Differences in gene expression in Drosophila eye imaginal disc underlie morphological diversification. Isabel Almudi¹, Montserrat Torres², Saad Arif¹, Maria D. Santos Nunes¹, Maarten Hilbrant¹, Alistair McGregor¹, Nico Posnien². 1) Biological and Medical Sciences, Oxford Brookes University, Oxford, United Kingdom; 2) Georg-August-University Göttingen Johann-Friedrich-Blumenbach Institute for Zoology and Anthropology Department of Developmental Biology Ernst-Caspari-Hause (GZMB) Göttingen, Germany.

   Animals exhibit a huge variation in size and form. In the last decade, the genetic basis for the evolution of particular traits have been identified but, nevertheless, our understanding of the evolution of complex morphological features, and how their underlying genetic changes arose and spread in populations is still limited. The compound eye of insects is a paradigmatic example of the tremendous variation exhibited by some of these complex traits: the number of its constituent ommatidia can range from 1 in some worker ants to 30,000 in dragonflies, while ommatidia size can vary from 5 to 50 m in diameter. We have also found considerable variation in ommatidia size and number within and among species of the Drosophila melanogaster subgroup (D. melanogaster, D. simulans, D. mauritiana and D. sechellia). For example, D. mauritiana has larger eyes than its sibling species, which is mainly due to differences in ommatidia size. By contrast, differences in eye size among populations of D. simulans are due mainly to variation in ommatidia number. In order to study the genetic and developmental origin of these differences in eye size and shape, we investigated the developmental stages at which differences in eye size first arise among different strains of D. mauritiana and D. simulans in concert with gene expression profiling in the eye-antennal imaginal discs using RNA-Seq. By comparing our RNA-Seq datasets from these different strains at different developmental points, we have identified differentially expressed genes that lie in QTL for differences in eye size, and therefore, that could be responsible for the variation in ommatidia size and number.