Rapid movement and instability of an invasive hybrid swarm

Abstract

Unstable hybrid swarms that arise following the introduction of non‐native species can overwhelm native congeners, yet the stability of invasive hybrid swarms has not been well documented over time. Here, we examine genetic variation and clinal stability across a recently formed hybrid swarm involving native blacktail shiner (Cyprinella venusta) and non‐native red shiner (C. lutrensis) in the Upper Coosa River basin, which is widely considered to be a global hot spot of aquatic biodiversity. Examination of phenotypic, multilocus genotypic, and mitochondrial haplotype variability between 2005 and 2011 revealed that the proportion of hybrids has increased over time, with more than a third of all sampled individuals exhibiting admixture in the final year of sampling. Comparisons of clines over time indicated that the hybrid swarm has been rapidly progressing upstream, but at a declining and slower pace than rates estimated from historical collection records. Clinal comparisons also showed that the hybrid swarm has been expanding and contracting over time. Additionally, we documented the presence of red shiner and hybrids farther downstream than prior studies have detected, which suggests that congeners in the Coosa River basin, including all remaining populations of the threatened blue shiner (Cyprinella caerulea), are at greater risk than previously thought.

Genetic admixture accelerates invasion via provisioning rapid adaptive evolution

“…Interbreeding multiple sources are also frequent (Facon et al, 2005;Keller & Taylor, 2010;Nelson, Wallberg, Simões, Lawson, & Webster, 2017;Rius & Darling, 2014;Yang et al, 2017), and even the "hybrid swarm" we observe in S. alterniflora is not unique and has been reported for several invasive species (Boyer, Muhlfeld, & Allendorf, 2008;Gammon, Grimsby, Tsirelson, & Kesseli, 2007;Glotzbecker, Walters, & Blum, 2016;Roy et al, 2015). Our study thus suggests that it is crucial to consider the long-term impact of admixture while evaluating the risk of multiple introductions and predicting the velocity of geographic scale expansion.…”

Molecular and ecological signatures of an expanding hybrid zone

“…It is recognized that hybrid zones vary greatly in their structures depending on the degree of the molecular and ecological differentiation between the introgressing species and affect associated levels of dispersal (Buggs, ; Glotzbecker, Walters, & Blum, ). Our molecular results suggest that introgressive hybridization between I. elegans and I. graellsii is chronic, and our niche modeling indicates that this introgression is enabling the niche shift of introgressed I. elegans into the Iberian Peninsula.…”

“…Adaptation to local environments can be achieved by selection on standing genetic variation (i.e., variation present in the species at the time of the environmental change) or de novo mutations. Another less explored path for species to acquire beneficial alleles is through introgression via interspecific hybridization (Arnold, ; Glotzbecker et al., ; Rieseberg & Wendel, ; Whitney, Randell, & Rieseberg, ). The outcomes of such introgressive hybridization are manifold and include the fusion of species, genetic swamping of one species by another, elicit reinforcement of reproductive isolation between incompletely isolated species, transfer of genetic material between species, potentially facilitating their adaptive evolution, and ultimately, the origin of new species (Seehausen, ; Zemanova, Knop, & Heckel, ).…”

Rapid, complete reproductive isolation in two closely relatedZosteropsWhite‐eye bird species despite broadly overlapping ranges*

“…; Glotzbecker et al. ), which can sometimes cause the rarer species to go extinct (see Rhymer and Simberloff ). Alternatively, with secondary isolation of a hybrid population, a novel hybrid taxon can be created (e.g., Robertson et al.…”

“…to a collapse back into a hybrid swarm (e.g., Katch et al 2011;Glotzbecker et al 2016), which can sometimes cause the rarer species to go extinct (see Rhymer and Simberloff 1996). Alternatively, with secondary isolation of a hybrid population, a novel hybrid taxon can be created (e.g., Robertson et al 2004;Brelsford et al 2011;Hermansen et al 2014;Lavretsky et al 2015;Barrera-Guzmán et al 2017).…”