Eye size in geckos of various ecological types (reptilia: Gekkonidae and sphaerodactylidae)

As a contribution to the study of ecological types among gekkonoid lizards, eye size, expressed as a percentage of rostrum-anus length (percra), was examined. Preliminary tests showed that preservation effects and sexual dimorphism are negligible, that ontogenetic allometry and geographic variation have to be considered, and that external spectacle diameter is proportional to whole-eye size. Species means of spectacle diameter vary: Diplodactylinae (13 spp.), 5–7 percra; Gekkoninae (37 spp.), 3.7–8.7 percra; Sphaerodactylidae (4 spp.), 4.2–5.5 percra. The eye is larger (in percra) in nocturnal than in diurnal species, and independently, is larger in ground-dwelling than in climbing species. The evolution of the latter condition is attributed mainly to the difficulties of visual hunting on the level ground, as compared to scouting from perches. Other hypotheses are also discussed.