Variation in adult stress resistance does not explain vulnerability to climate change in copper butterflies

Abstract

Ongoing climate change is a major threat to biodiversity. However, although many species clearly suffer from ongoing climate change, others benefit from it, for example, by showing range expansions. However, which specific features determine a species' vulnerability to climate change? Phenotypic plasticity, which has been described as the first line of defence against environmental change, may be of utmost importance here. Against this background, we here compare plasticity in stress tolerance in 3 copper butterfly species, which differ arguably in their vulnerability to climate change. Specifically, we investigated heat, cold and desiccation resistance after acclimatization to different temperatures in the adult stage. We demonstrate that acclimation at a higher temperature increased heat but decreased cold tolerance and desiccation resistance. Contrary to our predictions, species did not show pronounced variation in stress resistance, though plastic capacities in temperature stress resistance did vary across species. Overall, our results seemed to reflect population-rather than species-specific patterns. We conclude that the geographical origin of the populations used should be considered even in comparative studies. However, our results suggest that, in the 3 species studied here, vulnerability to climate change is not in the first place determined by stress resistance in the adult stage. As entomological studies focus all too often on adults only, we argue that more research effort should be dedicated to other developmental stages when trying to understand insect responses to environmental change.

Effects of temperature and drought on early life stages in three species of butterflies: Mortality of early life stages as a key determinant of vulnerability to climate change?

“…In contrast to the above results on egg mortality, the respective interaction between species and treatment was not significant for hatchling mortality, although the pattern obtained was very similar (see Figure 2). These results may suggest that vulnerability to stress decreases during development, which is in line with an earlier study on the same species as investigated here, in which we found that differences in vulnerability to climate change are unlikely to be caused by differential responses to thermal and desiccation stress during (later) larval and pupal development or in the adult stage (Klockmann, Wallmeyer, et al, 2017). Thus, in the species considered here, the early developmental stage, especially the egg stage, seems to be the most critical life stage determining vulnerability to climate change.…”

“…Importantly, we found that closely related species, arguably differing in their vulnerability to climate change, seem to differ in their responses to environmental stress. However, such variation was restricted to early developmental stages, while different levels of stress seem to have little effect on fitness during further development (i.e., in older larvae, pupae, and adults; Potter et al., ; Klockmann, Günter, et al., ; Klockmann, Karajoli, et al., ; Klockmann, Schröder, et al., ; Klockmann, Wallmeyer, et al., ). We suggest that, in the three species investigated here, stress tolerance during early development might be a major determinant of vulnerability to climate change and may explain recent population declines in L. helle along with habitat deterioration (Bauerfeind, Theisen, & Fischer, ; Fischer et al., ).…”

“…Consequently, these species may also differ in (heat) stress tolerance and concomitantly in their vulnerability to climate change, ranging from low to high risk (Ebert & Rennwald, 1991;Settele et al, 2008;Habel et al 2011; see further below and Table 1). We focus on early developmental stages because earlier studies showed that differences in vulnerability are unlikely to be caused by differential responses to thermal stress during larval and pupal development (Klockmann, Karajoli, Reimer, Kuczyk, & Fischer, 2016;Klockmann, Schröder, Karajoli, & Fischer, 2016) as well as adult stress resistance (Klockmann, Wallmeyer, & Fischer, 2017). We hypothesize that (i) mortality rates increase at higher temperature and additionally with reduced humidity in all species, (ii) and that L. helle will suffer most strongly from simulated heat and drought stress.…”

Low winter precipitation, but not warm autumns and springs, threatens mountain butterflies in middle-high mountains

“…The beneficial effects of warmer temperatures apply only up to species-specific limits, set by heat tolerance ( Terblanche et al, 2017 ), diapause/moulting triggers ( Gonzalez-Tokman et al, 2020 ), or thermal effects mediated via host plants ( Barrio, Bueno & Hik, 2016 ). Caterpillar feeding may be impaired by temperatures above their thermal limits ( Klockmann, Wallmeyer & Fischer, 2018 ), and feeding efficiency may decline with increased respiration rates ( Bauerfeind & Fischer, 2013 ; Kukal & Dawson, 1989 ). As we found no negative effects of warm autumns or springs, we presume that the warmer conditions of the last decade had not yet exceeded the studied species’ thermal optima.…”

“…The physiological triggers speeding-up development may be intuitive, such as warm springs ( Gutiérrez & Wilson, 2020 ; Stewart et al 2020 ), or less straightforward, and may include warm periods in autumn ( Pak, Biddinger & Bjornstad, 2019 ) or deep winter frosts ( Stalhandske, Gotthard & Leimar, 2017 ). On the other hand, too warm temperatures during larval periods may impair energy assimilation ( Klockmann, Wallmeyer & Fischer, 2018 ) and even increase mortality ( Karl et al, 2011 ), and adult mortality may increase due to heat shocks ( Janowitz & Fischer, 2011 ).…”