Differences in relative heart mass among deep-sea and coastal sharks with increasing depth
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ORIGINAL PAPER
Differences in relative heart mass among deep‑sea and coastal sharks with increasing depth M. E. Larsen1 · D. C. Abel2 · D. P. Crane1 · R. D. Grubbs3 Received: 30 March 2020 / Accepted: 29 September 2020 © Springer-Verlag GmbH Germany, part of Springer Nature 2020
Abstract Cardiac morphology and mass have been associated with activity levels for bony fishes and elasmobranchs; however, there is little information on cardiac morphology of deep-sea sharks (living primarily below 200 m) and how that morphology compares to cardiac morphology of shallow coastal species. We examined relative heart mass and relative ventricle dry mass in 10 species of sharks from coastal to bathydemersal habitats (23–870 m) to test our hypothesis that relative heart mass decreases with depth. Relative heart mass and relative ventricle dry mass decreased with increasing depth of capture for sharks. The coastal, obligate ram ventilator Carcharhinus limbatus had the highest relative heart mass (1.17 g/kg) and relative ventricle dry mass (0.18 g/kg), whereas the deep-sea species Centrophorus uyato had the lowest (relative heart mass, 0.34 g/kg; relative ventricle dry mass, 0.057 g/kg). Our findings of decreasing relative heart and ventricle size with increasing depth support the visual interaction hypothesis as an explanation for reduced metabolic capacity in deep-sea sharks.
Introduction Cardiac morphology in vertebrates has been examined previously with extensive research on the relationship among heart mass, ventricle mass, body mass, behavior, and ecology (Poupa 1972; Poupa and Lindstrom 1983; Farrell and Jones 1992). In vertebrates, heart mass and ventricle mass increase relative to body mass with increasing activity levels. Despite the widespread literature available on terrestrial and aquatic vertebrates there is a lack of information cardiac morphology of deep-sea organisms (depths > 200 m; Cotton and Grubbs 2015). Prior studies of deep-sea crustaceans, cephalopods, teleosts, and elasmobranchs have supported the visual Responsible Editor: J. Carlson. Reviewed by J. Drazen and J. Grim. * M. E. Larsen [email protected]; [email protected] 1
Department of Biology, Coastal Carolina University, Conway, SC 29528, USA
2
Department of Marine Science, Coastal Carolina University, Conway, SC 29528, USA
3
Florida State University Coastal and Marine Laboratory, St. Teresa, FL 32358, USA
interactions hypothesis as a driver of metabolic capacity in these species (Childress and Somero 1990; Childress 1995; Drazen and Seibel 2007; Seibel and Drazen 2007; Condon et al. 2012). The visual interaction hypothesis is based on evidence showing a correlation between decreasing activity and metabolic capacity with increasing depth in sighted taxa to 1000 m (Drazen and Seibel 2007; Seibel and Drazen 2007). The ecological basis for this hypothesis is that light penetration decreases with increasing depth and visually dependent predator–prey interactions become limited (Drazen and Seibel 2007; Condon et al. 2012). Th
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