Reduction in muscle fibre number during the adaptive radiation of notothenioid fishes: a phylogenetic perspective

• Published in: Journal of Experimental Biology
• Main Authors: Johnston, Ian A., Fernández, Daniel A., Calvo, Jorge, Vieira, Vera L. A., North, Anthony W., Abercromby, Marguerite, Garland, Theodore
• Format: Text
• Language: English
• Published: Company of Biologists 2003
• Subjects: Research Article; Antarctic; Southern Ocean; Antarctic Peninsula; Adelaide Island; Shag Rocks; Antarc*; Tierra del Fuego
• Online Access: http://jeb.biologists.org/cgi/content/short/206/15/2595; https://doi.org/10.1242/jeb.00474

The fish fauna of the continental shelf of the Southern Ocean is dominated by a single sub-order of Perciformes, the Notothenioidei, which have unusually large diameter skeletal muscle fibres. We tested the hypothesis that in fast myotomal muscle a high maximum fibre diameter ( FD max ) was related to a reduction in the number of muscle fibres present at the end of the recruitment phase of growth. We also hypothesized that the maximum fibre number ( FN max ) would be negatively related to body size, and that both body size and size-corrected FN max would show phylogenetic signal (tendency for related species to resemble each other). Finally, we estimated ancestral values for body size and FN max . A molecular phylogeny was constructed using 12S mitochondrial rRNA sequences. A total of 16 species were studied from the Beagle Channel, Tierra del Fuego (5-11°C), Shag Rocks, South Georgia (0.5-4°C), and Adelaide Island, Antarctic Peninsula (-1.5 to 0.5°C). The absence of muscle fibres of less than 10 μm diameter was used as the criterion for the cessation of fibre recruitment. FD max increased linearly with standard length ( SL ), reaching 500-650 μm in most species. Maximum body size was a highly significant predictor of species variation in FN max , and both body size and size-corrected FN max showed highly significant phylogenetic signal ( P <0.001). Estimates of trait values at nodes of the maximum likelihood phylogenetic tree were consistent with a progressive reduction in fibre number during part of the notothenioid radiation, perhaps serving to reduce basal energy requirements to compensate for the additional energetic costs of antifreeze production. For example, FN max in Chaenocephalus aceratus (12 700±300, mean ± <scp>s</scp>.<scp>e</scp>.<scp>m</scp>., N =18) was only 7.7% of the value found in Eleginops maclovinus (164 000±4100, N =17), which reaches a similar maximum length (85 cm). Postembryonic muscle fibre recruitment in teleost fish normally involves stratified ...