Actinidia

Hidaka, Chiho, Yang, Chien-Hui & Wakabayashi, Kaori, 2022, Scyllarides squammosus Nisto, Zoological Studies 61 (39), pp. 1-13 : 9

Actinidia -associated Pseudasphondylia species

Host spectrum, ecology, and distribution of gall midges provide us valuable information to solve the biogeography and speciation processes of other species groups, such as Ilex- associated Schizomyia and Cinnamomoum -associated Bruggmanniella ( Tokuda et al. 2004; Lin et al. 2020b). In Actinidia -associated Pseudasphondylia species, P. matatabi occurs only in mainland Japan, whereas P. kiwiphila sp. nov. occurs in Taiwan and Kyushu. Both species have not yet been reported from the Ryukyu Islands ( Tokuda and Yukawa 2005; Yukawa 2021), but host distribution and our findings provide a favorable opportunity to infer their biogeography.

Because A. rufa is also distributed on the Ryukyu Islands between Taiwan and Kyushu, further intensive field surveys may find P. kiwiphila sp. nov. there. Taiwanese individuals became a paraphyletic group to the Japanese individual ( Fig. 5 ) and the genetic distance was short between the two populations. These suggest that P. kiwiphila sp. nov. has a southern origin and its northward expansion through the Ryukyu Islands. In contrast, P. matatabi has been reported from Honshu, Shikoku, and Kyushu ( Yuasa and Kumazawa 1938; Yukawa 1971; Tokuda and Yukawa 2005). However, its host A. polygama is not distributed on the Ryukyu Islands and Taiwan, suggesting that P. matatabi does not occur in southern parts of East Asia.

Morphological, phylogenetic, and ecological similarities between P. kiwiphila sp. nov. and Japanese P. matatabi demonstrated in the present study indicate that they are sibling species. Based on the phylogenetic analysis, P. kiwiphila sp. nov. has a southern origin while P. matatabi currently occurs only in mainland Japan. This supports the allopatric speciation scenario between the two species via geographical isolation. However, the two species still may have speciated sympatrically via ecological divergence, and then respectively dispersed along with their host species. The following ecological features will support the sympatric speciation scenario: the hosts of these two species belong to different groups of Actinidia , i.e., A. polygama belongs to the smooth-skinned fruit species group that occurs in relatively cool or highaltitudinal areas including northern China, Korea, and mainland Japan, whereas A. rufa belongs to hairy and/ or spotted (lenticillate) fruit species groups that occurs in relatively warm and moist environments such as southern China and Taiwan (Huang 2014; Huang and Liu 2014; Liu et al. 2017). This implies that a host shift may have occurred in the common ancestor of Actinidia -associated Pseudasphondylia , leading to ecological speciation. To confirm the speciation process, further taxonomic and phylogenetic studies of Actinidia -associated Pseudasphondylia are needed, such as unidentified Pseudasphondylia species associated with fruit of Actinidia valvuta Dun in China ( Liu and Larsson 1996) and Actinidia callosa var. discolor and A. chinensis var. setosa in Taiwan ( Tung et al. 2018).

Figures

Fig. 5. Phylogenetic tree of Pseudasphondylia species based on DNA partial COI region. (A) Bayesian tree of Pseudasphondylia species, supported values are shown beside nodes with the Bayesian posterior probability (lift) and ultrafast bootstrap of the IQ tree (right). Taxa with different colors refer to distinct species based on summarized results of species delimitation (Automatic Barcode Gap Discovery analysis). (B) Cladogram of Pseudasphondylia kiwiphila sp. nov. lineage in IQ tree.