Evolution of the gecko's adhesive toes

Effective locomotion is critical for the survival of animals, which has led to the evolution of specialised morphological structures. Such morphological adaptations can lead to adaptive radiations. Studies of intermediate forms in morphological series, i.e. species that have evolved some, but not all, of the morphological features that form the complex structure, can make a crucial contribution to understanding the evolution of complex morphological structures.

The adhesive toes of geckos represent such a complex morphological structure and have attracted great research interest from both biologists and engineers (bionics). The adhesive toes consist of rows of widened scales (lamellae) controlled by specialised muscles and tendons and covered by microscopic adhesive structures (setae). Adhesive toes facilitate the utilisation of complex three-dimensional habitats. The evolution of adhesive toes is poorly understood, partly due to the lack of studies on intermediate morphological forms.

Based on the scale shape of the toes, members of the genus Cyrtodactylus (e.g. C. brevipalmatus) have been repeatedly proposed as potential intermediate forms in a morphological series from toeless species to the fully developed adhesive toes of the sister genus Hemidactylus. However, the morphology of the microstructures of these species is largely unknown and histological studies on the internal morphology are only available for a few species. Furthermore, the adhesive properties of these potential intermediate forms and their effect on the locomotor abilities of the animals are unknown.

The aim of this research project is therefore to investigate the evolution of geckos' adhesive toes using the genus Cyrtodactylus as an example. Modern morphological methods of investigation (including scanning electron microscopy and computer tomography) are combined with experiments on locomotion and data on ecology in order to investigate the role of the morphology of proto-adhesive toes in the locomotion of animals, and how and under what ecological conditions proto-adhesive toes have evolved.