A Comparison of Juvenile and Adult Sunflower Sea Star Transcriptomic Responses to Challenge With Sea Star Wasting Disease Tissue Homogenates.

Sea star wasting disease (SSWD) has impacted over twenty sea star species along the Northeast Pacific Coast, with some seemingly more susceptible than others. The once common sunflower sea star, Pycnopodia helianthoides, has been driven to endangerment. Observations from natural SSWD outbreaks have indicated higher mortality rates in adults than juveniles, suggesting that susceptibility may be age-dependent. The hypothesis of age-related differences in immunity was assessed by challenging both juvenile and adult P. helianthoides in controlled laboratory exposures to unfiltered tissue homogenates prepared from SSWD-affected adult P. helianthoides. Using a transcriptomic approach, we compared the immune response of adult and juvenile P. helianthoides exposed to SSWD in two independent disease challenge trials. In both trials, all disease-exposed sea stars showed disease signs consistent with SSWD with no observable differences in outcome across age class, although age-driven differentially expressed genes were identified, related to development, signaling, differentiation, and stress and metabolism regulation. Transcriptomic sequencing datasets showed a majority of differentially expressed genes were shared across the two experiments, suggesting a core response to SSWD that did not differ between age classes in the second trial. Functional annotation identified a core transcriptional response to challenge with grossly SSWD-affected tissue homogenates, including genes annotated as having roles in defense response to bacterium.