Selection and demography in the alpha-Est-5 gene region inferred from nucleotide polymorphism data in the cactophilic sibling species Drosophila buzzatii and D. koepferae

PICCINALI ROMINA, MASCORD LISA, BARKER STUART AND HASSON ESTEBAN

Florianopolis, Brasil

Congreso; 50ª Congresso Brasileiro de Genética; 2004

Sociedade Brasileira de Genética

The neutral theory has become the null hypothesis for testing adaptation at the molecular level, because it makes precise predictions about levels and patterns of intraspecific nucleotide variation. If data do not fit genetic drift-mutation equilibrium predictions, then alternative demographic or selective scenarios can be proposed. In this work we performed a comparative analysis of nucleotide variation and applied neutrality tests to the aEst-5 gene region in two South American cactophilic sibling species, D. buzzatii and D. koepferae. We also included D. buzzatii flies sampled in Australia, an area of recent colonization. We sequenced a fragment of ~ 800 bp in several lines from each species, estimated the levels of variation using qW and p estimators and applied Tajima’s, Fu and Li’s and McDonald and Kreitman’s tests. The analyses showed that: 1) Total levels of nucleotide polymorphism were slightly higher in D. koepferae than in D. buzzatii, although nonsynonymous variation in D. buzzatii was 1.6 times greater than in D. koepferae; 2) Total nucleotide variation was similar between Argentinian and Australian populations of D. buzzatii, though 3) An important loss of singletons in colonized populations was observed, probably due to a founder effect; 4) According to Fu and Li’s tests, D. buzzatii could have experienced a recent increase in population effective size; 4) There is an excess of nonsynonymous polymorphism in D. buzzatii that could be the result of episodic selection; 5) D. koepferae seems to be an species in equilibrium genetic drift-mutation.