A Study of the Diets and Nutritional Preferences of Tropical Species of Drosophila

Abstract

The existence of isolating mechanisms is not the only necessary condition for the sympatric coexistence of species. Besides being genetically isolated, sympatric species must be ecologically compatible (Mayr 1949). This is a consequence of the well known Gause's principle according which two or more species cannot live together indefinitely if they exploit the same ecological niche in the same ways. Natural selection might then favor the development of differences between species which would lead to an ecological divergence and will minimize the competition. Development of different nutritional preferences is one of the many mechanisms which can promote the ecological compatibility of related sympatric species. To understand the ecological interrelations of the tropical species of Drosophila we have chosen to analyse the composition of their food and the attractivity to Drosophila of different yeasts. Studies of this type have been initiated by Carson (1951), da Cunha, Dobzhansky and Sokoloff (1951), Dudgeon (1954), Shehata and Mrak (1952), and Wagner (1944, 1949) in North America. An exploratory work was started by Dobzhansky and da Cunha (1955) in Tropical Brazil. The results obtained indicated that species of Drosophila differ in their diets and the attraction to different yeasts. The purpose of the present work is to examine further the food preferences of tropical Drosophila and to compare the behavior of temperate and tropical species in this regard. The authors wish to express grateful appreciation to Profs. C. Pavan and Th. Dobzhansky and to Miss Therezinha M. Ungaretti for their manifold help throughout the work. Thanks are also due to Miss Hebe M. Laghi, to Miss Jeannette S. de Toledo and to Mr. L. E. de Magafhaes for their aid in the classification of the flies collected. The work was made possible by the Rockefeller Foundation and by the Conselho Nacional de Pesquisas do Brasil whose grants gave the opportunity for one of us (Shehata) to stay for more than a year in Brazil and permitted the acquisition of the necessary equipment. We leave here our warmest thanks for the two Institutions.