Transposable elements (TEs) are middle repetitive DNA sequences classified into families according to their sequence similarities, such elements can playing an important role in the evolutionary process of their host genomes. There are many reports on the distribution of TEs in the fruit fly genus Drosophila, although there is relatively little information relating to the Neotropical mesophragmatica group of Drosophila, probably the most typical cluster of species occurring almost exclusively in the Andes mountains. Dot Blot and PCR analyses was used to study the distribution of some TEs (I, mariner, hobo, gypsy, Tom/17.6, micropia and P elements) within the mesophragmatica group of Drosophila. We found gypsy elements in all the mesophragmatica group species studied and mariner elements were absent only from Drosophila pavani but P element homologous sequences were present only in D. pavani and Drosophila gasici and the other TEs (I, hobo, Tom/17.6, micropia) were not found in any of the species investigated.

Foram descritas e correlacionadas as variações fenotípicas no período de desenvolvimento, tamanho e variações causadas por assimetria flutuante em Musca domestica L., induzidas por seleção para competição larval por alimento. Dez densidades de 100 a 1000 larvas por 75 g de farelo de trigo umedecido foram estabelecidas em laboratório e acompanhadas até a emergência dos adultos. A curva ajustada de sobrevivência foi semelhante a uma hipérbole. O período de desenvolvimento se estendeu com o aumento da densidade, mas o tamanho foi inversamente proporcional ao grau de agregação larval. Machos e fêmeas respondem de modo distinto às pressões de seleção para competição, sendo machos mais variáveis que fêmeas quanto ao tamanho. Embora ajustes morfológicos e fisiológicos provocados por ação ambiental tenham sido detectados, os níveis de assimetria flutuante permaneceram invariáveis. Não foram, portanto, detectadas correlações genéticas entre estes tipos de variações fenotípicas. Pode-se supor, entretanto, que níveis de assimetria flutuante, que podem ser indicativos de estresse, tenham sido minimizados pelo grande potencial plástico da espécie. Assim, ajustes fisiológicos e morfológicos estariam diminuindo dificuldades no desenvolvimento e promovendo a sobrevivência de maior número de indivíduos.

Phenotypic variations on developmental period, size and fluctuating asymmetry (FA) of Musca domestica L., induced by larval competition for food were described and correlated. Ten densities, varying from 100 to 1000 larvae per 75 g of wheat medium, were established in the laboratory and observed until adult emergence. The adjusted curve of survival was similar to a hyperbola. The developmental period extended with increasing densities, and the size was inversely proportional to the degree of larval crowding. Males and females responded differently to the selection pressures of competition, being size of the males much more variable than those of the females. Although morphological and physiological adjustments caused by environmental interaction were detected, the levels of fluctuating asymmetry remained invariable. Genetic correlation between these types of phenotypic variation was not detected. It can be supposed, however, that levels of FA, which are stress indicative, were minimized by the considerably plastic potential of the species. Thus, physiological and morphological adjustments reduced developmental difficulties and promoted survival of a greater number of individuals.