Microparasite challenge and subsequent energy trade-offs in an invasive crab species

Zain Aryanpour, a student at the University of Alabama, worked with Dr. Jeb Byers and Carrie Keogh to examine the cost of infection on immune response of an invasive crab species.

Abstract: Invasive species often show phenotypic distinctions in relation to their native-range species. A topic of current interest in populations of invasive species is their immune systems and functions, and whether costs of immune function are altered given the differences in selective pressures they experience in the invasive range. In our study, an invasive Asian shore crab species, Hemigrapsus sanguineus, was utilized as the model system for investigating the short-term energy demand in response to microparasite challenge, the potential relationship between supposed immune stimulation and bacterial killing ability, and the potential relationship between bacterial killing ability and respiration rate. For experimental variables, we utilized LPS injections as the microparasite challenge, optimized a bacterial killing assay to measure immune strength, and used a Qubit Respirometer to measure oxygen consumption for pre- and post-injection crabs. We then ran ANCOVA analyses on bacterial killing and oxygen consumption data and analyzed the relationships between data. The data suggests that microparasite challenge had no effect on energy expenditure in LPS crabs but PBS-injected control crabs showed significantly higher oxygen consumption than LPS crabs after injection. The challenge had little to no effect on bacterial killing ability on either experimental or control crabs. And finally, there is no significant relationship between bacterial killing ability and respiration rate. The results could either be explained by experimental errors in LPS injections (insufficient concentration of LPS, although 0.25 mg/mL was sufficient in previous studies) or the potential explanation that microparasite challenges are not costly on these crabs. A further comprehensive study with a combination of micro- and macroparasite challenges plus additional replicates would most likely give a clearer overview of the immune response and function in this wild population. Further experiments comparing native and invasive parasite response would also improve this study.

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