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Dryad

Pervasive heteroplasmy in an invasive ambrosia beetle (Scolytinae) in southern California

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Sep 06, 2024 version files 67.79 KB

Abstract

Heteroplasmy, the presence of multiple distinct mitochondrial genotypes (mitotypes) within an individual, has long been thought to be a rare aberrance that is quickly removed by selection or drift. However, heteroplasmy is being reported in natural populations of eukaryotes with increasing frequency, in part due to the development of better diagnostic molecular methods. Here, we report a seemingly stable heteroplasmic state in California populations of the polyphagous shothole borer (PSHB), Euwallacea fornicatus; an exotic invasive ambrosia beetle that is causing significant tree dieback. We develop and validate a qPCR assay that utilizes novel locked nucleic acid probes to detect different mitotypes, and qualitatively assess heteroplasmy in individual PSHB. We prove the utility of this assay by: a) mitotyping field-collected PSHB to document the prevalence of heteroplasmy across its invasive range in southern California; and, b) measuring relative titers of eac h mitotype across multiple generations of heteroplasmic PSHB colonies in the laboratory to assess the stability of transmission through the maternal germline. We rule out the possibility that heteroplasmy is due to a NUMT, and find that heteroplasmic individuals are common in Californian field populations of PSHB, and that heteroplasmy persists in a stable state for at least 10 generations in experimental colonies. We also looked for evidence of the common occurrence of paternal leakage, but found none. In light of our results, we discuss competing hypotheses as to how heteroplasmy may have first arisen, and continues to perpetuate, in Californian PSHB populations.