Three-dimensional characterization of first instar horse and rhinoceros stomach bot fly larvae (Oestridae: Gasterophilinae:Gasterophilus,Gyrostigma): novel morphology and evolutionary implications

Abstract

Larval characters are of importance in systematic and evolutionary studies of Diptera but lag behind characters of adults due to difficulties in obtaining relevant information. Larvae of stomach bot flies are obligate parasites completing development exclusively in the alimentary tract of equids and rhinoceroses. They possess diversified morphological adaptations, providing remarkable examples to further our understanding of larval evolution. Herein, three-dimensional structures of first instar Gasterophilus pecorum and Gyrostigma rhinocerontis are compared using confocal laser scanning microscopy (CLSM) and scanning electron microscopy (SEM). We suggest CLSM has a large potential for exploiting cryptic character systems of micro fly larvae, as spectral range and intensity of autofluorescence emitted by sclerotized structures and soft tissues are distinct, presenting a high-contrast mechanism for multistructural visualization with non-destructive sample preparation. Five new potential synapomorphies are proposed to corroborate the sister-group Gasterophilus and Gyrostigma. The upward curving mouth-hooks of first instar Gasterophilus and Gyrostigma are distinctive in Cyclorrhapha and possibly serve to facilitate the larval subcutaneous migration within the host. Three types of mouthhooks are recognized in first instar Oestridae, with the gently curved and gradually tapered type optimized as the ancestral state, from which the gasterophiline and hypodermatine types evolved independently.

Larval anatomy of the digestive and excretory systems of the pharyngeal bot fly, Pharyngomyia picta (Diptera: Oestridae)

“…The observed anatomical features of the digestive and excretory systems of P. picta may therefore reflect parasitic adaptations to the infestation of the nasopharyngeal cavities of mammal hosts in all the Oestrinae. Combining the study of both the internal and external anatomy (Colwell, 2006b) could provide not only new insights into our understanding of the parasitic adaptations of oestrid larvae and their impact on the host but also further support for phylogenetic and evolutionary analyses of the family (Li, Pape, Colwell, Dewhurst, & Zhang, 2021). The unparalleled opportunities provided by non‐invasive imaging techniques like X‐ray micro‐CT (Hall & Martín‐Vega, 2019) enable the high‐quality visualisation and analysis of potentially informative internal anatomical structures that may have been overlooked and/or poorly understood, and their potential incorporation into morphological and phylogenetic studies, traditionally focused on external anatomical characters (Colwell et al, 2006; Li et al, 2021).…”

Larval morphology of the avian parasitic genusPasseromyia: playing hide and seek with a parastomal bar

“…To provide greater certainty on these structures, we analysed additional material including some species from the muscid genera Alluaudinella This study provides the first comprehensive documentation of the cephaloskeleton of muscid species obtained by confocal laser scanning microscopy (CLSM). Despite earlier evidence of the utility of CLSM in visualizing morphological structures, this powerful tool has rarely been used on immature stages of Diptera Li et al, 2021;Szpila et al, 2016Szpila et al, , 2021. The main obstacles are high costs, equipment availability and lack of standard protocols for the preparation and visualization of specimens.…”