We wish to bring attention to the following correction to Marsden et al. (2012). The legend for Fig. 3 contained an error with regards to the description of which genetic marker corresponds to the different symbols in the graph. Specifically, the printed legend stated that DLA-DRB1 is represented by white symbols (not black), and microsatellite loci by black symbols (not white). These discrepancies do not influence any of the results or conclusions of our work. A corrected version for the Fig. 3 legend is shown here.