Effects of environmental temperature on biology of cold-adapted Chironomidae (Diptera) from Minnesota and Iceland

Abstract

Chironomids are an abundant and speciose family of aquatic flies which dominate freshwater environments globally. Additionally, chironomids are important food sources for fish and can be used as bioindicators of water quality. This family includes species that are adapted to emerge as adults in winter and under cold conditions across the globe. Both air and water temperatures influence these insects since they grow in aquatic habitats and then emerge as terrestrial adults. However, little research has focused on the effects of thermal heterogeneity in shaping community structure along stream length, how stream temperatures may influence thermal acclimatization in adult chironomids, and the impacts of warm temperature exposure on biology of Arctic, winter-active chironomids. These questions become significant considering climate change since warming temperatures will threaten aquatic systems and cold-adapted organisms including cold-adapted chironomids. The goal of this dissertation was to investigate the influence of water temperature on winter emerging chironomid species composition and air temperature on adult Arctic chironomid lifespan and reproduction. Field work investigating thermal heterogeneity in streams was conducted in Minnesota. Collections of pupal exuviae along the length of thermally variable groundwater-fed streams revealed thermal portioning in taxa along stream length. Thermal partitioning in chironomids indicates that chironomids develop in and emerge from different thermal regimes, and, thus, may display developmental acclimatization to warm temperatures if they emerge from warm springs. Chironomids were collected from geothermally heated and cold springs in southwestern Iceland and placed into warm and cold incubation treatments. Results indicate that chironomids with long degree-day requirements emerging from warm springs have a maximized lifespan under both cold and warm air temperatures. Investigations of winter-active chironomids have been conducted in Europe and North America with little work focused on the Arctic. Iceland, a near Arctic country, faces increasing climate change threats and, thus, documenting warming effects on cold-adapted biota is essential. Winter-active chironomids were documented in Iceland for the first time and investigations of longevity and oviposition timing revealed susceptibility to warm air temperatures in winter emerging Icelandic chironomids. Chironomids comprise a large portion of aquatic food webs, and in Arctic regions, are the predominant aquatic insects. Investigating how environmental conditions control both community composition and population dynamics will further the conservation of cold-water systems by increasing the understanding of how climate change may impact cold-adapted biota.