Tropical butterflies use thermal buffering and thermal tolerance as alternative strategies to cope with temperature increase

Abstract

Climate change poses a severe threat to many taxa, with increased mean temperatures and frequency of extreme weather events predicted. Insects respond to non-optimal temperatures using behaviours or local microclimates to thermoregulate (thermal buffering ability), or through physiological tolerance. We studied the thermal buffering ability and thermal tolerance of a community of 54 butterfly species in Panama. Thermal buffering ability and tolerance were influenced by family, size, and colour, with Pieridae, large, and dark butterflies having the strongest thermal buffering ability, and with Hesperiidae, small, and dark butterflies tolerating the highest temperatures. We identified an interaction between thermal buffering ability and physiological tolerance, where species with stronger thermal buffering abilities had lower thermal tolerance, and vice versa. This interaction implies that most species will be vulnerable to climate change to an extent, considering that species appear to adapt to one strategy at the expense of the other.

Day‐flying lepidoptera larvae have a poorer ability to thermoregulate than adults

“…However, there is a possibility that strong thermal buffering ability may inhibit adaptation to tolerate higher temperatures, as individuals would rarely be exposed to selection to evolve mechanisms to cope with non‐optimal temperatures (Muñoz, 2022). For example, a recent study on tropical adult butterflies has shown that species with a weaker buffering ability also had lower thermal tolerance (Ashe‐Jepson et al., 2023). This theory, dubbed the ‘Bogert effect’ (Huey et al., 2003), may mean that species with strong buffering abilities may initially be less impacted by changing temperatures.…”

“…However, should microclimates be lost or an extreme weather event were to occur whereby temperatures rise or fall outside tolerable ranges (such as during a heatwave), species with strong buffering abilities could have a reduced thermal tolerance compared to species with weak buffering abilities, and may be disproportionately affected. This implies that most species may be vulnerable to climate change; however, further study is needed to determine whether thermal buffering ability interacts with thermal tolerance in Lepidoptera larvae (Ashe‐Jepson et al., 2023).…”

“…A previous study on adult British butterflies identified traits that influence their ability to thermoregulate (maintain a stable body temperature across a range of air temperatures; thermal buffering ability), with species with larger wings and those in the family Pieridae having the strongest buffering abilities, compared to smaller species and those in the family Nymphalidae (Bladon et al, 2020). This pattern is also reflected in a community of tropical butterflies (Ashe-Jepson et al, 2023), which also identified colour as an important factor, whereby butterflies with dark wings had stronger thermal buffering abilities than pale butterflies. This implies that these traits (taxonomic family, size and colour) could play a relatively consistent role in adult butterfly thermoregulation.…”

“…To test whether gregarious versus solitary behaviour affects buffering ability, and to separate this from effects of body length, two species with gregarious instars ( A. urticae and P. brassicae ) were paired with similar but non‐gregarious species within the same family ( A. urticae with V. atalanta and P. brassicae with P. rapae ) and tested individually. Although A. io is also gregarious, it was excluded from this analysis as there wasn't a suitable paired non‐gregarious species available with similar traits known to influence thermal buffering abilities in butterflies (such as size, colour and family identity; Ashe‐Jepson et al., 2023; Bladon et al., 2020). We calculated a new size category variable for each pair, where the size of the largest gregarious larva was used to define size categories (‘large’ for larvae above this length, ‘small’ for larvae equal to or below this length).…”

“…We found that larval day-flying Lepidoptera are worse at buffering their body temperature than adults. As air temperatures increase, most adult Lepidoptera can slow their rate of heat gain, and at high air temperatures, even lower their body temperature below ambient conditions (Ashe-Jepson et al, 2023;Bladon et al, 2020).…”