On the Distribution and the Cactiphilic Niche of Drosophila martensis in Venezuela

Abstract

Drosophila martensis Wasserman and Wilson is shown to be a cactiphilic fly, emerging from five species of cacti: Ritterocereus griseus, Subpilocereus repandus, Acanthocereus tetragonus, Opuntia elatior, and 0. ficus-indica. Thus, it can be considered a polyphagic species. The known distribution of D. martensis indudes localities as distant as 900 km on an east-west axis in Venezuela, and gene flow seems to occur freely between the sampled populations. It is suggested that D. martensis is an opportunistic invader fly, and that population interfertility and polyphagy are concomitant phenomena for the species. Drosophila martensis WAS FIRST COLLECTED IN SANTA MARTA, COLOMBIA, the type locality for the species (Wasserman and Wilson 1957). Later collections in Venezuela have indicated that D. martensis is restricted to cactusdominated regions (Wasserman et al. 1973, Wasserman and Koepfer 1979, Ruiz and Fontdevila 1981) as are other species in the cluster martensis of the mulleri complex. Since all other species in this complex are cactiphilic (Wasserman 1982), we wished to determine if D. martensis also lives and breeds in close association with cacti. The experiments and observations reported here establish the cactiphilic nature of D. martensis and its distribution in Venezuela, and several host plants are described for the species. The cactiphilic niche of the martensis cluster is dealt with in a separate paper (in preparation). MATERIAL AND METHODS The 11 localities sampled are given in Table 1 and are indicated in Figure 1. They cover over 900 km along an east-west axis in northern Venezuela. Flies were obtained by bait sampling or from rot pockets. El Playon, La Boca, Cata 2, and Cuyagua were sampled for rot pockets only. Coro 16, Prudencio, Piritu, Guaca and Tetas were both baitand rot pocket-sampled. Oricao 1 was just baitsampled and Zuata was sampled for rot pockets only (Table 1). ROT POCKET SAMPLING.-The fermenting cacti were transported in large glass jars to the laboratory in Caracas, where the flies were allowed to emerge at room temperature. After 5 days, to optimize insemination, isofemale lines were set up and their specific status established through reciprocal cross-matings with tester strains. In some cases, circular matings were made among the isolines from the same cactus and locality before any test cross was attempted. At least four replicates were made of each mating, which was considered successful when abundant F2's were obtained. The specific status of the isolines was usually doublechecked by morphological or cytological analysis at the Departamento de Genetica of the Universidad Autonoma de Barcelona in Spain. 'Received 17 December 1982; revised 20 September 1983; accepted 26 September 1983. 120 BIOTROPICA 16(2): 120-124 1984 This content downloaded from 157.55.39.83 on Sun, 09 Oct 2016 04:53:51 UTC All use subject to http://about.jstor.org/terms