Gene expression of sexual development genes in heads and trunks of developing male A. burtoni . (A) Wnt4B and wt1A were the only detected early testis genes, here shown with their paralogous gene copies wnt4A and wt1B (grey background). (B) Cyp19a1A, gsdf and dmrt1 are examples of late testis genes, cyp19a1B is the teleost specific paralog of cyp19a1A (grey background). (C) Nanos1A, nanos1B, sox9A and sox9B are examples for brain genes. Gene expression is shown as fold change (Livak) ± SE in heads (green) and trunks (blue) from 7 – 48 dpf using rpl7 as reference gene and a juvenile tissue mix as reference tissue (see Additional file 3 for further details).