Biology subjects

Unckless, R. L.

Publications and source records attributed to Unckless, R. L..

3 recordsLinked to original sources

bioRxiv2018

Antiviral genes are not rapidly evolving in Drosophila innubila

Viruses make up a considerable proportion of the pathogens infecting animals. They can spread rapidly between hosts, and sicken or even kill their hosts to promote their own proliferation. Due to this strong selective pressure, antiviral immune genes are some of the fastest evolving genes across metazoans, as highlighted in mammals and insects. While Drosophila melanogaster are frequently exposed to pathogenic RNA viruses, little is known about D. melanogasters ecology in terms of viral exposure, or if they are representative of other Drosophila species. Here, we sequence and assemble the genome of a highly diverged, mushroom-feeding Drosophila species, Drosophila innubila, a species frequently exposed to a highly pathogenic DNA virus. We investigate the evolution of the immune system and find little evidence for rapid evolution of the antiviral RNAi genes, though we do find rapid evolution of several other pathways, suggesting alternate means of viral resistance. This contrasts with D. melanogaster, and suggests that evolution of resistance to DNA viruses differs greatly from that of RNA viruses.

genomics↗

bioRxiv2018

Balancing selection drives maintenance of geneticvariation in Drosophila antimicrobial peptides

Genes involved in immune defense against pathogens provide some of the most well-known examples of both directional and balancing selection. Antimicrobial peptides (AMPs) are innate immune effector genes, playing a key role in pathogen clearance in many species, including Drosophila. Conflicting lines of evidence have suggested AMPs may be under directional, balancing or purifying selection. Here, we use a case-control gene approach to show that balancing selection is an important force shaping AMP diversity in two species of Drosophila. In D. melanogaster, this is most clearly observed in ancestral African populations. Furthermore, the signature of balancing selection is even clearer once background selection has been accounted for. Balancing selection also acts on AMPs in D. mauritiana, an isolated island endemic separated from D. melanogaster by about 4 million years of evolution. This suggests that balancing selection may be acting to maintain adaptive diversity in AMPs in insects as it does in other taxa.

evolutionary biology↗

bioRxiv2017

Evolutionary dynamics of male reproductive genes in the Drosophila virilis subgroup

Postcopulatory sexual selection (PCSS) is a potent evolutionary force that can drive rapid changes of reproductive genes within species, and thus has the potential to generate reproductive incompatibilities between species. Male seminal fluid proteins (SFPs) are major players in postmating interactions, and likely the main targets of PCSS in males. The virilis subgroup of Drosophila exhibits strong interspecific gametic incompatibilities, and can serve as a model to study the genetic basis of PCSS and gametic isolation. However, reproductive genes in this group have not been characterized. Here we use short-read RNA sequencing of male reproductive organs to examine the evolutionary dynamics of reproductive genes in members of the virilis subgroup: D. americana, D. lummei, D. novamexicana, and D. virilis. For each of the three male reproductive organs (accessory glands, ejaculatory bulb, and testes), we identify genes that show strong expression bias in a given tissue relative to the remaining tissues. We find that the majority of male reproductive transcripts are testes-biased, accounting for ~15% of all annotated genes. Ejaculatory bulb-biased transcripts largely code for lipid metabolic enzymes, and contain orthologs of the D. melanogaster ejaculatory bulb protein, Peb-me, which is involved in mating-plug formation. In addition, we identify 71 candidate SFPs, and show that this set of genes has the highest rate of nonsynonymous codon substitution relative to testes- and ejaculatory bulb-biased genes. Furthermore, these SFPs are underrepresented on the X chromosome and are enriched for proteolytic enzymes, which is consistent with SFPs in other insect species. Surprisingly, we find 35 D. melanogaster SFPs with conserved accessory gland expression in the virilis group, suggesting these genes may have conserved reproductive roles in Drosophila. Finally, we show that several of the SFPs that have the highest rate of nonsynonymous codon substitutions reside on the centromeric half of chromosome 2, which contributes to paternal gametic incompatibility between species. Our results suggest that SFPs are under strong selection in the virilis group, and likely play a major role in PCSS and/or gametic isolation.

evolutionary biology↗