Environment, taxonomy and morphology constrain insect thermal physiology along tropical mountains

Abstract

1. Tropical mountains display limited variation in monthly temperatures, but high spatial climatic variability. It is assumed this stability promotes ecological and physiological adaptations to local temperatures, which may preclude dispersal up or downslope. Determining how environmental, taxonomic and morphological factors affect thermal limits is fundamental to understand biotic responses to global warming. 2. We selected 54 species of dragonflies and damselflies (Order Odonata) distributed from 300 to 2,550 m along one of the most biodiverse regions on the planet, the Tatamá elevational gradient in the Andean-Choco region transition.We estimated for 846 individuals three thermal tolerance parameters: CT max , the highest temperature preceding the loss of motor control, T vol , the temperature at which individuals avoid heat, and CT min , the minimum temperature required for wing movement.3. For each thermal tolerance parameter, we evaluated associations between physiological and behavioural responses, species elevational distribution and specialization to forests or open areas. We also evaluated the effect of autecological characteristics such as body mass, sex and taxonomy on temperature regulation. 4. Temperatures prevalent at different elevations and habitats are associated with odonate upper thermal limits. However, tolerance to low temperatures is not associated with habitat use or elevation. Forest species display lower thermal tolerances. Small species are more tolerant to high temperatures than larger species.Dragonflies are more tolerant to high temperatures than damselflies with similar body mass. Females are more tolerant to high temperatures than males. 5. Our results highlight the importance of considering differences in morphology, life history and behaviour when comparing thermal tolerances of organisms along elevational gradients. Only by incorporating such factors, it would be possible to generate accurate predictions on the impact of climate change on tropical organisms.

Diversity of Nearctic Dragonflies and Damselflies (Odonata)

“…We found that non-forest-dependent species generally have larger range sizes than forest-dependent species, similar to the pattern reported in the tropical Andes, where nonforest species occupy larger elevation ranges compared to forest-dependent species [84]. This is likely due to forest-dependent species being more specialized [41][42][43] than open-area species which can reproduce in a wide variety of broadly available habitats. We classified 43.4% (221 species) as unable to have lasting populations in the absence of a lotic habitat.…”

“…We expected lentic species to have larger range sizes, as hypothesized by [40]. Similarly, forest species are expected to have smaller ranges than non-forest-dependent ones since they are highly specialized [41][42][43] in patchy distributed habitats.…”

Relatively large wings facilitate life at higher elevations among Nearctic dragonflies

“…Here, we used the total area encompassed by all of the species' occupied grid cells from the presence/absence matrix that we generated (Rotenberry & Balasubramaniam, 2020). Second, we also sought to account for features of a species' thermal biology because species that are adapted to the cold are likely capable of living at higher elevations (Bota‐Sierra et al, 2022; Sheldon et al, 2018). Data on direct measurements for species' thermal physiology are available for only a small number of dragonflies (Bennett et al, 2018), and so we instead used the average temperature that a species encounters across its geographic range as a continuous proxy of whether the species is relatively adapted to cold or warm conditions (e.g.…”

“…We included the mean annual temperature across a species' range to control for the expectation that cold-adapted species are likely to be found at higher elevations (e.g. Bota-Sierra et al, 2022). Because elevation can also filter animal species based on body size (e.g.…”

Adaptive variation in avian eggshell structure and gas conductance across elevational gradients?

“…temperature, humidity). The role that such factors play in establishing the elevational distributions of tropical montane species has been increasingly studied, partly owing to an interest in forecasting species responses to climatic change (Sheldon et al, 2011; García-Robledo et al, 2016; Slatyer & Schoville, 2016; Zuloaga & Kerr, 2016; Freeman et al, 2018; Linck et al, 2021; Bota-Sierra et al, 2022). Because of their narrow elevational ranges and often abrupt replacement of closely related species along mountain slopes, tropical birds have been a model system for the study of elevational range limits (Terborgh, 1971; Diamond, 1973; Sheldon et al, 2011; Jankowski et al, 2013; Londoño et al, 2015; Freeman et al, 2019; 2022).…”