Many small-effect mutations in a transcriptional enhancer caused evolution of Drosophila larval morphology

FRANKEL N; EREZYILMAZ DF; MCGREGOR AP; WANG S; PAYRE F; STERN DL

San Diego

Congreso; 52nd Drosophila Research Conference; 2011

Genetics Society of America

Morphology evolves often through changes in developmental genes, but the number and effects of the causal mutations remain largely unknown. The differentiation of naked cuticle—rather than trichomes—on larvae of Drosophila sechellia evolved through changes in five transcriptional enhancers of shavenbaby, a gene encoding a transcription factor that governs trichome morphogenesis. Here we show that the function of one of these enhancers evolved through many nucleotide substitutions that altered both the timing and level of expression of shavenbaby. The consequences of these nucleotide substitutions on larval morphology were quantified with a novel functional assay. Each substitution had a small phenotypic effect and the substitutions displayed non-additive effects to generate a large phenotypic change. These data provide unprecedented resolution of the phenotypic effects of evolved mutations and show how individual nucleotide substitutions can lead to morphological evolution.