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Evans, Simon
Alternative names
Publications (8 of 8) Show all publications
Evans, S. R. & Gustafsson, L. (2017). Climate change upends selection on ornamentation in a wild bird. NATURE ECOLOGY & EVOLUTION, 1(2), Article ID UNSP 0039.
Open this publication in new window or tab >>Climate change upends selection on ornamentation in a wild bird
2017 (English)In: NATURE ECOLOGY & EVOLUTION, ISSN 2397-334X, Vol. 1, no 2, article id UNSP 0039Article in journal (Refereed) Published
Abstract [en]

Secondary sexual traits have high heritabilities and are exposed to strong, environmentally sensitive selection, and so are expected to evolve rapidly in response to sustained environmental change. We examine the eco-evolutionary dynamics of ornament expression in a long-term study population of collared flycatchers, Ficedula albicollis, in which forehead patch size, which positively influences male reproductive success, declined markedly over 34 years. Annual fitness selection on forehead patch size switched from positive to negative during the study, a reversal that is accounted for by rising spring temperatures at the breeding site: highly ornamented males were selectively favoured following cold breeding seasons but selected against following warm breeding seasons. An 'individual animal model' describes a decline in the genetic values of breeding males during the study, which simulations showed was unlikely to result from drift alone. These results are thus consistent with adaptive evolution of a sexually selected trait in response to climate change.

National Category
Evolutionary Biology
Identifiers
urn:nbn:se:uu:diva-344541 (URN)10.1038/s41559-016-0039 (DOI)000417169600014 ()28812603 (PubMedID)
Funder
Swedish Research Council
Available from: 2018-03-07 Created: 2018-03-07 Last updated: 2018-03-07Bibliographically approved
Evans, S. R. & Sheldon, B. C. (2015). Colour in a new light: a spectral perspective on the quantitative genetics of carotenoid colouration. Functional Ecology, 29(1), 96-103
Open this publication in new window or tab >>Colour in a new light: a spectral perspective on the quantitative genetics of carotenoid colouration
2015 (English)In: Functional Ecology, ISSN 0269-8463, E-ISSN 1365-2435, Vol. 29, no 1, p. 96-103Article in journal (Refereed) Published
Abstract [en]

1. Carotenoid-based colours are model traits for research on animal signalling and sexual selection but, whereas the consequences of variable expression have been extensively studied, its causes are rarely quantified. This issue is complicated by the composite nature of carotenoid-based colour patches, which combine pigments and a reflective background. Ultimately, the evolution of such colours will be determined by the processes that govern variable expression of these mechanisms. We present a novel approach to assessing the quantitative genetics of colour expression, in which reflectance spectra are analysed directly, thereby avoiding the data loss and inherent subjectivity of summary colour variables. Further, the influence of the component mechanisms can be distinguished in spectral analyses due to their contrasting wavelength-dependencies. Using data from a 6-year study of carotenoid-based plumage reflectance in wild great tits (Parus major), we employ a multi-parallel animal modelling' approach to estimate sources of variance for narrow (2nm) wavebands across the visible spectrum. Moderate heritability estimates were limited to the violet-blue region of the spectrum, diagnostic of the carotenoid content of plumage being heritable. The natal environment effect was limited entirely to the violet-blue, again indicating that it relates to variation in carotenoid content of feathers. Other wavelengths were sensitive to annual and permanent environmental variation but only marginally influenced by additive genetic variation. Hence, background reflectance is the component that is more sensitive to the environment. Analysing reflectance spectra directly provided an objective perspective of the dynamics of colour expression that is not apparent when relying on summary colour scores. In this case, our results suggest that carotenoid deposition may be an effective target of selection and hence could explain the important role carotenoids frequently play in intraspecific signalling.

Keywords
animal model, great tit, heritability, natal environment, plumage reflectance
National Category
Zoology
Identifiers
urn:nbn:se:uu:diva-246666 (URN)10.1111/1365-2435.12297 (DOI)000348562600012 ()
Available from: 2015-03-18 Created: 2015-03-09 Last updated: 2017-12-04Bibliographically approved
Evans, S. (2015). Sports doping vastly underestimated [Letter to the editor]. Nature, 519(7541), 33-33
Open this publication in new window or tab >>Sports doping vastly underestimated
2015 (English)In: Nature, ISSN 0028-0836, E-ISSN 1476-4687, Vol. 519, no 7541, p. 33-33Article in journal, Letter (Refereed) Published
National Category
Other Natural Sciences
Identifiers
urn:nbn:se:uu:diva-249053 (URN)000350304000021 ()25739619 (PubMedID)
Available from: 2015-04-20 Created: 2015-04-10 Last updated: 2017-12-04Bibliographically approved
Evans, S. R., Schielzeth, H., Forstmeier, W., Sheldon, B. C. & Husby, A. (2014). Nonautosomal Genetic Variation in Carotenoid Coloration. American Naturalist, 184(3), 374-383
Open this publication in new window or tab >>Nonautosomal Genetic Variation in Carotenoid Coloration
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2014 (English)In: American Naturalist, ISSN 0003-0147, E-ISSN 1537-5323, Vol. 184, no 3, p. 374-383Article in journal (Refereed) Published
Abstract [en]

Carotenoid-based coloration plays an important role in signaling, is often sexually dimorphic, and is potentially subject to directional and/or sex-specific selection. To understand the evolutionary dynamics of such color traits, it is essential to quantify patterns of inheritance, yet nonautosomal sources of genetic variation are easily overlooked by classical heritability analyses. Carotenoid metabolism has recently been linked to mitochondria, highlighting the potential for color variation to be explained by cytoplasmically inherited factors. In this study, we used quantitative genetic animal models to estimate the importance of mitochondrial and sex chromosome-linked sources of genetic variation in coloration in two songbird populations in which dietary carotenoids are either unmodified (great tit plumage) or metabolized into alternative color forms (zebra finch beak). We found no significant Z-linked genetic variance in great tit plumage coloration, while zebra finch beak coloration exhibited significant W linkage and cytoplasmic inheritance. Our results support cytoplasmic inheritance of color in the zebra finch, a trait based on endogenously metabolized carotenoids, and demonstrate the potential for nonautosomal sources to account for a considerable share of genetic variation in coloration. Although often overlooked, such nonautosomal genetic variation exhibits sex-dependent patterns of inheritance and potentially influences the evolution of sexual dichromatism.

Keywords
cytoplasmic inheritance, great tit, mitochondria, W linkage, Z linkage, zebra finch
National Category
Ecology Evolutionary Biology
Identifiers
urn:nbn:se:uu:diva-232576 (URN)10.1086/677397 (DOI)000340844300011 ()
Available from: 2014-09-24 Created: 2014-09-22 Last updated: 2017-12-05Bibliographically approved
Evans, S. R. & Sheldon, B. C. (2013). Pigments versus structure: examining the mechanism of age-dependent change in a carotenoid-based colour. Journal of Animal Ecology, 82(2), 418-428
Open this publication in new window or tab >>Pigments versus structure: examining the mechanism of age-dependent change in a carotenoid-based colour
2013 (English)In: Journal of Animal Ecology, ISSN 0021-8790, E-ISSN 1365-2656, Vol. 82, no 2, p. 418-428Article in journal (Refereed) Published
Abstract [en]

Within-population colour variation is widespread in animals, yet the determinants of variable coloration have been relatively neglected by ecologists. Age-dependent expression of conspicuous coloration is prevalent, particularly in birds. Such patterns can be generated by multiple combinations of demographic heterogeneity or within-individual change; longitudinal analyses are necessary to establish the importance of these processes. Further, although pigment-based colours are composite traits, produced by multiple component mechanisms (e.g. feather microstructure and carotenoid pigmentation), the contributions of these mechanisms to components of age dependence are rarely considered, even though doing so may yield information about the ecological causes for age-dependent coloration. We used a large-scale, longitudinal study of carotenoid-based plumage coloration in great tits (Parus major) to show age dependence of plumage coloration is driven almost exclusively by within-individual effects in the first 2years of life. Using wavelength-specific analyses, we show that feather microstructure, while sensitive to annual variation, is independent of age, with increased carotenoid deposition driving changes in coloration. However, estimates of local carotenoid availability did not explain the change in coloration within individuals, suggesting that pigment availability may not be limiting. We thus show that it is individual-level changes in the pigment component of carotenoid-based coloration that determines age-dependent colour expression in great tits. More generally, our study highlights the utility of wavelength-specific analyses in determining the mechanisms underlying changes in expression of composite colour traits.

Keywords
aging, age dichromatism, carotenoid availability, great tit, within-individual change
National Category
Natural Sciences
Identifiers
urn:nbn:se:uu:diva-197045 (URN)10.1111/1365-2656.12008 (DOI)000315122100014 ()
Available from: 2013-03-19 Created: 2013-03-18 Last updated: 2017-12-06Bibliographically approved
Evans, S. R. & Sheldon, B. C. (2012). Quantitative Genetics of a Carotenoid-Based Color: Heritability and Persistent Natal Environmental Effects in the Great Tit. American Naturalist, 179(1), 79-94
Open this publication in new window or tab >>Quantitative Genetics of a Carotenoid-Based Color: Heritability and Persistent Natal Environmental Effects in the Great Tit
2012 (English)In: American Naturalist, ISSN 0003-0147, E-ISSN 1537-5323, Vol. 179, no 1, p. 79-94Article in journal (Refereed) Published
Abstract [en]

The information content of signals such as animal coloration depends on the extent to which variation reflects underlying biological processes. Although animal coloration has received considerable attention, little work has addressed the quantitative genetics of color variation in natural populations. We investigated the quantitative genetics of a carotenoid-based color patch, the ventral plumage of mature great tits (Parus major), in a wild population. Carotenoid-based colors are often suggested to reflect environmental variation in carotenoid availability, but numerous mechanisms could also lead to genetic variation in coloration. Analyses of individuals of known origin showed that, although plumage chromaticity (i.e., color) was moderately heritable, there was no significant heritability to achromaticity (i.e., brightness). We detected multiple long-lasting effects of natal environment, with hatching date and brood size both negatively related to plumage chromaticity at maturity. Our reflectance measures contrasted in their spatiotemporal sensitivity, with plumage chromaticity exhibiting significant spatial variation and achromatic variation exhibiting marked annual variation. Hence, color variation in this species reflects both genetic and environmental influences on different scales. Our analyses demonstrate the context dependence of components of color variation and suggest that color patches may convey multiple aspects of individual state.

Keywords
brightness, chromaticity, multiple signals, plumage coloration, structural coloration, visual model
National Category
Evolutionary Biology
Identifiers
urn:nbn:se:uu:diva-316704 (URN)10.1086/663198 (DOI)000298379200010 ()22173462 (PubMedID)
Funder
EU, European Research Council, AdG 250164
Available from: 2017-03-06 Created: 2017-03-06 Last updated: 2017-11-29Bibliographically approved
Evans, S. R., Summers, A. G. R. & Sheldon, B. C. (2012). Seasonality of carotenoid-based plumage coloration: modelling wavelength-specific change through spectral reconstruction. Journal of Avian Biology, 43(3), 234-243
Open this publication in new window or tab >>Seasonality of carotenoid-based plumage coloration: modelling wavelength-specific change through spectral reconstruction
2012 (English)In: Journal of Avian Biology, ISSN 0908-8857, E-ISSN 1600-048X, Vol. 43, no 3, p. 234-243Article in journal (Refereed) Published
Abstract [en]

Plumage coloration has provided important model systems for research on signal expression. Whilst it had previously been assumed that moulting provided the only mechanism to change plumage coloration, recent studies have shown plumage colours to be seasonally dynamic, with implications both for the quantification of expression and for any signalling role. However, the mechanistic processes underlying such change remain uncertain. Here, we describe within-moult shifts in expression of a carotenoid-based colour trait the yellow ventral plumage of the great tit Parus major over a nine-month timespan. We report that plumage chromaticity (colour) but not achromaticity (brightness) exhibits a marked seasonal decline, independent of sex, age or body condition, and at a constant rate across twelve environmentally heterogeneous plots within our study site. To gain a greater understanding of the mechanisms underlying this change we employed a spectral reconstruction approach, that generates predicted spectra for any timepoint within the sampling period. By comparing spectra for both early and late in the moult we show that the seasonal decline in chromaticity is driven by both a marked reduction in ultraviolet (UV) reflectance and, to a lesser extent, loss of active carotenoid pigments. Thus, our study shows that seasonal loss of chromaticity in the great tit is driven by altered reflectance primarily in the UV section of the spectrum, a finding made possible by the use of spectral compartmentalisation and multi-parallel modelling to produce reconstructed spectra. Whether change in plumage coloration influences signal function will depend on the dynamics of the signalling system but it could clearly inflate patterns such as assortative mating and should be considered in studies of colour expression.

National Category
Zoology
Identifiers
urn:nbn:se:uu:diva-316662 (URN)10.1111/j.1600-048X.2012.05654.x (DOI)000305185000005 ()
Funder
EU, European Research Council
Available from: 2017-03-06 Created: 2017-03-06 Last updated: 2017-11-29Bibliographically approved
Evans, S. & Sheldon, B. (2008). Interspecific patterns of genetic diversity in birds: correlations with extinction risk. Conservation Biology, 22(4), 1016-1025
Open this publication in new window or tab >>Interspecific patterns of genetic diversity in birds: correlations with extinction risk
2008 (English)In: Conservation Biology, ISSN 0888-8892, E-ISSN 1523-1739, Vol. 22, no 4, p. 1016-1025Article in journal (Refereed) Published
Abstract [en]

Birds are frequently used as indicators of ecosystem health and are the most comprehensively studied class in the animal kingdom. Nevertheless, a comprehensive, interspecific assessment of the correlates of avian genetic diversity is lacking, even though indices of genetic diversity are of considerable interest in the conservation of threatened species. We used published data on variation at microsatellite loci from194 bird species to examine correlates of diversity, particularly with respect to conservation status and population size. We found a significant decline in mean heterozygosity with increasing extinction risk, and showed, by excluding species whose heterozygosity values were calculated with heterospecific primers, that this relationship was not dependent on ascertainment bias. Results of subsequent regression analyses suggested that smaller population sizes of threatened species were largely responsible for this relationship. Thus, bird species at risk of extinction are relatively depauperate in terms of neutral genetic diversity, which is expected to make population recovery more difficult if it reflects adaptive genetic variation. Conservation policy will need to minimize further loss of diversity if the chances of saving threatened species are to be maximized.

National Category
Ecology
Research subject
Biology with specialization in Animal Ecology
Identifiers
urn:nbn:se:uu:diva-167316 (URN)10.1111/j.1523-1739.2008.00972.x (DOI)
Available from: 2012-02-02 Created: 2012-01-25 Last updated: 2017-12-08Bibliographically approved
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