Adult thermoregulatory behaviour does not provide,by itself,an adaptive explanation for the reflectance–climate relationship (Bogert's pattern) in Iberian butterflies

1. The association of darker, less reflective insect wings with cooler environments (Bogert's rule) is thought to be related to adult thermoregulation, but the adaptive explanation and the implications for sensitivity to climate warming are yet to be tested. We re-evaluate the pattern for butterflies using finer resolution data than in previous approaches, both geographically and morphologically, and test its correlation with recent evidence of impacts of warming on butterflies.
2. We compared reflectance–climate relationships at different grid sizes, selected the best subset of reflectance measurements and tested the contribution of the species basking mode, the phylogenetic structure of the data and the correlation between reflectance and published abundance or altitudinal shifts. We used standardised RGB (Red, Green, Blue) values from 222 species from the Iberian Peninsula, and regional mean temperature and precipitation data from the study area (10 and 50-km resolutions) and Europe (50-km resolution).
3. Correlations between reflectance and temperature increased at finer geographical and morphological resolutions. However, the butterfly basking mode did not improve the statistical explanation of the pattern. Reflectance shows a strong phylogenetic structure, while variance partitioning indicated a poor pure contribution of the climate variables in the reflectance–climate correlation.
4. Overall, mean temperature and precipitation were only modest predictors of butterfly reflectance. No correlation between reflectance and recent abundance or altitudinal shifts was found using the hypothesised best estimates of reflectance. Although significant correlations between butterfly shading and altitudinal shifts were found for two of the reflectance measurements, this is interpreted as weak, probably artifactual evidence on the predictive power of this relationship.
5. The strong phylogenetic pattern of the reflectance and the low fraction of the reflectance measures analysed suggest that tests for alternative explanations are still needed to shed light on the meaning of the colour–environment relationships in butterflies, which probably are of a complex nature. From an adaptive point of view, unravelling the basis of Bogert's pattern in butterflies requires a closer, habitat-level approach and alternative variables to adult thermoregulatory behaviour to be tested.

     

Gloger's rule in plants: The species and ecosystem levels

Gloger''s rule posits that darker birds are found more often in humid environments than in arid ones, especially in the tropics. Accordingly, desert-inhabiting animals tend to be light-colored. This rule is also true for certain mammalian groups, including humans. Gloger''s rule is manifested at 2 levels: (1) at the species level (different populations of the same species have different pigmentation at different latitudes), and (2) at the species assembly level (different taxa at a certain geography have different pigmentation than other taxa found at different habitats or latitudes). Concerning plants, Gloger''s rule was first proposed to operate in many plant species growing in sand dunes, sandy shores and in deserts, because of being white, whitish, or silver colored, based on white trichomes, because of sand grains and clay particles glued to sticky glandular trichomes, or because of light-colored waxes. Recently, Gloger''s rule was shown to also be true at the intraspecific level in relation to protection of anthers from UV irradiation. While Gloger''s rule is true in certain plant taxa and ecologies, there are others where “anti-Gloger” coloration patterns exist. In some of these the selective agents are known and in others they are not. I present both Gloger and “anti-Gloger” cases and argue that this largely neglected aspect of plant biology deserves much more research attention.     

Are long‐term widespread avian body size changes related to food availability? A test using contemporaneous changes in carotenoid‐based color

Recent changes in global climate have been linked with changes in animal body size. While declines in body size are commonly explained as an adaptive thermoregulatory response to climate warming, many species do not decline in size, and alternative explanations for size change exist. One possibility is that temporal changes in animal body size are driven by changes in environmental productivity and food availability. This hypothesis is difficult to test due to the lack of suitable estimates that go back in time. Here, we use an alternative, indirect, approach and assess whether continent‐wide changes over the previous 100 years in body size in 15 species of Australian birds are associated with changes in their yellow carotenoid‐based plumage coloration. This type of coloration is strongly affected by food availability because birds cannot synthesize carotenoids and need to ingest them, and because color expression depends on general body condition. We found significant continent‐wide intraspecific temporal changes in body size (wing length) and yellow carotenoid‐based color (plumage reflectance) for half the species. Direction and magnitude of changes were highly variable among species. Meta‐analysis indicated that neither body size nor yellow plumage color showed a consistent temporal trend and that changes in color were not correlated with changes in size over the past 100 years. We conclude that our data provide no evidence that broad‐scale variation in food availability is a general explanation for continent‐wide changes in body size in this group of species. The interspecific variability in temporal changes in size as well as color suggests that it might be unlikely that a single factor drives these changes, and more detailed studies of museum specimens and long‐term field studies are required to disentangle the processes involved.