Meeting Abstract
Visually guided organisms depend on their ability to collect information about their environment in order to capture prey, avoid predation, and find mates. Visual performance therefore represents a proxy of whole-organism fitness. Physiological optics predicts that large eyes improve both acuity and sensitivity, and in particular night-active (nocturnal) species are considered to benefit from large eyes. However, large eyes come with extra metabolic cost, hence there is a potential trade-off between the benefits to visual performance and the cost attached to it. To better understand the evolutionary drivers of eye size, we turned to geckos (Gekkota), a diverse squamate clade with many night-active (nocturnal) species. Geckos are unusual in that they feature at least 19 evolutionary transitions between different diel activity patterns, offering the opportunity to evaluate the effects of changes in the photic environment on eye size. We collected species average data for 90 gekkotans and used time-calibrated molecular phylogenies to model eye size evolution. Phylogenetic generalized least squares models show that diurnal species have smaller eye diameters for given snout-vent length compared to other geckos, validating earlier non-phylogenetic comparisons. Quantitative analyses of residual eye size evolution in a Bayesian framework confirmed these initial results and added important new information. Selective regimes shifts towards smaller residual eye size are strongly supported for the major, but not all transitions to diurnality. We also found strong support for a regime shift towards larger eyes not linked with a change in activity pattern, but rather with a change of habitat to semi-arid, open habitats with unobstructed view of the surroundings. Our results suggest that diel activity pattern and habitat interact to control eye size evolution in geckos.
