The Effect of Fluctuating Temperatures During Development on Fitness-Related Traits ofScatophaga stercoraria(Diptera: Scathophagidae)

Abstract

Development of ectotherms is highly temperature dependent. Studies using variable thermal environments can improve ecological relevance of data because organisms naturally face day-to-day stochastic temperature fluctuations as well as seasonal changes in the amplitude of such daily fluctuations. The objective of this study was to investigate if, and to what extent, the use of constant temperatures is justified in studies of the model species, yellow dung fly, Scatophaga stercoraria (L.). We examined the effect of temperature fluctuation on the expression of several life history traits and the effect on subsequent adult longevity. We used two fluctuating temperature treatments with the same mean but different amplitudes (15/21°C, 12/24°C; 12/12 h), and three constant temperature treatments spanning the wide temperature range faced in the wild (12, 18, and 24°C). Large temperature fluctuation was mostly detrimental (lower juvenile survival, slower growth, smaller body size, and longer development), whereas moderate temperature fluctuation usually gave responses similar to the constant regime. When developing in fluctuating temperatures, adult longevity (no effect), body size (lower), and wing shape (narrower wings) deviated from the expectations based on the constant temperature reaction norms, presumably because of acclimation responses. Contrary to some studies no obvious beneficial effects of moderate temperature fluctuation were observed. Instead, yellow dung flies seem to canalize development in the face of temperature fluctuation up to a point when detrimental effects become unavoidable. The relatively greater effects of extreme constant developmental temperatures question their biological relevance in experiments.

Insects in Fluctuating Thermal Environments

“…These delays are likely a consequence of direct cold or heat injuries and of the costs of subsequent physiological and biochemical repair (23,43). By contrast, FTs that remain within the permissive thermal range can result in diverse responses, including accelerated development (2,13,44,65,66), slower development (25,42,66), or no change in developmental rate (65). One explanation of this variation in responses is that the effect of FTs on the development may depend on the thermal mean that is used and its proximity to developmental thresholds (65).…”

“…Accelerated development appears to be the norm if the lower temperature of the FT is not injurious, but falls below a species' thermal threshold for development (93). Finally, the effect of FTs on development time also depends on the 9 amplitude of the variation (14,42,46,66), likely because of Jensen's inequality. For example,…”

Ecological and evolutionary impacts of changing climatic variability

“…Indeed, Kjærsgaard et al . () advocate the use of more relevant fluctuating temperatures in experimental studies of the ecological impact of climate change.…”

“…Likewise, Kjærsgaard et al . () reported that increased temperature variability decreased the individual performance of yellow dung flies Scatophaga stercoraria . Furthermore, some studies have shown that moderate amounts of environmental variability do not necessarily have detrimental effects on performance, compared to greater levels of variability (Pétavy et al, ; Folguera et al, ).…”

Effects of daily fluctuating temperatures on the Drosophila–Leptopilina boulardi parasitoid association

“…However, thermoperiods can have profound effects on the development time of insects in comparison to constant temperatures (reviewed in Colinet et al, 2015), with an accelerating effect of fluctuating thermal regimes in many cases (Beck, 1983;Ratte, 1984;Fischer et al, 2011;Ragland & Kingsolver, 2008;Kingsolver et al, 2009;Radmacher & Strohm, 2011;Bahar et al, 2012;Kjaersgaard et al, 2013). In our study, we used a thermal fluctuation around a mean temperature of 20 °C, which is much colder than the optimal temperature for this species (around 13 25 °C) (Fleury et al, 2009;Moiroux et al, 2012), and thus is situated in the convex part of its performance curve.…”