Colonization of drying temporary wetlands by Coptotomus loticus (Coleoptera: Dytiscidae): a unique strategy for an aquatic wetland insect

Abstract

Predaceous diving beetles (Coleoptera: Dytiscidae) are well-known for their ability to colonize both permanent and temporary aquatic habitats. They often move predictably between these two habitats, colonizing recently flooded habitat and returning to permanent habitat during the dry-down phase. However, Coptotomus loticus Hilsenhoff does not appear to utilize this same strategy. The objective of our study was to investigate the spatial and temporal patterns of C. loticus distribution in wetland habitats of the southeastern USA. Floodplain wetlands were sampled seasonally over 2 years (a drought year and a flood year), and Carolina bays were sampled seasonally over 3 years. During the drought year, C. loticus remained primarily in permanent water bodies on the floodplain. During the flood year, C. loticus utilized temporary habitats on the floodplain to a greater degree than in the drought year. High densities of C. loticus were more common in temporary habitat during the latter half of the year (dry-down phase) versus the early actively-flooding portion of the year. The highest density of C. loticus in Carolina bays was also found during the dry-down phase. These results suggest C. loticus may be accessing temporary wetland habitat in which fish and other vertebrates may be stranded as the habitat dries down. Dytiscids have been known to consume vertebrate carrion, and in this study system, C. loticus may be utilizing the dry-down effect to hone in on stranded vertebrates as a readily available food source, a strategy not yet described among wetland macroinvertebrates. This phenomenon warrants further study in this and other systems, however, to verify its existence across time and space.