Mechanisms explaining polymorphism shared between taxa (based on [19
]). The three proposed mechanisms are depicted in alleles’ genealogy: (1) trans-species polymorphism, TSP (incomplete lineage sorting; allelic lineages predate speciation and are passed to descendent species), (2) convergence (allelic lineages evolve similar features independently in separate lineages), and (3) introgression (allelic lineages are horizontally transferred either from recipient species to donor species or in both directions). Each row depicts a gene pool of one generation, each circle/square an allele of specific features. Different colours highlight individual allelic lineages, where interconnecting lines mark antecedent-descendent relationships. Green and purple dashed arrows represent directions of introgression.