Transformation of Testis to Ovary in Heteroplastic Parabiosis in Amblystoma

Abstract

A study of sex reversal in heteroplastic combinations of Amblystoma has been in progress for some time, and a total of 146 pairs of A. tigrinum—A. punctatum have been studied, in which both partners are sexually differentiated. The advantage of heteroplastic combination lies in the more rapid development and larger size of the tigrinum member, which invariably becomes sexually dominant at a relatively early stage, regardless of its own sex. Likewise, the gonads of the punctatum member, irrespective of sex, undergo modification and reversal in varying degree. In the present paper we shall confine ourselves to an outline of the process of transformation from testis to ovary in the gonads of punctatum males joined to large tigrinum females.

In accordance with the laws of chance combination, 4 sex-species combinations are possible, and up to about 90 days in the experiment these occur in the expected ratio, as follows: .∗ From this it is apparent that such factors as early mortality, or atypical sex ratios in the eggs used, can be excluded as influencing the result. And since the mortality subsequent to sex differentiation was low, and moreover included in the data, this factor, difficult to rule out in past experiments, is here completely eliminated from the result.

In the later stages of the experiment the expected ratio is greatly modified due to complete reversal of sex in the punctatum member of many pairs of the group. This is accompanied by a corresponding excess of pairs: . These data, coupled with the histological evidence to be summarized, force us to conclude that virtually all punctatum males united to large tigrinum females undergo reversal of sex, which is, in many instances, already complete. The histological evidence may be summed up in the following principal points:

(1) Histological transformation of testis to ovary is seen in the gonads of almost all punctatum members of pairs prior to 90 days, beyond which few such pairs can be found. The only exceptions are found in a few quite young pairs.