Brain size is widely used as a measure of behavioural complexity and sensory-locomotive capacity in avians but has largely relied upon laborious dissections, endoneurocranial tissue displacement, and physical measurement to derive comparative volumes. As an alternative, we present a new precise calculation method based upon coupled magnetic resonance (MR) imaging and computed tomography (CT). Our approach utilizes a novel interactive Fakir probe cross-referenced with an automated CT protocol to efficiently generate total volumes and surface areas of the brain tissue and endoneurocranial space, as well as the discrete cephalic compartments. We also complemented our procedures by using sodium polytungstate (SPT) as a contrast agent. This greatly enhanced CT applications but did not degrade MR quality and is therefore practical for virtual brain tissue reconstructions employing multiple imaging modalities. To demonstrate our technique, we visualized sex-based brain size differentiation in a sample set of Ring-necked pheasants (Phasianus colchicus). This revealed no significant variance in relative volume or surface areas of the primary brain regions. Rather, a trend towards isometric enlargement of the total brain and endoneurocranial space was evidenced in males versus females, thus advocating a non-differential sexually dimorphic pattern of brain size increase amongst these facultatively flying birds.

Department of Biomathematics Institute of Physiology The Czech Academy of Sciences Vídeňská 1083 142 20 Prague Czech Republic

Institute of Biophysics and Informatics 1st Medicine Faculty Charles University Prague Czech Republic

MR Unit Department of Diagnostic and Interventional Radiology Institute for Clinical and Experimental Medicine Vídeňská 1958 9 140 21 Prague Czech Republic

Museum of Evolution Uppsala University Norbyvägen 16 SE 752 36 Uppsala Sweden

Palaeobiology Programme Department of Earth Sciences Uppsala University Villavägen 16 SE 752 36 Uppsala Sweden

Zobrazit více v PubMed

Healy S. D. & Rowe C. A critique of comparative studies of brain size. Proc. R. Soc. B 274, 453–464 (2007). PubMed PMC

Iwaniuk A. N. & Nelson J. E. Can endocranial volume be used as an estimate of brain size in birds? Can. J. Zool. 80, 16–23 (2002).

Iwaniuk A. N. & Nelson J. E. Developmental differences are correlated with relative brain size in birds: a comparative analysis. Can. J. Zool. 81, 1913–1928 (2003).

Marino L., Sol D., Toren K. & Lefebvre L. Does diving limit brain size in cetaceans? Mar. Mammal. Sci. 22, 413–425 (2006).

Sutton M. D. Tomographic techniques for the study of exceptionally preserved fossils. Proc. R. Soc. B 275, 1587–1593 (2008). PubMed PMC

Corfield J. R., Wild J. M., Cowan B. R., Parsons S. & Kubke M. F. MRI of postmortem specimens of endangered species for comparative brain anatomy. Nature Protoc. 3, 597–605 (2008). PubMed

Zelenitsky D. K., Therrien F., Ridgely R. C., McGee A. R. & Witmer L. M. Evolution of olfaction in non-avian theropod dinosaurs and birds. Proc. R. Soc. B 278, 3625–3634 (2011). PubMed PMC

Mace G. M., Harvey P. H. & Clutton-Brock T. H. Brain size and ecology in small mammals. J. Zool. 193, 333–354 (1981). PubMed PMC

Iwaniuk A. N., Dean K. M. & Nelson J. E. A mosaic pattern characterizes the evolution of the avian brain. Proc. R. Soc. B 271, S148–S151 (2004). PubMed PMC

Sahin B. et al. Brain volumes of the lamb, rat and bird do not show hemispheric asymmetry: a stereological study. Image Anal. Stereol. 20, 9–13 (2001).

Garamszegi L. Z., Eens M., Erritzoe J. & Møller A. P. Sperm competition and sexually size dimorphic brains in birds. Proc. R. Soc. B 272, 159–166 (2005). PubMed PMC

Garamszegi L. Z., Eens M., Erritzoe J. & Møller A. P. Sexually size dimorphic brains and song complexity in passerine birds. Behav. Ecol. 16, 335–345.

Møller A. P., Erritzoe J. & Garamszegi L. Z. Covariation between brain size and immunity in birds: implications for brain size evolution. J. Evol. Biol. 18, 223–237 (2005). PubMed

Glen C. L. & Bennett M. B. Foraging modes of Mesozoic birds and non-avian theropods. Curr. Biol. 17, R911–R912 (2007). PubMed

Dial K. P., Jackson B. E. & Segre P. A fundamental avian wing-stroke provides a new perspective on the evolution of flight. Nature 451, 985–989 (2008). PubMed

Wang X., McGowan A. J. & Dyke G. J. Avian wing proportions and flight styles: first step towards predicting the flight modes of Mesozoic birds. PloS ONE 6(12), e28672 (2011). PubMed PMC

Hopson J. A. Relative brain size and behavior in archosaurian reptiles. Ann. Rev. Ecol. Syst. 8, 429–448 (1977).

Larsson H. C., Sereno P. C. & Wilson J. A. Forebrain enlargement among non-avian theropod dinosaurs. J. Vertebr. Paleont. 20, 615–618 (2000).

Dominguez P. A., Milner A. C., Ketcham R. A., Cookson M. J. & Rowe T. B. The avian nature of the brain and inner ear of Archaeopteryx. Nature 430, 666–669 (2004). PubMed

Kurochkin E. N., Dyke G. J., Saveliev S. V., Pervushov E. M. & Popov E. V. A fossil brain from the Cretaceous of European Russia and avian sensory evolution. Biol. Lett. 3, 309–313 (2007). PubMed PMC

Metscher B. D. MicroCT for comparative morphology: simple staining methods allow high-contrast 3D imaging of diverse non-mineralized animal tissues. BMC Physiology 9, 11 (2009). PubMed PMC

Kotrotsou A. et al. Ex vivo MR volumetry of human brain hemispheres. Magn. Reson. Med. 71, 364–374 (2014). PubMed PMC

Vellema M., Verschueren J., Van Meir V. & Van der Linden A. A customizable 3-dimensional digital atlas of the canary brain in multiple modalities. NeuroImage 57, 352–361 (2011). PubMed

Ebel K.-D. & Benz-Bohm G. CT and MRI features of brain neoplasms. In Ebel K.-D., Blickman H., Willich E. & Richter E. Eds. Differential Diagnosis in Pediatric Radiology. Stuttgart, Thieme, 538–547 (1999).

Güntürkün O., Verhoye M., De Groof G. & Van der Linden A. A 3-dimensional digital atlas of the ascending sensory and the descending motor systems in the pigeon brain. Brain Struct Funct 218, 269–281 (2013). PubMed

De Groof G. et al. A three-dimensional digital atlas of the starling brain. Brain Struct Funct (2015) 10.1007/s00429-015-1011-1. PubMed DOI

Cosgrove K. P., Mazure C. M. & Staley J. K. Evolving knowledge of sex differences in brain structure, function, and chemistry. Biol. Psychiat. 62, 847–55 (2007). PubMed PMC

Schoenemann P. T. Brain size scaling and body composition in mammals. Brain Behav. Evol. 63, 47–60 (2004). PubMed

Barton R. A. & Harvey P. H. Mosaic evolution of brain structure in mammals. Nature 405, 1055–1058 (2000). PubMed

Chiappe L. M., Marugán-Lobón J. & Zhou Z. Life history of a basal bird: morphometrics of the Early Cretaceous Confuciusornis. Biol. Lett. 4, 719–723 (2008). PubMed PMC

Peters W. S. & Peters D. S. Life history, sexual dimorphism and ‘ornamental’ feathers in the Mesozoic bird Confuciusornis sanctus. Biol. Lett. 5, 817–820 (2009). PubMed PMC

Chiappe L. M., Marugán-Lobón J. & Chinsamy A. Palaeobiology of the Cretaceous bird Confuciusornis: a comment on Peters & Peters (2009). Biol. Lett. 6, 529–530 (2010). PubMed PMC

Peters W. S. & Peters D. S. Sexual size dimorphism is the most consistent explanation for the body size spectrum of Confuciusornis sanctus. Biol. Lett. 6, 531–532 (2010).

(2010).

Milner A. C. & Walsh S. A. Avian brain evolution: new data from Palaeogene birds (Lower Eocene) from England. Zool. J. Linn. Soc. 155, 198–219 (2009).

Jarvis E. D. et al. Avian brains and a new understanding of vertebrate brain evolution. Nature Rev. 6, 151–159 (2005). PubMed PMC

Garamszegi L. Z., Møller A. P. & Erritzoe J. Coevolving avian eye size and brain size in relation to prey capture and nocturnality. Proc. R. Soc. B 269, 961–967 (2002). PubMed PMC

Sharp G., Kandasamy N., Singh H. & Folkert M. GPU-based streaming architectures for fast cone-beam CT image reconstruction and demons deformable registration. Phys. Med. Biol. 52, 5771–5783 (2007). PubMed

Kennan R. P., Richardson K. A., Zhong J., Maryanski M. J. & Gore J. C. The effects of cross-link density and chemical exchange on magnetization transfer in polyacrylamide gels. J. Magn. Reson. B 110, 267–277 (1996). PubMed

Fishbein K. W. et al. Effects of formalin fixation and collagen cross-linking on T2 and magnetization transfer in bovine nasal cartilage. Magn. Reson. Med. 57, 1000–1011 (2007). PubMed

Medawar P. B. The rate of penetration of fixatives. J. Roy. Microsc. Soc. 61, 46–57 (1941).

Dempster W. T. Rates of penetration of fixing fluids. Am. J. Anat. 107(1), 59–72 (1960). PubMed

Dawe R. J., Bennett D. A., Schneider J. A., Vasireddi S. K. & Arfanakis K. Postmortem MRI of human brain hemispheres: T2 relaxation times during formaldehyde fixation. Magn. Reson. Med. 61, 810–818 (2009). PubMed PMC

Cruz-Orive L. M. Stereology of single objects. J. Microsc. 186, 93–107 (1997).

Sandau K. How to estimate the area of a surface using the spatial grid. Acta Stereol. 6, 31 (1987).

Kubínová L. & Janáček J. Estimating surface area by the isotropic Fakir method from thick slices cut in an arbitrary direction. J. Microsc. 191, 201–211 (1998). PubMed

Mattfeldt T., Mobius H. J. & Mall G. Orthogonal triplet probes: an efficient method for unbiased estimation of length and surface of objects with unknown orientation in space. J. Microsc. 139, 279–289 (1985). PubMed

Janáček J. & Kubínová L. Variances of length and surface area estimates by spatial grids: preliminary study. Image Anal. Stereol. 29, 45–52 (2011).

Beucher S. & Lantuéjoul C. Use of watersheds in contour detection. In Proceedings International Workshop on Image Processing, Real-Time Edge and Motion Detection/Estimation, Rennes, France. September (1979).

Volume of the crocodilian brain and endocast during ontogeny