Integrating phylogenetic, morphological and behavioural approaches to explore the function and evolution of vision within Stromboidea

Abstract

Members of the gastropod superfamily Stromboidea have camera-type eyes that range widely in size, including some of the largest eyes of any gastropod. In this study, estimates of visual acuity from anatomical and behavioural data suggest that the large eyes of the conch snail family Strombidae can resolve objects as small as 1° in its visual field surprisingly fine resolution vision for a herbivorous snail. Contemporary imaging techniques (serial block-face scanning electron microscopy, transmission electron microscopy) reveal a greater complexity in the strombid retina ultrastructure than previous studies, with six retinal cell types identified in contrast to four described from TEM alone. This raises exciting new questions about how visual information is processed within strombids, and why this group has such fine spatial resolution. In contrast to the strombids, and to other large-eyed families in Stromboidea, estimates of visual acuity from the small-eyed families in the group indicate much coarser resolution.

This distinguishes Stromboidea as an excellent group for studying trends in eye evolution; however, a robust phylogenetic framework of the group is so far lacking. Therefore, new mitochondrial genome data were used to investigate the relationships among these families, which support monophyly of Stromboidea as redefined here to include Xenophoridae. To explore the evolution of large eyes within Stromboidea, Sanger sequences from three mitochondrial genes and one nuclear gene were used to build a robust phylogenetic framework of the superfamily. Morphological traits from rapid µCT-scanning were plotted onto the phylogeny to investigate factors that might drive evolution of eye change. Finally, the inclusion of fossil data in time-calibrated analyses from the excellent stromboid fossil record allowed the determination of key transition points in the evolution of these amazing eyes.

Date of Award	6 Dec 2022
Original language	English
Awarding Institution	University of Bristol
Sponsors	Natural History Museum
Supervisor	Nicholas W Roberts (Supervisor), Suzanne Williams (Supervisor) & Elizabeth Harper (Supervisor)