Fig. 14

Direct- versus indirect-development – A. burtoni versus zebrafish. The direct-development of A. burtoni (blue) is characterized by the completion of the body plan before the onset of feeding (embryo to larva transition at 14 dpf). This is reflected in a very homogenous progression of development, as has been described in this paper, and a very homogenous overall growth with only minor variation in standard length (Y-axis, data points included for 10 embryos/juveniles per day coming from different clutches). In comparison, zebrafish (red) develops only synchronously until the start of the embryo to larva transition, marked by the onset of feeding at 5 dpf. After this point, growth trajectories of individual fish strongly diverge (data range included from Parichi et al. 2009 [22], a very similar range was described in Grandel & Schulte-Merker 1998 [25]). The zebrafish' larva- to juvenile transition is indicated after references [4, 22]. When we consider the development of the pectoral fins for zebrafish (after [25]) and A. burtoni (this article), we see that in both species these follow very similar developmental trajectories (stages indicated after Fig. 7). In A. burtoni, pectoral fin formation is completed before 10 dpf, well before feeding stages, and differentiation occurs at a steady progression, and is predictable amongst individuals from the same clutch (developmental progression indicated along the X-axis in relation to time after fertilization). In zebrafish, pectoral fin formation starts similar with the formation of the endoskeletal disk (stage II). From the embryo to larva transition onward however, overall development slows down and growth becomes heterogeneous amongst similarly aged larvae. Therefore, time is not a good predictor of the progression of pectoral fin development, but standard length has to be used instead (pectoral fin stages indicated along the Y-axis in relation to standard length). Abbreviations: dpf: days post fertilization; SL: standard length