The Relationship Between Allozyme and Chromosomal Polymorphism Inferred From Nucleotide Variation at the Acph-1 Gene Region of Drosophila subobscura

Corresponding author: Carmen Segarra, Departament de Genètica, Facultat de Biologia, Universitat de Barcelona, Diagonal 645, 08071 Barcelona, Spain., carme{at}porthos.bio.ub.es (E-mail)

Communicating editor: A. G. CLARK

The Acph-1 gene region was sequenced in 51 lines of Drosophila subobscura. Lines differ in their chromosomal arrangement for segment I of the O chromosome (O_st and O₃₊₄) and in the Acph-1 electrophoretic allele (Acph-1¹⁰⁰, Acph-1⁰⁵⁴, and Acph-1^>100). The ACPH-1 protein exhibits much more variation than previously detected by electrophoresis. The amino acid replacements responsible for the Acph-1⁰⁵⁴ and Acph-1^>100 electrophoretic variants are different within O_st and within O₃₊₄, which invalidates all previous studies on linkage disequilibrium between chromosomal and allozyme polymorphisms at this locus. The Acph-1^>100 allele within O₃₊₄ has a recent origin, while both Acph-1⁰⁵⁴ alleles are rather old. Levels of nucleotide variation are higher within the O₃₊₄ than within the O_st arrangement except for nonsynonymous sites. The McDonald and Kreitman test shows a significant excess of nonsynonymous polymorphisms within O_st when D. guanche is used as the outgroup. According to the nearly neutral model of molecular evolution, this excess is consistent with a smaller effective size of O_st relative to O₃₊₄ arrangements. A smaller population size, a lower recombination, and a more recent bottleneck might be contributing to the smaller effective size of O_st.

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