Climate change at the air-water interface affects giant salmonfly (Pteronarcys californica) emergence timing and adult lifespan

Abstract

Aquatic invertebrates experience complex temperature regimes throughout their life history, especially during the vulnerable life stage transition from aquatic to terrestrial habitats. When climate warming interacts with snowmelt in high elevation systems, it creates a novel set of conditions in which spring water temperatures remain within a narrow range from year-to-year while summer water and air temperatures rise. Giant salmonflies (Pteronarcys californica) depend on spring water temperature cues to time their large, synchronous emergence in early summer, but it is unknown how variable temperatures after this springtime cue affect life-history traits. We experimentally tested how changes in temperature in the 6 weeks before and after emergence affect emergence timing, emergence success, and adult lifespans. We found that the timing of emergence was 2.8 days earlier with each degree of warming during the weeks preceding emergence. However, there was no evidence that emergence success was affected by higher water temperature within our test temperature range (13-23°C). In the terrestrial adult stage, adult lifespans were shortened by increased air temperatures, especially when water temperatures during the aquatic juvenile stage had also been increased. The predicted lifespan was almost five times longer at the coldest air and water temperature combination than at the warmest (28 vs. 6 days). The shortest lifespans observed (3 days) are not likely to prevent successful reproduction, given that salmonflies can mate and oviposit within days of emergence. Still, because salmonflies can oviposit repeatedly for up to 80% of their lifespan, shortened lifespans may reduce total egg production and thus fitness. Our results indicate that rising water and air temperatures will impact not only the life history of the insects, but also the organisms in the riparian zone that rely on salmonfly emergence by altering the timing, magnitude, and duration of the nutrients provided by these large-bodied aquatic insects.