The Role of Introgressive Hybridization in the Evolution of the Gila Robusta Complex (Teleostei: Cyprinidae)

Abstract

The extent and impact of introgressive hybridization was examined in the Gila robusta complex of cyprinid fishes using mitochondrial DNA (mtDNA) sequence variation. Lower Colorado River basin populations of G. robusta, G. elegans, and G. cypha exhibited distinct mtDNAs, with only limited introgression of G. elegans into G. cypha. The impact of hybridization was significant in upper Colorado River basin populations; most upper basin fishes sampled exhibited only G. cypha mtDNA haplotypes, with some individuals exhibiting mtDNA from G. elegans. The complete absence of G. robusta mtDNA, even in populations of morphologically pure G. robusta, indicates extensive introgression that predates human influence. Analysis of the geographic distribution of variation identified two distinctive G. elegans lineages; however, the small number of individuals and localities sampled precluded a comprehensive analysis. Analysis of haplotype and population networks for G. cypha mtDNAs from 15 localities revealed low divergence among haplotypes; however, significant frequency differences among populations within and among drainages were found, largely attributable to samples in the Little Colorado River region. This structure was not associated with G. cypha and G. robusta, as morphotypes from the same location are more similar than conspecific forms in other locations. This indicates that morphological and mtDNA variation are affected by different evolutionary forces in Colorado River Gila and illustrates how both hybridization and local adaptation can play important roles in evolution.

Introgressive hybridization as a promoter of genome reshuffling in natural homoploid fish hybrids (Cyprinidae, Leuciscinae)

“…New data on independent HZs involving AOL Â PDU were endowed, while confirming the occurrence of AOL Â PPO hybrids (Figure 1). Previous works strongly expressed the necessity of using multiple approaches when studying natural hybrids (Gerber et al, 2001;Scribner et al, 2001;Gante et al, 2004;Gromicho and CollaresPereira, 2007;Mavárez and Linares, 2008;Lajbner et al, 2009), especially when second-generation crossing might be occurring, as it seems to be the case (Aboim et al, 2010). The combination of three different identification methods and a vast population screening data set allowed to successfully sort all the selected 13 individuals as admixed, whereas, if using each method independently, some hybrids were probably untraceable (Table 2 and see also Supplementary Material), as observed in Serra R. where hybrids were undetected by genetic markers (Supplementary Figure S1).…”

“…The extent of hybridization Hybridization may have multiple effects at different stages and spatial contexts (Gerber et al, 2001;Costedoat et al, 2007;Broughton et al, 2011;Abbott et al, 2013). The already surveyed HZs of AOL Â PDU seem to behave differently (Aboim et al, 2010) with character displacement happening towards one or the other parental species (Collares- Pereira and Coelho, 1983;Gante et al, 2004;Aboim et al, 2010).…”

“…Genetic novelty is thus generated for selection to operate and for species to persist under newly imposed stressful conditions (environmental and/or genomic) (Dowling and Secor, 1997;Gerber et al, 2001;Seehausen, 2004;Mallet, 2005;Abbott et al, 2013;Mable, 2013). In this case study, ecological barriers between hybrids and parental species might be altered and/or degraded, so that gene flow back to pure species never actually ceases.…”

“…In this case study, ecological barriers between hybrids and parental species might be altered and/or degraded, so that gene flow back to pure species never actually ceases. However, the ultimate consequences of such apparently extensive and recurrent events to these populations and species remain unknown, and the probability of fixation of the resulting rearrangements depends on the demography of the hybrid swarms (Gerber et al, 2001;Seehausen, 2004;Costedoat et al, 2007;Broughton et al, 2011;Abbott et al, 2013). Usually disregarded (reviewed in Costedoat et al, 2007), these interactions might ultimately result in speciation or extinction faster than expected.…”

“…Natural introgression is commonly found among freshwater fishes, particularly in Cyprinidae (Scribner et al, 2001), where several cases have been comprehensively evaluated (Gerber et al, 2001;Costedoat et al, 2007;Aboim et al, 2010;Broughton et al, 2011). The different outcomes witnessed (reviewed in Abbott et al, 2013) reinforce the opportunity of using cyprinid fish to search for genomic signatures of hybridization.…”