Who are you calling a shrimp? Evaluating aggression, boldness, territoriality, and behavioral strategies in an invasive stomatopod (Gonodactylaceus falcatus)

Abstract

Biological surveys conducted on Oʻahu, Hawaiʻi have indicated the stomatopod (Order Stomatopoda), Gonodactylaceus falcatus, to be the most widely distributed invasive marine invertebrate in nearshore marine ecosystems. Similar to marine crustaceans around the world, G. falcatus was introduced to Hawaiʻi due to the combination of increased maritime activity following WWII and their planktonic larval phase. While this pathway has been documented for facilitating its introduction into the islands, it remains unclear what characteristics have supported the establishment and successful invasion of this species into this non-native environment. Previous work has focused on the role behavior can play in this scenario, suggesting that differences in specific behavioral traits between invasive and native species contribute to the invasion success and overall interactions between these species and their new environment. In particular, studies have identified behavioral syndromes (consistency of single behavior across contexts and/or correlation between two traits) as a behavioral strategy that has contributed to the invasion success of many taxa. I tested the boldness and aggression of G. falcatus (n = 101) to determine if a behavioral syndrome was present and to characterize the overall behavioral variation within these traits. Three syndrome analyses were conducted (mixed model, intraclass correlation coefficient, Spearman's correlation) and a lack of evidence for a behavioral syndrome in this species was identified. While a syndrome wasn't present, these behavioral traits may still be contributing to their success if as a species they are more bold and/or aggressive than the native stomatopod species. When analyzing the individual traits, boldness and aggression increased across trial number (replicate) and this study also found larger individuals to respond more aggressively than smaller counterparts. Some factors typically found to impact how bold or aggressive an individual is (e.g., sex) were not significant within this study.In addition to testing the boldness and aggression of G. falcatus, I also analyzed their territorial contests to determine the outcomes between size-matched individuals and what characteristics might drive these results. I conducted 86 size-matched contests that included three categories: intrasexual females, intrasexual males, and intersexual. The same individual won the majority (84%) of repeated trials but questions regarding what is driving these results, individual recognition or behavioral consistency, remain. Of the intrasexual contests (females and males), residents won the majority of contests supporting previous work that has identified a bias towards the resident in matched contests. On the other hand, during intersexual contests there was a substantial decrease in the proportion of contests won by residents. Further analysis determined that males were winning more frequently than females in intersexual contests. While it remains unknown why this shift has occurred, I hypothesize that sexual dimorphism in the weaponry of G. falcatus is impacting the resource holding potential and the perceived strength of their competitor. Overall, this thesis provides a behavioral characterization of G. falcatus and how their behavior may influence their success as invasive species, although additional studies should be performed to gain a deeper understanding of this invasion. This study also uncovered an interesting trend in the contest outcome during intersexual contests, which have rarely been included in previous work and proposes a hypothesis to explain what might be driving differences in context outcomes between females and males. Finally, this thesis has identified an overall lack of studies focused on the role of behavior in the invasions of marine crustaceans and how it may differ from other taxa (e.g., terrestrial vertebrates).