Species Delineation Within the Euwallacea fornicatus (Coleoptera: Curculionidae) Complex Revealed by Morphometric and Phylogenetic Analyses

Abstract

The ambrosia beetle Euwallacea fornicatus Eichhoff sensu lato is a complex of genetically divergent emerging pests responsible for damages to tree industries and ecosystems around the world. All lineages within the species complex are currently considered morphologically identical, presenting problems for their delineation and highlighting the shortcomings of species concepts based solely on type-specimen morphology. The objectives of this work were to 1) broaden the geographic sampling of the E. fornicatus complex in Asia, 2) reconstruct relationships between clades and populations, 3) find morphological characters or combinations of characters which are useful in delimiting the genetic lineages of the E. fornicatus species complex, and 4) propose taxonomic delimitation of species where morphology and phylogenetic identity correlate. Our integrated approach using molecular and morphological evidence suggests four clades that differ morphologically, but with overlap, therefore, cytochrome oxidase c subunit I (COI) barcoding remains necessary for assigning specimens to a clade. The following taxonomic changes are proposed: E. fornicatus (Eichhoff 1868) (= ‘Tea Shot Hole Borer Clade a’); E. fornicatior (Eggers 1923), stat. rev. (= ‘Tea Shot Hole Borer Clade b’); E. whitfordiodendrus (Schedl 1942), stat. rev. (= ‘Polyphagous Shot Hole Borer’); and E. kuroshio Gomez and Hulcr, sp. nov. (= ‘Kuroshio Shot Hole Borer’). This approach delivers a practical, evidence-based guidance for species delineation that can address overlapping variation in morphological characters of an emerging pest species complex.

The Essential Role of Taxonomic Expertise in the Creation of DNA Databases for the Identification and Delimitation of Southeast Asian Ambrosia Beetle Species (Curculionidae: Scolytinae: Xyleborini)

“…Most of the morphologically defined species for all genera exhibit 10-12% difference; thus, we contend that this observation is not the result of rampant cryptic speciation that one would expect given a 2% standard sequence divergence between species as promoted by the Barcode initiative (Hebert et al, 2003b; Ashfaq and Hebert, 2016). Cryptic species are evident at intraspecific differences ∼13%, such as in the E. fornicatus species complex and other lineages (Gomez et al, 2018;Cognato et al, 2019;Smith et al, in preparation). Our sequence data shows no evidence of Wolbachia or pseudogenes.…”

“…Global trade and the use of wood products as ballast and crating have contributed to an accelerated rate of dispersal of these beetles in many parts of the world (Haack and Rabaglia, 2013;Cognato et al, 2015;Gohli et al, 2017;Meurisse et al, 2018). The first recored introduction of a xyleborine species in the US dates to 1817, but the rate of introduction accelerated with 17 new out of the total 28 exotic species in just the last 30 years (Haack and Rabaglia, 2013;Smith and Cognato, 2015;Gomez et al, 2018;Hoebeke et al, 2018). A subset of these species has also been introduced into Europe in the last two decades (Kirkendall and Faccoli, 2010;Dodelin, 2018).…”

“…It is estimated that only 75% of the Southeast Asian and 25% of the South American faunas have been described so far (Wood and Bright, 1992;Hulcr et al, 2015;Smith et al, 2017). Even with taxonomic tools, the small and subtle morphological differences that define many xyleborine species make it difficult for non-experts to accurately identify species (Cognato et al, 2015;Gomez et al, 2018;Hoebeke et al, 2018;Smith et al, 2019). Identification of immature stages to species or genus presents the greatest challenge even for experts.…”

“…Although there are potential issues and limitations of DNA barcoding using COI, preliminary data suggest the feasibility of identification and delimiting xyleborine species (Dole et al, 2010;Cognato et al, 2011Cognato et al, , 2015Cognato et al, , 2019Jordal and Kambestad, 2014;Stouthamer et al, 2017;Gomez et al, 2018). Studies of a few closely related species of different genera demonstrated: (1) The universal or scolytine specific barcoding COI primers produce PCR products and DNA sequences for most species; (2) nonmonophyletic species; (3) high intraspecific nucleotide difference (> 10% as compared to 2-3% for outbreeding scolytines) (4) the use of nuclear genes as alternative diagnostic loci; and (5) the results of a few studies identified new species (Gomez et al, 2018;Cognato et al, 2019). In addition, there are currently overlapping generations of scolytine taxonomists that can identify specimens to species and can interpret the DNA results in reference to these identifications.…”

Morphometric criteria to differentiate Drosophila suzukii (Diptera: Drosophilidae) seasonal morphs

“…We used a classification tree model because the interpretation is straightforward relative to other analytical approaches [52,59]. Decision trees have been used previously in entomological research for determining predictor variables in both field and systematic studies [60][61][62]. For these reasons, a classification tree was appropriate for our research goal of developing a potential objective criterion that would differentiate D. suzukii morphs.…”