McCracken, A. | Search bioRxiv

bioRxiv2025

Precursors of Sea Star Wasting: Immune and Microbial Disruption During Initial Disease Outbreak in Southeast Alaska

Sea Star Wasting Disease (SSW) has devastated sea star populations along the North American Pacific coast since 2013, yet the mechanisms of disease progression, particularly in natural environments, remain unclear. Here we integrate transcriptomic and microbial data from wild Pycnopodia helianthoides sampled across sites affected and unaffected by SSW in southeast Alaska during the initial outbreak recorded in the region in 2016. Individuals exposed to SSW but lacking visible symptoms showed elevated expression of complement system components, pathogen recognition genes, immune regulatory and cell death pathways. Alongside signs of immune activation, genes involved in maintaining extracellular matrix composition, tissue remodeling, and cell adhesion were differentially expressed, indicating early disruption of tissue homeostasis preceding visible wasting symptoms. Gene ontology analysis revealed enrichment of immune response, cell-cell adhesion, response to oxygen levels and nervous system regulatory pathways. Furthermore, network analyses revealed differentially abundant microbes in Exposed individuals--notably Vibrio spp.--were highly correlated with immune response, tissue integrity, stress and detoxification genes in network modules. Together, our findings offer insight into early host-pathogen dynamics in wild populations, underscoring putative links between immune activation and microbial community shifts with the onset of SSW disease.

ecology↗

bioRxiv2021

Genomics analysis of hexanoic acid exposure in Drosophila species

Drosophila sechellia is a dietary specialist endemic to the Seychelles islands that has evolved to consume the fruit of Morinda citrifolia. When ripe, the fruit of M. citrifolia contains octanoic acid and hexanoic acid, two medium chain fatty acid volatiles that deter and are toxic to generalist insects. D. sechellia has evolved resistance to these volatiles allowing it to feed almost exclusively on this host plant. The genetic basis of octanoic acid resistance has been the focus of multiple recent studies, but the mechanisms that govern hexanoic acid resistance in D. sechellia remain unknown. To understand how D. sechellia has evolved to specialize on M. citrifolia fruit and avoid the toxic effects of hexanoic acid, we exposed adult D. sechellia, D. melanogaster and D. simulans to hexanoic acid and performed RNA sequencing comparing their transcriptional responses to identify D. sechellia specific responses. Our analysis identified many more genes responding transcriptionally to hexanoic acid in the susceptible generalist species than in the specialist D. sechellia. Interrogation of the sets of differentially expressed genes showed that generalists regulated the expression of many genes involved in metabolism and detoxification whereas the specialist primarily downregulated genes involved in the innate immunity. Using these data we have identified interesting candidate genes that may be critically important in aspects of adaptation to their food source that contains high concentrations of HA. Understanding how gene expression evolves during dietary specialization is crucial for our understanding of how ecological communities are built and how evolution shapes trophic interactions.

genomics↗