlation exists between the rapidity of the response to LH‐RH and the genetically determined age at which spontaneous maturation takes place. The maturity induced by LH‐RH was not permanent. After cessation of LH‐RH administration the gonadotrops became inactive and regressed. These observations suggest that the P locus is not concerned with the production of LH‐RH. Rather, the P locus appears to control the physiological function or the fate of LH‐RH.