Molecular Evolutionary Studies On Bat Hearing And Dietary Genes

Bats (order Chiroptera) are traditionally divided into suborders Megachiroptera and Microchiroptera by morphological studies. Megabats have advanced visual and olfactory systems, and they take fruits or nectar as food. On the other hand, microbats have poor vision and, however, sophisticated laryngeal echolocation. These bats hunt insects by echolocation and ultrasonic hearing ability. However, molecular phylogenetic studies provide two new suborders, so-called Yinpterochiroptera and Yangochiroptera. Suborder Yinpterochiroptera includes both megabats and Rhinolophoidea species, and Yangochiroptera contains the other microbats. Thus, microbats are actually paraphyletic according to molecular studies. Based on the new phylogeny, more scientific questions concerning bat evolution are proposed.Bats exhibit a variety of specialized characters, which are important for their adaptation in nature. Except for echolocation, they also have the ability of powered flight. The evolution of bat wing and body plan is fundamental for their flight. The recombination of flight and echolocation helps bat hunt prey and occupy night niche successfully. The evolution of bat diet, which is related to sensory organs, is also crucial for their survival. Indeed, bats also have several other unique characters, such as high energy metabolism during flight and hibernation. This dissertation only focuses on the evolution of bat hearing and dietary functions and the genetic bases.The first part of this dissertation is the evolution of bat hearing genes. Firstly, we studied molecular evolution of motor protein prestin in bats and whales. The results not only confirmed the convergent evolution in echolocating bats, but also revealed convergent sequence evolution between echolocating bats and whales. The result demonstrates potential functional importance of prestin in bats and whales, both of which have ultrasonic hearing. The study of hearing gene KCNQ4provided further evidence that more genes involved in the evolution of bat ultrasonic hearing. The parallel KCNQ4substitutions in echolocating bats suggest its modified function in outer hair cells, which probably related to bat ultrasonic hearing. However, CHRNA10gene does not show adaptive evolution in echolocating bats. The second part is the evolution of dietary genes. The study of alanine-glyoxylate aminotransferase1(AGT) showed that subcellular targeting of AGT changed from mitochondria to peroxisomes in both Old World and New World fruit bats. Peroxisome targeting of AGT has been proved associated with plant-eating diet. Thus, the targeting changes in both Old World and New World fruit bats indicate adaptation to their fruit-eating diet. Lysozyme is a bactericidal enzyme and important for animal immune system. However, several studies reported that lysozyme was modified to digestive function in some animals, such as ruminants and leaf-eating monkeys. Here, we studied the evolution of lysozyme in bats, and found the gene underwent gene duplications in most vespertilionid species. The new genes could be related to digestion of insect exoskeleton.In a word, we have found several key hearing and dietary genes, which probably have important consequences for bat evolution. Note, the current studies only uncover a small part of knowledge for understanding bat sensory organ and diet evolution. However, I hope the dissertation could promote more research interest on bat evolution and more relevant studies will be reported in the future.