Effects of experimental warming on survival, phenology, and morphology of an aquatic insect (Odonata)

Abstract

1. Organisms can respond to changing climatic conditions in multiple ways including changes in phenology, body size or morphology, and range shifts. Understanding how developmental temperatures affect insect life-history timing and morphology is crucial because body size and morphology affect multiple aspects of life history, including dispersal ability, while phenology can shape population performance and community interactions. 2. We experimentally assessed how developmental temperatures experienced by aquatic larvae affected survival, phenology, and adult morphology of dragonflies (Pachydiplax longipennis). Larvae were reared under 3 environmental temperatures: ambient, +2.5 °C, and +5 °C, corresponding to temperature projections for our study area 50 and 100 years in the future, respectively. Experimental temperature treatments tracked naturally-occurring variation. 3. We found clear effects of temperature in the rearing environment on survival and phenology: dragonflies reared at the highest temperatures had the lowest survival rates, and emerged from the larval stage approximately 3 weeks earlier than animals reared at ambient temperatures. There was no effect of rearing temperature on overall body size. Although neither the relative wing nor thorax size was affected by warming, a non-significant trend towards an interaction between sex and warming in relative thorax size suggests that males may be more sensitive to warming than females, a pattern that should be investigated further. 4. Warming strongly affected survival in the larval stage and the phenology of adult emergence. Understanding how warming in the developmental environment affects later life-history stages is critical to interpreting the consequences of warming for organismal performance.

Effects of environmental warming during early life history on libellulid odonates

“…These studies have found that growth rates increase in warmer temperatures (except see Van Doorslaer and Stoks 2005a), an expected result because ectotherm growth rates are known to scale allometrically with temperature (Angilletta et al 2004). Faster growth rates are likely to underlie observed patterns of advancing phenology, such as earlier adult emergence in odonates (Hassall et al 2007;McCauley et al 2015). Whether accelerated growth rates in the context of a warming environment has net benefits or costs for populations will depend on the species and the ecological context in which these animals exist.…”

“…Increases in temperature as a result of climate change could potentially add additional sources of mortality to populations that already have low larval survival (Cornell and Hawkins 1995;Hirst and Kiørboe 2002;Forster and Hirst 2012). Temperature appears to increase odonate mortality when larvae develop and metamorphose in heated conditions (McCauley et al 2015). These types of studies, however, often do not track survival throughout development and therefore it remains unclear at what stage mortality is occurring.…”

“…For example, in freshwater systems, adult odonates (dragonflies and damselflies) are advancing the timing of their emergence from aquatic habitats earlier in the season (Hassall et al 2007;Dingemanse and Kalkman 2008). Experimental warming of water temperatures has also been observed to result in earlier emergence in a dragonfly species (McCauley et al 2015). Increasing temperatures can also hasten egg development rate, therefore advancing the timing of hatching (Howe 1967;Elliott 1978;Leggott and Pritchard 1985).…”

“…Therefore, it remains unclear at what stage higher temperatures are causing observed increases in mortality (Klockmann et al 2017). In one dragonfly species, higher mortality occurred when larvae were reared in warmer temperatures; however, survival was only measured at metamorphosis (McCauley et al 2015). The timing of mortality in odonates exposed to warming will influence aquatic food webs; mortality early in development has very different effects on the role of these predators in aquatic systems than if most of this mortality is occurring at or near metamorphosis.…”

Differential larval responses of two ecologically similar insects (Odonata) to temperature and resource variation

“…A range of other odonate responses to climate change have also been documented, including body size reductions (Forster, Hirst, & Atkinson, 2012), northerly range shifts (Flenner&Sahlén, 2008; Grewe, Hof, Dehling, Brandl, & Braendle, 2013; Hickling, Roy, Hill, & Thomas, 2005), and advancing phenologies (Dingemanse & Kalkman, 2008; Hassall, Thompson, French, & Harvey, 2007). Larval dragonflies exposed to experimental warming show a range of responses including increased mortality and advancing phenologies (McCauley, Hammond, Frances, & Mabry, 2015; Richter, Suhling, Mueller, & Kern, 2008; Suhling, Suhling, & Richter, 2015). Further, there is evidence of variation between odonate species in response to warming (Suhling & Suhling, 2013).…”