Factors Affecting Host Plant Selection in Desert‐Adapted Cactiphilic Drosophila

Abstract

Three types of tests were conducted to determine the causal factors for the narrow larval niche breadth and the low amount of larval niche overlap observed among common species of Drosophila breeding in rotting cereus cacti in the Sonoran Desert. (1) Field test and observations show that host plant discrimination for feeding adults is very high but not absolute. (2) Substrate substitution experiments conducted individually with four species of cactiphilic Drosophila on six kinds of artificially rotted cacti show that every species except D. mojavensis reproduces bests on the cactus (or cacti) on which it is resident in nature. Even so D. mojavensis and D. arizonensis, both of which are polyphagic, emerge in large numbers from five kinds of cacti. (3) Laboratory competition tests with mixed species established in three cases that the resident species was unaffected, as compared with monoculture controls, while the alien species usually emerged in significantly fewer numbers. In two other competition situations neither the alien nor resident species was significantly affected. Inability of the polyphagic species to invade certain non—host cacti in nature could be due to competition in the first three cases. In the latter two cases either the physical characteristics of the substrate or the climate affecting distribution (and/or density) appears to be the principal restricting factor. Narrow host plant specificity is accompanied by specialized nutritional requirements and more continuously available rot pockets in the host plants.

The Molecular Basis of Host Adaptation in Cactophilic Drosophila: Molecular Evolution of a GlutathioneS-Transferase Gene (GstD1) inDrosophila mojavensis

“…Each host race, mainland Sonora Desert, Baja California, Catalina Island, and Mojave Desert, utilizes a different species of cactus: organpipe (Stenocereus thurberi), agria (S. gummosus), prickly pear (Opuntia spp. ), and barrel (Ferocactus cylindraceus), respectively (Fellows and Heed 1972;Ruiz and Heed 1988). D. mojavensis has been proposed (Ruiz et al 1990) to have originated in Baja California, utilizing a Stenocereus cactus (possibly agria), and then migrated up the peninsula and colonized Catalina Island and the Mojave Desert, shifting cactus hosts in the process.…”

Environment-dependent trade-offs between ectoparasite resistance and larval competitive ability in the Drosophila–Macrocheles system

“…Thus, the complex interaction we detected here may be operating in the fly's natural environment. Additionally, larval densities can vary and potentially reach high levels in natural rot pockets (Fellows and Heed, 1972;Mangan, 1982). Although exact estimates of larval densities are not available for natural populations of D. nigrospiracula, Breitmeyer and Markow (1998) reported a mean population size of 512371713 s.e.…”

“…Medium and high-density vials were seeded with 40:40 and 80:80 experimental and tester larvae, respectively. Comparable density levels have been shown to generate negative effects on survival, body size and developmental time in D. nigrospiracula (Fellows and Heed, 1972;Mangan, 1982). Each treatment  temperature  density combination was replicated across two vials.…”

Genotype-specific habitat selection for oviposition sites in the cactophilic species Drosophila buzzatii

“…Drosophila where closely related taxa use different but closely related host plants (Heed, 1971;Fellows & Heed, 1972). In these examples, the host plants represent a spatial hierarchy onto which the genetic hierarchy is overlaid.…”