Rapid evolution of a few members of nasuta-albomicans complex of Drosophila: study on two candidate genes, Sod1 and Rpd3.

Drosophila nasuta nasuta (2n = 8) and D. n. albomicans (2n = 6) are morphologically identical, cross fertile and karyotypically dissimilar pair of chromosomal races belonging to nasuta subgroup of immigrans group of Drosophila. Interracial hybridization between these two races yielded karyotypically stabilized newly evolved Cytoraces with new combinations of chromosomes and DNA content, and are called nasuta-albomicans complex of Drosophila. Along with many other features, striking plasticity in the lifespan has been observed in the karyotypically stabilized members of nasuta-albomicans complex of Drosophila. These findings provide a strong background to understand any changes at the molecular levels. In view of this, we cloned and characterized Sod1 and Rpd3 in the members of nasuta-albomicans complex of Drosophila. The evolution of Sod1 and Rpd3 in D. n. nasuta and D. n. albomicans is contrasting with the other species of Drosophila, at the level of synonymous mutations, intron variation, InDels and secondary structure changes in protein. In the members of NAC of Drosophila there were synonymous changes, variations in intron sequences of Sod1, whereas, in Rpd3, synonymous, nonsynonymous, intron variation, and secondary structure changes in protein were observed. The contrasting differences in the levels of Rpd3 (and Sir2) proteins were also noticed among short-lived and long-lived Cytoraces. The Cytoraces have exhibited not only specific changes in Sod1 and Rpd3, but also show pronounced changes in the levels of synthesis of these proteins, which indicates rapid evolution of these Cytoraces in laboratory. Further these Cytoraces have become a model system to understand the process of anagenesis.

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