Speciation in Eurasian Lampreys

       In lamprey speciation process, a fluvial-nonparasitic species is thought to be derived from ancestry anadromous-parasitic one in direct or via intermediate life-history form. In the present study, the population structure and multitemporal gene flow among Arctic lamprey Lethenteron camtschaticum populations, including polymorphic life-history forms; anadromous-parasitic and fluvial-nonparasitic, were analyzed to determine the speciation process in lampreys. Abundant gene flow was revealed in multitemporal scales, resulting in non-significant population structure, among anadromous-parasitic populations. On the other hand, the genetic independence of the landlocked fluvial-nonparasitic populations in the upper region of dams was detected using microsatellite loci analysis. The temporal heterogeneity of gene flow was also elucidated; little contemporary gene flow but significant gene flow was noted over the long term between the landlocked fluvial-nonparasitic and anadromous-parasitic populations. The estimated divergence time of isolation of the landlocked populations from the ancestral anadromous-parasitic population was mostly consistent with the construction times of the initial dams. These data indicate that the landlocked populations should have very recently been established, and subsequent accumulation of divergence and development of reproductive isolation are predicted. The present landlocked fluvial-nonparasitic populations should be analogous to the founder populations in terms of lamprey speciation. The present data also strongly support the hypotheses of multitemporal and multispatial speciation in lampreys.