Meeting Abstract
Birds show large variation in olfactory morphology, including the olfactory bulb and olfactory turbinates, yet studies on the relationship between these structures are lacking. To test the hypothesis that these olfactory elements co-vary across development and evolution, we first examined their scaling relationship in a developmental series of the chicken. Results show coordinated growth, with the olfactory bulb and olfactory turbinate scaling isometrically, and developing with some independence from other neighboring structures. Such a high degree of coordination in the growth of these structures is somewhat surprising given that olfactory epithelium extends over more than just the turbinate and may theoretically expand or contract independent of turbinate morphology. Numerous possibilities exist, but it may be that the size of the olfactory cavity is constrained by the surrounding craniofacial architecture or that the respiratory function of the nasal cavity limits the forward spread of olfactory receptors within the nasal cavity. Our first step in exploring these possibilities was to determine whether ontogenetic coordination translates to conserved patterns of phylogenetic isometry. Initial sampling, which included all the major avian crown clades, indicates a significant level of phylogenetic allometry, but with isometry dominating within certain groups, including Passeriformes. Although no specific hypotheses can currently be ruled out, our data indicate a complex structural history for avian olfaction. One that needs to be studied in combination with both the physiology of olfaction in mind, as well as the structure of neighboring systems.
