Evolution of genome size in Arachis (Fabaceae): a history linked to chromosomal dynamics and dispersal across the South American seasonally dry diagonal

Abstract The South American genus Arachis provides a suitable model to study genome size (GS) evolution due to its genomic, karyotypic, and ecological diversity. This study utilizes flow cytometry data, along with phylogenetic, statistical, and biogeographic approaches, to investigate the patterns and processes of GS variation in Arachis. Covering approximately 70% of the species across the nine taxonomic sections of the genus, the study reveals a 4.3-fold variation in 1Cx values (0.46–1.98 pg), with an ancestral estimate of 0.89 pg. Phylogenetic analyses suggest an origin of the genus in the Caatinga–Cerrado transition zone, followed by diversification and GS shifts along the South American seasonally dry diagonal. Genome size exhibited a strong phylogenetic signal, with clade-specific expansions and reductions associated with genome type, karyotype characteristics, and environmental factors. General trends indicate GS reductions under dry, seasonal environments and expansions in more humid and stable habitats, although exceptions exist. While phylogenetic inertia emerged as the primary structuring force, the interaction between genome architecture, chromosome number, and ecological conditions differentially influenced GS among lineages. These findings underscore the complex interplay among phylogenetic constraints, genome organization, and ecological adaptation in shaping GS evolution in Arachis.