Evolution of invasive traits in nonindigenous species: Increased survival and faster growth in invasive populations of rusty crayfish (Orconectes rusticus)

Background/Question/Methods

Some nonindigenous species cause extensive ecological and economic harm, and those species that have strong impacts often share a suite of r-selected life history traits (such as rapid growth and reproduction) that allow them to reach high densities. The importance of evolution in the invasive range in shaping these traits is not well understood, especially in invasive animals. We examined the genetic basis for differences in growth, survival, and response to predators between native and invasive range populations of rusty crayfish (Orconectes rusticus). We hypothesized that repeated introductions into lakes would select for increased investment in growth and reproduction to overcome Allee effects. We collected O. rusticus as eggs from three native range and three invasive range populations and reared young of year crayfish in two common garden experiments. In summer 2011, we reared crayfish from both ranges in three lakes within the invasive range. In summer 2012, we reared crayfish in the laboratory where we controlled the presence of predatory fish, food quality, and temperature, which are likely important for O. rusticus growth.

Results/Conclusions

O. rusticus from invasive populations had significantly faster growth rates in laboratory conditions (P<0.001) and in lakes (P<0.001) compared to those from native populations. Predatory fish presence reduced crayfish growth in the laboratory (P=0.004), and had a similar effect on crayfish from both ranges. Egg size was similar between crayfish from the native and invasive range, and did not significantly affect crayfish growth, suggesting that maternal effects do not account for growth differences. Survival was significantly greater in O. rusticus from invasive populations in laboratory conditions (P<0.001) and in lakes (P<0.001). Fish presence did not affect the survival of crayfish from invasive populations, but reduced survival in crayfish from native populations (through nonconsumptive effects) (P=0.003). In summary, O. rusticus in the invasive range had faster growth, higher survival, and a weaker response to predatory fish than O. rusticus from the native range. Our data indicate that these r-selected life history traits have evolved since O. rusticus were introduced to the invasive range, and are consistent with our predictions of how selection in the invasive range would shape life history characteristics of nonindigenous populations. These traits likely contribute to the strong community level impacts of this invasive species.