Endocrine and environmental aspects of sex differentiation in gonochoristic fish

Temperature-Dependent Sex Determination in Vertebrates

“…(From Dournon and Houillon 1985 and unpublished results. ) ratios are in agreement with a strict GSD, XX/XY or ZZ/ZW, mechanism (Baroiller and Guiguen 2001;Conover, Chapter 2). Thus, extreme (low or high) temperatures, generally not or rarely encountered in natural habitats, induce sex reversal of one sex.…”

“…Thus, as shown above in the salamanders, both sex chromosomes have the same size and differ only in their banding patterns (T. c. cristatus and T. c. carnifex) or the loop patterns in lampbrush chromosomes (P. poireti and P. waltl). Variable thermosensitivity between individuals (in fish and amphibians) and between progenies (in some fish species) reflects interactions between temperature and genotype ( Conover and Kynard 1981; reviewed in Baroiller and Guiguen 2001). In reptiles, species with temperature-dependent sex determination (TSD) do not display heteromorphic sex chromosomes but present variable responses in incubation at pivotal temperature, potentially reflecting genetic differences between individuals and clutches (Bull 1983;reviewed in Pieau 1996; see also Valenzuela,Chapter 14).…”

“…In amphibians and fish, gonads appear histologically undifferentiated for most of the thermosensitive period, and begin to differentiate only by the end of this period (reviewed in Baroiller and Guiguen 2001;this chapter). Alternatively, in reptiles gonads are still undifferentiated at the beginning of the TSP but rapidly exhibit histological signs of sexual differentiation; thus, the TSP corresponds to the first steps of gonadal sex differentiation (reviewed in Pieau 1996).…”

Sex determination: the amphibian models

“…King [43] already observed that steeping toad eggs for a few minutes prior to fertilisation in a 2% salt or cane sugar solution, could bias the sex ratio at metamorphosis in favour of females. But as in many reptiles [44] and certain fishes [45,46], it is the temperature that seems to have the most outstanding effects on sex determination. For example, Witschi [47] observed sex reversal of all females in Rana sylvatica by rearing larvae at high temperature (32°C ± 2°C).…”

Functional characterization and expression analysis of the androgen receptor in zebrafish (Danio rerio) testis

“…As regards sex differentiation, fish appear to be particularly sensitive to androgen action, considering that fully functional female-to-male sex reversal can be induced by exposure of juvenile (Baroiller & Guiguen 2001) and even adult fish (Kobayashi et al 1991) to androgens; in some species, sex change is part of the normal life cycle (Baroiller & Guiguen 2001).…”