Phylogenetic Relationships of Extant Esocid Species (Teleostei: Salmoniformes) Based on Morphological and Molecular Characters
The phylogenetic relationships of extant species of Esox were investigated using both morphological and molecular data. The complete mtDNA cytochrome b gene (cytb) and the second intron of the RAG1 gene were sequenced from multiple specimens of each species and analyzed using maximum parsimony and maximum likelihood. The resulting cladograms were compared with each other and to the morphological cladogram for congruence. Data from all three sources strongly support the monophyly of the genus, and the monophyly of the subgenera Esox (i.e., pikes) and Kenoza (i.e., pickerels). Our data support the sister-group relationship between Esox reicherti and Esox lucius (the Amur and Northern Pike, respectively). Incongruent results between the morphological and RAG1 data and the cytb data, with respect to pickerel interrelationships, suggest hybridization and introgression among pickerel species. Additional research is necessary to explore these results further. This study represents the first study to integrate both morphological and molecular data into a phylogenetic analysis of Esox. It aims to provide a better understanding of esocid evolution and lay the foundation for the interpretation of fossil material assigned to Esox. It also provides preliminary genetic evidence of hybridization among the pickerels.Abstract
Morphological cladogram (64 steps, CI = 0.92). Bootstrap values are given at each node. Number in brackets indicates character state. Characters are discussed in the text. The nodes are supported by the following synapomorphies: Esox: 6(1), 9(1), 10(1), 11(1), 15(1), 17 (1), 29 (1), 33(1); subgenus Esox: 4(1), 13(1), 14(1), 22(2), 23(1), 25(2), 27(2), 30(2); Esox lucius + Esox reicherti: 2(2), 16(2), 20(1), 21(2), 35(2), 36(2); Kenoza: 2(1), 4(1), 16(1), 21(1), 22(1), 25(1), 26(1), 27(1), 28(1), 30(1), 34(1), 36(3); Esox americanus: 8(1), 18(1), 31(1), 32(1)
Illustrations of anterior vertebral region in (A) Esox reicherti (SL = 135 mm, CU 64229), (B) Umbra limi (SL = 74 mm, FMNH 99738), (C) Novumbra hubbsi (composite drawing from UMMZ 187427, SL = 48 mm, and UAMZ 3714, Wilson and Veilleux, 1982). sn, supraneural, v1–v4, vertebra 1 through 4. Anterior directed to the left
Caudal fin skeleton of (A) Esox masquinongy (SL = 133 mm, CU 9118), (B) Esox americanus vermiculatus (SL = 128 mm, FMNH 7187). hy1, hypural 1, pu1, preural centrum 1; pu2, preural centrum 2; u1, ural centrum 1. Epurals drawn in black. Anterior directed to left
(A) MP bootstrap consensus tree based on cytochrome b data. (B) MP bootstrap consensus tree based on based on RAG 1 intron 2 sequence data. Bootstrap and decay values, in that order, are given at each node. Catalog numbers followed by geographic localities are given for each specimen
Contributor Notes
(TG, HL) Department of Biology, Loyola University Chicago, 6525 North Sheridan Road, Chicago, Illinois, 60626; and (JAL) Department of Zoology, Division of Fishes, Field Museum of Natural History, 1400 South Lake Shore Drive, Chicago, Illinois 60605. E-mail: (TG) tgrande@luc.edu; (HL) hlaten@luc.edu; and (JAL) alopez@fmnh.org Send reprint requests to TG.