Diversity underfoot of agromyzids (Agromyzidae, Diptera) mining thalli of liverworts and hornworts

Abstract

Agromyzidae is a dipteran family that has diversified as internal plant feeders. Although most agromyzid species feed on herbaceous angiosperms, only a limited number of species has been recorded as miners of bryophytes. Extensive searches and rearing of bryophytivores in the Japanese Archipelago were made, resulting in that thallus-mining agromyzids are overwhelmingly widespread and diverse on thalloid liverworts and hornworts. By examining the morphology of adult flies, it was revealed that the agromyzid fauna comprise 39 species, of which 37 species are newly described. All the species are assigned to the genus Phytoliriomyza Hendel based on some shared morphological character states as follows: costa reaching M1; orbital setulae minute and erect (rarely proclinate); male epandrium with combs of fused tubercle-like setae and/or hypertrophied arms bearing tubercle-like setae; male distiphallus comprising a pair of stout, extended tubules; female cercus with two stout, apical, trichoid sensilla. Of the 39 agromyzid species in Japan, 36 species are associated with liverworts: 5 spp. on Marchantia (Marchantiaceae), 2 spp. on Dumortiera (Dumortieraceae), 3 spp. on Plagiochasma, 1 sp. on Asterella, 6 spp. on Reboulia (Aytoniaceae), 1 sp. on Wiesnerella (Wiesnerellaceae), 15 spp. on Conocephalum (Conocephalaceae), and 3 spp. on Riccia (Ricciaceae). Three species are associated with hornworts: 1 sp. on Folioceros (Anthocerotaceae), 1 sp. on Megaceros (Dendrocerotaceae), and 1 sp. on Notothylas,Phaeoceros (Notothyladaceae), and Anthoceros (Anthocerotaceae). The results suggest that 37 of the 39 species are host-specific at least to plant genus level, and that the inter-specific differences in male genitalia and color patterns of scutum, antenna, and maxillary palpus have contributed to reproductive isolation on the bryophytes that the flies share.

Recent origin and diversification accompanied by repeated host shifts of thallus-mining flies (Diptera: Agromyzidae) on liverworts and hornworts

“…Thalloid liverworts are further divided into morphologically distinct groups, complex and simple thalloid liverworts. Among these, the larvae of Phytoliriomyza mine thalli of either complex thalloid liverworts or hornworts [35].…”

“…[30]. Recently, we discovered 39 species of bryophyte-associated Phytoliriomyza through extensive sampling effort in Japan [35].…”

“…While most agromyzid flies are known for their leaf-mining behaviour on tracheophytes, a recent study has revealed a significant diversity of species that mine the thalli of liverworts or hornworts [35]. In Japan, 39 species of Phytoliriomyza species are known to only mine the thalli of a single genus, demonstrating their high level of host specificity [36].…”