Genomic structural variants constrain and facilitate adaptation in natural populations of Theobroma cacao, the Chocolate Tree

Genomic structural variants (SVs) can play important roles in adaptation and speciation. Yet, the overall fitness effects of SVs are poorly understood, partly because accurate population-level identification of SVs requires multiple high-quality genome assemblies. Here, we use 31 chromosome-scale, haplotype-resolved genome assemblies of Theobroma cacao – an outcrossing, long-lived tree species that is the source of chocolate – to investigate the fitness consequences of SVs in natural populations. Among the 31 accessions, we find over 160 thousand SVs, which together cover eight times more of the genome than SNPs and short indels (125 Mb vs. 15 Mb). Our results indicate that a vast majority of these SVs are deleterious: they segregate at low frequencies and are depleted from functional regions of the genome. We show that SVs influence gene expression, which likely impairs gene function and contributes to the detrimental effects of SVs. We also provide empirical support for a theoretical ...