RESUMEN
Shark populations are declining globally, yet the movements and habitats of most species are unknown. We used a satellite tag attached to the dorsal fin to track salmon sharks (Lamna ditropis) for up to 3.2 years. Here we show that salmon sharks have a subarctic-to-subtropical niche, ranging from 2 degrees to 24 degrees C, and they spend winter periods in waters as cold as 2 degrees to 8 degrees C. Functional assays and protein gels reveal that the expression of excitation-contraction coupling proteins is enhanced in salmon shark hearts, which may underlie the shark's ability to maintain heart function at cold temperatures and their niche expansion into subarctic seas.
Asunto(s)
Ambiente , Corazón/fisiología , Miocardio/metabolismo , Tiburones/fisiología , Aclimatación , Sistemas de Identificación Animal , Migración Animal , Animales , Conducta Animal , Temperatura Corporal , Calcio/metabolismo , ATPasas Transportadoras de Calcio/metabolismo , Frío , Ecosistema , Femenino , Ventrículos Cardíacos/metabolismo , Masculino , Contracción Miocárdica , Océano Pacífico , Conducta Predatoria , Canal Liberador de Calcio Receptor de Rianodina/metabolismo , Retículo Sarcoplasmático/metabolismo , ATPasas Transportadoras de Calcio del Retículo Sarcoplásmico , Comunicaciones por Satélite , Estaciones del Año , Natación , TemperaturaRESUMEN
A comparative echocardiographic study was carried out on five shark species that differ in heart morphology and in aspects of their behavior and natural history. The study contrasted the ventricular function in the highly active mako shark (heart type IV) and four other sharks (heart type III) that differ in activity levels (i.e. the sedentary horn and swell sharks vs. the moderately active blue and smooth-hound sharks). All five species exhibited biphasic ventricular filling characterized by an early (conduit) and late (atrial systole) phase. In the mako shark, early filling was dominant as indicated by a higher early flow peak velocity, a greater early:late velocity ratio, and a greater early velocity time integral. In contrast, the late filling phase was the more important filling agent in the other species. Indices of systolic function such as ventricular ejection fraction and ventricular fractional shortening also reflect a more efficient cardiac pumping capacity in mako shark relative to the other four sharks. The comparative echocardiographic assessment of in vivo ventricular function integrates structural and functional features with shark activity level to arrive at a new perspective blending the occurrence of biphasic filling with functional concepts based on heart morphological typology and changing views regarding the role of factors such as central filling pressure and pericardial pressure on end-diastolic ventricular volume.