Macroecology and Potential Drivers of Diversity in Webspinner Maternal Care (Order Embioptera)

Abstract Embioptera display variability in egg-handling as part of their defense against natural enemies. Because species living in tropical regions experience potentially higher risks of predation than those in temperate climes, we hypothesized that variable risk might explain this variability. We used actual evapotranspiration (AET) rates as a stand-in for climate, region, and potential interactions with natural enemies. We predicted that more complex investments, such as coating individual eggs, organizing them, and topping the cluster with thick silk would co-occur with greater predation threats in tropical regions, scored as higher AET. We predicted that simpler organization of eggs would occur where predator risk would be lower, as in temperate regions (lower AET). We used phylogenetic comparative methods to assess whether more complex egg handling behavior correlated with high AET scores. We quantified five traits of egg handling from field and laboratory evidence for 29 species from habitats ranging from low to high AET. Initial pGLS and pGLM analyses showed a weak effect of AET on parental care index. Upon exclusion of three exotic species spread artificially by trade and collected outside their native ranges, we found strong effects of predation threat in both pGLS and pGLM analyses. These analyses revealed that species that experience potentially greater predation threats exhibited behaviors that corresponded to more complex handling and organization of eggs by the mother. These results align nicely with analyses that also detected that additional lines of defense of eggs typify the behavior of tropical species of other primitively social arthropods.