Honors Program Theses


Honors Program Thesis (UNI Access Only)

First Advisor

Nathan C. Bird, Honors Thesis Advisor


Weberian apparatus--Anatomy;


The Weberian apparatus is a novel hearing adaptation diagnostic of the superorder Otophysi. The order Cypriniformes, which consists of over 10,000 species including carp, suckers, and loaches, is widely distributed in the freshwater habitats of Europe, North America, and Asia (Berra, 2001; Nelson et al., 2016). Due to this environmental diversity, several modifications have occurred in the non-auditory structures of the Weberian apparatus (Bird & Hernandez 2007). Four major morphologies are currently recognized, including Open (typical of Cyprinidae), Anterior Shield (typical of Botiidae, Catostomidae, and Gyrinocheilidae), Single Capsule (typical of Cobitidae), and Double Capsule (found in many loach families such as Nemacheilidae and Balitoridae) (Bird and Hernandez 2007). We used HBQ quad-stained paraffin histology, whole-mount clearing and staining, and micro-CT skeletal analysis to document and describe the hard and soft tissue of the Weberian apparatus in species representing six genera (Danio, Gyrinocheilus, Ambastaia, Pangio, Schistura, and Sewellia) that characterize all morphologies. Little variation was seen among species in most aspects of direct sensory reception, including the shape of the ossicles, swim bladder, and otic sensory structures. Two notable exceptions are the articular processes of the scaphium and intercalarium, which are completely lost in certain species. Variation was seen among morphologies in terms of the size of these sensory elements, such as the progressive reduction in size of the tripus as the system increases in encapsulation, and in the morphology of non-auditory structures. Variation was found between species in terms of otic chamber size, ossification within ossicles and other vertebral elements, the size and shape of lateral openings in the swim bladder capsule, and composition of ligaments. Much of this variation is likely evolutionary in origin, although it may be influenced by the environmental niche occupied by each clade These results reveal previously undescribed variation within the Weberian apparatus and demonstrate the need for further comparative analysis of this structure, particularly histological and auditory studies.

Year of Submission



Department of Biology

University Honors Designation

A thesis submitted in partial fulfillment of the requirements for the designation University Honors

Date Original


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