A typical lamprey mating involves a female attaching to a stone near thc upstream end of the nest A male then attaches to the back of the female's head and wraps his body around hers. Both vibrate vigorously as gametes are released. In some cases, a second male, the satellite, circles about the urogenital area of a mating pair at the moment of gamete release in what has been interpreted as an attempt to gain fertilizations. Analysis of videotapes of' spawning Larnpetra appendix in the North Branch Whitewater River in Minnesota (Mississippi River drainage) and Jambo Creek in eastern Wisconsin (Great Lakes drainage) revealed that at both sites at least 50% of matings in nests with at least three lampreys included a satellite male. Nest associations involving more that onc lamprey species in the same nest are known to involve many combinations of species, but especially relevant are cases involving closely related parasitic and nonparasitic species. For example, we have observed nonparasitic Ichthyomyzon gugei and parasit~c Ichthyomyzon castarzeus spawning in the same nests and have observed a male I. xugei attached to a female I. castuneus. Conventional wisdom IS that the size difference between parasitic and nonparasitic lampreys prevents successful mating, but a combination of interspecific nest association and satellite male behavior could conceivably permit gene flow between paired nonparasitic and parasitic Corms. This combination is displayed by at least some Lampetra species.
INTRODUCTIONEach small nonparasitic lamprey species is thought to have evolved from a larger parasitic ancestor. In those cases in which the parasitic lineages are still extant, the conventional view has been that the related parasitic and nonparasitic forms are reproductively isolated, and they are referred to as paired species. If more than one nonparasitic species has been derived from the same parasitic species, the former arc sometimes referred to as satellites of the latter. The conventional view, however, has not gone unchallenged. Evidence for gene flow between paired species has mounted (Schre~ber and Engelhorn 1998). and some recent studies have failed to find genetic differences between paired forms Withler 1986, Neave et al. 2007). Moreover, the nonparasitic American brook lamprey (Lnmpefm appendix) apparently retains within its genome the ability to produce a larger parasitic form (Cochran 2008). It is important to examine lamprey spawning behavior to reveal potential mechanisms for recombination of genetic information from parasitic and nonparasilic forms.Lamprey spawning behavior and ecology were summarized by Manion and