Malformations of the sacculus and the semicircular canals in spider morph pythons

Spider morph ball pythons are a frequently bred design morph with striking alterations of the skin color pattern. We created high resolution µCT-image series through the otical region of the skulls, used 3D-reconstruction software for rendering anatomical models, and compare the anatomy of the semicircular ducts, sacculus and ampullae of wildtype Python regius (ball python) with spider morph snakes. All spider morph snakes showed the wobble condition. We describe the inner ear structures in wild-type and spider-morph snakes and report a deviant morphology of semicircular canals, ampullae and sacculus in spider morph snakes. We also report about associated differences in the desmal skull bones of spider morph snakes. The spider morph snakes were characterized by wider semicircular canals, anatomically poorly defined ampulla, a deformed crus communis and a small sacculus, with a highly deviant x-ray morphology as compared to wildtype individuals. We observed considerable intra- and interindividual variability of these features. This deviant morphology of spider morph snakes can easily be associated with an impairment of sense of equilibrium and the observed neurological wobble condition. Limitations in sample size prevent statistical analyses, but the anatomical evidence is strong enough to support an association between the wobble condition in design bread spider morph snakes and a malformation of the inner ear structures. A link between artificially selected alterations in pattern and specific color design with neural-crest associated developmental malformations of the statoacoustic organ as known from other vertebrates is discussed.

Inner ear biomechanics reveals Late Triassic origin of mammalian endothermy

Endothermy (“warm-bloodedness”) underpins the ecological dominance of mammals and birds in diverse environmental settings1-3. However, it is unclear when this crucial feature emerged during mammalian evolutionary history, as most fossil evidence is ambiguous4-25. Here, we show that new information on this key evolutionary transition can be obtained from the morphology of the endolymph-filled semicircular ducts of the inner ear that monitor head rotations and are essential for motor coordination, navigation, and spatial awareness26-31. Increased body temperature during the ectotherm–endotherm transition of mammal ancestors would decrease endolymph viscosity, negatively impacting the biomechanics of the semicircular ducts32,33, while simultaneously increasing activity levels34,35 required improved performance36. Specific morphological changes to the membranous ducts and enclosing bony canals were, therefore, necessary to maintain optimal functionality. We track these morphological changes in 341 vertebrates, including 56 extinct synapsids, and show that canals with relatively thin cross-sections and small radii of curvature are indicative of mammalian endothermy. This inner ear morphotype evolved abruptly ~233 million years ago, during the Late Triassic, in Mammaliamorpha. Our conclusion differs from previous suggestions3-17, and we interpret most stem-mammals as ectotherms. Endothermy as a crucial physiological characteristic joins other distinctive mammalian features that arose during this period of climatic instability37-39.

Mechanical aspects of the semicircular ducts in the vestibular system

The semicircular ducts (SCDs) of the vestibular system play an instrumental role in equilibration and rotation perception of vertebrates. The present paper is a review of quantitative approaches and shows how SCDs function. It consists of three parts. First, the biophysical mechanisms of an SCD system composed of three mutually connected ducts, allowing endolymph to flow from one duct into another one, are analysed. The flow is quantified by solving the continuity equations in conjunction with the equations of motion of the SCD hydrodynamics. This leads to mathematical expressions that are suitable for further analytical and numerical analysis. Second, analytical solutions are derived through four simplifying steps while keeping the essentials of the coupled system intact. Some examples of flow distributions for different rotations are given. Third, the focus is on the transducer function of the SCDs. The complex structure of the mechano-electrical transduction apparatus inside the ampullae is described, and the consequences for sensitivity and frequency response are evaluated. Furthermore, both the contributions of the different terms of the equations of motion and the influence of Brownian motion are analysed. Finally, size limitations, allometry and evolutionary aspects are taken into account.

Combined Buoyancy Effects of Thermal and Mass Diffusion on Laminar Mixed Convection in Vertical and Horizontal Semicircular Ducts

The development of laminar mixed convection with heat and mass transfer in vertical and horizontal semicircular ducts has been investigated for the case of thermal boundary conditions of uniform heat input, concentration at the fluid–solid interface axially, and uniform peripheral wall temperature at any axial station. The governing equations were solved numerically over the following conditions: Pr = 0.7, Le = 1, Re = 500, Grt = 1.66 × 105, and Grc = 1.66 × 105. The combined effects of solutal and thermal Grashof numbers on the flow and thermal fields were observed in terms of the axial velocity, temperature, and concentration distributions, as well as, friction factor, Nusselt number, and Sherwood number. Further, the development of velocity, temperature, and concentration at different axial stations was found to be influenced by the solutal and thermal Grashof numbers. The results also showed that the forced-convection boundary layer development dominates very close to the duct inlet, while further downstream, the heat and mass transfer rates are enhanced due to the effect of solutal buoyancy.