Early generation hybrids may drive range expansion of two invasive fishes

Abstract

Introgressive hybridisation between two invasive species has the potential to contribute to their invasion success and provide genetic resiliency to rapidly adapt to new environments. Additionally, differences in the behaviour of hybrids may lead to deleterious ecosystem effects that compound any negative impacts of the invading parental species. Invasive silver carp (Hypophthalmichthys molitrix) and bighead carp (Hypophthalmichthys nobilis) provide an opportunity to evaluate how hybridisation may influence the behaviour, dispersal, and spread of an invasive species introgressive complex. In order to investigate the role hybrids may have in the invasion ecology of bigheaded carps, we examined the distribution, movements, and environmental cues for movement of two invasive fishes and their hybrids in the Illinois River (U.S.A.). Early generation hybrids (e.g. F1,F2, and first‐generation backcross individuals) composed a greater proportion of the population at the invasion front where abundances of bigheaded carp were low. A greater proportion of early hybrids passed through dams upstream towards the invasion front than did other hybrids and parental species. The movements and environmental cues for movement of late‐generation backcrosses (more genetically similar to parental genotype) were not different from the parental species with which they shared the most alleles. Although the direction of the relationship between movement and environment was sometimes different for the parental species and associated advanced generation hybrids, these results indicate that management for parental species will also affect most hybrids. Although early generation hybrids are rare, our results indicate they may disperse towards low‐density population zones (i.e. invasion fronts) or are produced at greater frequency in low‐density areas. These rare hybrids have the potential to produce a variety of unique genetic combinations that could result in more rapid adaptation of a non‐native population to their invaded range potentially facilitating the establishment of invasive species.

Evolution and genetics of bighead and silver carps: Native population conservation versus invasive species control

“…Early generation hybrids are suspected to play a role in driving range expansion of two invasive fishes (Coulter et al, 2019). A long-term demographic survey of pure and hybrid bigheaded carps in conjunction with genomic studies may unveil the mechanisms and evolutionary consequences of hybridization and introgression in bigheaded carps.…”

Nesting microhabitat use and hybridisation of endemic Bartram's Bass in Savannah River tributaries

“…Moreover, while our focus on spawning and young‐of‐year individuals provides evidence of proximate spawning, an analysis of multiple age classes will provide a more robust understanding of the full scope of introgression with nonnative congeners. Further work should also focus on determining the role of dispersal of introgressed individuals for transporting nonnative alleles up the tributaries (Coulter et al., 2020). Studies in their native range have shown that Alabama Bass can make considerable upstream movements (Earley, 2012), and movement of Bartram's Bass remains understudied.…”

Spatial variation in invasive silver carp population ecology throughout the upper Mississippi River basin*

“…Coulter et al. (2020) reported that smaller silver carp moved more frequently over greater distances in areas where carp are established, suggesting that smaller mature carp, and thereby younger fish, frequently move upstream, but size‐specific movement patterns may also be river‐specific (see Prechtel et al., 2018). Further, latitude and the time since first detection are moderately correlated since the silver carp invasion progressed gradually upstream, and some relationships can therefore be confounded.…”

“…As previously discussed, intra-and interspecific competition and river characteristics likely lead to spatial variation in silver carp populations; however, the negative relationship between silver carp maximum age and latitude could also be explained by movement patterns. Coulter et al (2020) reported that smaller silver carp moved more frequently over greater distances in areas where carp are established, suggesting that smaller mature carp, and thereby younger fish, frequently move upstream, but size-specific movement patterns may also be river-specific (see Prechtel et al, 2018). Further, latitude and the time since first detection are moderately correlated since the silver carp invasion progressed gradually upstream, and some relationships can therefore be confounded.…”