Colour lightness of dragonfly assemblages across North America and Europe

Abstract

Dark‐coloured ectotherms absorb energy from the environment at higher rates than light‐coloured ectotherms. The thermal melanism hypothesis (TMH) states that this physical mechanism links the colour lightness of the body surfaces of ectotherms to their thermal environment and hence to their geographical distribution. Studies on different insect taxa in Europe found support for this prediction of the TMH. However, whether these results hold also for other biogeographical regions remains unclear. Here, we quantify and map the colour lightness of dragonfly species in North America and directly compare our results to previously published findings for Europe. We estimated the colour lightness of 152 North American dragonfly species from published illustrations, compiled their distribution data from the literature and combined all these data with six biologically relevant environmental variables. We evaluated the importance of phylogenetic autocorrelation for the spatial variation of mean colour lightness of dragonfly assemblages (grid cells of approximately 50 × 50 km size) by repeating all analyses also for the phylogenetically predicted component of the colour lightness of species and the species‐specific deviation from this prediction. We also accounted for spatial autocorrelation with autoregressive error models. All statistical approaches showed that dragonfly assemblages from both continents consistently tended to be darker coloured in regions with cold climates and lighter coloured in regions with warm climates. Regression slopes, however, were significantly less steep, and the amount of variance explained by environmental variables was lower for North America than for Europe. Our results highlight the importance of colour lightness for the distribution of dragonfly species, but they also indicate that idiosyncrasies of the continents modify the general pattern.

The dark side of Lepidoptera: Colour lightness of geometrid moths decreases with increasing latitude

“…These declines in colour lightness with latitude and elevation are reflected in the overall geographical pattern of geometrids of the Western Palearctic. Strikingly, this geographical variation in colour lightness strongly resembles the outlined pattern expected if only thermoregulatory functions of dark or light coloration were of importance, as has been discussed with regard to heliophilic insects, such as butterflies and dragonflies (Pinkert et al, ; Zeuss et al, ).…”

“…Recent studies revealed contrasting geographical patterns in the colour lightness of insects, the majority of which are ectothermic. Among insects, darker‐coloured species occur at high latitudes, presumably because of the thermoregulatory advantages of dark coloration (Bishop et al, ; Pinkert, Brandl, & Zeuss, ; Schweiger & Beierkuhnlein, ; Zeuss, Brandl, Brändle, Rahbek, & Brunzel, ). Hence, whether dark or light coloration is favoured in a particular environment might depend on different selection pressures that operate simultaneously and are not mutually exclusive but vary in their relative importance depending on the physiology and behaviour of animals.…”

“…All macroecological studies of insects published so far have interpreted the observed pattern of a decrease in colour lightness with latitude in the context of the thermal melanism hypothesis (Bishop et al, ; Clusella‐Trullas, van Wyk, & Spotila, ; Pinkert et al, ; Zeuss et al, ). According to this hypothesis, dark coloration increases absorption of solar radiation; hence, it allows dark‐coloured insects to heat up faster and attain higher steady‐state body temperatures compared to light‐coloured insects (Gates, ).…”

Dark butterflies camouflaged from predation in dark tropical forest understories

“…Ants are natural enemies of caterpillars, but not for healthy adult butterflies (Shapiro, 1974;Floren et al, 2002). Light-coloured butterfly assemblages primarily found in hot open habitats are therefore likely to be attributable to thermoregulation purposes other than predation avoidance (Pinkert et al, 2016;Xing et al, 2016). However, in open habitats, only D. leucophaeus and C. emma were regularly observed (W. Cheng, pers.…”

Divergent melanism strategies in Andean butterfly communities structure diversity patterns and climate responses

“…Similarly, across Western Europe, dark‐coloured insect species are more prevalent in cooler climates (Zeuss et al., ). Pinkert, Brandl, and Zeuss () uncovered comparable patterns of colour lightness in dragonfly assemblages in North America, even though the geographical settings and biogeographical history are likely to be different between these two continents. Finally, in Asia, Xing et al.…”