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Title:Bighead and silver carp hybridization in the Mississippi River Basin: prevalence, distribution, and post-zygotic selection
Author(s):Lamer, James T.
Director of Research:Sass, Greg G.; Epifanio, John M.
Doctoral Committee Chair(s):Brawn, Jeffrey D.
Doctoral Committee Member(s):Paige, Ken N.; Suski, Cory D.; Jenkins, Sean E
Department / Program:Natural Res & Env Sci
Discipline:Natural Res & Env Sciences
Degree Granting Institution:University of Illinois at Urbana-Champaign
Subject(s):Asian carp
single nucleotide polymorphisms (SNPs)
Restriction site Associated DNA (RAD) sequencing
bighead carp
silver carp
Mississippi River Basin
Abstract:Hybridization is a pervasive evolutionary phenomenon in plant and animal taxa. Understanding the evolutionary consequences of hybridization is dependent upon the ability to adequately detect genetically admixed individuals, characterize the maternal contribution and structure of hybrid zones, and understand post-zygotic selection acting on recombinant genotypes. Bighead carp (Hypophthalmichthys nobilis) and silver carp (H. molitrix) are U.S. federally injurious species, and although suspected to be reproductively isolated in their native range in eastern Asia, form multi-generational hybrids within the Mississippi River Basin (MRB). My dissertation explores the complexity and structure of bighead and silver carp hybridization in the MRB through molecular marker development, implementing those markers to test for the extent of hybridization, and to assess post-zygotic effects of hybridization. I used restriction-associated DNA sequencing to develop fifty-seven species-diagnostic single nucleotide polymorphisms (SNPs) to distinguish parental bighead and silver carp from their hybrids in the MRB and China. All SNPs were isolated from conserved regions of the genome and thirty-two of fifty-seven were annotated to functional gene loci. During validation, evidence of hybridization in the Amur River, China was first documented. I developed a diagnostic mtDNA SNP and applied the nuclear SNP assay developed earlier to determine the prevalence and degree of introgression of bighead and silver carp introgression at nine locations throughout the MRB. Bighead and silver carp hybrids were present among all MRB locations (45%) and a silver carp maternal bias was present in 13 of 21 (62%) F1 hybrids, all silver carp backcrosses and maintained throughout many bighead carp backcrosses. Bighead and silver carp hybrids contained bighead and silver carp mitochondrial DNA and followed a bimodal distribution consisting primarily of parental or parental-like genotypes and phenotypes. All described hybrid categories were present among individuals from 1999-2008, with parents and late generation backcrosses representing the largest proportion of individuals. I compared body condition and reproductive potential of bighead and silver carp hybrids to test for their post-zygotic success in the MRB. Body condition (Wr) decreased as bighead and silver carp species-specific allele frequencies became more distant from parental allele frequency. Mean Wr was lowest in early generation bighead and silver carp hybrids (F1, F2, first generation backcross) compared with their respective parentals and late generation backcrosses. Despite an initial reduction in hybrid body condition, females displaying stage IV and V gonads (spawning stage gonads containing mature oocytes) and mean gonadosomatic index (GSI) of spawning stage females did not differ between parentals and hybrids throughout the MRB. Bimodal hybrid distribution indicated high densities of parentals and late generation hybrids and low densities of early generation hybrids. My results suggest that hybrids have the same reproductive potential as parents and the low frequency of early generation hybrids in the MRB is likely attributed to reproductive behavioral isolation or poor body condition, rather than genetic incompatibility. Overall, my findings provide a spatial and temporal examination of bighead and silver carp introgression in the MRB and demonstrate the importance of molecular and ecological influences in shaping this hybrid swarm.
Issue Date:2015-04-23
Rights Information:Copyright 2015 James Lamer
Date Available in IDEALS:2015-07-22
Date Deposited:May 2015

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