Geographic distribution of sex chromosome polymorphism in Anastrepha fraterculus sp. 1 from Argentina

Abstract

Background Anastrepha fraterculus is recognized as a quarantine pest in several American countries. This fruit fly species is native to the American continent and distributed throughout tropical and subtropical regions. It has been reported as a complex of cryptic species, and at least eight morphotypes have been described. Only one entity of this complex, formerly named Anastrepha fraterculus sp. 1, is present in Argentina. Previous cytogenetic studies on this morphotype described the presence of sex chromosome variation identified by chromosomal size and staining patterns. In this work, we expanded the cytological study of this morphotype by analyzing laboratory strains and wild populations to provide information about the frequency and geographic distribution of these sex chromosome variants. We analyzed the mitotic metaphases of individuals from four laboratory strains and five wild populations from the main fruit-producing areas of Argentina, including the northwest (Tucumán and La Rioja), northeast (Entre Ríos and Misiones), and center (Buenos Aires) of the country. Results In wild samples, we observed a high frequency of X1X1 (0.94) and X1Y5 (0.93) karyomorphs, whereas X1X2 and X1Y6 were exclusively found at a low frequency in Buenos Aires (0.07 and 0.13, respectively), Entre Ríos (0.16 and 0.14, respectively) and Tucumán (0.03 and 0.04, respectively). X2X2 and X2Y5 karyomorphs were not found in wild populations but were detected at a low frequency in laboratory strains. In fact, karyomorph frequencies differed between wild populations and laboratory strains. No significant differences among A. fraterculus wild populations were evidenced in either karyotypic or chromosomal frequencies. However, a significant correlation was observed between Y5 chromosomal frequency and latitude. Conclusions We discuss the importance of cytogenetics to understand the possible route of invasion and dispersion of this pest in Argentina and the evolutionary forces acting under laboratory conditions, possibly driving changes in the chromosomal frequencies. Our findings provide deep and integral genetic knowledge of this species, which has become of relevance to the characterization and selection of valuable A. fraterculus sp. 1 strains for mass rearing production and SIT implementation.

Ecological phylogeography and coalescent models suggest a linear population expansion ofAnastrepha fraterculus(Diptera: Tephritidae) in southern South America

“…The sample from this site showed the highest variability, which is expected to occur in the centre from which the expansion originated (Ruiz-Arce et al, 2015). This result is consistent with a recent study by Giardini et al (2020), based on chromosomal polymorphism, which supports one possible route of invasion of A. fraterculus sp. 1 from south-east Brazil, followed by a wide dispersion of this pest throughout the Argentinian territory.…”

“…However, all the analyses were highly consistent with each other, indicating statistical robustness. Moreover, our results on the colonization route of A. fraterculus are in agreement with cytogenetic evidence (Giardini et al, 2020). Further studies integrating ecological, morphological and genomic perspectives, and a sampling over the entire distribution range of A. fraterculus are needed, and the results would help us to understand more fully the origin and evolution of the species and its geographical expansion.…”

Comparative Genomic Hybridization (CGH) in Anastrepha fraterculus sp. 1 reveals active divergence between sex chromosomes

“…This strain, which harbors X 1 Y 5 (males) and X 1 X 1 and X 1 X 2 (females), was puri ed from the Af-IGEAF colony. This laboratory strain has been maintained for at least 80 generations under laboratory conditions (Instituto de Genética, INTA, Buenos Aires, Argentina) 12,56 .…”

“…More recent and exhaustive studies on wild and laboratory populations from Argentina described the presence of cytotypes (or karyomorphs) composed of two variants of each sex chromosome (named X 1 , X 2 and Y 5 , Y 6 ) 11,12 . The X 1 is a large submetacentric chromosome with two DAPI-positive bands located at each telomere, the distal band being more prominent than the proximal one 7,11,13,14 .…”

“…In the present study, we aimed to explore the molecular composition of the sex chromosome variants identi ed in the A. fraterculus sp.1 laboratory strain Af-Y-short by CGH. From the A. fraterculus strains cytologically analyzed in our lab 12 , we selected the Af-Y-short strain to perform the present cytogenetic analysis as it possesses the most frequent sex chromosome variants detected in this A. fraterculus morphotype. The results obtained for the molecular differentiation of the sex chromosomes of A. fraterculus sp.…”