Sassone, A. B. | bioRxiv Science

bioRxiv2026

Genomic instability within a sympatric complex of South American garlics (Nothoscordum spp., Amaryllidaceae)

Background and AimsThe evolution of reproductive isolation between previously interbreeding populations is a fundamental driver of plant speciation. Within Amaryllidaceae, Nothoscordum represents an evolutionarily complex genus, characterized by an unusually high incidence of chromosomal rearrangements. During fieldwork, Nothoscordum montevidense and Nothoscordum bonariense were found growing in sympatry, along with individuals exhibiting intermediate morphological traits, suggesting a putative hybrid origin. To test this hypothesis, we employed an integrative approach to characterize the morphologically intermediate specimens and the two sympatric populations. Materials and methodsTo characterize the putative hybrids we have combined morphological, cytogenetic analyses (chromosome counts, CMA/DAPI banding, and FISH) and flow cytometry-based genome size estimation. Phylogenetic relationships and genomic structure were also investigated through Genotyping-by-Sequencing (GBS), complete chloroplast genome assembly, and comparative repetitive DNA analysis. We also performed species distribution modeling and phenological analyses of the putative parental species. Key ResultsMultiple lines of evidence confirm the hybrid origin of the studied plants. Cytogenetic analyses revealed specimens with 2n = 21 (1C {approx} 33 pg = 32.274 Mbp) and 2n = 25 (1C {approx} 37 pg = 36.186 Mbp), accompanied by meiotic irregularities consistent with interspecific hybridization. Chloroplast genome phylogeny identified N. montevidense (2n = 16, 1C {approx} 25 pg) as the maternal lineage, while GBS data confirmed N. bonariense (2n = 26, 1C {approx} 41 pg) as the paternal contributor and revealed evidence of subsequent backcrossing. Comparative analysis of repetitive DNA showed reduced 35S rDNA diversity in the hybrid, indicative of post-hybridization genomic restructuring. Despite the observed genomic complexity, no clear morphological differentiation was detected among hybrid individuals. Phenological analyses and species distribution models demonstrated broad overlap between parental species. ConclusionsOur findings highlight the role of hybridization in shaping genome architecture in cytogenetically labile plant lineages. Furthermore, our results underscore that morphological similarity can mask profound genomic complexity, reinforcing the value of integrative approaches to understand genera characterized by reticulate evolution and genomic instability.

plant biology↗

bioRxiv2025

An area-resolved phylogeography of bulbous barley (Hordeum bulbosum; Poaceae)

Hordeum bulbosum, the closest relative of barley (H. vulgare), is an important source of resistance genes for cereals in the Triticeae. This perennial and mainly outcrossing species occurs with two cytotypes: diploids thrive in the western and central parts of the Mediterranean, while autotetraploids extend from Greece mainly eastwards to western Asia. To elucidate H. bulbosums origin, colonization patterns, population relationships, and distinctions between the two cytotypes, we determined ploidy and performed genotyping-by-sequencing analyses on 314 individuals from across the species distribution range. Our results revealed two distinct lineages within diploid H. bulbosum: individuals from Libya vs. all other diploids. Southeastern Italian populations were the origin for the species expansion eastward into Albania/Greece and westward into mainland Italy, Sicily/Sardinia, Tunisia, and Spain. The tetraploid cytotype originated early in the evolution of the species, thus retaining alleles found in extant Libyan diploids. Tetraploids underwent local introgression from diploids in Greece, where also a secondary origin of tetraploids was detected. We found that ecoclimatic conditions alone cannot account for the clear geographic separation of the cytotypes, as habitats across much of the central Mediterranean would be suitable for both. We conclude that minority cytotype exclusion is the most plausible explanation for the distinct distribution patterns observed. While both cytotypes are morphologically indistinguishable, diploid populations typically occur in scattered stands within their range, while tetraploids tend to form larger, often contiguous populations.

evolutionary biology↗