Evolution of coding sequence and gene expression of blowflies and botflies with contrasting feeding habits

Divergent Genetic Pathways Underlying Convergent Parasitic Behaviours in Blowflies

Blowfly (Diptera: Calliphoridae) exhibit diverse feeding strategies, with most species developing on decomposing organic matter. However, parasitism has evolved within the family, and some species convergently gained the ability to explore the tissues of living vertebrate hosts, which imposes critical veterinary, medical, and agricultural issues worldwide. It is yet unknown how this phenotype has evolved and whether it is determined by the same genetic architecture in different species or not. To address these questions, we evaluated key behavioural phenotypes in species with contrasting feeding habits, focusing on female oviposition preferences and larval survival on distinct diets, both critical aspects of their life cycles. These assays allowed us to propose hypotheses of how oviposition and larval behaviours contribute to feeding habits displayed in nature for parasitic and saprophagous species. Additionally, a transcriptome-wide analysis revealed genes and functional pathways potentially linked to parasitic behaviour by comparing gene expression profiles and coding sequence evolution. In the genetic analysis, we identified genes with important functions related to the measured behaviours, revealing that distinct genes may underlie each independent case of parasitism evolution, suggesting a non-parallel evolutionary pathway for this convergent trait.

A chromosomal-scale reference genome of the New World Screwworm, Cochliomyia hominivorax

The New World Screwworm, Cochliomyia hominivorax (Calliphoridae), is the most important myiasis-causing species in America. Screwworm myiasis is a zoonosis that can cause severe lesions in livestock, domesticated and wild animals, and occasionally in people. Beyond the sanitary problems associated with this species, these infestations negatively impact economic sectors, such as the cattle industry. Here, we present a chromosome-scale assembly of C. hominivorax's genome, organized in 6 chromosome-length and 515 unplaced scaffolds spanning 534 Mb. There was a clear correspondence between the D. melanogaster linkage groups A-E and the chromosomal-scale scaffolds. Chromosome quotient (CQ) analysis identified a single scaffold from the X chromosome that contains most of the orthologs of genes that are on the D. melanogaster fourth chromosome (linkage group F or dot chromosome). CQ analysis also identified potential X and Y unplaced scaffolds and genes. Y-linkage for selected regions was confirmed by PCR with male and female DNA. Some of the long chromosome-scale scaffolds include Y-linked sequences, suggesting misassembly of these regions. These resources will provide a basis for future studies aiming at understanding the biology and evolution of this devastating obligate parasite.

Typical intracranial myiasis in Nigerian red river hogs (Potamochoerus porcus) caused by an unknown bot fly (Diptera: Oestridae)

We report an unknown taxon of bot fly (Diptera: Oestridae: Oestrinae) in red river hogs (Potamochoerus porcus Linnaeus, 1758) in Cross River State, Nigeria. From direct observation and interviews with local hunters, we document that, remarkably, the parasite typically occurs within the intracranial supra-meningeal space - i.e., between the inner wall of the skull and the brain - but without causing visible inflammation or clinical signs. The parasite is most similar (up to 87.9%) to Rhinoestrus usbekistanicus based on cytochrome oxidase subunit 1 DNA sequencing but is sufficiently divergent phylogenetically to represent a new or previously un-sequenced taxon. Morphologically, the parasite shares some, but not all, features with R. nivarleti. Local cultural belief systems attribute aspects of red river hog behavior (e.g. intelligence, elusiveness) to the parasite, suggesting a prolonged presence in the red river hog population. The parasite's unusual anatomic location may be aberrant, or it may be a protective adaptation to life in red river hogs, which forage vigorously with their snouts.