The effect of morphological variation on the sensitivity of lateral line neuromasts

Abstract

Fish detect water flow with specialized structures of the lateral line system called neuromasts. Neuromasts are comprised of a cluster of hair cells that project kinocillia into a gelatinous cupula that is deflected by flow. The morphology of neuromasts dictate how fluid forces are transduced into mechanical stimuli by the hair cells. Analytical models predict that changes in morphology likely have a large effect on the mechanics of flow sensation. Therefore, we studied how differences in neuromast morphology in larval zebrafish (D. rerio) influence their sensitivity. This was achieved by morphometric analysis and mathematical modeling. In over 350 neuromasts that were imaged in 30 larvae, we recorded the dimensions of the cupula and kinocilia. We found that the shape and size of the neuromasts varied in ways that are predicted to greatly influence their sensitivity. Furthermore, this variation did not generally correlate with body position. One hypothesis for this high degree of variability is that observable neuromast morphology is the result of random wear and tear on the cupula rather than a consistently maintained form. One example of this is that total neuromast height may be constrained by the sloughing of cupular material from the end of the structure during free‐swimming activity. An investigation of pre‐hatch larvae supported this idea. It was found that the neuromasts of pre‐hatched individuals, which are insulated from wear, were longer than those of post‐hatch fish. Neuromasts in certain locations, such as those of the orbital canals, were consistently smaller than the body average suggesting that certain areas have developmentally ascribed differences in sensitivity but that in general the system must deal with a wide range of rapidly changing neuromast sensitivities.