The evolution of the eyes of labrid fishes.
Final Report Abstract
This project is an important contribution to a better understanding of the evolution of organismal diversity. I used the vertebrate eye of teleost reef fishes and other vertebrates as a model system to characterize the influence of physical constraints on the evolution of morphological diversity, asking whether diet and diel activity patterns influence the evolution of eye shape. My results show that physical characteristics of the visual environment emerge as major factors in the morphological evolution of the eyes of vertebrates. Evolutionary transitions to zooplanktivory in labrids lead to morphological modifications of the eye that improve visual acuity, matching predictions from visual optics. These modifications concern both macromorpholgy and retina structure. Current results also indicate that the evolution of macromorphology and retina structure may be de-coupled in some lineages, e.g., the fairy wrasse Cirrhilabrus. Light levels exert strong constraints on the evolution of eye shape. On the basis of a very large comparative dataset on eye shape in 265 species, I showed that nocturnal reef fish possess eye shape that improves visual light sensitivity, similar to the pattern previously observed in terrestrial vertebrates. Across vertebrates the physical requirements of dim-light vision seem to be met with similar morphological and optical modifications. In addition, I demonstrated that nocturnality constrains the morphological and functional diversity of eyes in teleost reef fish. The stringent constraints of low-light levels on eye shape render it possible to make quantitative retro-dictions of diel activity patterns in dinosaurs. I applied phylogenetically-informed discriminant analysis, a new method developed during this project, on a dataset on skeletal proxies of eye shape variables of 33 fossil dinosaurs (e.g., Velociraptor), birds (e.g., Archaeopteryx), and pterosaurs (flying reptiles, e.g., Rhamphorhynchus). The surprising result is that many dinosaurs, in particular the small predators, were nocturnal, a result of high public interest. To conclude, the results of this project highlight the important role of physical characteristics of the environment in the evolution of morphology. My approach was founded on the idea that functional morphology is a key to a better understanding of the origins of diversity, because it establishes linkages between organismal structure and major niche dimensions. As the physical requirements of vision are clearly defined, one can study morphological and functional adaptations to environments and behaviors that impose divergent physical challenges. The vertebrate eye offers a rich system for tests of hypotheses about the causes of diversity and is a key to a better understanding of the dynamics between physics and evolution.
Publications
- (2011). Nocturnality constrains morphological and functional diversity in the eyes of reef fishes. BMC Evolutionary Biology, 11: 338
Schmitz, L. & P. C. W. Wainwright
- (2011). Nocturnality in dinosaurs inferred from scleral ring and orbit morphology. Science, 332: 705-708
Schmitz, L. & R. Motani
