Genomic consequences of residual recombination in a hybrid apomictic hickory complex

Abstract

Abstract Apomixis, a form of clonal asexual reproduction in plants, is often accompanied by residual sex, yet its genomic consequences remain poorly understood. Here, we assembled a haplotype-resolved genome of Carya hunanensis and analyzed whole-genome resequencing data from 195 adults and 180 mature embryos across four hickory species, representing a hybrid apomictic complex with both sexual and asexual lineages. We find apomictic species exhibited genomic signatures of clonality, notably loss of heterozygosity (LOH), suggesting recombination induced by rare sexual events. Despite harboring more heterozygous deleterious variants, apomictic adults showed lower realized mutation loads, particularly in hybrid C. hunanensis , whose apomictic haplotype disproportionately carried deleterious alleles. Remarkably, rare embryos from apomicts underwent recombination-mediated LOH, exposing deleterious mutations to selection. These findings reveal the genetic cost of residual sex, while also indicating its role in generating novel genotypes, supported by close relatedness among adult apomicts. Our study provides a unique genomic snapshot of how residual sex and recombination mitigate mutation accumulation and potentially facilitate clonal maintenance in natural asexual systems.