Pleiotropy is hypothesized to be important in cave fish because there are genes that might be selected for one trait and automatically cause another trait to be selected for it if it is governed by the same gene. As selective pressure on one trait can coordinate change in others, pleiotropy could explain why independent adaptation to the cave environment has been observed in multiple populations of the species. One example is the relationship between taste bud amplification and eye loss controlled by sonic hedgehog expression (Shh) in cave fish. It has been shown that with an over expression of Shh there is an increased number of taste buds and reduced eye development. It is hypothesized that since caves are food and nutrient limited, having an increased amount of taste buds is important and may be under strong selection while at the same time causing evolution of eye loss.
plEiotropy Is hypOtheSized To be importANt in cavE FiSH becauSe thERe are Genes that MIgHt BE SelEcted fOr One TRait And AuTomAtIcAlly cAusE AnotHeR trait to Be selecTed for iT iF it iS gOvErned by thE sAme GEne. as seLEctive PReSSure On one tRait can cooRDInAte chAnge in others, pleiotropy cOulD exPlaIN why indepEndent aDAptAtIoN to tHe CaVE eNVironment has been obseRved iN mUltipLe popuLatIoNs of the SPeCies. onE ExAmplE is thE relatioNshIp BEtwEen tasTe bud AMplificAtion and eYE LOsS ConTrolled by SonIc HEdgEhog ExprESSion (shh) In caVE fiSh. It has bEeN showN that wIth An ovEr ExpreSsion of sHh tHere is an IncrEaseD NUmbeR of Taste Buds and rEduCed eYe deVelopmenT. it is hypoThesizEd that siNce caVES are fooD And nUTriEnt limIted, HaviNg An InCreaSed Amount of tAsTe bUds is imporTaNt and mAy Be undeR STrong SelEcTion wHile at tHe same Time Causing EVoluTion oF eYe Loss.