Does spatial sorting explain leading edge personality types in a spider's non-native range?

Expanding populations are often characterized by phenotypic shifts across the range. Processes like spatial sorting predict that phenotypes may be distributed along a range based on dispersal ability, where the most dispersive individuals are found at the leading edges and the least dispersive remain at the population core. Thus, traits correlated to dispersal may also become spatially distributed in the same pattern. Cyrtophora citricola is an orb-web spider with two expanding populations originating from the same core in its non-native Florida range. Since spiders at the leading edges were previously found to differ in various personality traits from those at the core, we measured dispersal latency and likelihood in laboratory-raised spiderlings to determine whether spatial sorting can account for these patterns. Only one of the two populations showed evidence of spatial sorting, suggesting this phenomenon is likely context dependent and is not always generalizable to expanding populations. Spiders from the leading edge of the eastern population were more dispersive than those at the core, although western spiders were the least dispersive of the three populations. Dispersal likelihood was correlated with the activity and exploratory tendencies of individuals. Population-level differences we had previously observed for foraging aggression and activity were not found in the captive-raised spiders, suggesting that they represent plastic responses to environmental conditions instead of being a result of dispersal-correlated trait evolution. However, mean population-level differences in exploration and boldness were maintained in captivity, suggesting that these behaviors have a heritable component. Overall, the eastern spiders were characterized as being bolder, whereas the western spiders were the least bold and exploratory. While this study provides evidence of spatial sorting of more dispersive, exploratory, and active individuals in the eastern population, the divergence in risk-taking behaviors between the two populations highlights the potential context dependency in spatial sorting and the importance of understanding the interactions between natural and spatial selection.

Automated summary

This study investigates the dispersal and exploratory tendencies in two spider populations and finds evidence of spatial sorting in one population, suggesting a context-dependent phenomenon. The study also reveals population-level differences in boldness and exploration, which have a heritable component. These findings highlight the importance of understanding the interactions between natural and spatial selection and the potential context dependency in spatial sorting.