Detecting Hybridization in Hawaiian Cyrtandra Using Genome-Wide Data

Abstract

Cyrtandra (Gesneriaceae) is a genus of flowering plants with over 800 species distributed throughout Southeast Asia and the Pacific Islands. On the Hawaiian Islands, 60 named species and over 62 putative hybrids exist, most of which are identified on the basis of morphology. Despite many previous studies on the Hawaiian lineage of Cyrtandra, questions regarding the reconciliation of morphology and genetics remain, many of which can be attributed to the relatively young age and evidence of hybridization between species. We utilized targeted enrichment, high-throughput sequencing, and modern phylogenomics tools to test 33 Hawaiian Cyrtandra samples (including 21 species, five putative hybrids, and two outgroups) for species relationships and hybridization in the presence of incomplete lineage sorting (ILS). Both concatenated and species-tree methods were used to reconstruct species relationships, and network analyses were conducted to test for hybridization. Based on prior studies of Cyrtandra and other Hawaiian lineages, we expected to see both a classic stepping-stone model, where species relationships group by island from oldest to youngest, and species relationships grouping by morphology. Additionally, we expected to see high levels of ILS and putative hybrids intermediate to their parent species. Phylogenies reconstructed from the concatenated and species-tree methods were highly incongruent, most likely due to high levels of incomplete lineage sorting. Network analyses inferred gene flow within this lineage, but not always between taxa that we expected. Of the five putative hybrids tested, only one was inferred to incorporate genetic material from both putative parents. The genomic methods utilized here have allowed us to reconstruct better resolved hypotheses and to test for hybridization in the presence of incomplete lineage sorting. Wider sampling within this lineage will allow us to better understand species relationships and gene flow within Hawaiian Cyrtandra in future studies.