Introduced Scotch broom (Cytisus scoparius) invades the genome of native populations in vulnerable heathland habitats

Abstract

Cytisus scoparius is a global invasive species that affects local flora and fauna at the intercontinental level. Its natural distribution spans across Europe, but seeds have also been moved among countries, mixing plants of native and non-native genetic origins. Hybridization between the introduced and native gene pool is likely to threaten both the native gene pool and the local flora. In this study, we address the potential threat of invasive C. scoparius to local gene pools in vulnerable heathlands. We used nuclear single nucleotide polymorphic (SNP) and simple sequence repeat (SSR) markers together with plastid SSR and indel markers to investigate the level and direction of gene flow between invasive and native heathland C. scoparius. Analyses of population structures confirmed the presence of two gene pools: one native and the other invasive. The nuclear genome of the native types was highly introgressed with the invasive genome, and we observed advanced-generation hybrids, suggesting that hybridization has been occurring for several generations. There is asymmetrical gene flow from the invasive to the native gene pool, which can be attributed to higher fecundity in the invasive individuals, measured by the number of flowers and seed pods. Strong spatial genetic structure in plastid markers and weaker structure in nuclear markers suggest that seeds spread over relatively short distances and that gene flow over longer distances is mainly facilitated by pollen dispersal. We further show that the growth habits of heathland plants become more vigorous with increased introgression from the invaders. Implications of the findings are discussed in relation to future management of invading C. scoparius.

Morphometrical characteristics of cryptic invasive and indigenous gene pools of field maple Acer campestre L. in southern Sweden

“…Using several microsatellite markers and sufficient number of samples the data analysis methods are rather straightforward. Such investigations have, for example, been conducted for Cytisus scoparius in Denmark (Rosenmeier et al 2013, Rostgaard Nielsen et al 2016), Phragmites australis in USA (Saltonstall 2002) and Meconopsis cambrica in UK (Valtuena et al 2011). For Cytisus scoparius , Rosenmeier et al (2013) suggest a Mediterranean origin of the alien gene pool, possibly introduced by the garden trade to Denmark.…”

hybriddetective: A workflow and package to facilitate the detection of hybridization using genomic data in r

“…These areas have provided opportunities to glean information to further model, and test hypotheses related to speciation (Abbott et al., ; Barton, ; Dowling & Secor, ) and the maintenance of reproductive barriers (Albrechtová et al., ; Griebel et al., ; Landry, Hartl, & Ranz, ), natural selection (Johnson, Fitzpatrick, & Shaffer, ; Pruvost, Hollinger, & Reyer, ) and genetic recombination. Hybridization can also have conservation, regulatory and legal ramifications related to the genetic structure and integrity of populations (Allendorf et al., ; Benson, Patterson, & Mahoney, ; Boyer, Muhlfeld, & Allendorf, ; Fitzpatrick, Ryan, Johnson, Corush, & Carter, ; Rostgaard Nielsen, Brandes, Dahl Kjaer, & Fjellheim, ), or the introgression of domesticated (Fraser, Minto, Calvert, Eddington, & Hutchings, ; Kidd, Bowman, Lesbarreres, & Schulte‐Hostedde, ; Noren, Dalen, Kvaloy, & Angerbjorn, ) or transgenic (Oke, Westley, Moreau, & Fleming, ; Warwick et al., ) alleles into wild populations.…”