Population genetic study of allozyme variation in natural populations of Drosophila antonietae (Insecta, Diptera)

Abstract

Drosophila antonietae is an endemic South American cactophilic species found in relictual xerophytic vegetation, mostly associated with Cereus hildmaniannus cactus. Low differentiation among populations of this species has been detected using several markers. In this work, we performed an allozyme genetic variability analysis of 11 natural populations of D. antonietae and included a discussion about the possible influences of several evolutionary processes that might be acting to maintain the pattern observed. The genetic variability of 14 isoenzyme loci was analysed and showed a high genetic diversity (average observed heterozygosity ¼ 0.319) and a moderate genetic differentiation among populations (F statistics ¼ 0.0723). A correlation between genetic and geographical and ecological distances was detected among pairs of populations and the regional equilibrium analysis was thus applied. This analysis resulted in Nm (number of migrants) of approximately 3.21, indicating that moderate levels of both gene flow and genetic drift occur in this species, with gene flow overlapping genetic drift. However, considering ecological features of drosophilids, we propose a hypothesis to explain the moderate differentiation encountered as a result of three different processes, or a combination of them: (1) gene flow; (2) a short period of differentiation, i.e. maintenance of ancestral polymorphism; and (3) action of natural selection. Moreover, if gene flow is present, the high genetic diversity compared with other cactophilic and non-cactophilic species could be due to differential selection in different populations followed by gene exchange among them. These factors are discussed in the light of D. antonietaeÕs historical and evolutionary association with the host cactus.

Spatial Variation of Genetic Diversity in Drosophila Species from Two Different South American Environments

“…However, the geographic distances between populations of this species raises the question of the possibility of a real and current gene flow among them. Mateus & Sene (2007) antonietae and the cactus Cereus hildmaniannus, which is distributed mainly along the rivers basin, it has been proposed that there is gene flow among Drosophila populations through these rivers "corridors" following the cacti distribution, preventing genetic differentiation among them (Monteiro & Sene, 1995;Machado, 2003;Mateus & Sene, 2007). Our results did not support this hypothesis.…”

“…However, it was higher than the Fst detected by Mateus & Sene (2003) for D. antonietae in the within population spatial and temporal allozyme variation approaches (Fst = 0.0355 and 0.0023, respectivelly). Considering a among population approach, the Fst obtained here was lower (almost half the value) than those obtained using allozymes (Fst = 0.0723; Mateus & Sene, 2007) and microsatellite (Fst = 0.0730;Machado, 2003). In the same way, Reynolds et al (1983) genetic distances (Tabela 3) showed values consistents with the Fst, sugesting that despite the low genetic differentiation there is population structure among the populations studied.…”

“…The genetic distance (Reynolds et al, 1983), the presence of exclusive allele and the Neighbor-Joining grouping analysis (Saitou e Nei, 1987) were performed using the GDA (Lewis e Zaykin, 2001) software. The correlation between D. antonietae populations genetic distances and both geographical (straight distances between populations) and ecological (distances between populations through the rivers) distances, according to Mateus et al (2007), were tested using the Mantel test in the TFPGA software. In this test, the pairwise populations were compared and the genetic distances applyed were Reynolds et al (1983), obtained in the GDA software.…”

“…In D. antonietae, Mateus & Sene (2003) verified the possible action of natural selection using temporal and spatial approaches of the allozymic variation. Later, Mateus & Sene (2007) pointed out that natural selection is a possible factor preventing genetic divergence among D. antonietae populations. Machado (2003) tested the occurrence of a hitchiking effect between 7 microsatellite and 10 allozymatic loci in D. antonietae and no correlation was found between these markers.…”

Gene Duplication and Subsequent Differentiation of Esterases in Cactophilic Drosophila Species

“…However, adults are generalists because they visit other food sources in their environment (Morais et al, 1994). This ecological specificity of cactophilic Drosophila directly influences species distribution, as they are always associated with the host cactus distribution (Tidon-Sklorz & Sene, 1995;Manfrin & Sene, 2006;Mateus and Sene, 2007). Drosophila has been used as a research model for more than a century, and the first report of gene duplication was described by Bridges for the Bar locus in D. melanogaster over 70 years ago (Bridges, 1936).…”