Between the jaws of the leptocephalus larva: biomechanically approaching a rarely observed organism

Being part of the Elopomorph group of fishes, Anguillidae species have a leptocephalus larval stage. Unfortunately, due to (mostly) unknown deep-water marine birthplaces, a catadromous lifestyle, and a transparent body morphology, these Anguilla larvae are rarely encountered in nature. Therefore, information regarding the early development of these larvae, including the exogenous feeding strategy and feeding performance, is rather scarce. To get some insight into these early ontogenetic changes and their influence on the functionality of the developing feeding apparatus, an ontogenetic series is put together from two artificially bred Anguillids. Throughout this series, graphical three-dimensional reconstructions (based on histological sections) of the musculoskeletal system of European (Anguilla anguilla) and Japanese eel (Anguilla japonica) larvae provide detailed descriptions of the changing feeding apparatus. Subsequently, theoretical bite forces are calculated for every reconstructed phase, using 3D data of joints, levers, and muscles derived from these reconstructions. Although the expected increase in bite force is observed with progressing age of the larvae, the obtained forces remain rather small (several µN). As a result, leptocephalus larvae are hypothesized to be anatomically constrained to feed only on soft and/or small food particles, which is in line with the current observations of small and/or gelatinous prey items (Hydrozoa, Thaliacea, Ctenophora, Polycystenia) in the guts of these larvae

Potentials and limitations of modeling bite forces: preliminary implications of simplifying real life musculoskeletal systems to simplified 3D and 2D models

In case the bite force of an organism can’t be measured in vivo, it can be estimated mathematically using static-state equilibrium models. However, these models represent different levels of simplifications of the reality. To investigate the impact of such simplifications of the musculoskeletal topography and the parameters describing muscle function, three different models are compared in this study. The first model describes the topography using 3D-coordinates and calculates muscle contraction force by using a series of parameters (including the muscle’s origin and insertion, fiber and tendon lengths and pennation angle). As the lower jaw becomes depressed, this model accounts for changes in muscle physiology parameters according to this movement. The second model uses the same 3D-coordinates, but calculates muscle force based on the physiological cross section area (PCSA) of the muscle. In this model, the muscle force is a theoretical maximal isometric force that remains constant throughout the simulation of different gape angles. The third model projects lever arms and the muscle’s line of action to the midsagittal plane and uses the PCSA (as measured in 3D) to infer muscle force. Input-data for these models is obtained from the European eel (Anguilla anguilla). Several isometric- and allometric-scaled morphs are deduced from a yellow eel specimen and implemented in the models. This poster illustrates the preliminary results of the three models. These results are compared, and validated against in vivo bite force data of yellow eels. Bite force calculations of earlier life stages (leptocephali and glass eels) were also simulated using the same models. These comparisons therefore allow defining constraints on the predictive power of different models generally used to calculate bite forces