Fetal echocardiographic evaluation of the bottlenose dolphin (Tursiops truncatus).

In humans, fetal echocardiography represents the most important tool for the assessment of the cardiovascular well-being of the fetus. However, because of logistic, anatomic, and behavioral challenges, detailed fetal echocardiographic evaluation of marine mammals has not been previously described. Because the application of fetal echocardiography to cetaceans could have both clinical and academic importance, an approach to evaluating the fetal dolphin's cardiovascular status was developed with conventional, fetal echocardiographic techniques developed in humans. Eight singleton fetal bottlenose dolphins (Tursiops truncatus) were evaluated, each between 6 and 11 mo gestation; six fetuses underwent two fetal echocardiographic evaluations each, four at 3-mo intervals, and two at 0.5-mo intervals. Evaluations were performed without sedation, using conventional, portable ultrasound systems. Multiple transducers, probes, and maternal dolphin positions were used to optimize image quality. Fetal echocardiography included two-dimensional imaging and color flow mapping of the heart and great arteries, as well as pulsed Doppler evaluation of the umbilical artery and vein. Thorough evaluations of the fetal dolphins' cardiovascular status were performed, with the greatest resolution between 8 and 9 mo gestation. With the use of published human fetal echocardiographic findings for comparison, fetal echocardiography demonstrated normal structure and function of the heart and great arteries, including the pulmonary veins, inferior vena cava, right and left atria, foramen ovale, tricuspid and mitral valves, right and left ventricles, ventricular septum, pulmonary and aortic valves, main pulmonary artery and ascending aorta, and ductus arteriosus. Pulsed Doppler techniques demonstrated normal umbilical arterial and venous waveforms, and color flow mapping demonstrated absence of significant valvar regurgitation. Fetal echocardiography, particularly between 8 and 9 mo gestation, can provide a safe and detailed assessment of the cardiovascular status of the fetal bottlenose dolphin.

Distribution and development of the highly specialized lipids in the sound reception systems of dolphins.

Fat bodies in the heads of toothed whales, which serve to transmit and receive sound, represent extraordinary examples of physiological specialization in adipose tissues among mammals, yet we know surprisingly little about their biochemical composition. We describe the spatial distributions and development of unusual endogenous lipids (branched-chain ["iso"] molecules and wax esters) in the mandibular fat bodies of bottlenose dolphins (Tursiops truncatus) using an ontogenetic series (fetus to adult; n = 10). Although concentrations of iso-acids, iso-alcohols and waxes were lower in younger dolphins than in adults, the same relative spatial arrangement was present in all age classes, implying a set "pattern" of acoustic lipid distribution that is established very early in life. In all age classes, a small region of blubber overlying the lateral region contained unusually high concentrations of iso-acids, exhibiting a tenfold increase over "normal" adjacent blubber. Being chemically more similar to the acoustic fat bodies, this region may serve as an entry point for sound into the head. Developmental accumulations of some iso-acids and iso-alcohols occurred more rapidly than others, implying that not only are the spatial distributions of branched-chain molecules under extremely fine-scale control, but the regulatory mechanisms controlling acoustic lipid synthesis are also highly complex.

Ontogenetic changes in the structural stiffness of the tailstock of bottlenose dolphins (Tursiops truncatus).

Late-term fetal bottlenose dolphins (Tursiops truncatus) are bent ventrolaterally en utero, requiring extreme flexibility of the axial skeleton and associated soft tissues. At birth, neonatal dolphins must immediately swim to the surface to breath, yet the dorsoventral oscillations used during locomotion may be compromised by the lateral flexibility evident in the fetus. The unique fetal position of dolphins, coupled with their need to swim at birth, places conflicting mechanical demands on the tailstock. Our previous research demonstrated that neonatal dolphins possess laterally placed, axial muscles that are functionally specialized to actively maintain the straightened posture of the tailstock. Here, we investigated the development of passive lateral stability in the tailstock of bottlenose dolphins by performing whole-body bending tests on an ontogenetic series of stranded dolphin specimens (N=15), including fetuses, neonates and juveniles (total length 58-171 cm). Structural stiffness increased, while overall body curvature decreased, with increasing body length. Scaling analyses suggest that increased structural stiffness is due to increases in size and probably changes in the passive material properties of the tailstock through ontogeny. The neutral zone was approximately constant with increasing size, while the relative neutral zone (neutral zone/total length) decreased. The lateral stability of the tailstock appears to be controlled by a combination of active and passive systems and the role of these systems varies through ontogeny. While neonates use active, muscular mechanisms to limit lateral deformations of the tailstock, the stability of the maturing tailstock is due primarily to its passive tissue properties.