Subterranean Fishes of the World

3081

2015

AIM 2015

Cave animals have undergone remarkable adaptive changes in order to survive in their dark, nutrient poor environment. For instance, cavefish exhibit a dramatic increase in number of sensory neuromasts relative to closely related surface-dwelling fish. Neuromasts are specialized components of the lateral line system in aquatic species encompassing hair cells that are stimulated by movements in the surrounding water. Neuromast expansion is particularly apparent in the cranial region and has been linked to vibration attraction behavior (“VAB”) in cavefish, which is associated with enhanced foraging ability in the absence of light. Interestingly, ablation of superficial neuromasts proximal to the third suborbital (SO3) bone decreases VAB, suggesting this region plays a key role in cave-associated behavioral changes. Interestingly, several independent cavefish populations harbor defects in the suborbital bony series, including the fragmentation of the SO3 bone into multiple, distinct elements. The cellular basis for this fragmentation has long remained unknown. Here, we integrate quantitative and qualitative analyses to determine if there is a relationship between cranial neuromast positioning and density, and SO3 bone fragmentation. Approximately 86% of our labreared Pachón cavefish exhibited SO3 fragmentation compared to zero observations in surface fish. In addition, despite greater numbers of SO3 neuromasts in cavefish (p<0.001), surface fish SO3 bones are significantly larger (p<0.001). Using Delaunay triangulation to quantify density, we found surface fish have a significantly greater distance between neuromasts than cavefish in the SO3 region (p<0.001). Since higher neuromast density is associated with SO3 fragmentation, there may be an antagonistic relationship between neuromast expansion and cranial bone development, leading to the failure of SO3 bony elements to fuse together to form an intact bone. Thus, maladaptive cranial phenotypes in cavefish may evolve through an indirect relationship with the strong selection of constructive phenotypes.

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