Climate change homogenizes habitat globally, facilitating the expansion and rapid proliferation of invasive species which damage the newly invaded ecosystem. Intraspecific aggression among an invasive species is an important focus in ecological studies because it can contribute to their overall success as invaders. The ability for species to recognize individuals from the same community can increase individual fitness by preventing wasteful displays of competition. The crayfish species Procambarus clarkii inhabits freshwater streams in the Santa Monica Mountains (Los Angeles, CA) as a highly aggressive invasive predator. These invasive crayfish disrupt stream communities by burrowing in the sediment and acting as a predator to native amphibians and macroinvertebrates. Additionally, they are well known for their highly aggressive interactions with conspecifics. It has been shown that body size, temperature, sex, and level of hunger influence the levels of aggression that crayfish exert toward conspecifics. However, there is a lack of research that investigates how population demography affects agonistic interactions between crayfish, in line with the my dear enemy hypothesis. In this study we investigated the effect of site origin on intraspecific aggression of Procambarus clarkii. We predicted that crayfish from the same site origin will display lower intensities of conspecific aggression than crayfish from different stream site origins. To test this hypothesis, we conducted experimentally controlled trials with pairs of crayfish from the same stream locale and different stream locales and scored their level of aggressive interaction.
Results/Conclusions
Crayfish from different stream locales displayed significantly higher intensities of intraspecific aggressive interactions compared to crayfish pairs from the same locale (P < 0.01, two tailed t test). Crayfish interactions that involved two crayfish from a different site had an average aggression score of 2.49, while crayfish interactions that involved two crayfish from the same site had an average aggression score of 1.60. Furthermore, crayfish aggression was seen to increase over time. In the first minute of interaction, the average aggression score was 1.37, while in the last minute of interaction, the score was 1.90. These results demonstrate that agonistic behavior in these invasive crayfish is influenced by recognition via residence. This study highlights the impact recognition plays in intraspecific crayfish aggression, which ultimately, can contribute to their success as an invasive species.