Evolution of miR-92a underlies natural variation in the naked valley in Drosophila melanogaster. Saad Arif¹, Sophie Murat², Isabel Almudi¹, Maria Nunes¹, Diane Bortolamiol-Becet³, Naomi McGregor¹, James Currie¹, Matthew Ronshaugen⁴, Elio Sucena⁵, Eric C. Lai³, Christian Schlötterer², Alistair McGregor¹. 1) Oxford Brookes University, Oxford, United Kingdom; 2) Institute for Population Genetics, Vetmeduni Vienna, Vienna, Austria; 3) Sloan-Kettering Institute, New York, NY, USA; 4) Faculty of Life Sciences, University of Manchester, Manchester, United Kingdom; 5) Instituto Gulbenkian de Ciência, Oeiras, Portugal.

   Identifying the genetic basis of phenotypic change is essential to understanding how gene regulatory networks evolve and ultimately the genotype-to-phenotype map. While a range of mechanisms lie at evolutions disposal, it is possible that particular mechanisms, and even specific nodes in GRNs are targeted. Characterising the basis of natural variation in phenotypic traits is a powerful approach to identify the underlying genetic mechanisms, and thus the routes of evolution. Drosophila melanogaster subgroup species display a portion of trichome-free cuticle on the femur of the second leg called the naked valley. It was previously shown that the Hox gene Ultrabithorax (Ubx) is involved in the naked valley variation between D. melanogaster and D. simulans. However, the size of the naked valley varies considerably among populations of D. melanogaster ranging from a small patch of 4000 um2 up to 40,000 um2. We investigated the genetic basis of this intra-specific variation in the naked valley in D. melanogaster and found that neither in Ubx or shavenbaby (svb), which underlies the evolution of larval trichomes, is responsible. Instead, we found a novel mechanism for the evolution of trichome patterns, where expression differences in miR-92a underlie changes in naked valley size in D. melanogaster via the differential down regulation of shavenoid. Therefore, our results show that morphological evolution can be caused by natural variation in microRNA expression and suggests that such changes in microRNAs may play a prominent role in fine scale morphological change within and between species.