Study On Brain Morphology Differences Of Gambusia Affinis

Western mosquitofish(Gambusia affinis)has invaded in China for nearly 100 years and is widely distributed in the Yangtze river basin and south of China.Due to the great environmental differences,the mosquito fish will produce corresponding physiological,morphological and other aspects of adaptation.Previous studies have shown that fish in extreme environments(e.g.low oxygen,high salt,lack of light in caves,acidity or toxicity)exhibit morphological changes that are comparable to those in conventional environments.Because brain is the control center of the neuromodulation and humoral regulation system,it is worth exploring whether the brain has adaptive structural variation with environmental differences and which structures and functions of the fish will be changed by the variation in brain structure.This study aims to answer the following two questions: 1)within the Chinese mainland,whether there are adaptive variations in the brain morphology of different western mosquitofish populations? 2)if variations occur,is this variation caused by local adaptation or phenotypic plasticity? Therefore,this study has studied the spatial variation of the brain morphology of the invasive mosquitofish in China.Brain morphology parameters contain brain mass,eye diameter and volumes of olfactory bulbs,telencephalic lobes,optic tectum,corpus cerebelli,hypothalamus and total brain.And the evolutionary mechanism of variation was described using laboratory common-garden experiments.The main research results are as follows:1.Brain morphology of mosquitofish populations from China showed significant variation along the climatic gradients.Brain morphological characteristics of seven mosquito fish populations were analyzed.It is found that the stability of temperature and environment is an important driving force for the difference of brain phenotypic characteristics in western mosquitofish.These driving forces contribute to the differences of brain morphology of western mosquito fish along the climatic gradients.In coastal areas,western mosquito fish have larger olfactory bulbs,telencephalic lobes,corpus cerebelli and total brain,which is conducive to survival in coastal areas with fierce intra-species competition.In the harsh environments of the inland of China,mosquitofish have smaller brains.However,the change trend of brain morphology was weaker along latitude.In southern regions of China,the olfactory bulbs,corpus cerebelli are smaller and telencephalic lobes are larger.2.Results of common garden experiments show that variations of brain morphology were mainly due to phenotypic plasticity,but the variation of total brain volumes was mainly caused by genetic differentiation(that is,local adaptation).The volumes of optic tectum and hypothalamus did not differ significantly along the climatic gradients,but they were heritable.To sum up,this thesis mainly focused on the adaptive differentiation of the brain morphology in G.affinis.Throughout of the thesis,I found that there are adaptive brain morphological variation along the climatic gradients in G.affinis,and total brain volume variation can be inherited,resulting in local adaptation.This study lays a foundation for further studies on the adaptive evolution of G.affinis,and will deepen the public’s understanding of it and facilitate the future control of this species.