Adaptive radiation at a low taxonomic level: Divergence in buoyancy of the ecologically similar Antarctic fish Notothenia coriiceps and N. rossii

• Main Authors: Eastman, Joseph T., Barrera Oro, Esteban, Moreira, María Eugenia
• Format: Article in Journal/Newspaper
• Language: English
• Published: Inter-Research
• Subjects: NOTOTHENIOID; ONTOGENETIC VARIATION; SKELETAL ANATOMY AND HISTOLOGY; SOUTH SHETLAND ISLANDS; https://purl.org/becyt/ford/1.6; https://purl.org/becyt/ford/1; Antarctic; King George Island; South Shetland Islands; Argentino; Argentina; Eastman; Antarc*; Dirección Nacional del Antártico; Instituto Antártico Argentino
• Online Access: http://hdl.handle.net/11336/193589

We studied the buoyancy of 263 specimens of the sympatric sister species Notothenia coriiceps and N. rossii captured at King George Island. In these species without a swim bladder, we expressed measurements of buoyancy as percentage buoyancy (%B = weight in water/weight in air × 100), with smaller numbers reflecting more buoyant (i.e. less dense) species. Mean %B of N. coriiceps (4.34%) was significantly greater than that of N. rossii (3.82%), reflecting the lower density and more active swimming, migratory, and feeding behavior of N. rossii compared to N. coriiceps. Skeletal weight as a percentage of body weight was also significantly greater in N. coriiceps (2.46%) than N. rossii (1.65%). Paradoxically, the weight of the vertebral column as a percentage of skeletal weight was significantly greater in N. rossii (28.01%) than in N. coriiceps (24.29%); however, this is intelligible in light of the bone anatomy and histology. Our sample encompassed a wide size and age range, and trend lines for scatter plots of %B against standard length were curvilinear for both species, peaking at 140 to 160 mm, a phenomenon not previously seen in studies of notothenioid buoyancy. We conclude that the ontogenetic increase in %B (reduced buoyancy) in fingerlings/young juveniles and the ontogenetic decrease in %B (increased buoyancy) in older juveniles/immature adults reflects disproportionate growth of skeletal and visceral tissues, respectively, and is not causally related to concurrent pelagic-demersal habitat shifts. Fil: Eastman, Joseph T. Ohio University; Estados Unidos Fil: Barrera Oro, Esteban. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Museo Argentino de Ciencias Naturales "Bernardino Rivadavia"; Argentina Fil: Moreira, María Eugenia. Ministerio de Relaciones Exteriores, Comercio Interno y Culto. Dirección Nacional del Antártico. Instituto Antártico Argentino; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina