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Abstract Anthropogenic changes are often studied in isolation but may interact to affect biodiversity. For example, climate change could exacerbate the impacts of biological invasions if climate change differentially affects invasive and native species. Behavioural plasticity may mitigate some of the impacts of climate change, but species vary in their degree of behavioural plasticity. In particular, invasive species may have greater behavioural plasticity than native species since plasticity helps invasive species establish and spread in new environments. This plasticity could make invasives better able to cope with climate change.Here our goal was to examine whether reproductive behaviours and behavioural plasticity vary between an introduced and a nativeOnthophagusdung beetle species in response to warming temperatures and how differences in behaviour influence offspring survival.Using a repeated measures design, we exposed small colonies of introducedO. taurusand nativeO. hecateto three temperature treatments, including a control, low warming and high warming treatment, and then measured reproductive behaviours, including the number, size and burial depth of brood balls. We reared offspring in their brood balls in developmental temperatures that matched those of the brood ball burial depth to quantify survival.We found that the introducedO. taurusproduced more brood balls and larger brood balls, and buried brood balls deeper than the nativeO. hecatein all treatments. However, the two species did not vary in the degree of behavioural plasticity in response to warming. Differences in reproductive behaviours did affect survival such that warming temperatures had a greater effect on survival of offspring of nativeO. hecatecompared to introducedO. taurus.Overall, our results suggest that differences in behaviour between native and introduced species are one mechanism through which climate change may exacerbate negative impacts of biological invasions. 

Abstract Ecologically relevant symbioses are widespread in terrestrial arthropods but based on recent findings these specialized interactions are likely to be especially vulnerable to climate warming. Importantly, empirical data and climate models indicate that warming is occurring asynchronously, with night‐time temperatures increasing faster than daytime temperatures. Daytime (DTW) and night‐time warming (NTW) may impact ectothermic animals and their interactions differently as DTW results in greater daily temperature variation and moves organisms nearer to their thermal limits, while NTW avoids thermal limits and may relieve constraints of cooler night‐time temperatures; a nuance that has largely been ignored in the literature.In laboratory experiments, we investigated how the timing of warming influences a widespread defensive mutualism involving the pea aphidAcyrthosiphon pisum, and its heritable symbiont,Hamiltonella defensa, which protects against an important natural enemy, the parasitic waspAphidius ervi.Three aphid sublines were experimentally created from single aphid genotype susceptible toA. ervi: one line infected with a highly protectiveH. defensastrain, one infected with a moderately protective strain and one without any facultative symbiont. We examined aphid fitness in the presence and absence of parasitoids and when exposed to an average 2.5°C increase occurring across three warming scenarios (night‐time vs. daytime vs. uniform) relative to no‐warming controls.An increase of 2.5°C, as predicted to occur by the IPCC before 2100, was sufficient to disable the aphid defensive mutualism regardless of the timing of warming; a surprising result given that the daily maxima for control and NTW scenarios were identical. We also found that warming negatively impacted (a) symbiont‐mediated interactions between host and parasitoid more than symbiont‐free ones; (b) species interactions (host–parasitoid) more than each participant independently and (c) aphids more than parasitoids even though higher trophic levels are generally predicted to be more affected by warming.Here we show that 2.5°C warming, regardless of timing, negatively impacted a common microbe‐mediated defensive mutualism. While this was a laboratory‐based study, results suggest that temperature increases predicted in the near‐term may disrupt the many ecological symbioses present in terrestrial ecosystems.