Meeting Abstract

P1.103  Monday, Jan. 4  Species differences in early patterning of the avian brain MCGOWAN , Luke *; STRIEDTER , Georg; University of California, Irvine; University of California, Irvine lukemcgowan1@yahoo.com

Adult brain region proportions vary across taxa—e.g., parrots have a proportionally larger telencephalon than galliformes, while having a proportionally smaller optic tectum. How do such species differences evolve? What differences in brain development account for such differences in adult morphology? We here examine species variation in early brain patterning as a possible mechanism underlying brain proportion evolution. In particular, we look at differences in early tissue territory allocation of the developing optic tectum in parakeets and bobwhite quail. Published embryonic morphometric data from our lab show that tectal growth curves in parakeets and bobwhite quail run roughly parallel all the way back to the time when tectal morphology first becomes apparent. Backward extrapolation from these data suggests that the parakeet’s tectum is smaller than the quail’s from the outset—that is from the time of initial tectal territory allocation or regionalization. To examine this regionalization difference we look at the expression domains of transcription factors Pax6 and Gbx2, which are expressed in the forebrain and hindbrain, respectively. These expression domains are known to form rostral and caudal borders with the presumptive midbrain tectum at around Hamburger Hamilton stages 8-12 when the tectal territory is specified. These borders allow us to measure and compare the sizes of a molecularly defined presumptive tectum in the two species. Our hypothesis predicts that the molecularly defined tectal territory is significantly smaller, in absolute size and relative to the remaining brain, in parakeets compared to bobwhite quail. Supported by NSF grant IOS-0744332.