Department of Ecology and Evolutionary Biology, Tulane University, New Orleans, LA 70118, USA Environmental Sciences Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831, USA Department of Ecology & Evolutionary Biology, University of Tennessee, Knoxville, TN 37996, USA
Biology Department, Woods Hole Oceanographic Institution, Woods Hole, MA 02543, USA School of Aquatic and Fishery Sciences, University of Washington, Seattle, WA 98103, USA
Brian S. Harmon
School of Aquatic and Fishery Sciences, University of Washington, Seattle, WA 98103, USA
Michael J. Blum
Department of Ecology and Evolutionary Biology, Tulane University, New Orleans, LA 70118, USA Department of Ecology & Evolutionary Biology, University of Tennessee, Knoxville, TN 37996, USA
Sculpins (coastrange and slimy) and sticklebacks (ninespine and threespine) are widely distributed fishes cohabiting 2 south-central Alaskan lakes (Aleknagik and Iliamna), and all these species are parasitized by cryptic diphyllobothriidean cestodes in the genus Schistocephalus. The goal of this investigation was to test for host-specific parasitic relationships between sculpins and sticklebacks based upon morphological traits (segment counts) and sequence variation across the NADH1 gene. A total of 446 plerocercoids was examined. Large, significant differences in mean segment counts were found between cestodes in sculpin (mean = 112; standard deviation [s.d.] = 15) and stickleback (mean = 86; s.d. = 9) hosts within and between lakes. Nucleotide sequence divergence between parasites from sculpin and stickleback hosts was 20.5%, and Bayesian phylogenetic analysis recovered 2 well-supported clades of cestodes reflecting intermediate host family (i.e. sculpin, Cottidae vs stickleback, Gasterosteidae). Our findings point to the presence of a distinct lineage of cryptic Schistocephalus in sculpins from Aleknagik and Iliamna lakes that warrants further investigation to determine appropriate evolutionary and taxonomic recognition.
