Meeting Abstract

P1-67   -   Distinct allometric trajectories underlie brain shape development in ratites (Aves: Palaeognathae) Forcellati, MR*; Green, TL; Watanabe, A; Columbia University, New York, NY; New York Institute of Technology College of Osteopathic Medicine, Old Westbury, NY; New York Institute of Technology College of Osteopathic Medicine, Old Westbury, NY mrf2167@columbia.edu

How do unique brain shapes evolve? Comparative neuroanatomical studies have long debated the role of developmental trajectories in the evolution of novel and diverse brain morphologies. Historically, these studies have focused on whether major neuroanatomical changes occur largely due to evolutionary shifts along conserved developmental trajectories or the acquisition of unique trajectories. Investigating how developmental trajectories contribute to diversification of brain morphologies requires sampling taxa with disparate brain shapes and adult sizes. In this study, we use a unified framework to examine brain development in ratites, which can attain large body sizes as adults (~60kg), compared to domestic chickens, a taxon with more modest adult body size among modern birds. We utilized a high-density 3-D geometric morphometric approach on endocasts from micro-CT data of late- and post-embryonic specimens of common ostriches (Struthio camelus; n≧8), emus (Dromaius novaehollandiae; n≧13), and southern cassowaries (Casuarius casuarius; n≧20). Then, we compared their developmental trajectories and shape differences with those of chickens (Gallus gallus; n=14). We find that i) chickens and ratites have distinct brain shapes; and ii) chickens and ratites consistently have distinct developmental trajectories regardless of whether endocranial size or temporal age are used as independent variables. Our results show that chickens and ratites have different brain shapes which come about through different developmental trajectories This may potentially arise from differences in neurogenic patterns. Furthermore, our study suggests that major differences in brain shape between differently sized taxa can arise from evolution of unique developmental trajectories, instead of simply as an extension of a conserved ontogenetic trend.