Larval dorsal shield morphology is highly correlated with gall type in the enigmatic gall-forming fly, Fergusonina Malloch (Diptera : Fergusoninidae)

Abstract

The gall-forming fly family Fergusoninidae, in association with a mutualist nematode, induces galls on Myrtaceae. Traditionally, each fly species has been thought to be host-specific and targets a particular site on its host plant. One host species may be host to as many as four fly species, each with different oviposition sites, giving rise to a range of gall types. Third-instar fly larvae possess a distinctive sclerotised ‘dorsal shield’ of unknown function that varies morphologically across the genus. We use a phylogenetic approach to examine the relationship of the dorsal shield morphology to other elements of this complex system. A phylogeny of 41 species, estimated using Bayesian analysis of mtCOI sequences, indicated a strong correlation between dorsal shield morphology and the gall type associated with the larva. We discuss possible functions of the dorsal shield, and other factors that may have led to their phylogenetic distribution. In addition, we have identified cases where fly species have formed galls on more than one host species. In some instances it is possible that these associations are an opportunistic response to artificial tree plantings.

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

“…Purcell et al (2016) developed a phylogeny correlating the structure of the sclerotized larval dorsal shield to gall type, and also supported the use of host and larval morphology in diagnosis. An updated molecular phylogeny of the family utilizing multiple and protein-coding genes is being developed (Purcell et al, 2016;S. Scheffer, pers.…”

“…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).…”

“…Molecular sequence data are currently being used to delimit and refine species boundaries and relationships for the Melaleuca-feeding Fergusonina (Scheffer et al, 2004). Purcell et al (2016) developed a phylogeny correlating the structure of the sclerotized larval dorsal shield to gall type, and also supported the use of host and larval morphology in diagnosis. An updated molecular phylogeny of the family utilizing multiple and protein-coding genes is being developed (Purcell et al, 2016;S.…”

“…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.…”

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

“…From the cumulative morphological and molecular evidence available to date, most fly/nematode associations appear to induce gall formation on a specific host tissue and on a specific host species, although some instances of feeding on multiple hosts are known (Giblin-Davis et al 2004;Davies and Giblin-Davis 2004;Nelson et al 2014;Purcell et al 2016). For example, some widespread eucalypts serve as hosts for multiple pairs of Fergusonina/Fergusobia mutualists (Taylor et al 2005;Nelson et al 2014;Purcell et al 2016). However, a considerable number of fly and nematode species are undescribed (the authors, pers.…”