For decades, biologists have sought predictive models of where and when biological invasions will occur. Much of this work has focused on characterizing traits of invasive species, such as competitive ability and predatory habits. Behavioral plasticity, or changes in an organism’s behavioral phenotype in response to environmental change, has been largely neglected in empirical studies. However, behavioral plasticity may allow invasive species to optimize their response to environmental change, allowing them to outcompete native species and become established. To close this knowledge gap, we examined whether an invasive dung beetle, Onthophagus taurus, has greater behavioral plasticity in breeding behavior compared to a closely related native species, O. hecate. Onthophagus dung beetles reproduce by burying brood balls made of dung and containing a single egg. The size and burial depth of brood balls affect offspring survival and size at emergence by altering the nutrients available to offspring and the temperatures they experience. We exposed colonies of beetles to three different temperature treatments (hot, warm, and mild) and recorded number, size, and burial depth of brood balls as well as offspring survival. We used the slope of reaction norms for colonies across the different treatments to examine degree of behavioral plasticity.
Results/Conclusions
We found that the degree of behavioral plasticity of brood ball size and burial depth was not significantly different between O. taurus and O. hecate. Both species adjusted reproductive behavior when exposed to warmer temperatures. Colonies of O. taurus buried brood balls deeper beneath the soil and produced larger brood balls in all three treatments compared to O. hecate, likely due to the fact that O. taurus has a larger body size. Both species buried brood balls deeper as temperatures increased, but mass of brood balls was not significantly affected by temperature in either species. By burying brood balls deeper in the soil and producing larger brood balls, O. taurus beetles better protected offspring from increased temperature gradients in the soil. O. taurus offspring survival rate and body size upon emergence was not affected by increased temperature while O. hecate offspring had decreased survival rates and body sizes. Thus, O. taurus may be better equipped to deal with warming compared to O. hecate, but not through increased behavioral plasticity. These results indicate that O. taurus may not be affected, or may even increase, due to climate change while O. hecate may decline, exacerbating the effects of the invasion.