Mass-Rearing Conditions Do Not Always Reduce Genetic Diversity: The Case of the Mexican Fruit Fly, Anastrepha ludens (Diptera: Tephritidae)

Abstract

The application of the sterile insect technique (SIT) requires the adaptation of insects to mass-rearing conditions. It is generally accepted that this adaptation may include a reduction in genetic diversity and an associated loss of desirable characteristics for the effective performance of sterile insects in the field. Here, we compare the genetic diversity of two mass-reared strains of the Mexican fruit fly, Anastrepha ludens, and a wild (WIL) population collected near Tapachula, Mexico, using seven DNA microsatellites as molecular genetic markers. The mass-reared strains were a bisexual laboratory strain (LAB) with approximately 130 generations under mass-rearing and a genetic sexing strain, Tapachula-7 (TA7), also under mass-rearing for 100 generations. Our results revealed an overall low level of genetic differentiation (approximately 15%) among the three strains, with the LAB and WIL populations being genetically most similar and TA7 most genetically differentiated. Although there were some differences in allele frequencies between strains, our results show that overall, the adaptation to mass-rearing conditions did not reduce genetic variability compared to the wild sample in terms of heterozygosity or allelic richness, nor did it appear to alter the level of inbreeding with respect to the wild populations. These results are contrary to the general idea that mass-rearing always results in a reduction in genetic diversity. Overall, our findings can contribute to a better understanding of the impact that adaptation to mass-rearing conditions may have on the genetic make-up of strains.

Keywords: Tephritidae; genetic differentiation; insect pest; mass-rearing adaptation; microsatellites markers; sterile insect technique.

Figure 1

Allele frequencies of seven microsatellite loci in three strains of Anastrepha ludens Loew. Significant results of a G-test for heterogeneity (G) and the number of private alleles by number of loci are presented. LAB = laboratory strain; TA7 = Tapachula-7 strain; WIL = wild strain. The squares next to the pie diagrams indicate the private alleles.

Figure 2

Average genetic diversity estimators for three strains of Anastrepha ludens Loew. (A) Number of alleles observed and effective. (B) Heterozygosity observed and unbiased expected by Hardy-Weinberg equilibrium and Fixation index. N = Average sample size, Na = observed number of alleles, Ne = effective number of alleles, uHe = unbiased expected heterozygosity, Ho = observed heterozygosity, uHe = unbiased expected heterozygosity, F = fixation index; LAB = laboratory strain, TA7 = Tapachula-7 strain, WIL = wild strain. F values from the analysis of variance (ANOVA) are presented over respective columns. An asterisk over the F bar indicates a significant result (p < 0.001) from the χ² = F²N(k − 1) analysis.

Figure 3

Principal component analyses (A) and UPGMA cluster (B) of genetic data of seven microsatellites in three strains of Anastrepha ludens Loew. LAB = laboratory strain; TA7 = Tapachula-7 strain; WIL = wild strain.

Figure 4

Scenarios (upper panels) of genetic differentiation of strains of Anastrepha ludens Loew (A), and probability values of logistic regression for each scenario evaluated simultaneously in DIYABC program (B). Time (t) is not to scale and indicates hypothetical sequences of differentiation over generations from the simulated data.