Meeting Abstract
When invasive populations become established in novel environments, they often leave behind enemies such as predators and parasites that may regulate populations in the native range. Parasite escape can confer fitness benefits to invaders when they no longer experience infection pathology, and also because relaxed selection on immune defenses may promote resource reallocation towards growth or reproduction. However, this relaxed selection may ultimately lead to increased susceptibility upon exposure to parasites. We conducted laboratory studies comparing shore crabs (Hemigrapsus sanguineus) from their invasive (USA) range where parasite escape is well-documented to crabs from the native (Japan) range to test for differences in susceptibility to infection by a native rhizocephalan parasite, and to explore potential differences in immune characteristics and energy allocation. While invasive-range individuals mounted a stronger non-specific encapsulation response against a parasite mimic, we found that invasive-range crabs were ultimately more susceptible to rhizocephalan infection than their native-range counterparts. Individuals from the invasive populations also showed lower resting oxygen consumption and higher juvenile growth compared to natives. Our results suggest that invaders’ ability to defend against parasites may be reduced in favor of increased fitness in the absence of the threat of infection, but that further work is needed to identify the immunological underpinnings of the observed increase in susceptibility.
