1. Seasonal plasticity in the telencephalon of a non-songbird the Ruffed Grouse (Bonasa umbellus). Andrew N. Iwaniuk, Justin M. Krilow Introduction Seasonal neuroplasticity has been well documented in a wide range of vertebrate species, but studies within birds are almost entirely constrained to songbirds. Further, the majority of studies on neuroplasticity in songbirds focus on the song system and, to a lesser extent, the hippocampal formation. The extent to which other telencephalic brains regions vary in size of cell number according to season in the 4,000+ non-songbirds is therefore unknown. Here, we specifically tested whether the size of telencephalic and other brain regions varies with season in Ruffed Grouse (Bonasa umbellus), a galliform bird (i.e., related to chickens and quail) that produces a unique, non-vocal courtship display. The Drumming Display Male Ruffed Grouse differ from other grouse and galliforms in that males do not vocalize as part of their courtship. Instead, they rely upon a unique, non-vocal wing beating display known as “drumming” to attract females. Males will drum up to 350 times per day, beating the wings as fast as 20 times per second. Although kinematics studies are lacking, the movements appear to differ from conventional wingbeats during flight. Fig. 3. Line drawings and Nissl stained halves of coronal sections through a Ruffed Grouse brain from rostral (A) to caudal (C). Abbreviations are as follows: A – arcopallium, AC – anterior commissure, Cb – cerebellum, HF – hippocampal formation, M – mesopallium, nRt – nucleus rotundus, SPC – striatopallidal complex. Fig. 1. Photographs of a male Ruffed Grouse drumming on his log. Methods Male Ruffed Grouse were trapped on drumming logs (Fig. 2) during the breeding season (spring). In the non-breeding season (fall), both males and females were obtained from hunters. All specimens were immersion fixed in 4% paraformaldehyde for several weeks, dissected, embedded in gelatin and serially sectioned in the coronal plane on a freezing stage microtome. Every second section was mounted onto slides and stained with thionin for Nissl substance. The size of multiple brain regions (Fig. 3) were then measured stereologiically with the Cavelieri estimator, as implemented in StereoInvestigator. All coefficients of error were < 0.03. We then used analyses of variance to test for differences in absolute and relative size of these brain regions across spring males, fall males and fall females. Hypothesis Male Ruffed Grouse exhibit seasonal changes in the size of motor regions of the telencephalon because of the motor control demands of the drumming display. Results Overall brain size was not significantly different across the three groups (Fig. 4). When brain region volumes were expressed as a proportion of overall brain size, no significant difference were detected in the size of the telencephalon, cerebellum, nucleus rotundus, mesopallium or hippocampal formation. Only the striatopallial complex (SPC) and arcopallium volumes differed significantly between spring and fall males (Fig. 4). Although not shown, the results were the same when we examined absolute volumes. Because ratios do not necessarily remove size effects, we also tested whether for differences among the three groups using mixed model ANOVAs of log-transformed brain region volumes plotted against log-transformed brain (not shown) or telencephalic volumes (Fig. 5). Again, the only significant differences detected were the SPC and arcopallium, oboth of which were significantly larger in spring males than in fall males or females. PO-2175 Fig. 5. Scatterplots of log-transformed volume of the telencephalon and the four regions measured within the telencephalon plotted against log-transformed brain and telencephalon volumes, respecitively. Colour coded linear regression lines are shown for both the striatopallidal complex and arcopallium because only these two regions were significantly larger in relative size in spring males. Abbreviations are as follows: TELE – telencephalon, HF – hippocampal formation, M – mesopallium, SPC – striatopallidal complex, A – arcopallium. Discussion and Conclusions Both the arcopallium and striatopallidal complex are significanlty larger in male during the spring than the fall. This seasonal difference is specific to these two regions and not related to telencephalon size or overall brain size. The seasonal difference is smaller (14-28%) than that observed in the songbird song system (up to 200%). Our data nevertheless represents the first evidence of seasonal changes in the telencephalon of a non-songbird species. This suggests that these two brain regions support the drumming display and that seasonal changes in the telencephalon may be widespread in birds Further research aims to determine whether changes in cell number or size are responsible for these volumetric differences. Acknowledgements We wish to thank George Iwaniuk and two excellent gun dogs for assisting in collecting grouse in the fall. Funding was provided by grants to ANI from NSERC and the Canada Foundation for Innovation. Fig. 2. A typical trap set up on a drumming log. Fig. 4. Box and whisker plots (min/max) of total brain volume and the relative size of each of the measured brain regions expressed as a proportion of overall brain volume or telencephalon volume. Asterisks indicate significant differences and abbreviations are as follows: TELE – telencephalon, nRt – nucleus rotundus, HF – hippocampal formation, and SPC – striatopallidal complex.