By shuffling biogeographic distributions, biological invasions can both disrupt long-standing associations between hosts and parasites and establish new ones. This creates natural experiments with which to study the ecology and evolution of host-parasite interactions. In estuaries of the Gulf of Mexico, the white-fingered mud crab (Rhithropanopeus harrisii) is infected by a native parasitic barnacle Loxothylacus panopaei (Rhizocephala), which manipulates host physiology and behavior. In the 1960s, L. panopaei was introduced to the Chesapeake Bay and has since expanded along the southeastern Atlantic coast, while host populations in the northeast have so far been spared. We use this system to test the host’s transcriptomic response to parasitic infection and investigate how this response varies with the parasite’s invasion history, comparing populations representing (1) long-term sympatry between host and parasite, (2) new associations where the parasite has invaded during the last sixty years, and (3) naïve hosts without prior exposure. A comparison of parasitized and control crabs revealed a core response, with widespread downregulation of transcripts involved in immunity and molting. The transcriptional response differed between hosts from the parasite’s native range and where it is absent, consistent with previous observations of increased susceptibility in populations lacking exposure to the parasite. Crabs from the parasite’s introduced range, where prevalence is highest, displayed the most dissimilar response, possibly reflecting immune priming. These results provide molecular evidence for parasitic manipulation of host phenotype and the role of gene regulation in mediating host-parasite interactions.

mRNA-seq of tissue from experiments described in Tepolt et al 2020 "Recent introductions reveal differential susceptibility to parasitism across an evolutionary mosaic", Evolutionary Applications. 13(3), 545-558. Host (Rhithropanopeus harrisii) and parasite (Loxothylacus panopaei) transcriptomes were assembled using Trinity v2.8.5. Expression matrices constructed using utility scripts within Trinity and were filtered using R. All processing/analysis are contained within a corresponding GitHub repository (https://github.com/tepoltlab/RhithroLoxo_DE).

See publication supplement for sample metadata.