92 



BIOLOGIC BASIS OF SEX 



is complete transformation of ovary to testis 

 or of testis to ovary, and in some cases the 

 transformed individuals have been proved 

 functional and capable of breeding. In other 

 si)ecies, however, negative, equivocal, and 

 in many cases paradoxical results have been 

 obtained by the use of the same substances. 

 A hormone that completely transforms all 

 individuals of the opposite sex in one species 

 may have only a weak or impermanent ef- 

 fect in another, or no effect at all in a third. 

 Obviously the gonads of different species 

 differ greatly in their responses to steroid 

 hormones. There is also a correlation with 

 sex. In some species the gonad of one sex 

 undergoes reversal with relative ease 

 whereas that of the other is difficult or im- 

 possible to transform, although increased 

 dosages are sometimes effective. In certain 

 species in which the sex chromosome com- 

 plex is known it is the homogametic sex 

 that is readily reversible (Gallien, 1955). It 

 is also clear that experimental conditions 

 strongly influence the result. The time fac- 

 tor, that is to say the stage of differentiation 

 at which treatment is initiated, is obviously 

 important; in general, the most complete 

 transformations are obtained when the hor- 

 mone has been present from the beginning 

 of the differentiation process. Dosage is like- 

 wise of great importance and the optimal 

 dosage varies greatly from one species to 

 another. A negative response at one dosage 

 may become positive when the dosage is in- 

 creased; on the other hand, strong "para- 

 doxical effects" (stimulation of the charac- 

 ters of one sex by the hormone of the other) 

 are often encountered with high dosages 

 which are absent at lower levels. At present 

 it is not possible to give consistent explana- 

 tions for all such contradictory results ; how- 

 ever, better understanding is gained when 

 they are classified into convenient cate- 

 gories. 



The effects of male hormones on sex dif- 

 ferentiation in frogs. On the whole, the most 

 successful reversals obtained by the use of 

 steroid hormones have been in frogs of the 

 family Ranidae, of which some six species 

 have now been studied with similar results. 

 Both male and female hormones induce re- 

 versal of sex in young tadpoles, but male 

 hormones are more effective and far more 

 consistent in their effects. In Rana tempo- 



raria treatment with testosterone propionate 

 transforms all genie females into males. The 

 transformation is complete and permanent; 

 moreover, transformed individuals are capa- 

 ble of functioning in their new capacity 

 (Gallien, 1944). A similar transformation 

 has been obtained in Rana sylvatica, a phe- 

 nomenally low concentration of the hor- 

 mone (1/500,000,000 parts dissolved in the 

 aquarium water) inducing complete histo- 

 logic transformation (Mintz, 1948). Com- 

 parable results have been reported after use 

 of the male hormone in several other species 

 of this genus (Table 2.1). In the case of 

 Rana catesbiana it was found necessary to 

 "prime" the gonads by simultaneous treat- 

 ment with gonadotrophin, otherwise they 

 were unresponsive; when so treated, how- 

 ever, complete transformation is obtained. 

 The gonadotrophic substance alone initiates 

 a precocious differentiation of sex but with- 

 out any tendency to transformation, serving 

 only to precipitate the normal differentia- 

 tion process. Complete and permanent mas- 

 culinization of females by testosterone pro- 

 pionate has also been reported recently in a 

 tree frog, Pseudacris (Witschi, Foote and 

 Chang, 1958), and a virtual transformation 

 at the age of metamorphosis in Rhacophonts 

 (Iwasawa, 1958), indicating that other anu- 

 ran families may resemble the Ranidae in 

 their reactions to the male hormone. In 

 marked contrast, male hormone is without 

 effect on gonad differentiation in the toad 

 (Chang, 1955). 



The effects of female hormones in the 

 Ranidae. These are variable and less con- 

 clusive. The results frequently depend on 

 dosage and the effective dose may vary 

 greatly in different species. Estradiol benzo- 

 ate in weak doses has a slightly feminizing 

 action in male tadpoles of Raiia temporaria 

 (Gallien, 1941), but stronger doses produce 

 complete feminization in an "undifferenti- 

 ated race" (one in which sex differentiation 

 of males occurs relatively late) of the same 

 species, all tadpoles at metamorphosis be- 

 ing females (Gallien, 1940, 1955) . It is note- 

 worthy that in this case both genie constitu- 

 tion (race) and the dosage of the hormone 

 may be factors in the result. In other ranid 

 species estradiol, administered in low dos- 

 ages during the period of sex differentiation, 

 has a completely feminizing effect ; at meta- 



