The Effect of Vegetation on the Breeding of Newts, Molge cristata and Molge vulgaris

Abstract

Listen

Translate article

According to Stolte (192ia, b), in some aquatic oligochaetes (Naiads) sexual reproduction is governed by the oxygen given off by algae. Here there is an optimum, deficiency or superfluity of oxygen being unfavourable. Miyazaki (1938), dealing with oysters, has reported a substance contained in green algae which produces spawning in the male oyster. In the observed breeding -habits of fishes, there is frequent reference to association with aquatic vegetation. Among the fresh-water fishes for instance, sticklebacks, the bowfin (Boulenger, I93i) and the gourami (cited by Meek, I9I6) are known to make nests among water plants, while the common carp, Cyprinus carpio (Boulenger, 193I) and the European catfish, Silurus glanis (Meek, I 9 I 6), both deposit eggs on water plants. Among marine fishes wrasses and the Saragossa fish (Boulenger, 193I) nest among seaweed and the eggs of skates and rays are anchored among weeds. To these instances of the association of a special type of environment with the reproduction of aquatic animals I must add a casual observation of my own on a fresh-water vertebrate. I noticed, one spring, that common newts kept for some days in a gold-fish bowl with clean water and no weed made no attempt to spawn, but proceeded to deposit ova almost immediately after the introduction of the pond-weed Elodea canadensis. During the course of experiments shortly to be described and which are prompted by this casual observation, Dr Harding of the British Museum informed me that he had had a similar experience with Amblystoma. I quote from his letter with his permission. 'The female had been in the water for some months.... There was no weed in the pond. On the I2th of last month (June 1938) a lab. boy brought me some weed which I had placed in the water and on the I3th there were eggs! The male was still on land, but one presumes that, either he went in the water for a time or the female came out for him.' Finally, long after the completion of the investigations dealt with in this paper, there came to my notice an account by Van Nieuwenhoven & Lever (1946) of similar work carried out in Holland during the war. The Dutch workers found snails of the genus Limnaea kept in aquaria without water plants and fed regularly on lettuce reacted to the addition of water plants by producing eggs within a few hours. In the account that follows I give the results of experiments designed to test the importance of vegetation and associated factors on the reproduction of newts. These experiments were carried out in I936 and 1938 at Roman Hill Boys' School, Lowestoft, and they were only made possible by the help and close co-operation of the Headmaster, Mr W. H. Bleby, and two members of his staff, Mr Railston, in I936 and Mr Bentley in 1938. In addition, I include some experiments on a smaller scale which I made in 1937. I have also to thank Dr E. S. Russell, Dr J. P. Harding, and Dr C. F. A. Pantin for reading through the paper and for helpful suggestions in interpreting the results.