Behavioral Tests For Sweet Taste Preference And Expression Pattern Of Sweet Taste Receptor Genes In Two Bat Species With Distinct Diets

Chiroptera,commonly called bats,are the only mammals that can truly fly.Bats,numbering over 1400 species,are the second most speciose group of mammals after rodents.In addition,bats exhibit a huge diversity in diets,including fruits,nectar,insects,blood,mammals,fish and birds.With the development of molecular biology,taste genes and taste functions related to diets in vertebrates have been discovered,especially for the sweet taste receptor encoded by both Tas1r2 and Tas1r3).This article attempts to investigate the functional evolution of sweet taste receptor genes in bats from the perspectives of animal behavior and gene expression.Firstly,I explored the bat's perception of sweetness using a behavioral study.Mammals use the sweet taste receptor to sense sweet substances in food.For some carnivorous animals,there are no sweet substances in their food,which makes their sweet taste receptor genes useless and therefore becomes pseudogenes,leading to the loss of their ability to sense sweet taste.The sweet receptor genes of insectivorous bats are intact,but the ability to perceive sweet taste is unknown.In this study,Rousettus leschenaultii and Myotis ricketti were taken as study subjects.In order to test the sweet taste ability of Rousettus leschenaultii and Myotis ricketti from the behavioral perspective,the two-bottle test was designed and conducted.A range of concentrations of sweet substances(sucrose,glucose and fructose)were added to the purified water or worm slurry to perform a two-bottle test,in other words,one container was added with a sugar-containing solution or worm slurry,and the other container was added with pure water or worm slurry.We found that Rousettus leschenaultii hada preference for the sugar solutions,but Myotis ricketti showed no preference for the two types of insect pulp.This study demonstrated that Rousettus leschenaultii can perceive sweetness,while Myotis ricketti can not perceive sweetness.These results confirmed that diet is an important determinant of bat sweet taste receptor function.Meanwhile,this study also revealed the importance of behavioral validation in the molecular evolutionary studies.Secondly,this work studied the function of sweet taste receptor genes in bats in terms of gene expression.There is no significant difference in the selection pressure of the Tas1r2 sequence between fruit-eating bats and insect-eating bats,but the ability to perceive sweet substances varies as their sweet taste receptors showed significant differences.It has been reported that sweet taste receptors are also expressed in many non-taste tissues and are thought to have metabolic regulatory functions.In this study,we analyzed the expression patterns of sweet taste receptor genes in various tissues of Rousettus leschenaultii and Myotis ricketti.These results showed that the bat sweet receptor genes are expressed throughout the body and may have other biological functions,which explained the sequence conservation of bat sweet taste receptor genes.No signal of Tas1r2 expression was detected in the tongue of Myotis ricketti,and since Tas1r3 protein alone cannot form a functional sweet taste receptor,failure to express Tas1r2 may have resulted in insensitivity to sweetness.This work explored the possibility of functions in a number of tissues other than the tongue only,looking for potential new functions of sweet taste receptor genes.The results of this paper also provided more solid evidence and reasonable explanations for the conclusions of molecular evolutionary analysis,cell-based assays and behavior preference experiments.