Unravelling the Web of Life: Incomplete Lineage Sorting and Hybridisation as Primary Mechanisms Over Polyploidisation in the Evolutionary Dynamics of Pear Species.

The traditional Tree of Life (ToL) model is increasingly challenged by the Web of Life (WoL) paradigm, which offers a more accurate depiction of organismal phylogeny, particularly in light of the incongruences often observed between gene and species trees. However, the absence of a standardised method for resolving evolutionary mechanisms - such as Incomplete Lineage Sorting (ILS), hybridisation, introgression, polyploidisation, and whole-genome duplication - remains a significant obstacle in defining the WoL. Characterised by extensive hybridisation events, the pear genus Pyrus provides an ideal model for exploring these complexities. In this study, we present a Step-by-Step Exclusion (SSE) approach for investigating the evolutionary pathways of Pyrus, based on Whole Genome Sequencing (WGS) and Deep Genome Skimming (DGS) data, and our results demonstrate that: (1) ILS, rather than polyploidisation, plays a dominant role in the origination of Pyrus; (2) the two subgenera of Pyrus followed independent evolutionary paths, influenced by geographical barriers formed through the uplift of the Tibetan Plateau and increased aridity in Central Asia; (3) both ILS and hybridisation have driven the diversification of subg. Pashia, while hybridisation alone has shaped the reticulate evolution of subg. Pyrus; (4) the establishment of the Silk Road during the Han Dynasty facilitated genetic exchange between subg. Pyrus and subg. Pashia. The SSE approach offers a versatile framework for studying the evolutionary mechanisms underlying the WoL paradigm.