Eye size in geckos: Asymmetry, allometry, sexual dimorphism, and behavioral correlates

Abstract

The function of the vertebrate eye depends on its absolute size, and the size is presumably adapted to specific needs. We studied the variation of eye size at all levels, from intra-individual to inter-specific, in lid- less, spectacled, gecko lizards (Gekkonomorpha). We mea sured 1,408 museum specimens of 62 species, representing subfamilies Diplodactylinae, Gekkoninae, and Sphaerodactylinae. Intra-individually, eye size showed significant directional asymmetry in Stenodactylus sthenodactylus. A latitudinal study of six species confirmed that during postnatal ontogeny eye size undergoes conventional negative allometry; the slope is steeper among adults than among juveniles, expressing the need of juveniles for relatively larger eyes. Within species with sexual size dimorphism, commonly the larger sex possessed larger eyes in absolute terms but not relative to head-and-body length. Interspecifically, eye size showed negative allometry, with slope significantly steeper than those of intraspecific ontogenetic allometry, again expressing the need of juveniles for relatively larger eyes and showing that eye-size differences among species do not merely result from body-size differences. Finally, adult eye size varied interspecifically in correlation with parameters of behavioral ecology: eyes were significantly larger in nocturnal than in diurnal species, and significantly larger in cursorial than in scansorial species.

Effects of age and size in the ears of gekkotan lizards: auditory sensitivity, its determinants, and new insights into tetrapod middle-ear function

“…It is unclear to what extent the traits of auditory function, which differ between the species studied here, really characterize the relevant higher gekkotan taxa, Eublepharidae and Diplodactylidae. To the extent that they do, these functional differences would accord with other morphological differences between these groups in middleear morphology [51], the vertebrae [41], and another gekkotan size-dependent sensory organ, the eye [45] and eyelids [19]. The fact that auditory sensitivity correlates with body size, intra-and interspecifically, has been interpreted as partly deriving from two morphological factors: (1) the number of hair cells in the inner ear that interspecifically (not intraspecifically) correlates with animal size; (2) the hydraulic lever in the middle ear's impedance matching mechanism (the ratio of tympanic membrane area to columella footplate area increases both inter-and intraspecifically with animal size).…”

“…The difference may have either or both reasons: First, RA as a factor may be emphasized in E. macularius because of its much wider range of values in our sample due to the availability of smaller juveniles. Second, evolutionary divergence between gekkotan groups (E. macularius, Eublepharidae; O. marmorata, Diplodactylidae); for example, Diplodactylidae and Gekkoninae differ in eye allometry [45].…”

Disentangling the Influence of Urbanization and Invasion on Endemic Geckos in Tropical Biodiversity Hot Spots: A Case Study ofPhyllodactylus martini(Squamata: Phyllodactylidae) along an Urban Gradient in Curaçao

“…We provide the first detailed analysis of the diet of P. martini based on specimens collected from around the island of Curaçao and test whether transitions to suburban habitats lead to a shift in dietary resources indicating dietary flexibility. Because many geckos are sexually dimorphic (Kratochvíl and Frynta 2002;Werner and Seifan 2006;Starostová et al 2010), including other species of Phyllodactylus (Ramírez-Sandoval et al 2006), we compare feeding habits between sexes to account for the possibility of males and females utilizing different prey resources. We contrast this data with a morphometric data set of limb and cranial elements in P. martini to test for the potential for sexual dimorphism as well as correlations between phenotype and diet.…”

The Circumorbital Bones of the Gekkota (Reptilia: Squamata)

“…1). Orbit size is related to eye size, which in turn is correlated with parameters of behavioral ecology; in gekkotans the eye is larger in nocturnal than in diurnal species and in cursorial than in scansorial species (Werner and Seifan, 2006). Some gekkotans are lidless and the eye is covered by a fixed transparent window or spectacle.…”