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Abstract Ambrosia beetles require their fungal symbiotic partner as their cultivated (farmed) food source in tree galleries. While most fungal‐beetle partners do not kill the host trees they inhabit, since their introduction (invasion) into the United states around ~2002, the invasive beetleXyleborus glabratushas vectored its mutualist partner (but plant pathogenic) fungus,Harringtonia lauricola, resulting in the deaths of over 300 million trees. Concerningly, indigenous beetles have been caught bearingH. lauricola. Here, we show colonization of the mycangia of the indigenousX. affinisambrosia beetle byH. lauricola. Mycangial colonization occurred within 1 h of feeding, with similar levels seen forH. lauricolaas found for the nativeX. affinis‐R. arxiifungal partner. Fungal mycangial occupancy was stable over time and after removal of the fungal source, but showed rapid turnover when additional fungal cells were available. Microscopic visualization revealed two pre‐oral mycangial pouches of ~100–200 × 25–50 μm/each, with narrow entry channels of 25–50 × 3–10 μm. Fungi within the mycangia underwent a dimorphic transition from filamentous/blastospore growth to yeast‐like budding with alterations to membrane structures. These data identify the characteristics of ambrosia beetle mycangial colonization, implicating turnover as a mechanism for host switching ofH. lauricolato other ambrosia beetle species.
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Fungi That Live Within Animals: Application of Cell Cytometry to Examine Fungal Colonization of Ambrosia Beetle (Xyleborus sp.) Mycangia
Ambrosia beetles bore into trees, excavating galleries where they farm fungi as their sole source of nutrition. These mutualistic fungi typically do not cause significant damage to host trees; however, since their invasion into the U.S., the beetle Xyleborus glabratus has vectored its fungal partner, Harringtonia lauricola, which has acted as a devastating plant pathogen resulting in the deaths of over 500 million trees. Here, we show differences in the mycangial colonization of the indigenous X. affinis ambrosia beetle by H. lauricola, and the native fungal species, H. aguacate and Raffaelea arxii. While X. affinis was a good host for H. lauricola, the related ambrosia beetle, X. ferrugineus, was only marginally colonized by H. lauricola. X. affinis beetles neither fed on, nor were colonized by, the distantly related fungus, Magnaporthe oryzae. Mycangial colonization was affected by the nutritional state of the fungus. A novel method for direct quantification of mycangial contents based on image cell cytometry was developed and validated. The method was used to confirm mycangial colonization and demonstrate alternating fungal partner switching, which showed significant variation and dynamic turnover. X. affinis pre-oral mycangial pouches were visualized using fluorescent and light microscopy, revealing that newly emerged pupae displayed uncolonized mycangia prior to feeding, whereas beetles fed H. lauricola contained single-celled fungi within 6 h post-feeding. Mixed populations of fungal cells were seen in the mycangia of beetles following alternating colonization. Nuclear counter-staining revealed insect cells surrounding the mycangia. These data highlight variation and specificity in ambrosia beetle–fungal pairings and provide a facile method for direct quantification of mycangial contents.
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- PAR ID:
- 10663321
- Publisher / Repository:
- MDPI
- Date Published:
- Journal Name:
- Journal of Fungi
- Volume:
- 11
- Issue:
- 3
- ISSN:
- 2309-608X
- Page Range / eLocation ID:
- 184
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Accepted Manuscript
- Journal Article:
- https://doi.org/10.3390/jof11030184
