Do syngameons exist in tropical trees? Challenges to determine their existence and estimate their frequency.

Syngameons consist of a group of species interconnected by repeated cycles of gene flow, where interbreeding can lead to fertile hybrid offspring capable of backcrossing with the parental species, facilitating the introgression of genomic regions among species. These networks have been known for over a century in plants, although mainly documented in temperate tree species. Emerging evidence from phylogenomic studies strongly suggests the existence of syngameons in tropical rainforest trees, challenging the traditional view that tree species hybridization is rare in these tropical ecosystems. Several biological characteristics of tropical trees, such as high number of co-occurring species in tropical ecosystems, generalist pollination strategies and predominantly outcrossing, could favour the evolution of syngameons. Here, we review the most recent approaches to distinguish the signal of hybridization from other evolutionary processes. We emphasize the need for robust methodologies to detect hybridization and introgression, advocating for an integrative framework combining phylogenomic, phylogeographic and population genomics analyses that will allow us to confirm the presence of syngameons in tropical trees. We argue that syngameons in tropical ecosystems may play a significant role in the distribution and maintenance of species diversity and discuss that a more integral approach of conservation is required to safeguard the integrity of these networks.