Fig. 2: Comparative analysis of the C. aceratus genome assembly.

a, Phylogenetic tree and gene family gain-and-loss analysis, including the number of gained gene families (+) and lost gene families (−). Blue numbers specify divergence times between lineages. The red dotted line indicates the appearance of Antarctic ice sheets (35 Ma), which allowed the circum-Antarctic current to form after the opening of the Drake Passage. Subsequent cooling of the Southern Ocean drove local extinction of most fish taxa and adaptive radiation of the Antarctic notothenioid suborder. E, Eocene; M, Miocene; O, Oligocene; P, Palaeocene. b, Inferring icefish population history by PSMC analysis. The left y axis represents the demographic history of C. aceratus (red line). During the Plio-Pleistocene (3–0.9 Ma), which is shaded blue, Antarctic sea-surface temperatures dropped by around 2.5 °C, judged by a proxy for marine palaeo-temperature changes based on oxygen isotope ratios^91,92 (right y axis). Concomitant decreases in marine temperatures (black line) probably allowed the cold-adapted C. aceratus populations to increase in size. The green shading represents the mid-Pleistocene transition, during which temperature fluctuations were large. g, generation time; μ, mutation rate.