Esterase Profile in Drosophila mercatorum pararepleta (Diptera; Drosophilidae), a Non-cactophilic Species of the repleta Group: Development Patterns and Aspects of Genetic Variability

Esterases are a diversified group of isozymes that performs several metabolic functions in Drosophila. In the D. repleta group, this class of enzymes was well described in cactophilic species, existing a lack of studies considering substrate specificity and life cycle expression in the non-cactophilic species. The larvae of cactophilic species of the D. repleta group develop in rotting cacti cladodes, but adults are generalists. Thus, different patterns expression can be found for esterases throughout development. In this work we analyzed esterase profile and substrate specificity during development, and genetic variability aspects in D. mercatorum pararepleta, a non-cactophilic and generalist species of D. repleta group that was understudied hitherto. Samples of 3rd (F3) and 104th (F104) generations of three D. mercatorum pararepleta strains, obtained after collections in xerophytic enclaves of southeastern Brazil (ITI and SER in Sao Paulo state and RIP in Parana state), and of D33 strain (obtained from Cristalina-GO, Midwest of Brazil, and established in the laboratory in 1987) were analyzed. Eight esterase loci, EST-1 to EST-8, were detected. EST-1 and EST-2 were adult exclusive. Only EST-3 and EST-8 were monomorphic; all the others presented between two (EST-6) and six (EST-7) alleles. EST-7 was the only dimeric locus and also the only one that showed to be a preferably beta-esterase regarding affinity to alpha- and beta-naphthyl acetates as substrates. The other seven loci were divided into three classes: alpha-esterase exclusive (EST-2); preferably alpha-esterase (EST-3, EST-4, EST-5 and EST-8); and alpha/beta-esterase (EST-1 and EST-6). The EST-3, EST-5 and EST-6 loci were not detected in all samples, suggesting that they could have become pseudogenes due to the mutation accumulation after the gene duplication. The allele frequency of EST-7 locus, which showed the highest number of alleles, in adults of D33 and SER-F3 evidenced a higher variability and diversity in the oldest strain (six alleles, Ho = 0.46) than in the youngest (five alleles, Ho = 0.26). Moreover, the analysis of SER-F104 revealed that this locus became monomorphic. The higher variability in the strain established in the laboratory at least two decades ago, together with the allele fixation in the SER-F104, indicate that the SER strain probably suffered a more severe action of founder effect/bottleneck when it was established in the laboratory and, therefore, even if the maintenance afterwards was performed using a high number of individuals, it did not assured the conservation of the existing genetic variability.