Drosophila mettleri

The species is most commonly found in North American deserts, specifically, in Mexico and Arizona. The species is also found on the southern coast of California, where they inhabit prickly pears. Of the four species of Drosophila found in the Sonoran Desert, D. mettleri have the lowest heat tolerance. D. mettleri are abundant through all seasons but are less prevalent during the summer period. Because the necrotic tissue of cacti in the arid environment of the desert characterizes intense heat conditions, the ability of D. mettleri to exploit the nearby soil of the cacti for breeding purposes provides a selective advantage wherein the pupa of this species have a higher survival rate than other Drosophila desert species. Other species of Drosophila are less successful in the heat of the Sonoran Desert in rearing young due to the intense conditions. Their inability to burrow into the soil has been shown to prove detrimental in increasing pupa survival, yet D. mettleri has an evolutionary advantage in their ability to exploit a niche environment for breeding. The hypothesis that the necrotic tissue of cacti serves as a similarly protective environment as the soil of the Sonoran Desert for other species of Drosophila has been disproven. While other Drosophila have higher heat tolerances due to their breeding grounds in the necrotic tissue of cacti that is higher in heat, D. …

Drosophila nigrospiracula solely exploits cactus sap on the plant itself (i.e. in the tissues of the cacti). However, D. mettleri adults are located on both the cactus and in nearby soil, as the fly has the specialized ability to detoxify the highly concentrated sap found in surrounding soil. Females are more commonly located in their breeding ground (the soil), whereas males are situated in both areas.

The unique ability of D. mettleri to detoxify the high concentration of alkaloids present in the soil surrounding cacti with rot spots enables adult females to lay their eggs and sustain their larvae in the same nesting area. Other species of desert Drosophila that inhabit the same geographic region lack this ability and thus reduce the amount of competition females face in finding nesting sites. One species (D. majavensis) is composed of adults who cannot withstand the high alkaloid concentration in cacti soil unlike the larva that is only slightly sensitive. While this may encourage larval deposits to form in the soil, the inability of adult females to survive in these soil conditions prevents them from nesting in the soil, thus decreasing the amount of competition D. mettleri faces in finding appropriate nesting sites.