Comparative Analysis of Locomotor Behavior and Descending Motor System Anatomy of Larval Zebrafish and Giant Danio

Abstract

A major challenge for comparative biology is understanding what aspects of an animal’s locomotor repertoire represent general features of motor organization, versus specialized adaptations for its anatomy and ecological niche. In this thesis I investigate the Giant Danio larvae (Devario aequipinnatus) as a potential model for comparative studies with Zebrafish, a well-established animal model in neuroscience. To this end, I study the locomotor behavior of both species and how its differences are reflected in the underlying neural circuit structure. Initially, I compare the anatomy of the descending pathways controlling locomotion in Giant Danio to Zebrafish using retrograde labelling of reticulospinal neurons. I see a striking resemblance of the circuit in both species, with a roughly similar organization and the general division and number of cell clusters being very well conserved. Following, I compare visually guided behaviours in Giant Danio to different Zebrafish strains. Giant Danio show a stronger optomotor response than Zebrafish. The optomotor response of Giant Danio first appear around 4 days post fertilization and can be consistently and reliably evoked. During optomotor tracking Giant Danio show shorter interbout intervals and are able to track motion at higher speeds than Zebrafish. I also observe that the higher manoeuvrability of Giant Danio is also reflected during prey capture. Interestingly, Zebrafish strains derived from more recently wild-caught fish show more robust optomotor behaviour, closer to Giant Danio. Lastly, I demonstrate the suitability of using Giant Danio in a head-restrained preparation with a 3D virtual reality environment. Combined with the potential for comparative approaches with Zebrafish, the faster development, larger neurons, and the rich behavioural repertoire of Giant Danio make it a promising model for neuroscience.