RESUMEN
Tail flukes as well as the dorsal fin are the apomorphic traits of cetaceans which appeared during the evolutionary process of adaptation to the aquatic life. Both appendages present a wing-like shape associated with lift generation and low drag. We hypothesized that the evolution of fins as lifting structures led to a generic wing design, where the dimensionless parameters of the fin cross-sections are invariant with respect to the body length and taxonomy of small cetaceans (Hypothesis I). We also hypothesized that constraints on variability of a generic fin shape are associated with the primary function of the fin as a fixed or flapping hydrofoil (Hypothesis II). To verify these hypotheses, we examined how the variation in the fin's morphological traits is linked to the primary function, species and body length. Hydrodynamic characteristics of the fin cross-sections were examined with the CFD software and compared with similar engineered airfoils. Generic wing design of both fins was found in a wing-like planform and a streamlined cross-sectional geometry optimized for lift generation. Divergence in a generic fin shape both on the planform and cross-sectional level was found to be related with the fin specialization in fixed or flapping hydrofoil function. Cross-sections of the dorsal fin were found to be optimized for the narrow range of small angles of attack. Cross-sections of tail flukes were found to be more stable for higher angles of attack and had gradual stall characteristics. The obtained results provide an insight into the divergent evolutionary pathways of a generic wing-like shape of the fins of cetaceans under specific demands of thrust production, swimming stability and turning control.
Asunto(s)
Cetáceos , Natación , Animales , Fenómenos Biomecánicos , Extremidades , Hidrodinámica , Modelos Biológicos , Alas de AnimalesRESUMEN
The lymphatic system in teleost fish has genetic and developmental origins similar to those of the mammalian lymphatic system, which is involved in immune response and fluid homeostasis. Here, we show that the lymphatic system of tunas functions in swimming hydrodynamics. Specifically, a musculo-vascular complex, consisting of fin muscles, bones, and lymphatic vessels, is involved in the hydraulic control of median fins. This specialization of the lymphatic system is associated with fish in the family Scombridae and may have evolved in response to the demand for swimming and maneuvering control in these high-performance species.
Asunto(s)
Aletas de Animales/fisiología , Vasos Linfáticos/fisiología , Músculo Esquelético/fisiología , Natación/fisiología , Atún/fisiología , Aletas de Animales/anatomía & histología , Animales , Hidrodinámica , Atún/anatomía & histologíaRESUMEN
The correlation between skin structure and hydrodynamic design of the dorsal fin of the harbor porpoise (Phocoena phocoena) was examined. For the study of fin morphology and geometry, a scheme of sampling representing a two-parameter mesh on the fin surface was used. At each data point the thickness of the epidermis, papillary and subpapillary layers of the dermis, the ligamentous layer of the fin, as well as the angle formed by the direction of dermal ridges and the fin root chord were measured. On the basis of fin cross-sections the three-dimensional surface models of the fin in a 1 : 1 scale were created with a CAD program. The shape of the model was evaluated by the wing and hydrofoil parameters (angle of leading edge sweep, leading edge radius, maximum thickness of the fin cross-section, and position of maximum thickness from the leading edge). Hydrodynamic performance of the fin cross-sections was studied with a CFD program. Regional variability of the parameters of morphology was compared with spanwise variability of the parameters of cross-sectional geometry. It was found that skin structure parameters correlate with the hydrodynamically relevant parameters of the fin and fin cross-sections. Regularities of skin structure of the harbor porpoise dorsal fin are considered indirect evidence of the adaptation of porpoise skin to the fin flow.