Phylogenetics of Australasian gall flies (Diptera: Fergusoninidae): Evolutionary patterns of host-shifting and gall morphology

Abstract

This study investigated host-specificity and phylogenetic relationships in Australian galling flies, Fergusonina Malloch (Diptera: Fergusoninidae), in order to assess diversity and explore the evolutionary history of host plant affiliation and gall morphology. A DNA barcoding approach using COI data from 203 Fergusonina specimens from 5gall types on 56 host plant species indicated 85 presumptive fly species. These exhibited a high degree of host specificity; of the 40 species with multiple representatives, each fed only on a single host genus, 29 (72.5%) were strictly monophagous, and 11 (27.5%) were reared from multiple closely related hosts. COI variation within species was not correlated with either sample size or geographic distance. However variation was greater within oligophagous species, consistent with expectations of the initial stages of host-associated divergence during speciation. Phylogenetic analysis using both nuclear and mitochondrial genes revealed host genus-restricted clades but also clear evidence of multiple colonizations of both host plant genus and host species. With the exception of unilocular peagalls, evolution of gall type was somewhat constrained, but to a lesser degree than host plant association. Unilocular peagalls arose more often than any other gall type, were primarily located at the tips of the phylogeny, and did not form clades comprising more than a few species. For ecological reasons, species of this gall type are predicted to harbor substantially less genetic variation than others, possibly reducing evolutionary flexibility resulting in reduced diversification in unilocular gallers.

Family groups of Diopsoidea and Nerioidea (Diptera: Schizophora)—Definition, history and relationships

“…Fergusoninidae has 40 described species in the genus Fergusonina (Purcell et al, 2016), but Scheffer et al (2017) identified 85 "putative species" in their study, and there are potentially upwards of hundreds of additional species awaiting discovery (Scheffer et al, 2004;Purcell et al, 2013). Species can be difficult to differentiate, with diagnosis often depending on minutae of the male and female genitalia-see Taylor (2004).…”

“…Eucalyptus species are host for most known Fergusonina, but flies have also been reared from over 65 species of Melaleuca, Leptospermum, Sygyzium and Metrosideros (Purcell et al, 2013;Scheffer et al, 2017). Females select ovipositions sites in areas of new growth, specifically in the developing buds of shoots, inflorescences, flowers, leaves or stems of the host plant, and the number, location and morphology of the resultant galls appear to be characteristic for each Fergusonina/Fergusobia pair (Currie, 1937;Giblin-Davis et al, 2003;Purcell et al, 2015).…”

“…Larvae in multilocular galls may have been laid by one or more females (Purcell et al, 2015). As many as four species of fly can be found on a single host species, and one species of fly may be found on one or more species of host plant, usually within the same host subgenus, but sometimes in more distantly related hosts if those hosts are sympatric, possibly as a result of the availability of novel host choice via artificial plantings (Purcell et al, 2017).…”

“…Overall host associations largely appear to be conservative, with all species restricted to a single host genus in Scheffer et al (2017), who analyzed fergusoninid phylogeny with respect to host usage and gall type. The authors found 73% of species on only a single host species, but they noted that this was a likely underestimate of monophagy in the group.…”

“…The egg of F. turneri was figured by Taylor (2004). Additional descriptions and/or photos and illustrations of the distinctive larvae of fergusoninid species are provided in Harris (1982), Taylor (2004), , Nelson et al (2011), Purcell et al (2016Purcell et al ( , 2017 and the references therein. Most fergusoninid larvae have a species-specific "dorsal shield" of sclerotized spicules, bands or combs extending from the mesothorax to abdominal segment 7; both the larva and puparium have a comb-like plate between abdominal segments 1 and 2.…”