EVOLUTIONARY HISTORY OF THE SEX-PEPTIDE (ACP70A) GENE REGION IN DROSOPHILA-MELANOGASTER

In Drosophila the products of the seminal fluid stimulate oviposition and suppress remating in the female. Of all the accessory gland peptid es (Acp's) involved in these two responses, the sex-peptide (coded by the Acp70A gene) is among the best characterized at the functional lev el. A 1.2-kb fragment encompassing the Acp70A gene of nine lines from a natural population of D. melanogaster and one allele of D. sechellia was sequenced to study the forces shaping nucleotide variation within and between species. The coding region of D. simulans and D. mauritia na was also sequenced. A Ser to Ala replacement polymorphism at the la st position of the signal peptide was detected in D. melanogaster. The Ser and Ala alleles are at intermediate frequencies. The level of nuc leotide variation is lower for the derived Ala allele, which is compat ible with a recent origin and an increase in frequency due to positive selection. Variation at the 5' flanking region is structured in two m ajor highly differentiated haplotypes, whose distribution does not con form to neutral expectations. Selective and/or historical factors coul d contribute to the observed overall patterning of nucleotide variatio n at the Acp70A region.