Hosta

Interspecific hybridization is the process where closely related [[species]] mate and produce offspring with [[Genetic admixture|admixed genomes]]. The genomic revolution has shown that [[Hybridisation (biology)|hybridization]] is common, and that it may represent an important source of novel [[Genetic variation|variation]]. Although most interspecific hybrids are [[Hybrid sterility|sterile]] or less fit than their parents, some may survive and reproduce, enabling the [[Horizontal gene transfer|transfer]] of adaptive variants across the species boundary, and even result in the formation of novel [[Speciation|evolutionary lineages]]. There are two main variants of hybrid species genomes: [[allopolyploid]], which have one full [[Ploidy|chromosome set]] from each parent species, and homoploid, which are a [[Mosaic (genetics)|mosaic]] of the parent species genomes with no increase in chromosome number. The establishment of hybrid species requires the development of [[reproductive isolation]] against parental species. Allopolyploid species often have strong intrinsic reproductive barriers due to differences in chromosome number, and homoploid hybrids can become reproductively isolated from the parent species through assortment of genetic incompatibilities. However, both types of hybrids can become further reproductively isolated, gaining extrinsic isolation barriers, by exploiting novel [[Ecological niche|ecological niches]], relative to their parents. Hybrids represent the merging of divergent genomes and thus face problems arising from incompatible combinations of genes. Thus hybrid genomes are highly dynamic and undergo rapid evolutionary change, including genome stabilization in which selection against incompatible combinations results in [[Fixation (population genetics)|fixation]] of compatible ancestry block combinations within the hybrid species. The potential for rapid [[adapation]] or [[speciation]] makes hybrid genomes a particularly exciting subject of in evolutionary biology. Here we summarize how [[Introgression|introgressed alleles]] or hybrid species can establish and how the resulting hybrid genomes evolve.