Author
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O Donnell, Kerry |
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Submitted to: Meeting Abstract
Publication Type: Abstract Only Publication Acceptance Date: 6/12/2014 Publication Date: 6/12/2014 Citation: O'Donnell, K. 2014. Phylogenetic diversity and fidelity of the Euwallacea (Coleoptera: Xyleborini) - Fusarium mutualism [abstract]. Interpretive Summary: Technical Abstract: This research was conducted in collaboration with scientists in Israel, Sri Lanka, and Australia together with researchers at five universities within the U.S. to elucidate the evolution and diversity of Euwallacea ambrosia beetles and the fusaria they farm. Adult female Euwallacea transport fusaria in mandibular mycangia to new trees where they cultivate them in galleries as a source of food. In contrast to the beetles, which are obligate mutualists, the fusaria can be cultured axenically where they typically produce highly modified, clavate macroconidia that may represent an adaptation for the symbiosis. Euwallacea appears to be native to Asia where they normally attack dead or dying trees. However, these highly inbreed, fungus-farming xyleborines have been introduced into several nonindigenous areas including Israel, Australia, and the US. There they attack a wide range of healthy trees in urban landscapes, forests, and agriculturally important fruit trees such as avocado. Unfortunately, avocado is a preferred host of several Euwallacea spp.; they can complete their haplodiploid life cycle on it. Repeated massive attacks by the beetles, coupled with obstruction of vascular tissue by their Fusarium symbionts, induce die back symptoms and ultimately death. Thus, the objective of this study was to assess symbiont fidelity by DNA typing Euwallacea and the fusaria they cultivate. Towards this end, robust phylogenetic frameworks were developed for the beetles and fusaria by analyzing 6- and 4-locus datasets, respectively. Analyses of these data revealed extensive morphological crypsis in both mutualists. Four of the seven Euwallacea spp. typed, for example, fit the description of E. fornicatus, the shot hole borer of tea in Asia. Two Euwallacea, including one on avocado in Miami-Dade County, Florida, and another on tea in Sri Lanka, appear to be multisymbiont generalists, given that they cultivate two different ambrosia fusaria. Discordance between cytochrome oxidase and the other gene genealogies may be due to introgression of the mitochondrial genome of E. validus into the Euwallacea sp. in Miami-Dade County. Fusaria cultivated by Euwallacea form a clade designated the Ambrosia Fusarium Clade (AFC), suggesting this mutualism's origin was monophyletic. The discovery of interspecific hybrids in two of the AFC species suggests that hybridization might provide a mechanism for generating novel genetic diversity within these putatively clonally reproducing fusaria. The phylogenetic results support multiple host switches during the evolution of this mutualism. |
