The discovery that the olfactory system of the anadromous sea lamprey is extremely sensitive to two unique bile acids (petromyzonol sulfate [PS] and allocholic acid [ACA]) produced by stream-resident larval conspecifics has lead us to hypothesize that these compounds function as a migratory pheromone. Here, we test whether lamprey release these bile acids to the water in quantities sufficient for them to function as a long distance attractant. Five experiments were conducted. First, high performance liquid chromatography (HPLC) of liver extracts from all three life history stages of this species established that only larvae produce PS and ACA; parasites and maturing adults produced no identifiable bile acids. Large quantities of PS and ACA were found in larval gall bladders. Second, HPLC analyses of larval lamprey holding waters established that recently-fed larvae held in the laboratory release these bile acids to the water, with PS being released at a rate of approximately 16 ng h-1 animal-1 and ACA at 5 ng h-1 animal-1. Fasted animals released little bile acid. Third, an investigation of bile acid release routes demonstrated that larvae release bile acids primarily via their feces. Fourth, a study of the stability of ACA and PS in river water found both to have a half-life of a day. Finally, theoretical extrapolations using these data suggest that PS and ACA are present in picomolar concentrations in lamprey streams, a concentration within the detection range of adults. In conclusion, these data demonstrate for the first time that bile acid release rates and modes are adequate for these compounds to have pheromonal function.
Bibliographical noteFunding Information:
The authors thank Cynthia Gallaher for her assistance with bile acid analysis and the personnel of both the Hammond Bay Biological Station and the Ludington U.S. Fish and Wildlife Service Office for collecting and sending us the lamprey used in this study. Mr. Sid Morkert deserves special thanks in this regard. Mr Jared Fine kindly provided assistance with 3-keto reduction and reviewed the manuscript prior to its submission. This research was supported by the Great Lakes Fishery Commission (contracts to P.W.S. and D.D.G.), Minnesota Sea Grant, Department of Commerce, under grant No. NA46-RG0101 (P.W.S). The U.S. Government is authorized to reproduce and distribute reprints for government purposes, not withstanding any copyright notation that may appear hereon. This paper is journal reprint No. JR476 of the Minnesota Sea Grant College Program.
- Bile acid
- Petromyzon marinus
- Sea lamprey