Abundance and Richness of Cryptic Species of the willistoni Group of Drosophila (Diptera: Drosophilidae) in the Biomes Caatinga and Atlantic Forest, Northeastern Brazil

Cryptic species meet the biological definition of species, but are morphologically identical or quite similar. Several ecological studies underestimate richness and neglect important information on cryptic species, as they are rather difficult to identify. Among insects, drosophilids of the willistoni subgroup, which includes Drosophila willistoni Sturtevant, Drosophila paulistorum Dobzhansky & Pavan, Drosophila equinoxialis Dobzhansky, Drosophila tropicalis Burla & da Cunha, Drosophila insularis Dobzhansky, and Drosophila pavlovskiana Kastritsis & Dobzhansky, are good examples of cryptic species. Although several studies have shown that this subgroup is one of the most abundant in the Neotropical region, no identification to species level has been reported for areas where these individuals live in sympatry. This study evaluates the seasonal oscillations in abundance of this subgroup in biomes with contrasting vegetation and rainfall regimes: the Caatinga and the Atlantic Forest, in northeastern Brazil. Approximately 39,000 drosophilids were captured in 24 collections, of which 18,000 belonged to the willistoni subgroup. The most abundant were D. willistoni, D. paulistorum, and D. equinoxialis, in this order. D. equinoxialis was recorded in only one of the environments surveyed, represented by few individuals. In all environments, individuals of the willistoni subgroup were more abundant in the rainy season, when richness often was higher. The results underline the importance of humidity and of temperature for the subgroup willistoni and indicate the ecological versatility of some of its species.