Candidate transcriptomic sources of inbreeding depression in Drosophila melanogaster

The genomic causes of inbreeding depression are poorly known. Several studies have found widespread transcriptomic alterations in inbred organisms, but it remains unclear which of these alterations are causes of the depression and which are mere responses to the ensuing physiological stress. We made a c-DNA microarray analysis in Drosophila melanogaster attempting to differentiate causes from responses of inbreeding depression. The rationale of the experiment was that, while depression is a general phenomenon producing similar consequences in different inbred lines, its first genetic causes would be different for each inbred line, as they are expected to be caused by the fixation of rare deleterious genes. Many changes in expression were common to all sets, but fourteen genes, grouped in four expression clusters, showed strong set-specific changes, and were therefore candidates to be sources of the inbreeding depression observed. We took four sets of inbred sublines, each set descending from a different founding pair obtained from a large outbred stock, and compared the expression of the three most depressed sublines and the three least depressed sublines from each set.