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 can respond to high temperatures using behaviour, such as angling their wings away from the sun or seeking cool local microclimates to thermoregulate or through physiological tolerance. In a butterfly community in Panama, we compared the ability of adult butterflies from 54 species to control their body temperature across a range of air temperatures (thermal buffering ability), as well as assessing the critical thermal maxima for a subset of 24 species. Thermal buffering ability and tolerance were influenced by family, wing length, and wing colour, with Pieridae, and butterflies that are large or darker in colour having the strongest thermal buffering ability, but Hesperiidae, small, and darker 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 species with more stable body temperatures in the field may be more vulnerable to increases in ambient temperatures, for example heat waves associated with ongoing climate change. Our study demonstrates that tropical species employ diverse thermoregulatory strategies, which is also reflected in their sensitivity to temperature extremes.

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

“…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).…”

“…A strong buffering ability could correspond to greater climate resilience, as individuals are able to elevate their body temperature in cold conditions, which would benefit larval development (Hong et al., 2014 ) and adult flight (Nève & Hall, 2016 ), but lower their body temperature in hot conditions, which would prevent irreversible protein denaturation, unsustainable rises in metabolism and other processes that would otherwise result in reduced survival and reproductive success (González‐Tokman et al., 2020 ; Heath et al., 1971 ; Svensson et al., 2020 ). However, it is also possible that a strong buffering ability may inhibit the evolution of tolerance to non‐optimal temperatures (Ashe‐Jepson et al., 2023 ); however, to date this has not been investigated for Lepidoptera larvae.…”

Hot topics in butterfly research: Current knowledge and gaps in understanding of the impacts of temperature on butterflies

“…However, behaviour can mediate the impacts of changing temperatures (Stevenson, 1985), for example, by shifts in habitat use (Ashton et al, 2009), behavioural thermoregulation (Kemp & Krockenberger, 2002), or oviposition preference (Eilers et al, 2013). Behavioural thermoregulation can help species persist outside of their climate niche, but recent evidence also suggests that it may hinder adaptation to thermal tolerance by reducing the selective pressures that individuals are exposed to (Ashe-Jepson, Cobo, et al, 2023;Buckley et al, 2015). As a result, behaviour may play a critical role in population persistence under future climate change.…”