Brain structures of echolocating and nonecholocating bats, derived in vivo from magnetic resonance images Kailiang Hu a,b,c , Yingxia Li a , Xiaoming Gu c , Hao Lei a and Shuyi Zhang b a State Key Laboratory of Magnetic Resonance and Atomic and Molecular Physics, Wuhan Institute of Physics and Mathematics,Chinese Academy of Sciences, Wuhan, b School of Life Science, East China Normal University, Shanghai PR China and c School of Geographic and Biologic Sciences, Guizhou Normal University, Guizhou Correspondence and requests for reprints to Hao Lei, PhD, Wuhan Institute of Physics and Mathematics, Chinese Academy of Sciences, No. 30 Xiaohongshan, Wuhan, Hubei 430071, PR China Tel: + 86 27 87198542; fax: + 86 27 87199291; e-mail: leihao@wipm.ac.cn Sponsorship: This work was supported by a special grant of East China Normal University to S.Y. Zhang, and grants 10234070, 30370419 and 30400136 from National Natural Science Foundation of China to H. Lei. Received 26 July 2006; accepted 3 August 2006 Magnetic resonance images of the brain of ¢ve species of wild bats, including three species of Microchiroptera, one species of echolo- cating Megachiroptera and one species of nonecholocating Mega- chiroptera, were obtained in vivo. The relative volumes of the inferior colliculus and the superior colliculus to the brainstem were derived from the magnetic resonance images and compared among di¡erent species. In general, the relative size of the inferior colliculus was much larger in Microchiropterans than in Megachiropterans, and in echolocating Megachiropterans than in nonecholocating Megachiropterans. The relative size of the superior colliculus was similar in these two suborders. Agreeing with the previous results and consistent with the current hypothesis that Megachiropterans originated from Microchiropterans, the results suggest that the inferior colliculus of Megachiropterans tends to degenerate during the process of evolution, as these fruit bats use more vision and smell than hearing when they forage. The results also demonstrate that magnetic resonance imaging can be used to study the neuroanatomy of wild bats noninvasively. NeuroReport 17:1743^1746  c 2006 Lippincott Williams & Wilkins. Keywords: bat, brain, echolocate, magnetic resonance imaging, Megachiroptera, Microchiroptera Introduction Bats (Chiroptera) are the only mammals that achieve true self-powered flight, and account for 1116 species [1]. This family is divided into Microchiroptera and Megachiroptera. Most Microchiropterans have the ability of echolocation and, in contrast, most Megachiropterans do not have this ability except for some bats of the genus Rousettus [2]. Echolocation calls of bats can be divided into three types: constant frequency/frequency-modulated, frequency- modulated and click-like echolocation [3]. Moreover, as insectivorous bats play an important role in controlling agricultural and forestry pest, and fruit bats play an important role in seed dispersal in primary forest, conser- ving these animals is becoming an issue for conservation biologists worldwide. Neuroanatomical and physiological techniques, often invasive, have been utilized to study the brain of bats. For example, electrophysiological techniques have been widely used to study the functions of the auditory system of bats [4,5]. Several investigators have measured the volumes of cochlear nuclei and other auditory centers in bats, and compared the relative sizes of these structures in different species [6–8]. Unfortunately, bats are unavoidably sacrificed in these types of studies. Magnetic resonance imaging (MRI) is a novel neuroima- ging technique that has been used extensively to obtain anatomical, morphological, biochemical, physiological and functional information noninvasively from animal brains [9]. Only a few studies, however, have applied this powerful tool to study the neuroanatomy and cerebral function of bats. Magnetic resonance microscopy has been used to study the cochleae of mustached bats ex vivo [10,11]. Thorne et al. [12] derived cochlear fluid space dimensions with three-dimensional magnetic resonance images. More re- cently, Kamada et al. [13] developed an experimental protocol to perform MRI studies in awake bats, with which the neuroanatomical structures and cerebral function of mustached bats (Pteronotus parnellii) were studied in vivo. In this study, we investigated the neuroanatomy of five species of bats in vivo using MRI, including three species of Microchiroptera, one species of echolocating Megachirop- tera and one species of nonecholocating Megachiroptera. Quantitative measurements of the dimensions/volumes of anatomically well defined brain structures were performed. BRAIN IMAGING NEUROREPORT 0959-4965  c Lippincott Williams & Wilkins Vol 17 No 16 6 November 2006 1743 Copyright © Lippincott Williams & Wilkins. Unauthorized reproduction of this article is prohibited.