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Interactions between temperature effects and genotype on Oreochromis niloticus sex determination

Baroiller J.F., Clota F.. 1997. In : Anon. Proceedings of the first international symposium on the biology of vertebrate sex determination = [Actes du premier symposium international sur la détermination biologique du sexe des vertébrés]. s.l. : s.n., p. 8-8. International Symposium on the Biology of Vertebrate Sex Determination. 1, 1997-04-07/1997-04-11, Honolulu (Etats-Unis).

In thermosensitive reptiles, extreme temperatures change the sex of all individuals, but there is no definitive demonstration of a genetic sex determination. In thermosensitive amphibians, sex chromosomes determine the sex at basal temperatures, while extreme temperatures totally override the genetic sex determination. In gonochoristic fish, very few studies have assessed the influence of temperature on sex differentiation in the Cichlid fish, Oreochromis niloticus, sex is determined by genetic factors, temperature levels, and genotype-temperature interactions. In order to analyse these interactions, thermosensitivity was examined in all the O. niloticus progenies from a diallele-type crosses using 5 males and 5 females: 70 different experimental groups of 150 fish were subjected for 30 days to a basal temperature (27°C) or to a high temperature treatment (36°C) during the thermosensitive period. Sex-ratios were determined on 7000 fish. Male proportions were significantly enhanced by high temperature treatment in 37% of the breeding combinations; among them, 98-100% males were produced in 2 different progenies. In these groups, temperature totally override the genetic sex determination. In the 63% other combinations, where an absence of thermosensitivity was observed, 9-18% of the sterile individuals were recorded in 2 different progenies. Interestingly, as female (but not male) proportions were significantly reduced in these 2 groups, we hypothesize that genetic females were mainly (if not only) affected by this thermal sterilization. Statiscal analysis of sex-ratio from the diallele-type crosses suggest additive effects. The induction of sterile gonads in some rare individuals is discussed.

Mots-clés : oreochromis niloticus; différenciation sexuelle; détermination du sexe; intéraction génotype environnement; température

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