Dietary preferences of Ninespine Stickleback in high Arctic tundra streams

Ninespine Stickleback Pungitius pungitius (Linnaeus, 1758) are generalist feeders of macroinvertebrates and zooplankton and are ubiquitous in Arctic freshwater and marine environments. Many invertivorous fish feed based on the abundance of different prey taxa, with this species known to select for abundant Baetidae and Daphniidae in Arctic ponds. Arctic stream invertebrate communities tend to be dominated by chironomids; however, these taxa may not hold the same nutritional value as others, such as Baetidae. Indeed, stickleback have previously shown selection for Baetidae in lentic environments, but little research has been conducted on selection in Arctic streams. Thus, the objectives of this study were to 1) describe the diet of Ninespine Stickleback across an Arctic tundra watershed and 2) identify dietary preferences, if any. DNA metabarcoding of stickleback gut contents from 14 different Arctic streams was used to examine stickleback diet, and electivity indices were used to determine prey selection. We found that stickleback in Arctic tundra streams fed primarily on chironomids because of their high abundance in the stream community, but stickleback showed higher preference for taxa known to provide higher caloric content, including Baetidae, Simuliidae, and Tipulidae. Diet and predatory preference differed between streams with cobble–boulder vs silt–pebble substrate types, but Chironomidae generally maintained lower importance than Baetidae, Simuliidae, and Tipulidae in both environments. With the progression of climate change loosening the physiological constraints on temperate invertebrates as they move north, further research should be conducted on how greater access to preferable (or higher nutritional quality) invertebrate food resources may affect Arctic fish populations and stream food webs.