In the version of the article initially published, in Fig. 2a, the colours of the dark green and pink boxes were switched and have now been corrected. In Fig. 3c, the top structure and labels were purple and the bottom ones light blue, but the colours should have been the other way around and have now been corrected. In Fig. 5c, a region in the yellow box was blue but should have been lime green and has now been corrected. These corrections have been made to the HTML and PDF versions of the article. The original figures are available for comparison in the Supplementary information accompanying this amendment.