Partial Evolutionary Divergence of a Migratory Pheromone between Northern and Southern Hemisphere Lampreys
Cindy F. Baker, Michael Stewart, Jared M. Fine, and Peter W. Sorensen
Lampreys are ancient cartilaginous fish. Around half of the lamprey species spend their entire life in freshwater and are not parasitic while the other half have an anadromous life history. Larvae feed in freshwater streams before metamorphosing into a parasitic phase that migrates to the sea (or lake) to feed on fish or mammals before returning to freshwater streams to spawn. The pouched lamprey Geotria australis is the only species in the southern hemisphere family Geotriidae and is migratory and parasitic. Previous radio tracking of pouched lampreys indicated that adult fish were attracted to certain rivers and not others (National Institute of Water and Atmospheric Research, unpublished data).
Sorensen et al. (2005) have demonstrated that migratory adult sea lamprey Petromyzon marinus locate spawning streams using a pheromone mixture released by upstream resident larvae. This mixture is composed of three sterols (petromyzonamine disulfate [PADS], petromyzosterol disulfate [PSDS], and petromyzonol sulfate [PS]) that are detected at subpicomolar concentrations (1 × 10–13 M). Fine et al. (2004) discovered that the pheromone is not species- specific, as sea lampreys exhibited a behavioral attraction to water that held three other lamprey species. The present study examined sterol release by pouched lamprey as a first step in determining if native New Zealand lamprey could be selecting spawning streams based on the same pheromone mixture as northern hemisphere lampreys.
We examined sterol release by larvae of three species of northern hemisphere lampreys: sea lamprey, American brook lamprey Lampetra appendix, northern brook lamprey Ichthyomyzon fossor, and the southern hemisphere pouched lamprey.
One-liter tank water samples were extracted using a reverse-phase C18 solid phase extraction cartridge. PADS, PSDS, and PS were detected by high performance liquid chromatography and quantified with electrospray ionization mass spectrometry (following Fine et al. 2006). Samples were analyzed by flow injection analysis. Detection was by selected reaction monitoring for PADS and PSDS and selected ion monitoring (SIM) for PS. The fragment ions ([M-H2SO4]–) for PADS and PSDS were analyzed at m/z (mass-to-charge ratio) 605.5 and 491.3, respectively. The pseudomolecular ion of m/z 473.5 ([M-Na]–) was detected for PS.
The three northern hemisphere species released PADS, PSDS and PS. All three standards were detected at low picomolar levels; however, only PS was detected in the tank water of pouched lamprey. Samples were concentrated fivefold further and analyzed by LC-MS, using SIM, to confirm results for pouched lamprey. PS was detected; however, no ions were observed for PADS or PSDS. Spiking samples with PADS and PSDS resulted in detection at the same levels as the standard alone.