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Functional Ecology 2006 20 678 688 Carotenoid accumulation strategies for becoming a colourful House Finch analyses of plasma and liver pigments in wild moulting birds Blackwell Publishing Ltd K J MCGRAW P M NOLAN and O L CRINO School of Life Sciences Arizona State University Tempe AZ 85287 4501 USA Summary 1 Male House Finches Carpodacus mexicanus colour their sexually selected plumage with carotenoid pigments and there has been much interest in the factors that affect their ability to become bright red rather than drab yellow 2 There is good support for the notions that health nutritional condition and total carotenoid intake influence colour expression but there are also suggestions that acquiring particular types of carotenoids from the diet may be important for developing red plumage 3 We used high performance liquid chromatography HPLC to analyse the types and amounts of endogenous in plasma and liver and integumentary in newly grown feathers carotenoids in a wild native population of moulting male and female House Finches from the south western United States to determine the carotenoid accumulation strategies for becoming optimally colourful 4 Four plant carotenoids lutein zeaxanthin cryptoxanthin and carotene were detected in plasma and liver However as was found previously 11 carotenoids were observed in colourful plumage with xanthophylls e g lutein dehydrolutein predominant in yellow feathers and ketocarotenoids e g adonirubin 3 hydroxy echinenone in red feathers This indicates endogenous modification of ingested carotenoids 5 Birds that accumulated more of one type of carotenoid in plasma and liver did not necessarily accumulate more of all other types suggesting that individuals are not employing a simple more is better strategy for coloration Instead when forward stepwise regression was used to examine the ability of individual types of carotenoids in plasma and liver to explain variation in red plumage pigments and plumage redness we found that the lone variable remaining in all models was cryptoxanthin concentration 6 This supports the idea that unlike some other songbirds e g yellow Carduelis finches there is a specialized biochemical strategy that male House Finches follow to become red and most sexually attractive to accumulate as much cryptoxanthin in the body as possible Cryptoxanthin is a less common dietary carotenoid than the typical xanthophylls and carotenes in grains and fruits and may be limited enough in the diet that to become colourful House Finches might adopt selective foraging strategies for the most cryptoxanthin rich foods Key words Carpodacus mexicanus ketocarotenoids plumage coloration sexual selection xanthophylls Functional Ecology 2006 20 678 688 doi 10 1111 j 1365 2435 2006 01121 x Introduction 2006 The Authors Journal compilation 2006 British Ecological Society Author to whom correspondence should be addressed E mail kevin mcgraw asu edu Present address Department of Biology Ithaca College Ithaca NY 14850 USA Present address Department of Zoology University of Florida Gainesville FL 32611 USA The variable red to yellow plumage of male House Finches Carpodacus mexicanus has emerged as a classic example of a sexually selected indicator of quality in birds reviewed in Hill 2002 Numerous field and laboratory studies demonstrate female mate choice for male House Finches with the reddest plumage e g Hill 678 679 Carotenoids in moulting house finches 2006 The Authors Journal compilation 2006 British Ecological Society Functional Ecology 20 678 688 1990 1991 and the associated reproductive benefits e g earlier timing of breeding increased young production reaped by colourful males and their mates Hill et al 1994 1999 McGraw et al 2001 Moreover a series of correlational and experimental studies indicate that males must ingest sufficient amounts of carotenoids from food to become colourful Hill 1992 1993 Hill et al 2002 as well as maintain adequate overall nutrition Hill Montgomerie 1994 Hill 2000 and health Thompson et al 1997 Brawner et al 2000 Hill et al 2004 during feather growth There are indications from other work however that acquiring certain types of carotenoids from foods might also be critical for developing red as opposed to yellow coloration Without exception House Finches housed in captivity on a normal seed diet during moult grow yellow plumage Hill 1992 2002 and it was only when additional sources of non xanthophyll carotenoids e g synthetic red carotenoids tangerine juice were added to their diet that they grew red feathers Hill 1992 2000 More recent biochemical studies of the carotenoid components in House Finch feathers Inouye et al 2001 show that important red carotenoids absent from other tissues and fluids in these birds McGraw 2004 are what determine red coloration and thus must be manufactured by birds from precursor molecules not commonly available to them Hill 2000 2002 speculated that it was the ability of birds to accumulate the precursors of red pigments in feathers candidate molecules such as cryptoxanthin based on purported chemical transformations that controls at the pigment level whether birds could acquire red plumage or not also see Stradi et al 1996 for similar predictions for other red coloured cardueline finches However to date there are no published studies on variation in the types of carotenoids that free ranging House Finches ingest and accumulate in the body or on the extent to which ingested carotenoids predict the pigment composition and expression of colourful plumage We studied carotenoid accumulation strategies during moult in a native population of House Finches from the desert south western United States We collected blood from live birds to obtain a recent record of dietary carotenoid assimilation liver tissue and feathers from freshly euthanized animals and analysed carotenoid content of all samples so that we could ask the following questions about the relationships between pigment accumulation and coloration 1 How do levels of different carotenoids covary within plasma or liver In those bird species for which the biochemical basis of carotenoid coloration has been investigated e g American Goldfinch Carduelis tristis McGraw Gregory 2004 Greenfinch Carduelis chloris Saks et al 2003 birds tended to accumulate more of all types of carotenoids within a fluid tissue type e g plasma feathers However if certain dietary pigments are 2 3 4 5 of special value to colour production in House Finches


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