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An investigation of a potential morphotype trigger in two Ichthyomyzon species
Fraser Neave1, Margaret Docker2, Todd Steeves1, Tom Pratt3, Robert McLaughlin4
1 Sea Lamprey Control Centre, Sault Ste. Marie, ON
2 Department of Biological Sciences, University of Manitoba, Winnipeg, MB
3 Great Lakes Laboratory for Fisheries and Aquatic Science, Sault Ste. Marie, ON
4Department of Integrative Biology, University of Guelph, Guelph, ON
In most lamprey genera, “paired” species exist in which the larvae are morphologically indistinguishable but adult feeding type differs. The lack of diagnostic genetic differences in many pairs has led to suggestions that they constitute a single gene pool with environmentally-influenced feeding types. To investigate whether stream characteristics are correlated with feeding type in the parasitic silver lamprey Ichthyomyzon unicuspis and non-parasitic northern brook lamprey I. fossor, eight variables (pH, alkalinity, conductivity, discharge, total dissolved solids, and density of larval sea lamprey Petromyzon marinus, Ichthyomyzon spp., and all species) were compared among 8 streams with only silver lamprey, 10 with only northern brook lamprey, and 13 with both species using Classification Tree Analysis. The best misclassification rate (23%) was achieved using both sea lamprey and Ichthyomyzon larval density; silver lamprey tended to inhabit streams with higher sea lamprey larval density and northern brook lamprey tended to inhabit streams with higher Ichthyomyzon larval density. We then tested for plasticity experimentally. In a lab-based common garden experiment, there was no larval survival beyond 3 months. In an in situ transplant experiment, >12,000 larvae were transplanted into 10 stream reaches in the Lake Huron basin; post-metamorphic individuals of the alternate feeding type were recaptured 4–5 years later in two streams, but genetic parentage analysis indicated that they were not offspring of the original known-phenotype parents. Thus, phenotypic plasticity was not demonstrated. Development of effective rearing procedures for Ichthyomyzon lampreys is essential for any future similar studies.