Pseudasphondylia, Monzen, 1955

Lin, Sheng-Feng, Yang, Man-Miao & Tokuda, Makoto, 2020, Molecular Phylogeny Revealing the Single Origin of - associated (Diptera: Cecidomyiidae) in Asia, with Descriptions of Three New and One Newly Recorded Species from Taiwan., Zoological Studies 59 (66), pp. 1-16 : 13-14

Pseudasphondylia and Asian Bruggmanniella

Garcia et al. (2020) proposed that most Asian Bruggmanniella species do not actually belong to the genus Bruggmanniella . In their scheme, B. cinnamomi and B. actinadaphnes are sister and members of Pseudasphondylia . In addition, B. brevipes was treated as a distinct genus ( Odontokeros ) and became a sister group of Pseudasphondylia + Bruggmanniella . However, our tree ( Fig. 8 ) suggested that Pseudasphondylia and Asian Bruggmanniella are monophyletic and sister. In addition, our topology suggests that B. brevipes is sister to Cinnamomum - associated taxa with strong support, indicating that the species is more closely related to Cinnamomum - associated taxa than to Pseudasphondylia . That is, B. cinnamomi by no means belongs to genus P s e u d a s p h o n d y l i a a n d B. b re v i p e s s h o u l d b e treated as Asian Bruggmanniella . Characteristics of Bruggmanniella larvae and pupae have high heterogeneity in both Neotropcial and Asian groups. It is not suitable to erect a new genus or genera under the current taxonomic framework because it would lead to chaos in further taxonomic works. Presently, the phylogeny of Bruggmanniella is still inconclusive due to nodes with low support in the morphological-based cladogram ( Garcia et al. 2020) and insufficient sampling of DNA fragments and taxa, especially DNA of the type species, B. braziliensis . Thus, the comprehensiveness of data—including taxonomic unit, species, morphological features and DNA information—on Bruggmanniella is essential for resolving this situation.

Molecular information is a useful tool for species identification, especially for gall midges, whose adult specimens can be very difficult to obtain; in addition, adults of this species share similar morphological features with genera such as Asphondylia ( Yukawa et al. 2003; Uechi and Yukawa 2004; Elsayed et al. 2018). Three new Bruggmanniella species, B. turoguei sp. nov., B. shianguei sp. nov. and B. sanlianensis sp. nov., can be discriminated not only by morphological traits, but also based on COI sequences—even their galls are induced on the same host species or galling organ. Ours is the first paper to address the molecular phylogeny of Asian Bruggmanniella and confirm the single origin of Cinnamomum association in the genus. Their pairwise genetic distances in a partial COI gene were large: for example, the maximum distance of the region was 7.0% within the species pair of Cinnamomum - associated Bruggmanniella , but it was 13.5–16.4% compared with Neolitsea -associated Bruggmanniella ( B. brevipes ) and 12.4–14.1%. These variations are higher than the distance at the general generic level (9.3%) of the dipteran group ( Hebert et al. 2003). This could correspond to highly morphological heterogeneity between these two groups and implies that Asian Bruggmanniella species have diverged on different host genera early in the history.

Divergence among Cinnamomum -associated Bruggmmanniella

Diversification of gall inducers could be triggered by various biotic and/or abiotic factors. In gall inducing cecidomyiids, host plant and organ shifts are considered important mechanisms of divergence ( Tokuda et al. 2004; Yukawa et al. 2005; Joy and Crespi 2007; Dorchin et al. 2009; Stireman et al. 2010; Mathur et al. 2012). For instance, the host shift of Dasineura folliculi Felt, 1908 within the host genus Solidago was reported via the behavioral, ecological and genetic evidences ( Dorchin et al. 2009). In addition, Joy and Crespi (2007) revealed that organ shifts are critical for divergence events in 14 Asphondylia species on their single host plant, the creosote bush Larrea tridentata (DC.) Coville.

In our study system of Cinnamomum -associated Bruggmmanniella, the evolutionary processes and speciation events seem to involve three different mechanisms: organ shift, host shift, and geographical isolation. We propose an evolutionary scenario based on the phylogenetic relationships. Leaf-galling habit is an ancestral trait, and the organ shift from leaf to stem is likely to have occurred later in the group. Among the stem gallers, the three species seem to have diverged via host plant shifts, but we need to further confirm whether the divergence time among the stem gallers is later than the speciation of their host plants. A later event happened in B. cinnamomi populations that diverged between Taiwan and the Ryukyu Islands, Japan, via geographical isolation and host plant shift. The COI genetic distance of Taiwanese and Japanese taxa of B. cinnamomi is approximately 0.8%, revealing that they diverged around 0.35–0.4 Mya based on a divergence distance of 2.0 or 2.3% per million years ( DeSalle et al. 1987; Brower 1994). It corresponds to the time of origination of the Ryukyu Islands the last time they were connected to Taiwan ( Kimura 1996; Osozawa et al. 2012), suggesting that B. cinnamomi expanded its range from Taiwan to the Ryukyu Islands and its host changed to C. yabunikkei (= C. japonica ) in Okinawa. As a whole, the evidence strongly suggests that B. cinnamomi in the Ryukyus has a southern origin.

Geographical distribution and host association

The host spectrum and geographical isolation are key factors for understanding divergence pathways of cecidomyiids. Bruggmanniella cinnamomi utilizes C. yabunikkei on the Southwest Islands of Japan and C. insularimontanum in Taiwan. Interestingly, C. yabunikkei is also distributed in Taiwan but B. cinnamomi does not induce galls on it. Two factors could be responsible for this phenomenon. From the host spectrum point of view, phenological asynchrony may be a key factor, because adult females need to oviposit when the host is in a suitable development stage ( Yukawa 2000). Alternatively, Taiwanese populations of C. yabunikkei may be resistant to B. cinnamomi . From a biogeographical point of view, B. cinnamomi has never been found in the Palearctic Region of Japan (i.e., Kyushu or northern areas) or the Korean Peninsula ( Yukawa and Masuda 1996; Paik et al. 2004; Tokuda and Yukawa 2006; Kim et al. 2015), even though its host plant is distributed in these areas. The mechanism inhibiting the distributional expansion of B. cinnamomi northward would be an interesting study subject because the Tokara Strait, which is the geographical border between Palearctic and Oriental Regions, does not seem to act as a barrier for northward expansion by gall midges ( Tokuda 2018).

The other three Bruggmanniella species are known only from Taiwan. Bruggmanniella turoguei sp. nov. and B. sanlianensis sp. nov. are associated with a Taiwanese endemic species, C. osmophloeum , while B. shainguei sp. nov. induces galls on C. subavenium , which is distributed widely in southern China ( Lu et al. 2000). Although Bruggmanniella species and their galls have never been found in China, it is assumed that Cinnamomum -associated Bruggmanniella will be found there and Southeast Asian countries because these regions are parts of the origins of Taiwanese fauna and flora, and also species-rich areas of the genus Cinnamomum ( Huang et al. 2016) .

Figures

Fig. 8. Cladogram of East Asian Bruggmanniella based on the Neighbor-joining method based on the DNA COI region. Support values at the nodes are Neighbor-joining (left)/ Maximum-likelihood (media)/ Bayesian inference (right). “–” indicates support values less than 50% in ML and NJ, and 0.5 in BI inference.