Transpacific coalescent pathways of coconut rhinoceros beetle biotypes: Resistance to biological control catalyses resurgence of an old pest

Authors: REIL, JONATHAN - University Of Hawaii; DOORENWEERD, CAMIEL - University Of Hawaii; SAN JOSE, MICHAEL - University Of Hawaii; Sim, Sheina; Geib, Scott; RUBINOFF, DANIEL - University Of Hawaii

Submitted to: Molecular Ecology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/7/2018
Publication Date: 9/25/2018
Citation: Reil, J.B., Doorenweerd, C., San Jose, M., Sim, S.B., Geib, S.M., Rubinoff, D.Z. 2018. Transpacific coalescent pathways of coconut rhinoceros beetle biotypes: Resistance to biological control catalyses resurgence of an old pest. Molecular Ecology. 27:4459-4474. https://doi.org/10.1111/mec.14879.
DOI: https://doi.org/10.1111/mec.14879

Interpretive Summary: The Coconut Rhinoceros Beetle is a destructive invasive pest of palms. It was recently found on the island of Oahu, but the origin of this recent introduction is unknown. To identify the invasion pattern of the Coconut Rhinoceros Beetle, a population genomic study was performed on beetles collected from its native and introduced range. Genomic analysis revealed the beetles from the introduced range had lower genetic variation as expected in populations subject to severe bottlenecking. Though lack of genetic variation was also seen in one of the native populations, this is potentially explained by a lack of sampling. Phylogenetic analysis revealed the newly detected beetles in Hawaii were most closely related to beetles collected in Guam, but the genetic distance between the different populations in the introduced range suggests that invasion events are a rare occurrence.

Technical Abstract: The Coconut Rhinoceros Beetle (Oryctes rhinoceros), is a serious plant pest that began invading Pacific islands in the early 20th century through human-mediated dispersal. First detected on Samoa in 1909, the beetle has since spread across the Pacific, reaching Hawaii in 2013 and Mexico in 2017. We performed a population genomic analysis on 172 O.rhinoceros collected from the beetles’ native and invasive range. Using a de novo ddRAD approach to DNA sequencing, we generated multiple datasets ranging from 4,000 to 209,000 loci using the RAD-seq software pipelines STACKS and ipyrad, then compared how their different filtering methods affect the outcome of population genetic and phylogenetic analyses. We found that different filtering algorithms favor either older separations or more recent hybridization and both perspectives are necessary for a full understanding of the invasion history. We also found that software developed for similar purposes, e.g., STRUCTURE and fastStructure, preferred different population assignment patterns corresponding to older and younger genetic hybridization events , respectively. In all analyses, the populations from Guam and Hawaii were more closely related than any other population pair. Among populations historically considered part of the beetle’s native range, Thailand contained the greatest genetic diversity, and Hainan (China) and Taiwan lacked the genetic diversity that might be expected of a native population. Palau was the only invasive population with a multi-cluster assignment, suggesting time-separated invasions from different source populations. A phylogenetic approach, using maximum likelihood and quartet methods, suggested two likely pathways across the Pacific which further complicate coalescence in the populations from Palau. Overall, we found that there is a high degree of genetic isolation between Pacific island beetle populations and invasions have likely been rare events, but with significant ecological consequences.