O'Grady, P. M. | bioRxiv Science

bioRxiv2025

Host plant nutrition drives fitness outcomes in the cactus specialist Drosophila mettleri

Organisms must navigate complex interactions with host plants, microbial communities, and environmental cues to ensure their survival and reproductive success when adapting to novel environments. Host plant specialists can be used to study how these interactions affect fitness due to their ecological constraints. In specialist species, such as cactophilic Drosophila, it remains unclear how feeding preferences, nutritional value of the substrate, and microbial interactions collectively shape fitness outcomes. We used diverse laboratory media formulations to examine the fitness implications in Drosophila mettleri, a species that exclusively uses Saguaro cactus (Carnegiea gigantea) as its natural host plant. We found that D. mettleri did not preferentially feed on one medium compared to others, nor on C. gigantea supplemented media compared to controls. Microbial communities, especially on banana media with C. gigantea additives, appear to improve developmental success and can influence D. mettleri post-pupation success. Taken together, our results highlight the behavioral and environmental interplay between host plant substrate and microbial communities.

ecology↗

bioRxiv2023

Single-fly assemblies fill major phylogenomic gaps across the Drosophilidae Tree of Life

Long-read sequencing is driving rapid progress in genome assembly across all major groups of life, including species of the family Drosophilidae, a longtime model system for genetics, genomics, and evolution. We previously developed a cost-effective hybrid Oxford Nanopore (ONT) long-read and Illumina short-read sequencing approach and used it to assemble 101 drosophilid genomes from laboratory cultures, greatly increasing the number of genome assemblies for this taxonomic group. The next major challenge is to address the laboratory culture bias in taxon sampling by sequencing genomes of species that cannot easily be reared in the lab. Here, we build upon our previous methods to perform amplification-free ONT sequencing of single wild flies obtained either directly from the field or from ethanol-preserved specimens in museum collections, greatly improving the representation of lesser studied drosophilid taxa in whole-genome data. Using Illumina Novaseq X Plus and ONT P2 sequencers with R10.4.1 chemistry, we set a new benchmark for inexpensive hybrid genome assembly at US $150 per genome while assembling genomes from as little as 35 ng of genomic DNA from a single fly. We present 183 new genome assemblies for 179 species as a resource for drosophilid systematics, phylogenetics, and comparative genomics. Of these genomes, 62 are from pooled lab strains and 121 from single adult flies. Despite the sample limitations of working with small insects, most single-fly diploid assemblies are comparable in contiguity (>1Mb contig N50), completeness (>98% complete dipteran BUSCOs), and accuracy (>QV40 genome-wide with ONT R10.4.1) to assemblies from inbred lines. We present a well-resolved multi-locus phylogeny for 360 drosophilid and 4 outgroup species encompassing all publicly available (as of August 2023) genomes for this group. Finally, we present a Progressive Cactus whole-genome, reference-free alignment built from a subset of 298 suitably high-quality drosophilid genomes. The new assemblies and alignment, along with updated laboratory protocols and computational pipelines, are released as an open resource and as a tool for studying evolution at the scale of an entire insect family.

evolutionary biology↗