Preliminary Investigations in to the Reproductive Water Drive of Bufo-Carens Smith and the Humidity Reaction Of RanA Natalensis (Smith)

Abstract

G.K. Noble has suggested that the spring migration of amphibians to water prior to breeding ’’may be considered a secondary sexual character found in both sexes'* (Noble, # * 1933), p,402), and in addition he points out that the sex 0 hormones, which determine the appearance of the anatomical secondary sexual characters, may also influence the appearance of the seasonal movement to water* Blair (1946) also considers that what he terms the "mating reaction*1 of ✓ Bufo fowleri. which consists of the spring migration to 0 water and the subsequent breeding activities, are under hormonal control* He was, however, unable to elicit any of these reactions by hormonal treatment. Other workers have recorded that the clasp reflex can be induced in Bufo by pituitary implants (e.g. Houssay, Guisti & Lascano- Gongales, 1929), but there appears to be no report in the literature of the induction of the complete sexual behaviour in Bufo by the injection of the sex hormones. It seems that 0 in this respect Bufo is very peculiar, since a review of the literature shows that it is characteristic of animals studied from all the vertebrate olasoes that sexual behavior is as much a part of the reproductive equipment of the animal as are the organs of reproduction, and, like these organs, it falls under a marked and specific influence of the sex hormones* Blair and Noble believe that there 0x0 also environmental factors which influence the seasonal * water drive and sexual behaviour, in addition to the hormonal factors, and certainly while it is clear from the literature that the environment, acting on the central nervous system, is of critical importance in the appearance of sexual behaviour, the level of the sex hoinones must also be a critical factor in its appearance. The literature indeed shows that sensory stimulation and the sex hormone level (among other internal factors) appear to be complementary elements in the evocation of sexual behaviour, and it is therefore reasonable to look for the effects of the sex hormones on the breeding behaviour of Bufo. in spite of the largely negative results that have so far been obtained. It is, moreover, evident from the literature that the development of the cerebral cortex in the vertebrate series seems to be inversely related to the indispensibility of the sex hormones in the appearance of sexual behaviour* Because of the relatively poor development of the anuran brain, it is further to be expected that Bufo should show any responses to sex hormone treatment that might exist in a particularly well marked manner. A review of the literature does, 121 fact, show that there is ample justification for further investigations into the effects of the sex hormones on the general breeding behaviour of ✓ toads, and the following review will be concerned with the two main considerations given above, namely that i) sensory stimulation and the sex hormone level appear to exert a finqi role in the evocation of sexual behaviour, and that ii) the influence of the sex hormones on behaviour seems to be Inversely related to the development of the cerebral cortex.