Cytogenomic signatures of hybridisation in the genus Carpobrotus reveal biased parental dominance
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Hybridisation is frequently associated with plant invasions; however, its consequences for genome organisation and chromosome evolution remain poorly understood in invasive species. We investigated the extent of hybridisation in the invasive Carpobrotus edulis—acinaciformis hybrid complex and determined the cytogenomic contribution of parental species in hybrid accessions.
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We combined whole-genome sequencing, population genomic analyses, genome size estimation, repeatome characterisation, chromosome counting and fluorescence in situ hybridisation to compare parental species and hybrid accessions from South Africa and the Mediterranean Basin.
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Population genomic analyses revealed widespread hybridisation and introgression, with most invasive accessions showing admixed ancestries. Patterson’s D-statistic supported asymmetric allele sharing towards C. edulis . Hybrid accessions displayed genome sizes indistinguishable from C. edulis , whereas C. acinaciformis possessed significantly larger genomes. Repeatome analyses identified marked differences in repetitive DNA composition, particularly in satellite DNA abundance and chromosomal distribution. A newly identified satellite repeat (CarpoSat) showed contrasting chromosomal patterns between parental species, whereas hybrids resembled C. edulis’ satellite pattern.
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Our results demonstrate that Carpobrotus hybrid accessions are a swarm of later-generation hybrids and backcrosses showing a strong bias towards C. edulis , indicating asymmetric introgression. These findings highlight the value of integrating cytogenetic and genomic approaches to understand genome evolution in invasive hybrid complexes.
