| 1. |
- Andersson, Staffan, 1959, et al.
(författare)
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Multiple receivers, multiple ornaments, and a trade-off between agonistic and epigamic signaling in a widowbird.
- 2002
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Ingår i: The American naturalist. - : University of Chicago Press. - 1537-5323 .- 0003-0147. ; 160:5, s. 683-91
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Tidskriftsartikel (refereegranskat)abstract
- Sexual displays often involve several different ornamental traits. Yet most indicator models of sexual selection based on a single receiver (usually a choosy female) find that multiple handicap signals should be unstable. Here we study reasons for this contradiction, analyzing signal function, signal content, and trade-offs between signals in the polygynous red-collared widowbird Euplectes ardens. Males have both a long, graduated tail and a red carotenoid collar badge. Territory-holding "residents" have slightly shorter tails than the nonbreeding "floaters," but their carotenoid collars are 40% larger, and they have (on the basis of reflectance spectrometry and objective colorimetry) a 23-nm more long-wave ("redder") hue than floaters. This corroborates experimental evidence that the red collar is selected by male contest competition, whereas female choice is based almost exclusively on male tail length. Tail length is negatively correlated with the carotenoid signal, which together with body size and condition explains 55% of the variation in tail length. The trade-off in tail length and carotenoid investment is steeper among residents, suggesting an interaction with costs of territory defense. We propose that the "multiple receiver hypothesis" can explain the coexistence of multiple handicap signals. Furthermore, the trade-off between signal expressions might contribute to the inverse relation between nuptial tail elongation and coloration in the genus Euplectes (bishops and widowbirds).
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| 2. |
- Griffith, S C, et al.
(författare)
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Correlations between ultraviolet coloration, overwinter survival and offspring sex ratio in the blue tit.
- 2003
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Ingår i: Journal of evolutionary biology. - 1010-061X. ; 16:5, s. 1045-54
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Tidskriftsartikel (refereegranskat)abstract
- We studied the correlations between offspring sex ratio, UV coloration and overwinter survival in a population of blue tits, breeding in Gotland, Sweden, over three consecutive breeding seasons. In 2 of 3 years, we found that females paired to males with relatively brighter UV-coloration produced a greater proportion of sons in their broods, and that this effect was significant with all 3 years combined, despite a significant year by male UV interaction. In addition, we found other correlates of sex ratio (breeding time, female age and clutch size) in some, but not all years, and some of these showed significantly different relationships with sex ratio between years. In both years for which data were available, there were indications that males with relatively brighter UV coloration, and that paired with females that produced male-biased clutches, were more likely to survive to the next year. In addition, we also found that in both males and females, individuals produced similar sex ratios in consecutive years. Because correlations with the sex ratio may be expected to be weak, variation in results between years within the same population may be explained by low statistical power or genuine biological differences. Our results suggest that conclusions about sex ratio variation in birds should be based on multiple years. The correlations that we found in some years of this study are consistent with models of adaptive sex ratio adjustment in response to mate quality. However, careful experimental work is required to provide tests of the assumptions of these models, and should be a priority for future work.
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| 3. |
- Isaksson, Caroline, 1976, et al.
(författare)
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Plasma Glutathione and Carotenoid Coloration as Potential Biomarkers of Environmental Stress in Great Tits
- 2005
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Ingår i: EcoHealth. - : Springer Science and Business Media LLC. - 1612-9202 .- 1612-9210. ; 2, s. 138-146
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Tidskriftsartikel (refereegranskat)abstract
- Measures of oxidative stress in animals may be useful biomarkers of environmental stressors, such as anthropogenic pollution. In birds, studies of oxidative stress have focused on dietary antioxidants, primarily carotenoids, which are interesting due to their multiple physiological and pigmentary functions but therefore also unspecifically related to oxidative stress. A useful complementary biomarker may be the glutathione system, commonly used in human medicine, but rarely applied to wild, terrestrial vertebrates. In this study of urban versus rural adult and nestling great tits Parus major, we investigated both the carotenoid-based yellow plumage (by reflectance spectrometry) and the plasma levels of glutathione, the latter measured as total glutathione (tGSH) and as the ratio between oxidized and reduced glutathione (GSSG:GSH), respectively. We found that urban adults had higher current oxidative stress (GSSG:GSH) and paler yellow plumage compared to rural adults, suggesting elevated stress in the urban environment. Total glutathione levels (tGSH), however, which may indicate long-term up-regulation of the GSH reservoir, did not differ between the environments. Nestlings did not show any consistent pattern between environments in either tGSH or GSSG:GSH and, among individuals, glutathione levels were uncorrelated with carotenoid coloration. The results thus suggest some population-level correspondence between the two stress biomarkers in adult birds, but more work is obviously needed to understand how the two antioxidant systems interact in different individuals and in response to different environmental disturbances.
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| 4. |
- Isaksson, Caroline, 1976, et al.
(författare)
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Sex and age differences in reflectance and biochemistry of carotenoid-based colour variation in the great tit Parus major
- 2008
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Ingår i: Biological Journal of the Linnean Society. - : Oxford University Press (OUP). - 0024-4066 .- 1095-8312. ; 95:4, s. 758-765
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Tidskriftsartikel (refereegranskat)abstract
- The plumage coloration in great tits (Parus major) is the subject of much behavioural and ecophysiological research, yet there is a lack of analyses of the natural colour variation and its mechanisms. We used reflectance spectrometry and high-performance liquid chromatography to explore individual, sexual and age-related variation in carotenoid coloration and pigmentation, paramount to the often presumed, but rarely substantiated, costs and 'honesty' of carotenoid displays. In adults, we found that sex was the strongest predictor of 'brightness' (higher in males) and of 'hue' (longer wavelength in females). There was no sex difference in 'carotenoid chroma' or carotenoid content of feathers which also was unrelated to adult age (1 or 2+ years) and condition. Similar patterns were revealed for nestlings. Regarding the biochemical 'signal content', 'carotenoid chroma', but not 'hue', was significantly related to the carotenoid content (lutein and zeaxanthin) of feathers. These results refute the previously assumed exaggeration of carotenoid pigmentation in male great tits, and question the condition-dependence of carotenoid coloration in this species. However, the sexual dimorphism in total reflectance or 'brightness', most likely due to melanins rather than carotenoids, may have implications for signalling or other adaptive explanations that need to be explored.
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| 5. |
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| 6. |
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| 7. |
- Sheldon, B C, et al.
(författare)
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Ultraviolet colour variation influences blue tit sex ratios
- 1999
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Ingår i: Nature. - : Springer Science and Business Media LLC. - 0028-0836 .- 1476-4687. ; 402, s. 874-877
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Tidskriftsartikel (refereegranskat)abstract
- Brilliant blue and violet structural colours are common plumage ornaments in birds, but their signalling functions are poorly understood. This may be because birds also communicate in ultraviolet (UV-A) wavelengths (320–400 nm) invisible to humans, but a strong spectral component of many structural colours. From a wild population of blue tits—Parus caeruleus, sexually dimorphic primarily in the ultraviolet —we report experimental evidence that females skew the sex ratio of their offspring in response to the ultraviolet plumage ornamentation of their mates. Masking male ultraviolet reflectance reversed a positive correlation between reflectance and brood sex ratio observed in control pairs, demonstrating a causal effect of male ultraviolet ornamentation on offspring sex ratio. Ultraviolet reflectance also predicted male survival to the following breeding season, suggesting that it serves as a viability indicator. When taken together with ecological effects (laying date, nesting area), our experiments reveal that an unexpected amount of control exists over the primary sex ratio in birds, suggesting that chromosomal sex determination may not constrain the sex ratios of multiparous vertebrates.
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| 8. |
- Smiseth, P.T, et al.
(författare)
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Is male plumage reflectance correlated with paternal care in bluethroats?
- 2001
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Ingår i: Behavioral Ecology. - 1045-2249. ; 12:2, s. 164-170
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Tidskriftsartikel (refereegranskat)abstract
- Although it is now well established that the conspicuous male plumage colors of many birds have been subject to sexual selection by female choice, it is still debated whether females mate with colorful males to obtain direct or indirect benefits. In species where males provide substantial parental care, females may obtain direct benefits from mating with the males that are best at providing care. The good parent hypothesis suggests that male plumage coloration signals a male's ability to provide parental care. Alternatively, the differential-allocation hypothesis suggests that colorful males reduce their care in response to increased investment by females mated to attractive males. We tested these hypotheses on the bluethroat (Luscinia s. svecica), a socially monogamous, sexually dichromatic bird, in which males have a colorful throat patch consisting of a structurally derived blue area surrounding a melanin-based chestnut spot. Male plumage coloration was objectively quantified by use of reflectance spectrometry. We found no evidence of a relationship between male coloration of either the blue patch or the chestnut spot and the level of paternal care. Nor were there any correlations between male coloration and body size or body condition. Thus, our study does not support the hypothesis that male coloration signals male parental quality (the good parent hypothesis) or the hypothesis that colorful males reduce their care in response to increased investment by females (the differential-allocation hypothesis).
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| 9. |
- Örnborg, Jonas, 1968, et al.
(författare)
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Seasonal changes in a ultraviolet structural colour signal in blue tits, Parus caeruleus
- 2002
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Ingår i: Biological Journal of the Linnean Society. - : Oxford University Press (OUP). - 0024-4066 .- 1095-8312. ; 76:2, s. 237-245
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Tidskriftsartikel (refereegranskat)abstract
- Recent studies of blue tits, Parus caeruleus, have found sexual selection and a viability-indicating function of the structural ultraviolet and blue crown plumage, but the reasons for this signal variation are not understood. Furthermore, studies in England and Sweden have yielded somewhat different results (particularly with regard to the spectral position of the reflectance peak). Here we investigate whether the blue tit UV/blue ornament varies with time of year since such variation might be relevant to the signalling function as well as the apparent difference between populations. From 400 blue tits captured at two different localities in Sweden, we found that objective measures of 'hue' (spectral location), 'chroma' (spectral purity) and 'brightness' (spectral intensity), varied substantially with season. Just after moult (October), crown 'hue' is maximally UV-shifted (359 nm for males and 373 nm for females). Thereafter the peak drifts upwards and by the time of nestling feeding (June) male reflectance peaks at 404 nm and female at 413 nm. This change is probably due to feather wear as well as fat and dirt accumulation, which might constitute an additional male quality cue. Our results suggest that it is important to consider plumage age when exploring variation in structural plumage coloration, and that it can largely explain the difference between the British and Swedish studies.
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