76.4 Friday, Jan. 6 Nocturnality limits morphological and functional diversity in the eyes of reef fishes SCHMITZ, Lars*; WAINWRIGHT, Peter C.; Univ. of California, Davis; Univ. of California, Davis firstname.lastname@example.org
Ambient light levels are often considered to drive the evolution of eye form and function. Diel activity pattern is the main mechanism controlling the visual environment of teleost reef fish, with day-active (diurnal) fish active in well-illuminated conditions, whereas night-active (nocturnal) fish cope with dim light. Physiological optics predicts several specific evolutionary responses to dim-light vision that are expected to be reflected in visual performance features of the eye. We analyzed morphological traits of the eye in 265 teleost reef fish, with a total number of 849 specimens. 54 species were classified as nocturnal, representing at least seven independent origins of nocturnality. Eye morphology of nocturnal reef fish is characterized by a syndrome that indicates better light sensitivity, including large relative eye size, high optical ratio and large, rounded pupils. Improved dim-light image formation comes at the cost of reduced depth of focus and reduction of accommodative lens movement. Diurnal teleost reef fish, released from the stringent functional requirements of dim-light vision have much higher morphological and optical diversity than nocturnal reef teleosts, with large ranges of optical ratio, depth of focus, and lens accommodation. Physical characteristics of the environment are an important factor in the evolution and diversification of the vertebrate eye. Both teleost reef fish and terrestrial amniotes meet the functional requirements of dim-light vision with a similar evolutionary response of morphological and optical modifications. The trade-off between improved dim-light vision and reduced optical diversity may be a key factor in explaining the uneven trophic diversity in reef teleosts.