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The effect of mycoplasmosis on carotenoid plumage coloration in male house finches

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Parasites are widely assumed to cause reduced expression of ornamental plumage coloration, but few experimental studies have tested this hypothesis. We captured young male house finches Carpodacus mexicanus in Alabama before fall molt and randomly divided them into two groups. One group was infected with the bacterial pathogen Mycoplasma gallicepticum (MG) and the other group was maintained free of MG infection. All birds were maintained through molt on a diet of seeds with tangerine juice added to their water as a source of β-cryptoxanthin, the natural precursor to the primary red carotenoid pigment in house finch plumage. All males grew drab plumage, but males with MG infection grew feathers that were significantly less red (more yellow), less saturated, and less bright than males that were not infected. MG targets upper respiratory and ocular tissue. Our observations show that a pathogen that does not directly disrupt carotenoid absorption or transportation can still have a significant effect on carotenoid utilization.
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2095
It is widely assumed that parasites affect expression of
ornamental coloration in animals and that color displays serve
as honest indicators of parasite resistance (Hamilton and Zuk,
1982). This assumption is supported primarily by correlations
between ornament expression and parasite load measured in
wild animals (for a review, see Hamilton and Poulin, 1997). In
only relatively few studies have the effects of parasites on
ornament expression been studied through carefully controlled
infection experiments. Zuk et al. (1990) conducted infection
experiments on red-jungle fowl Gallus gallus with intestinal
roundworms Ascaridia galli, and showed that roundworm
infection reduced comb size in males. Moreover, in a field
experiment with barn swallows Hirundo rustica, Møller (1990)
showed that males infected with blood-sucking mites grew
shorter tails than males that were not infected. These
experimental studies show that parasites can affect expression
of morphological traits. The effects of parasites on animal
coloration, and especially the brilliant plumage coloration of
birds, is of special interest because it was plumage coloration
that was the focus of the original statement of the
Hamilton–Zuk hypothesis (Hamilton and Zuk, 1982) that
ornamental traits evolve as indicators of parasite resistance.
Carotenoid pigmentation is one of the most widespread
mechanisms for ornamental coloration, particularly in fish and
birds (Goodwin, 1984), and carotenoid pigmentation has
become a text-book example of a condition-dependent display
trait (e.g. Gill, 1995; Alcock, 2001). Carotenoids are a class of
molecules that cannot be synthesized by vertebrates – they
must be ingested to be used as integumentary pigments
(Völker, 1934, 1938). Expression of carotenoid-based
ornamental coloration is thus partly a function of the type and
quantity of pigments that are ingested (Hill, 2002). Once
carotenoids are ingested, however, they still have to be
properly utilized to create ornamental coloration, and parasites
can disrupt this utilization process. Previous experimental
studies have shown that monogenean parasites and the
protozoan parasite, Ichthyophthirius multifillis, can affect
expression of carotenoid pigmentation in guppies Poecilia
reticulata and three-spined stickleback Gasterosteus
aculeatus, respectively (Milinski and Bakker, 1990; Houde and
Torio, 1992). Field correlational studies of yellowhammers
Emberiza citrinella (Sundberg, 1995) and greenfinches
Carduelis chloris (Merila et al., 1999) suggest that parasites
can affect expression of carotenoid-based plumage coloration
in birds. Controlled aviary experiments with American
goldfinches Carduelis tristis also showed that coccidiosis
(McGraw and Hill, 2000) and mycoplasmosis (Navara and
Hill, 2003) can affect expression of ornamental carotenoid
coloration.
In this study we tested the effects of the bacterium
Mycoplasma gallicepticum (MG) on expression of plumage
coloration in the house finch Carpodacus mexicanus, a species
in which males have carotenoid-based ornamental coloration
that varies from pale yellow to bright red (Hill, 1993). Several
The Journal of Experimental Biology 207, 2095-2099
Published by The Company of Biologists 2004
doi:10.1242/jeb.00998
Parasites are widely assumed to cause reduced
expression of ornamental plumage coloration, but few
experimental studies have tested this hypothesis. We
captured young male house finches Carpodacus mexicanus
in Alabama before fall molt and randomly divided them
into two groups. One group was infected with the bacterial
pathogen Mycoplasma gallicepticum (MG) and the other
group was maintained free of MG infection. All birds were
maintained through molt on a diet of seeds with tangerine
juice added to their water as a source of β-cryptoxanthin,
the natural precursor to the primary red carotenoid
pigment in house finch plumage. All males grew drab
plumage, but males with MG infection grew feathers that
were significantly less red (more yellow), less saturated,
and less bright than males that were not infected. MG
targets upper respiratory and ocular tissue. Our
observations show that a pathogen that does not directly
disrupt carotenoid absorption or transportation can still
have a significant effect on carotenoid utilization.
Key words: sexual selection, plumage coloration, carotenoid,
parasite, house finch, Carpodacus mexicanus,Mycoplasma
gallicepticum.
Summary
Introduction
The effect of mycoplasmosis on carotenoid plumage coloration in male house
finches
Geoffrey E. Hill*, Kristy L. Farmer and Michelle L. Beck
Department of Biological Sciences, 331 Funchess Hall, Auburn University, Auburn, Alabama 36849, USA
*Author for correspondence (e-mail: ghill@acesag.auburn.edu)
Accepted 23 March 2004
2096
studies have been conducted on the effects of parasites on
expression of plumage coloration in the house finch.
Thompson et al. (1997) found that males that that were infected
with avian pox prior to molt grew feathers that were less
brightly pigmented compared to males that did not have pox
infection prior to molt. They found a similar relationship
between feather mites and coloration (Thompson et al., 1997).
Brawner et al. (2000) conducted an experiment to test the effect
of Isospora coccidia on plumage coloration. They found that
males that they infected with Isospora during molt grew
drabber plumage than males that were maintained free of
coccidial infection. In this experiment, some birds contracted
mycoplasmal conjunctivitis and birds with MG grew drabber
plumage than birds that were free of MG.
Although these studies represent a substantial body of
work on the effects of parasites on carotenoid-based plumage
coloration, and the house finch has been the focus of more
research than any other passerine bird, fundamental questions
remain regarding the effects of parasites on carotenoid-based
plumage coloration in the house finch. First, the only
carefully controlled experiment looking at the effects of
parasites on plumage coloration was conducted with
isosporan coccidia. Coccidia are parasites of the gastro-
intestinal tract. They are known to directly inhibit carotenoid
absorption and the production of carotenoid carrier proteins
(Allen, 1987a,b). Thus, coccidiosis is a disease that is
expected to have direct effects on expression of carotenoid-
based plumage coloration. The effects on plumage coloration
of diseases that are more systemic and that are not known to
directly inhibit carotenoid uptake have not been tested
experimentally. In the Brawner et al. (2000) study, MG broke
in cages of birds – individuals were not assigned to treatment
groups. Whether or not individual birds became infected was
likely to have been related to their ability to resist the
pathogen. Thus, the effect of parasites is confounded by the
overall health and condition of individual birds. Finally, in
previous aviary studies looking at the effects of parasites on
plumage coloration in house finches, males were maintained
on diets supplemented with the red carotenoid canthaxanthin
(Brawner et al., 2000). Canthaxanthin is used by male house
finches directly as a plumage pigment without being modified
(Inouye et al., 2001; Hill, 2002). The dominant red pigment
in the plumage of wild male house finches, however, is 3-
hydroxy-echinenone, which is the metabolic derivative of the
dietary pigment β-cryptoxanthin (Inouye et al., 2001). By
feeding males a red pigment and bypassing metabolic
pathways, previous feeding experiments may have
underestimated the effects of parasitism on plumage
coloration.
In the present study we tested the effects of Mycoplasma
gallicepticum on expression of plumage coloration in male
house finches. Two groups of males were maintained on a
diet supplemented with β-cryptoxanthin. One group was
experimentally infected with MG while the other group was
maintained free of MG through the molt period. This study was
designed as an experimental test of the effects of a systemic
infection on expression of carotenoid pigmentation when birds
are utilizing a natural dietary precursor for plumage pigments.
Materials and methods
We captured hatch year house finches Carpodacus
mexicanus Müller in Auburn, Alabama, USA from early July
through August. Upon capture, we took 100·µl of blood from
each bird. Blood was spun to separate plasma and red blood
cells, which were stored in TNE buffer at –80°C. Plasma was
stored at 4°C for serological analysis (see below). In juvenile
plumage, male and female house finches cannot be
distinguished morphologically, so we used a molecular-sexing
technique to determine the sex of the birds that we captured.
Briefly, the DNA was extracted from stored red blood cells
using a standard phenol/chloroform technique (Quinn and
White, 1987; Westneat, 1993). Extracted DNA was
resuspended in TE buffer and stored at –20°C. We identified
the sex of the hatch year birds using P2 and P8 microsatellite
primers and the PCR protocol outlined by Griffiths et al.
(1998). These primers amplify introns on the CHD1-W and
CHD1-Z genes. Two bands are present in females, which are
the heterogametic sex, whereas males as the homogametic sex
have a single band (Griffiths et al., 1998). PCR products were
separated on a 1.5% agarose gel laced with ethidium bromide
by electrophoresis at 150·V for 2·h.
Males were housed in small cages with 2 birds per cage for
the duration of the experiment. Birds within a cage received
the same experimental treatment – either infected or not
infected (see below). They were held near windows so they
experienced a natural light cycle. All birds had ad libitum
access to a canary pellet diet (canary maintenance, Avi-Sci
Inc., St Johns, Michigan, USA). Through the molt period, we
added one part tangerine juice (100% pure juice, not from
concentrate, never frozen) to one part drinking water for all
birds. Tangerine juice tended to spoil at room temperature so
tangerine juice/water was changed every 24·h.
To ensure that none of the birds in our experiments had been
previously exposed to MG, we tested the serum of each bird
for antibodies to MG using a serum plate agglutination assay
as described in Roberts et al. (2001). We also tested birds for
the presence of MG by polymerase chain reaction (PCR;
Roberts et al., 2001). We collected samples for analysis by
PCR by swabbing the choanal cleft using a micro-tip swab
(Becton Dickinson and Co. Maryland, USA). Any birds that
were found to have antibodies to MG or that were PCR-
positive were excluded from the study. Coccidiosis is another
widespread disease of house finches that is known to affect
expression of carotenoid coloration (Brawner et al., 2000). To
be certain that coccidiosis did not confound the effects of
mycoplasmosis in this experiment, we added sulfadimethoxine
to the water of all birds to ensure that they remained free of
coccidiosis (Brawner et al., 2000)
We cultured MG from symptomatic wild house finches caught
in Auburn, Alabama. We infected the birds in the MG treatment
group by dropping 10·µl of SP4 medium containing 1×106color-
G. E. Hill, K. L. Farmer and M. L. Beck
2097Mycoplasmosis and plumage color
changing units·ml–1 into each eye for a total dose of 2×104color-
changing units. This dose of MG has been effective in previous
studies in inducing a modest infection among captive house
finches (Roberts et al., 2001). Birds in the uninfected treatment
group were sham infected with the same amount of sterile SP4.
We monitored the birds daily for onset of disease. Disease was
measured for each eye on a five-point scale, where 0=normal eye
and 4=blindness caused by swelling (Roberts et al., 2001). We
captured all birds three weeks post-inoculation to collect blood
for serology and swabs for MG detection by PCR.
Following molt, we measured plumage coloration of all
males using a Colortron reflectance spectrophotometer (Hill,
1998). Male house finches display carotenoid-based plumage
coloration on their crown, breast and rump, and a technician
with no knowledge of the experiment scored plumage color by
taking three measurements in each of these areas. We averaged
these measurements to obtain an overall hue, saturation and
brightness for each male. We photographed the breast patch of
each male along with a size standard and used Sigma Scan 5.0
to measure breast patch size. We calibrated each picture using
the size standard and then traced the breast patch three times
and used the average size in all analyses.
All infection protocols carried out in this study were
approved by the Institutional Animal Care and Use Committee
(IACUC) at Auburn University. We used the smallest sample
of birds that would give us reasonable power to detect
differences among groups.
Results
Birds in the uninfected group remained free of MG
throughout the study. No birds in the uninfected group showed
symptoms of mycoplasmosis nor did any birds show a positive
antibody response to MG. All PCR tests of birds in the
uninfected group were negative.
All birds that were inoculated with MG developed
conjunctivitis in both eyes within 10 days of inoculation. All
birds in this group developed antibodies to MG and all tested
positive for MG by PCR. For most birds the infection lasted
throughout the 8-week molt period, with the most severe
clinical symptoms occurring 2–6 weeks after infection.
After molt on the pellet diet supplemented with tangerine
juice (as a source of β-cryptoxanthin; Hill, 2000), all males
grew pale orange plumage, much drabber than the average wild
male in the Auburn, Alabama population. There was a
significant effect of MG infection on ornamental plumage
coloration. Males that were infected with MG during molt
grew breast feathers that were more yellow/less red (Z=–1.90,
N=15,16, P=0.03), less saturated (Z=–1.86, N=15,16, P=0.03),
and less bright (Z=–1.78, N=15,16, P=0.04) than males that
had no MG infection (Mann–Whitney U Tests) (Fig.·1). There
was no significant effect of the cage in which males held on
any component of plumage coloration (hue: F-ratio=1.62,
P>0.17; saturation: F-ratio=1.84, P>0.12; brightness: F-
ratio=1.33, P=0.29).
Patch size was measured on males several months after molt
and by that time several males had died or been used in other
experiments. Therefore we had only 12 infected and 13 control
males for patch size comparison. We found no significant
difference in the patch sizes of male that were infected with
MG during molt and the patch sizes of males that were not
infected (Z=–0.65, P=0.51).
Discussion
Understanding the effects of parasites on production of
Hue
28
30
32
34
36
38
30
35
40
45
50
55
60
65
30
35
40
45
Saturation (%)
Brightness (%)
Infected Not infected
Red Yellow
Treatment
N=15N=16
Fig.·1. The effects of Mycoplasma gallicepticum (MG) infection on
expression of carotenoid plumage coloration in male house finches.
Plotted as horizontal lines are the median and 10th, 25th, 75th and
90th percentiles of the hue, saturation and brightness. Comparisons
were made with the mean color of the crown, breast and rump
feathers for each male following molt within experimental treatment
group. Infected males all had conjunctivitis during the molt period.
Uninfected males tested negative for MG both in antibody tests and
PCR tests at capture and were held in a quarantine facility away from
sources of MG during molt. All birds were fed a low-carotenoid
pellet diet and water supplemented with tangerine juice as a source
of carotenoid pigments.
2098
ornamental traits is central to a general understanding of the
signal function of these displays. Signaling parasite resistance
has been proposed to be a key function of color displays and
to have been the driving force in the evolution of such traits
(Hamilton and Zuk, 1982). This theory relies crucially on
parasitic infection reducing the magnitude of display traits.
Despite the importance of the hypothesis that parasites reduce
expression of display traits, few experimental studies have
been conducted to test this idea.
Previous research had shown that in controlled infection
experiments, coccidiosis caused male house finches to grow
less red and less saturated plumage coloration (Brawner et al.,
2000). In these infection experiments that controlled the
exposure of males to coccidiosis, some males contracted
mycoplasmal conjunctivitis, and it was found that males with
mycoplasmal conjunctivitis grew less red, less saturated, and
less bright plumage than males that were not infected (Brawner
et al., 2000). Because males in the Brawner et al. (2000) study
were not infected with MG by researchers, but rather either
contracted or resisted contracting the disease, there is the
chance than male health and condition affected both plumage
coloration and disease state.
In the present study we eliminated the uncertainty of
previous studies and show definitively that mycoplasmal
conjunctivitis during molt depressed expression of ornamental
plumage coloration in male house finches. In our experiment,
we randomly assigned males to treatment groups eliminating
any confounding effects of condition or health. We also fed
males the precursor to the red pigment that is the most
abundant red pigment in the plumage of wild house finches.
By feeding the metabolic precursors to red feather pigments,
we forced birds to include more steps in the utilization of
pigments. Interestingly, even though we forced birds to
metabolically modify dietary pigments to produce red
ornamental coloration, and thus added at least one step to the
process of carotenoid utilization, we saw no greater effect of
MG on plumage coloration in this study, compared to the
previous study in which males were fed red feather pigments
directly (Brawner et al., 2000).
We found a significant negative effect of mycoplasmosis on
plumage coloration, but no significant effect of mycoplasmosis
on the size of carotenoid breast patches. This observation is
consistent with observations from feeding experiments in
which access to carotenoid pigments had a large effect on
plumage coloration but a small effect on patch size (Hill, 1992,
1993). This finding is also consistent with the idea that the
quality of ornament pigmentation (coloration) and the area of
the body with pigment (patch size) are under distinct
developmental control, with largely independent responses to
environmental challenges and different signaling function
(Badyaev et al., 2001).
As a source of β-cryptoxanthin, we fed males in this
experiment tangerine juice (Hill, 2000). β-cryptoxanthin is
the predominant carotenoid in tangerine juice (Mangels et
al., 1993), but the amount of β-cryptoxanthin ingested by
male house finches in this study was probably still small
compared to the amount of the pigment that is likely to be
ingested by wild finches feeding on fruits. Males in both
treatment groups appeared to have fewer pigments available
than they needed for maximum expression of ornamental
coloration, and all males were drab at the end of the feeding
experiment. Experimentally infected males were simply
drabber on average than uninfected males. We assume that
we may have seen larger differences in plumage coloration
between control and infected groups if males had been fed
larger doses of β-cryptoxanthin, but it is also conceivable
that access to more β-cryptoxanthin may have masked the
effects of mycoplasmosis.
Previous experimental studies of parasites and plumage
coloration in house finches have focused on coccidiosis. In one
sense, these studies are particularly valuable because they
focus on a parasite for which a mechanism for direct inhibition
of carotenoid utilization is known (Brawner et al., 2000). On
the other hand, studies of coccidia leave open the question of
the effects of parasites that do not directly inhibit carotenoid
uptake or transport, but that have more general systemic effects
on the bird and would have indirect effects on pigment
utilization. MG is an upper respiratory disease (Jordan, 1996).
It does not infect gastro-intestinal tissues and thus it is unlikely
to directly affect carotenoid absorption. Nevertheless, we
found that MG depressed expression of ornamental coloration.
The present study, coupled with previous experiments on the
effects of disease on house finches, shows that both parasites
that specifically target gastro-intestinal tissues and directly
disrupt carotenoid utilization as well as parasites that infect
tissues outside the gastro-intestinal track can have a significant
effect on how carotenoid pigments are utilized. The relative
importance of these two types of parasites on expression of
plumage coloration among males in wild populations remains
to be determined.
One intriguing possibility is that, in birds infected with MG,
carotenoids that could have been used for ornamental display
were instead diverted to bolster the immune system against the
infection (Lozano, 1994; Møller et al., 2000). We cannot assess
this hypothesis with the data at hand, but it has yet to be shown
for any species that there is a trade-off between use of
carotenoids for ornamental plumage coloration and use of
carotenoids for immune defense (Hill, 1999). A recent study
on American goldfinches failed to find such a trade-off in a
carefully controlled infection experiment (Navara and Hill
2003). A simpler explanation is that the house finches in this
study that were infected with MG diverted energy away from
pigment utilization to immune defense and this diversion of
energy caused the loss of plumage coloration in infected males.
We thank Lisa Snowberg and Brad Staton for caring for the
birds. This study was funded by NSF grants DEB0077804 and
IBN9722171 to G.E.H.
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... Therefore, carotenoid deposition may be an honest signal for parasite resistance (but not pigments producing structural coloration; see [14]). Intensely parasitized individuals usually have dull plumage because of (i) an energetic imbalance between investing in plumage coloration and mounting an immune response against parasites [15] or (ii) direct damage to feathers by parasites [16]. Also, parasites that do not directly reduce circulating carotenoids may depress the utilization of this pigment [15]. ...
... Intensely parasitized individuals usually have dull plumage because of (i) an energetic imbalance between investing in plumage coloration and mounting an immune response against parasites [15] or (ii) direct damage to feathers by parasites [16]. Also, parasites that do not directly reduce circulating carotenoids may depress the utilization of this pigment [15]. For example, plumage coloration saturation, brightness and carotenoid chroma were associated with haemosporidian parasite occurrence and prevalence in different passerine species, and differences between parasitized and non-parasitized individuals are greater in sexually dimorphic species [17][18][19]. ...
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The Blue-tailed Bee-eater (Merops philippinus) is a cooperatively breeding and socially monogamous member of the Coraciiformes that displays conspicuous coloration and elongated central rectrices (“streamers”). Humans cannot distinguish males from females; both sexes are brightly colored with a chestnut throat patch, a yellow chin, and green body coloration fading into a turquoise-blue rump and tail. We quantified coloration with ultraviolet- (UV) visible spectrometry and measured morphology to determine the extent of sexual dichromatism and dimorphism. Males displayed more exaggerated coloration, longer tail streamers, and were larger than females. Multiple plumage ornaments (measures of plumage coloration and streamer length) were positively correlated in both sexes. Males in better body condition expressed darker chestnut throats and more chromatic green body plumage. Females in better body condition, however, exhibited more chromatic blue rumps and yellow chins. This study represents the first objective description of plumage ornamentation in the order Coraciiformes.
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Many passerines lay protoporphyrin-pigmented eggs, and the degree of spotting seems to be related to female condition and environmental characteristics. However, most studies have ignored the relationship between the male's quality and eggshell pigmentation. Because ornaments can act as honest indicators of individual quality, spottiness could be related to the parents' feather colouration. Using models of bird vision, we investigated whether male and female ornamentation explained variation in spotting coverage in a free-living population of blue tits (Cyanistes caeruleus). We also explored the associations between other important individual characteristics (i.e. the pair's infection status) and spotting coverage. Females that laid more pigmented eggs suffered from higher parasitaemia by the blood parasite Leucocytozoon, had smaller clutches, more saturated yellow breasts feathers and reduced body mass. Male plumage colour and infection status explained a higher percentage of the variation in eggshell pigmentation than female characteristics. Males with more saturated white cheeks, less saturated yellow breasts, more intensely infected by the parasite Haemoproteus and less by Plasmodium, attended nests with more spotted eggs. Additionally, these males were younger and more likely to father extra-pair offspring. These results, although observational, suggest that male attractiveness, male age, extra-pair paternity, and parasitic infections could be important determinants in eggshell pigmentation. Males in poorer condition might have provided less food to laying females, which in turn laid more pigmented eggs and were also in poor condition. Alternatively, increased eggshell pigmentation could result from female differential allocation or breeding in low quality territories.
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Carotenoid pigments produce the ornamental red, orange, and yellow integumentary coloration of many species of animals. Among individuals of a population, the hue and saturation of carotenoid-based ornaments can be extremely variable, and studies of fish and birds have shown that females generally prefer males that display the most saturated and reddest coloration. Consequently, there has been a great deal of interest in determining the proximate factors that affect individual expression of carotenoid-based pigmentation. Parasites might affect production of ornamental coloration, and the Hamilton-Zuk hypothesis proposes that parasitized males will show decreased expression of the secondary sexual traits preferred by females. We found that captive male House Finches (Carpodacus mexicanus) experimentally infected with Isospora spp. (coccidians) and/or Mycoplasma gallisepticum produced carotenoid-based plumage coloration that was significantly less red and less saturated than that of noninfected males. These observations validate a necessary condition of the Hamilton-Zuk hypothesis, but heritable resistance to the pathogens we examined remains to be demonstrated.
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The Colortron (Light Source, San Rafael, California) is an inexpensive, compact, Macintosh-compatible reflectance spectrophotometer that can be used to quantify the coloration of the plumage and soft parts of birds. The Colortron provides a reflectance spectrum (390-700 nm) of the object being measured as well as tristimulus color scores that can be compared to scores from the Methuen or Munsell color references. Because the Colortron fails to measure ultraviolet light (wavelength <390 nm), which is visible to some species of birds, Colortron output must be interpreted cautiously when it is used to describe plumage that may reflect UV, especially if the focus of the study is understanding the function of coloration. The Colortron is especially useful for quantifying carotenoid-based plumage coloration, which reflects primarily in the visible spectrum. I compared visual scores of carotenoid-based ornamental plumage of House Finches (Carpodacus mexicanus) made by comparison to The Methuen Handbook of Colour to tristimulus color scores generated by the Colortron. Hue and saturation scores from visual assessment were significantly positively correlated with hue and saturation scores from the Colortron. I recommend the use of the Colortron as a means to quantify plumage and soft-part coloration.
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I tested three assumptions of the Hamilton and Zuk hypothesis (1982), which suggests that the extravagant male plumage of many bird species allows females to choose mates that are resistant to the parasites exploiting the host population at a given time. By choosing such males as mates, females will rear offspring carrying the genes for resistance. I tested three necessary conditions for the Hamilton and Zuk model: (1) whether parasites affect the fitness of their hosts; (2) whether there is heritable variation in parasite resistance, and (3) whether the expression of the sexual ornament varies with parasite burden. The haematophagous mite Ornithonyssus bursa (Macronyssidae, Gamasida) sucks blood from their Barn Swallow (Hirundo rustica) hosts. Experimental manipulation of mite loads and partial cross-fostering experiments on Barn Swallows, where half of the nestlings in the brood were exchanged with nestlings from another nest, shows that parasite burdens and origin, but not rearing conditions, of Bam Swallow nestlings, affected their adult tarsus length and maximum body weight shortly before fledging. Mite loads of adult Barn Swallows at spring arrival were more similar to mite loads of their own offspring, whether reared in their own or in foster nests inoculated with mites, than to loads of foster offspring. Parent Barn Swallows with long tail ornaments had offspring with smaller mite loads in the partial cross-fostering experiments. The amount of increase in male tail ornaments from one year to another was negatively related to experimentally manipulated mite loads of Barn Swallow nests during the preceding breeding season. In conclusion, the three assumptions of the hypothesis were supported by the experimental tests.
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The test of the association between dietary intake of specific carotenoids and disease incidence requires the availability of accurate and current food composition data for individual carotenoids. To generate a carotenoid database, an artificial intelligence system was developed to evaluate data for carotenoid content of food in five general categories, namely, number of samples, analytic method, sample handling, sampling plan, and analytic quality control. Within these categories, criteria have been created to rate analytic data for beta-carotene, alpha-carotene, lutein, lycopene, and beta-cryptoxanthin in fruits and vegetables. These carotenoids are also found in human blood. Following the evaluation of data, acceptable values for each carotenoid in the foods were combined to generate a database of 120 foods. The database includes the food description; median, minimum, and maximum values for the specific carotenoids in each food; the number of acceptable values and their references; and a confidence code, which is an indicator of the reliability of a specific carotenoid value for a food. The carotenoid database can be used to estimate the intake of specific carotenoids in order to examine the association between dietary carotenoids and disease incidence.
Book
The House Finch is among the most mundane birds, so ubiquitous and familiar across the U.S. and Canada that it does not rate a glance from most bird enthusiasts. But males have carotenoid-based plumage coloration that varies markedly among individuals, making the House Finch a model species for studies of the function and evolution of colorful plumage. In more depth and detail than has been attempted for any species of bird, this book takes a tour of the hows and whys of ornamental plumage coloration. The book begins by reviewing the history of the study of colorful plumage, which began in earnest with the debates of Darwin and Wallace but which was largely forgotten by the middle of the 20th century. Documenting the extensive plumage variation among males both within and between populations of House Finches, the book explores the mechanisms behind plumage variation and looks at the fitness consequences of condition-dependent ornament display for both males and females. The book concludes by examining the processes by which carotenoid-based ornamental coloration may have evolved.
Article
The prevalence and intensity of haematozoan parasites, with special emphasis on Haemoproteus coatneyi, was studied in relation to male plumage coloration, and reproductive success in a population of yellowhammers (Emberiza citrinella). Parasite prevalence and intensity were found to vary with time in season, emphasising the need to take samples during times of developed infection. Males were found with a peak intensity during the early breeding period and females slightly later, during the nestling period. The hypothesis of parasite-mediated sexual selection, according to which bright plumages have evolved in relation to degree of parasite infection, was tested. Male colour was found to reliably reveal the intensity of parasites during the breeding period. Males with high parasite intensity produced fewer fledglings. In spite of the negative correlation between parasite load and colour, males with more colour did not produce more offspring. No cost of parasites was found in females, and pairing was not assortative with respect to parasite infection. However, contrary to the hypothesis, no relationship between male colour and number of fledglings was found. Conclusively, some support was found for the hypothesis of parasite-mediated sexual selection, i.e. bright male plumages in the yellowhammer may thus have evolved or is maintained as a signal of level of parasite infection since a reduced reproductive success may be a cost imposed by high parasite load.