Disruptive selection and the genetic basis for repeated evolution of nonparasitism in lampreys

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My proposed research will use molecular genetic and developmental techniques to investigate the mechanisms responsible for creating and maintaining dramatically different feeding types in lamprey species pairs.  Lampreys are ancient eel-like vertebrates; they are called "jawless fishes" since they possess a toothed suctorial disc rather than hinged jaws.  All lampreys spend the first years of life as blind larvae in the silt bottoms of rivers and streams and feed on microscopic organisms.  Following metamorphosis, they may feed parasitically on fish or they may reproduce and die without ever feeding as adults (i.e. are nonparasitic).  Approximately half of the 38 described species worldwide are nonparasitic, and it is believed that these nonparasitic species evolved from parasitic ancestors.  This has happened independently within many different lamprey groups, and most lamprey species can be grouped into pairs in which the larvae are indistinguishable but the two feeding types diverge at metamorphosis.  Paired parasitic and nonparasitic lampreys have traditionally been considered distinct species, but recent research indicates that they may be different feeding types of a single species.  However, if both types are produced by a common gene pool, why are lampreys intermediate to the two feeding types not observed in nature?  This is the question that my research will attempt to answer.  For example, using field surveys and DNA parentage analysis, I will determine if there are ecological mechanisms that prevent interbreeding (e.g., do the two different types spawn at different times or places? do size differences between the types prevent them from interbreeding?).  There may also be genetic mechanisms (e.g., selection against "unfit" hybrids) that maintain two distinct feeding types even with significant gene flow.  There are several other fish species with similarly divergent feeding types (e.g., "dwarf" and normal whitefishes), and lampreys provide another good model system to investigate processes that permit this independent, repeated, and rapid morphological diversification.  Research into these species pairs will help answer an important fundamental evolutionary question: how are species formed and maintained?