Warming tolerance across insect ontogeny: influence of joint shifts in microclimates and thermal limits

Sylvain S. Pincebourde (1) , Jérome Casas (1)

1 IRBI - Institut de recherche sur la biologie de l'insecte

Not all species will experience global warming equally. First, organisms liv e in microcli mates, the temperatures of which can deviate substantially from macroclimate temperatures (Gates 1980, Angilletta 2009). Second, the physiological performance and tolerance of organisms filters microclimate conditions, often nonlinearly (Huey and Kingsolver 1993, Huey et al. 2012). Consequently, the impact of warming on the persistence and distribution of species cannot be inferred solely from macroclimatic observations. Instead, what is required is a mechanistic understanding of both microclimate and the physiological tolerance of species (Williams et al. 2008, Helmuth et al. 2010). For instance, tropical ectotherms were predicted to suffer the most from global warming because they already live close to their ther mal li mits, wh ereas temperat e ectother ms would benefit from a higher warming tolerance: a larger difference between macroclimate temperature and ther- mal limits (Deutsch et al. 2008, Tewksbury et al. 2008). Recently, a study showed that equilibrium body temperatures of most ectotherms at all latitudes are higher than both their thermal limits and ambient air temperature (inferred as the highest monthly mean of daily maximum air temperature), suggesting the need to thermo regulat e for the mai ntenanc e of popula tions (Sunday et al. 2014). However, the importance of microclimates is often neglected in studies on warming tolerance of ectotherms, as we will detail (Potter et al. 2013, Scheffers et al. 2013a). Warming tolerance (WT) is calculated as the devia- tion between the thermal limit—e.g., the critical maximal temperature, CTmax, or the uppe r letha l temperature, ULT—and the habitat temperature, which usually is taken as a monthly or annual average of macroscale air temperature (Deutsch et al. 2008). On that basis, a dire ct r elatio nshi p betwe en warming tolerance and absolute latitude is expected in ectotherms because macroclimate temperature increases from the poles to the equator and there is no clear pattern of CTmax or ULT over latitudes (Addo-Bediako et al. 2000, Deutsch et al. 2008, Sunday et al. 2011, Diamond et al. 2012, Arau´ jo et al. 2013). Frequently, this latitudinal pattern of warming tolerance is used to forecast potential distribution shifts in ectotherms caused by global warming (Sunday et al. 2012). Macro- climate temperature, however, can be uninformative regarding the actual relationship between physiological tolerance and latitude, because the pertinent variable often is the microclimate temperature (Fig. 1; see Huey et al. 2012, Sunday et al. 2014). Two lines of evidence suggestthatlackofknowledgeonmicroclimates

Mots clés: biophysical ecology; ectotherms; global warming; heat tolerance; herbivores; insect ontogeny; leaf temperature; life cycle; microclimate; Phyllonorycter blancardella; upper thermal limit; warming tolerance.

Domaines: Sciences du Vivant [q-bio]

Sylvain S. Pincebourde, Jérome Casas. Warming tolerance across insect ontogeny: influence of joint shifts in microclimates and thermal limits. Ecology, 2014, 96 (4), pp.986-997. ⟨10.1890/14-0744.1⟩. ⟨hal-01312923⟩