Fig. 5

Biased development of anterior-ventral skeleton during early development in notothenioids. a-b Cleared and stained skeletal preparations. CA: icefish species C. aceratus. LF: cichlid species Labeotropheus fuelleborni. Note the dramatically enlarged anterior-ventral cartilages in CA compared to LF. ch, ceratohyal; eth, ethmoid plate; hs, hyosymplectic; m, Meckel cartilage; pq, palatoquadrate. We hypothesized that this pattern is key to the highly integrated skull of notothenioids, and that ventral patterning genes may be involved in this change. Differences in hand2 expression in the developing pharyngeal arches between the pelagic notothenioid species P. antarcticum (c) and LF (d) support this hypothesis. p1–7, pharyngeal arches 1–7. (C’-D’) schematic illustration of hand2 expression domain in P. antarcticum and LF. Note in particular the dorsal expansion of hand2 expression in the hyoid arch (red asterisk). e Comparison of developmental trajectories of pharyngeal cartilages between notothenioids and two other percomorph fishes. Following Kimmel et al. 2007, the dorsal portion of the pharyngeal cartilage was measured as the length of hyosymplectic posterior-dorsal to the interhyal, and the ventral portion was measured as the length of ceratohyal anterior-ventral to the interhyal. Scale bar = 100 μm