DiagnosticSNPs reveal widespread introgressive hybridization between introduced bighead and silver carp in theMississippiRiverBasin

Abstract

Hybridization among conspecifics in native and introduced habitats has important implications for biological invasions in new ecosystems. Bighead (Hypophthalmichthys nobilis) and silver carp (H. molitrix) are genetically isolated and occur in sympatry within their native range. Following their introduction to North America, however, introgressant hybrids have been reported throughout their expanded range within the Mississippi River Basin (MRB). The extent of introgression, both spatially and generationally, is largely unknown. Therefore, we examined mixed-species populations from across the MRB to characterize the extent of interspecific gene flow. We assayed 2798 individuals from nine locations with a suite of species-diagnostic SNPs (57 nuclear and one mitochondrial). Forty-four per cent (n = 1244) of individuals displayed hybrid genotypes. Moreover, the composition of hybrid genotypes varied among locations and represented complex hybrid swarms with multiple generations of gene flow. Introgressive hybrids were identified from all locations, were bidirectional 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 to 2008, with parents and later-generation backcrosses representing the largest proportion of individuals among years. Our mitochondrial SNP (COII), tested on a subset of 730 individuals, revealed a silver carp maternal bias in 13 of 21 (62%) F1 hybrids, in all silver carp backcrosses, and maintained throughout many of the bighead carp backcrosses. The application of this suite of diagnostic markers and the spatial coverage permits a deeper examination of the complexity in hybrid swarms between two invasive, introduced species.

Patterns of hybridization among cutthroat trout and rainbow trout in northern Rocky Mountain streams

“…2015), and the first to contrast patterns of introgression between cutthroat trout and rainbow trout inside and outside the latter's historical range. This suite of diagnostic markers allowed us to detect hybridization at extremely low levels and to evaluate the distribution of alleles within individual fish.…”

Early generation hybrids may drive range expansion of two invasive fishes

“…The Illinois River (U.S.A.), a large ( c. 75,100 km 2 ), impounded tributary to the Mississippi River is invaded by both species of bigheaded carps and their hybrids (Lamer et al, , , ). Bigheaded carp densities in the Illinois River decrease from downstream to the upstream invasion front (Coulter, McNamara, Glover, & Garvey, ).…”

“…Some individuals were not able to be resolved at all loci due to failure to call based on DNA or primer failure. Therefore, assignment of hybrid category was based on the percentage of hybrid genotypes (alleles) as described in Lamer et al (). Additional details are included in the Supplementary Materials.…”

Body condition (Wr) and reproductive potential of bighead and silver carp hybrids: Postzygotic selection in the Mississippi River Basin

“…NewHybrid assignments, defined in Lamer et al, 2015, were used to characterize hybrid categories, that is, the following groups are de- We grouped NewHybrid categories to produce the following variables for W r comparison (F 1 's were used twice, once for each species comparison): bighead carp; silver carp; earlyBH (F 1 and B x BH-firstgeneration bighead carp backcross); lateBH (F 2 , F x BH-fish genotypes containing heterozygous loci and homozygous loci of both species, but predominantly bighead carp, B x 2BH-second-generation bighead carp backcross, B x 3BH-third-generation bighead carp backcross, and B x 4BH-fourth-generation bighead carp backcross); earlySV (F 1 and B x SV-first-generation silver carp backcross); and lateSV (F 2 , F x SV-fish genotypes containing heterozygous loci and homozygous loci of both species, but predominantly silver carp, B x 2SV-second-generation silver carp backcross, B x 3SV-third-generation silver carp backcross, and B x 4SV-fourth-generation silver carp backcross; Lamer et al, 2015).…”

“…Hybrid zones also provide greater resolution for genetic incompatibilities and postzygotic isolation (Maheshwari & Barbash, 2011) and are not constrained by the size or generation time of the organism as are many artificial cross investigations. Lamer et al (2015) described a hybrid swarm between two invasive cyprinid fishes within the Mississippi River Basin (MRB). Comparing ecological characteristics of hybrids to those of parental species is critical to understand the structure of hybrid zones (Stolzenberg et al, 2009).…”