Meeting Abstract
Eye loss occurs in many troglobitic, fossorial and deep-sea animals but there is no clear consensus on its evolutionary mechanism. Given the highly conserved and pleiotropic nature of many genes instrumental to eye development, degeneration might be expected to follow consistent evolutionary trajectories in closely-related animals. Molluscs are renowned for the enormous diversity of eye designs they exhibit, and they occupy a wide variety of light environments. Eyeless deep-sea gastropods offer a model study system, both taxonomically and biogeographically, for examining broader evolutionary processes involved in loss and regression. We conducted a comparative study of ocular anatomy in solariellid snails from deep and shallow marine habitats using morphological, histological and tomographic techniques, contextualised phylogenetically. Independent instances of reduction follow numerous different morphological trajectories. We estimate eye loss has evolved at least seven times within Solariellidae, in at least three different ways: characters such as pigmentation loss, obstruction of eye aperture and ‘lens’ degeneration can occur in any order. In one instance, two morphologically distinct reduction pathways appear within a single genus, Bathymophila. Even amongst closely related animals living at similar depths and presumably with similar selective pressures, the processes leading to eye loss have more evolutionary plasticity than previously realised. Although there is selective pressure driving eye reduction, it is apparently not morphologically or developmentally constrained as has been suggested by previous studies.
