European great tit, Parus major.
In an example of how the environment, and in this case probably the availability of different food items, can cause changes on which natural selection can act, a study by an international team or reserchers led by Pablo Salmón of Lund University, Sweden, has shown that great tits, Parus major living in an urban environment have paler breasts than those living in a forest environment.
Although this is probably not an evolutionary change, i.e., a change in the frequency of alleles in the population gene pools, as the cause is probably dietary difference, it illustrates how an environmental change can produce changes in features on which natural selection can act to bring about true evolutionary changes, and so begin the process of allopatric speciation.
Of course, there will be creationists who will misrepresent the scientific fact of evolution, either deliberately, or mendaciously in order to mislead others, who will dismiss this as "not evolution", not for the reason given above but because "they're still great tits/still birds" and haven't grown a new structure or turned into an unrelated taxon.
The research is explained in a Lund University press release:
More detail is given in the researchers open-access paper published in the Journal of Animal Ecology:A new study conducted by researchers in Europe shows that urban great tits have paler plumage than their countryside counterparts. Since the yellow pigment of the breast feathers of great tits comes from the food they eat, the paler yellow plumage of urban birds indicates that the urban environment affects the entire food chain.We used feather samples collected from great tits in cities and forests across Europe. Different methods all confirmed that urban great tits are paler. Our findings suggest that birds in the city are not getting the right diet. This can help us understand how to create urban environments that are more beneficial for biodiversity. By planting more native trees and plants in our gardens and parks we can help small birds, such as great tits, by providing them with a healthy diet of insects and spiders for themselves and their chicks.
We need further research to understand why some cities have more favourable environments for birds and wildlife than others. This can help urban planners develop biodiversity-friendly policies and improve the quality of life for people living in cities.
Hannah Watson, co-author
Department of Biology
Lund University, Lund, Sweden.
As urban areas expand, animals increasingly find themselves living in towns and cities. While some animals may benefit from milder temperatures and fewer natural predators in urban settings, they also have to cope with pollutants and changes in their diet. Previous research has shown that animals in cities are “duller” in terms of yellow-orange-red colour tones compared to their non-urban counterparts. However, previous studies have only focused on single geographic locations.
The yellow colour in the great tit’s feathers comes from carotenoids, which the birds get from the insects they eat. These insects, in turn, obtain the nutrient from the plants they feed on. Carotenoids are important antioxidants that help the body combat the toxic effects of pollution. If great tits in cities cannot obtain enough carotenoids from their food, their plumage becomes paler, resulting in weaker defences against the adverse health effects of pollution.
AbstractMaybe not an example of evolutionary change, but an example of the beginnings of environment-driven changes on which natural selection can operate, in other words, an example of the earliest stages of evolutionary diversification in the European great tit.
- Urbanisation is accelerating across the globe, transforming landscapes, presenting organisms with novel challenges, shaping phenotypes and impacting fitness. Urban individuals are claimed to have duller carotenoid-based colouration, compared to their non-urban counterparts, the so-called ‘urban dullness’ phenomenon. However, at the intraspecific level, this generalisation is surprisingly inconsistent and often based on comparisons of single urban/non-urban populations or studies from a limited geographical area.
- Here, we combine correlational, experimental and meta-analytical data on a common songbird, the great tit Parus major, to investigate carotenoid-based plumage colouration in urban and forest populations across Europe.
- We find that, as predicted, urban individuals are paler than forest individuals, although there are large population-specific differences in the magnitude of the urban-forest contrast in colouration. Using one focal region (Malmö, Sweden), we reveal population-specific processes behind plumage colouration differences, which are unlikely to be the result of genetic or early-life conditions, but instead a consequence of environmental factors acting after fledging.
- Finally, our meta-analysis indicates that the urban dullness phenomenon is well established in the literature, for great tits, with consistent changes in carotenoid-based plumage traits, particularly carotenoid chroma, in response to anthropogenic disturbances.
- Overall, our results provide evidence for uniformity in the ‘urban dullness’ phenomenon but also highlight that the magnitude of the effect on colouration depends on local urban characteristics. Future long-term replicated studies, covering a wider range of species and feeding guilds, will be essential to further our understanding of the eco-evolutionary implications of this phenomenon.
Salmón, P., López-Idiáquez, D., Capilla-Lasheras, P., Pérez-Tris, J., Isaksson, C., & Watson, H. (2023).
Urbanisation impacts plumage colouration in a songbird across Europe: Evidence from a correlational, experimental and meta-analytical approach.
Journal of Animal Ecology, 00, 1–13. https://doi.org/10.1111/1365-2656.13982
Copyright: © 2023 The authors.
Published by John Wiley & Sons, Inc. Open access.
Reprinted under a Creative Commons Attribution 4.0 International license (CC BY 4.0)
Figure 1.(a) Locations of great tit Parus major populations across Europe included in this study. Black circles: urban/forest population pairs sampled in the empirical study in which differences in breast plumage colour traits were compared (see Table S1 for details); white and blue circles: populations from the literature on effects of urbanisation (white) or pollution (blue) on colour traits and included in the meta-analysis (see Table S3 for details). For adult birds (1 and 2+ years) sampled in the empirical study, that is black circles in (a): (b) chroma reflects the amount of pigment in the feathers (i.e. carotenoids) and (c) brightness reflects the structural quality of feathers. Sample sizes (urban/forest): Gothenburg (11/11), Malmö (41/41), Milan (16/18), Madrid (16/20), and Lisbon (18/16). Asterisks denote significant differences between urban and forest habitats with p < 0.05 (habitat main term see Table S5). n.s., non-significant differences. Model mean values (solid-coloured circles) with 95% confidence intervals are plotted, along with raw data (grey circles, 6 technical measurements per individual).
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