Testosterone treatment can increase circulating carotenoids but does not affect yellow carotenoid-based plumage colour in blue tits
Peters, A. ; Roberts, M.L. ; Kurvers, R.H.J.M. ; Delhey, K. - \ 2012
Journal of Avian Biology 43 (2012)4. - ISSN 0908-8857 - p. 362 - 368.
superb fairy-wrens - sexual attractiveness - trade-offs - interspecific variation - plasma testosterone - structural plumage - sturnus-vulgaris - malurus-cyaneus - zebra finches - molt
A number of mechanisms are responsible for producing the variation in natural colours, and these need not act in isolation. A recent hypothesis states that carotenoid-based coloration, in addition to carotenoid availability, is also enhanced by elevated levels of circulating testosterone (T). This has only been tested for carotenoid-coloured bare parts in birds. We performed an experimental manipulation of T levels and examined the effects on the yellow carotenoid-based breast plumage in captive yearling blue tits Cyanistes caeruleus, of which half received a diet supplemented with carotenoids. T treatment resulted in elevated plasma T compared to controls and carotenoid supplementation strongly increased plasma carotenoid levels. T treatment resulted in an additional increase in plasma carotenoid levels but only in the carotenoid-supplemented males. Carotenoid supplementation resulted in more intense breast colour (carotenoid chroma), as expected. However, there was no effect of testosterone on plumage coloration at either dietary carotenoid level. Our results suggest that T can cause an increase in plasma carotenoid concentration, but that this does not necessarily lead to improved carotenoid-based plumage coloration
No evidence for general condition-dependence of structural plumage colour in blue tits: an experiment
Peters, A. ; Kurvers, R.H.J.M. ; Roberts, M.L. ; Delhey, K. - \ 2011
Journal of Evolutionary Biology 24 (2011)5. - ISSN 1010-061X - p. 976 - 987.
white-crowned sparrows - melanin-based coloration - bluebirds sialia-sialis - male uv attractiveness - parus-caeruleus - sexual selection - cyanistes-caeruleus - feather growth - satin bowerbirds - postnuptial molt
Condition-dependence is a central but contentious tenet of evolutionary theories on the maintenance of ornamental traits, and this is particularly true for structural plumage colour. By providing diets of different nutritional quality to moulting male and female blue tits, we experimentally manipulated general condition within the natural range, avoiding deprivation or stressful treatments. We measured reflectance of the structural-coloured UV/blue crown, a sexually selected trait in males, and the white cheek, a nonpigmented structural colour, directly after moult and again during the following spring mating season. We employed a variety of colour indices, based on spectral shape and avian visual models but, despite significant variation in condition and coloration, found no evidence for condition-dependence of UV/blue or white plumage colour during either season. These and previously published results suggest that structural colour might be sensitive to stress, rather than reduced body condition, during moult.
No consistent female preference for higher crown UV reflectance in Blue Tits Cyanistes caeruleus: a mate choice experiment
Kurvers, R.H.J.M. ; Delhey, K. ; Roberts, M.L. ; Peters, A. - \ 2010
Ibis 152 (2010)2. - ISSN 0019-1019 - p. 393 - 396.
plumage coloration - sex-ratio - ornamentation - grosbeaks - traits
Although male UV structural plumage coloration can indicate male quality (e.g. Keyser & Hill 2000) and female reproductive investment strategies (e.g. Sheldon et al. 1999, Griffith et al. 2003), unambiguous evidence that such plumage is a direct target of female choice is still lacking. A straightforward way of testing this is by conducting controlled mate choice experiments that exclude confounding factors such as male–male competition or territory quality. The first experiments on the role of structural colours in mate choice used UV-blocking windows (e.g. Bennett et al. 1996, Hunt et al. 1999), thereby completely removing male UV reflectance. A better approach is to vary UV reflectance within the natural range under natural light conditions. Only two such mate choice experiments have been undertaken to date (Ballentine & Hill 2003, Liu et al. 2007). In neither study did females show a preference for more UV-ornamented males. In the present study, we manipulated crown reflectance of first-year male Blue Tits Cyanistes caeruleus to test the hypothesis that females prefer males with a higher crown UV reflectance, as predicted by patterns of sex allocation, paternity and female parental investment in this species (Johnsen et al. 2005, Delhey et al. 2007a,b). In a mate choice experiment, females were offered a choice of two males (matched for yellow breast colour), one with a UV-reduced crown reflectance and one control-manipulated male. The results indicated that female preference was inconsistent and may be context-dependent
Interaction between the blood fluke, Sanguinicola inermis and humoral components of the immune response of carp, Cyprinus carpio
Roberts, M.L. ; Lewis, J.W. ; Wiegertjes, G.F. ; Hoole, D. - \ 2005
Parasitology 131 (2005)2. - ISSN 0031-1820 - p. 261 - 271.
salmo-gairdneri richardson - ligula-intestinalis cestoda - diplostomum-spathaceum digenea - rainbow-trout - schistosoma-mansoni - cryptobia-salmositica - alternative pathway - oncorhynchus-mykiss - ichthyophthirius-multifiliis - antibody-response
The effect of Sanguinicola inermis on serum antibody and complement activity in Cyprinus carpio was assessed using an ELISA and haemolytic assays. Possible immune evasion strategies were assessed using immunodetection of host proteins on the surface of the parasite. Carp acclimatized to 20 or 25 °C were infected by exposure to 500 cercariae or injected intraperitoneally with 150 cercariae, and serum monitored over a 63-day period. In cercariae-injected carp, irrespective of time and temperature, a significant increase occurred in complement activity being greatest at 25 °C. In addition, fish exposed to the cercariae of S. inermis and maintained at 20 °C the level of complement activity was significantly higher after 5 weeks compared to controls. At 20 °C intraperitoneal injections of parasites increased serum antibody levels which peaked after 7 days. In contrast, at 25 °C, antibody levels were maintained over 63 days. Exposure offish to infection did not appear to stimulate antibody production. Immunofluorescence studies revealed 'host-like' molecules on the surface of the cercarial body exposed to carp serum and adult flukes obtained directly from the fish or cultured for 24 h in L15 medium. The possible role of 'host-like' molecules in immune evasion is discussed and the response at different temperatures is related to infection dynamics