Why climate change should generally lead to lighter coloured animals

Wild white-capped noddies keep a cool head in a heated situation

Sunning, or sunbathing, is a behavior observed in diverse birds from at least 50 taxonomic families. While sunning, birds exhibit signs of heat stress, notably panting, indicating a risk of overheating. Given that even modest increases in brain temperature can impair brain function, sunning birds may have mechanisms that selectively cool the brain. Sunning birds could cool the brain using active physiological mechanisms (e.g., an ophthalmic rete or sleeping) or passive adaptations, such as light-colored plumage over the cranium. White-capped noddies are tropical seabirds that sunbathe in direct sunlight on cloudless days. Using infrared thermography on wild birds, we found that the white cap is 20 °C cooler than that of the black back while sunning. A deceased bird showed the same thermal profile, indicating that this difference arises from dichromatic coloration and not underlying physiology. Thus, the white cap may extend the duration of time noddies can sunbathe and keep the brain cool, near core body temperature, while allowing the rest of the body to heat up, perhaps to displace or kill parasites.

Regional variation in climate change alters the range-wide distribution of colour polymorphism in a wild bird

According to Gloger's rule, animal colouration is expected to be darker in wetter and warmer climates. Such environmental clines are predicted to occur in colour polymorphic species and to be shaped by selection if colour morphs represent adaptations to different environments. We studied if the distribution of the colour polymorphic tawny owl (Strix aluco) morphs (a pheomelanic brown and a pale grey) across Europe follow the predictions of Gloger's rule and if there is a temporal change in the geographical patterns corresponding to regional variations in climate change. We used data on tawny owl museum skin specimen collections. First, we investigated long-term spatiotemporal variation in the probability of observing the colour morphs in different climate zones. Second, we studied if the probability of observing the colour morphs was associated with general climatic conditions. Third, we studied if weather fluctuations prior to the finding year of an owl explain colour morph in each climate zone. The brown tawny owl morph was historically more common than the grey morph in every studied climate zone. Over time, the brown morph has become rarer in the temperate and Mediterranean zone, whereas it has first become rarer but then again more common in the boreal zone. Based on general climatic conditions, winter and summer temperatures were positively and negatively associated with the proportion of brown morph, respectively. Winter precipitation was negatively associated with the proportion of brown morph. The effects of 5-year means of weather on the probability to observe a brown morph differed between climate zones, indicating region-dependent effect of climate change and weather on tawny owl colouration. To conclude, tawny owl colouration does not explicitly follow Gloger's rule, implying a time and space-dependent complex system shaped by many factors. We provide novel insights into how the geographic distribution of pheomelanin-based colour polymorphism is changing.

Systematics of Thraupis (Aves, Passeriformes) reveals an extensive hybrid zone between T. episcopus (Blue-gray Tanager) and T. sayaca (Sayaca Tanager)

The Neotropical avian genus Thraupis (Passeriformes, Thraupidae) currently comprises seven species that are widespread and abundant throughout their ranges. However, no phylogenetic hypothesis with comprehensive intraspecific sampling is available for the group and, therefore, currently accepted species limits remain untested. We obtained sequence data for two mitochondrial (ND2, cyt-b) and three non-coding nuclear (TGFB2, MUSK, and βF5) markers from 118 vouchered museum specimens. We conducted population structure and coalescent-based species-tree analyses using a molecular clock calibration. We integrated these results with morphometric and coloration analyses of 1,003 museum specimens to assess species limits within Thraupis. Our results confirm that Thraupis is a monophyletic group and support its origin in the late Miocene and subsequent diversification during the Pleistocene. However, we found conflicts with previous phylogenies. We recovered Thraupis glaucocolpa to be sister to all other species in the genus, and T. cyanoptera to the remaining five species. Our phylogenetic trees and population structure analyses uncovered phylogeographic structure within Thraupis episcopus that is congruent with geographic patterns of phenotypic variation and distributions of some named taxa. The first genetic and phenotypic cluster in T. episcopus occurs east of the Andes and is diagnosed by the white patch on the lesser and median wing coverts, whereas the second group has a blue patch on the wing and distributes to the west of Colombia's eastern Andes. Finally, we present evidence of hybridization and ongoing gene flow between several taxa at different taxonomic levels and discuss its taxonomic implications.

Response to Delhey et al

Predicting how organisms will respond to future climate change is a challenging task for biologists. In general, there are three ways to make such biotic predictions. First, by manipulating climatic conditions, such as temperature, humidity, etc. in laboratory experiments, it is possible to observe how adaptation or extinction occurs. Second, historical data can be synthesised using a meta-analysis to test for any relationship between biotic changes and climatic warming since the industrial revolution. Lastly, theoretical trends in biotic change can be associated with observed spatial variation (where, for example, climatic gradients result in spatial variations equivalent to climate changes).