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Advanced Search Abstract Red, orange, and yellow carotenoid-based colorations displayed by fishes and birds may function as honest sexual signals of the bearer's quality. However, the mechanisms underlying the expression of these traits and the information they convey are still controversial.
Because carotenoids are antioxidants and carotenoid-based pigmentation is bleached as a consequence of oxidative processes, it has been suggested that the pigmentation may signal antioxidant status. We tested this hypothesis in the yellow-legged gull Larus michahellisa seabird that exhibits a carotenoid-based red spot on the lower mandible.
The availability of a nonpigmentary antioxidant i. During the incubation period, breeding pairs were captured to assess the intensity of the color and the size of the red bill spots.
We measured the plasma level of lipid peroxidation, total antioxidant capacity, and carotenoids. We found that males that received vitamin E supplements had larger red spot than control birds but that color intensity was not affected by the supplements.
Moreover, we found that only those plasma carotenoids involved in the red coloration were affected by the antioxidant supplementation, suggesting an active mechanism to increase red coloration. Overall, our results provide experimental evidence for the hypothesis that carotenoid-based coloration reflects the bearer's antioxidant status in male gulls. Many animals exhibit elaborate ornamental traits that have evolved as signals of the bearer's quality and can be evaluated by prospective mates or opponents Andersson One of the major goals of animal communication studies has been to identify the information content of these signals and the entailed costs that may prevent cheating Zahavi ; Grafen ; Espmark et al.
However, the currency of these costs is still under debate and may depend on the nature of the signal involved. The red, orange, and yellow carotenoid-based colorations displayed by fishes and birds can be considered as good examples of honest sexual signals e. However, the information conveyed by these traits and the mechanisms underlying their expression are still controversial and have been subject of intensive research in recent decades.
Several experimental studies involving carotenoid supplementation have shown that an increase in dietary carotenoids leads to enhanced carotenoid-based ornament expression e. The honesty of carotenoid-based signals may also be reinforced by the important physiological functions of carotenoids Lozano ; von Schantz et al. Accordingly, it has been suggested that oxidative stress is the proximate cause of the genuine information revealed to prospective females through male carotenoid-dependent traits von Schantz et al.
Evidence of vitamin D synthesis in insects exposed to UVb light
Organisms produce reactive oxygen species ROS as by-products of physiological functions, which provoke oxidative damage to DNA, proteins, and lipids Finkel and Holbrook To mitigate oxidative injury, organisms use endogenous enzymes, such as superoxide dismutase, catalase, and glutathione peroxidase, as well as extracellular antioxidants such as uric acid, vitamin E, vitamin C, and carotenoids Godin and Garnett ; Fang et al. Thus, oxidative stress may also underlie the relationship between carotenoid-dependent expression and current immunological status Faivre et al.
The activation of the immune system produces ROS that must be counteracted by the mobilization of bodily antioxidants, including carotenoids, to balance oxidative stress at the expense of the expression of sexual coloration Blount et al.
Thus, it has been suggested that antioxidant activity is not the main biological role of carotenoids Hartley and Kennedy but that as they are bleached as a consequence of oxidative processes Woodall et al. The common prediction implicit in both hypotheses the antioxidant trade-off and the protection hypotheses is that increasing the availability of other nonpigmentary antioxidants should favor the expression of carotenoid-based signals Bertrand et al.
On the other hand, genetic characterization is important to some evolutionary questions, such as how to distinguish pleiotropy from physical linkage and how to identify the genetic basis of evolutionary constraints. Identifying the genetic locus within a QTL also provides evolutionary ecologists with the means to determine which genetic loci contribute to phenotypic evolution in natural populations and provides molecular biologists with a tool for gene discovery beyond the traditional mutagenic ones.
Even in genetic models, identifying the genetic locus is complicated by the fact that a QTL may span several hundred genetic loci Ungerer et al. Differentiating among the large number of positional candidate loci is a time-consuming process, although there are several recent examples of successful QTL cloning Remington et al.
Empirical analysis of QTL—environment interactions in simulated growth settings In a series of groundbreaking experiments, Mackay and colleagues have had excellent success over the past two decades both in testing several of the evolutionary hypotheses described above and in beginning to characterize the genes that underlie quantitative traits in Drosophila melanogaster using simulated natural environments.
In natural settings, D. Larvae of this species are likely to encounter variable fly densities as a consequence of varying oviposition patterns. Mackay and colleagues have given particular attention to the role that heterogeneity in diverse settings plays in maintaining genetic variation. There is variable evidence for this type of pleiotropy from studies in Drosophila, depending on the environments and traits studied.
Fry and colleagues found that different QTLs determined reproductive performance in RILs of Drosophila that were raised across combinations of temperature and ethanol environments, but there was no evidence of across-environment antagonistic pleiotropy.
A second study in Drosophila found that a single QTL had antagonistic effects on sensory bristle number in flies'growth across temperature settings Gurganus et al. Because only 1 marker out of 19 that affected bristle number in at least one temperature environment exhibited this mode of QTL—environment interaction Gurganus et al.
Additional studies with Drosophila, testing for longevity QTLs, have detected antagonistic pleiotropy across larval densities and temperatures. Alleles at QTLs that increased female life span at high larval densities reduced life span at low densities Leips and Mackayconsistent with the hypothesis that environmental heterogeneity might maintain genetic variation.
A similar pattern of antagonistic pleiotropy was observed at 10 out of 17 markers across temperature and starvation treatments Vieira et al. Despite the presence of many loci with antagonistic effects, it is worth noting that genetic correlations estimated across environments and across sexes were not significantly negative, underscoring the fact that the sum effects of all contributing loci can conceal significant heterogeneity in the behavior of individual loci.
Interestingly, antagonistic pleiotropy at the QTL level tends to appear more commonly in traits closely related to fitness, rather than phenotypic traits such as morphology. Antagonistic pleiotropy across environments has been found in a few crop studies, again in traits related to fitness i.
Although the number of studies is very small, the pattern is consistent with what would be expected as a result of variable selection Falconer and Mackay A further possibility is that ongoing selection will favor modifier alleles that reduce trade-offs associated with antagonistic pleiotropy. These findings constitute an extension of Williams's original hypothesis regarding the evolution and genetic origin of senescence, in which alleles that have favorable effects on survival or fecundity early in life have detrimental effects later in life and vice versaand the balance of selection across life-history stages, or across sexes, protects polymorphisms at longevity loci Vieira et al.
Moreover, because males and females are present in any viable fly population, sexually antagonistic pleiotropy acts to maintain genetic variation, in much the same way that pleiotropy acts to maintain variation across heterogeneous environments.
Empirical studies estimating QTLs in ecologically relevant natural settings The use of genetic models in evolutionary studies has been criticized on the basis that model organisms have uninteresting or unknown ecology. However, these organisms often derive from diverse natural settings and possess unique natural histories amenable to field study. Arabidopsis thaliana, for instance, exhibits variable germination patterns across its geographic range, presumably as a bet-hedging strategy against environmental heterogeneity Venable Plants within a single population may germinate in fall or spring, and subsequently flower and complete their life cycle either the following spring for those plants with fall germination or in the same season in which they germinated Napp-Zinn Most North American populations have been characterized as winter annuals Nordborg and Bergelsonin which all seedlings germinate in fall, overwinter as rosettes, and flower and set seed in the spring figure 2a.
However, plants in some populations at northern latitudes in North America complete their life cycle in a single season: Individuals germinate, flower, and set seed in approximately four months, either in spring or fall figures 2b2c.
These two alternative life-history strategies should be selectively advantageous when the likelihood of overwinter mortality is severe.
Evidence of vitamin D synthesis in insects exposed to UVb light
Where winters are predictably mild and summers harsh i. Arabidopsis is therefore well suited ecologically to test how selection at specific QTLs differs across environments, as well as how the expression of variation at specific loci differs across seasonal environments.
A recent field study mapped QTLs for the expression of life-history and architectural traits, as well as components of fitness, in natural seasonal environments experienced by A.
In this experiment, RILs of A. Fitness was estimated both in terms of survivorship to reproduction and in terms of fruit production, which is strongly correlated with seed number Westerman and Lawrence Consistent with hypotheses regarding the evolution of life histories in different regions, spring germinants attained higher fitness at the northern Rhode Island site, while winter annuals had higher fitness at the southern North Carolina site Weinig et al.
RILs differed significantly in fitness and in the expression of diverse life-history traits within any given environment, but analysis of the variance components revealed that genetic variation for all traits was explained primarily by interactions of RIL with specific combinations of site and season a significant RIL—season—site interaction Weinig et al. The significance of the three-way interaction suggests either that different genes determine a trait's phenotypic expression across the seasonal environments or that alleles at contributing loci vary in their environmental sensitivity.
Consistent with the quantitative genetic analyses, most traits showed significant QTL—season or QTL—site interactions. Most noteworthy is that the ERECTA marker, an induced phenotypic mutation in Ler, was associated with large phenotypic effects on flowering time in some, but not all, environments Weinig et al.
If ERECTA rather than a linked gene underlies the QTL, then the environmental interaction indicates that even a major developmental mutation may have no phenotypic effect in certain natural environments and thus may be sheltered from natural selection in those environments.
QTL—environment interactions for fecundity and survivorship may be viewed as evidence for heterogeneous selection, because components of fitness contribute directly to genetic representation in successive generations.
In the field study described above, selection did in fact act at different loci both in the different seasonal environments and across the geographic regions Weinig et al. In all but one setting fall in North Carolinasignificant QTLs for fecundity were detected, and significant QTL—environment interactions were observed.
Thus, different loci determine genetic representation in successive generations of different germination cohorts. The presence of QTL—season interactions, like that of QTL—site interactions, demonstrates that allelic variation at some loci is available to selection only in certain environments; it also indicates both that phenotypic evolution may be relatively slowed in some populations, and that phenotypic evolution may occur by way of alternative genetic pathways even when the initial populations are genetically identical.
In an initial experiment, we exposed four insect species which differ in ecology and morphology migratory locusts, house crickets, yellow mealworms and black soldier fly larvae BSFL to a low irradiance UVb source. In a second experiment we exposed these species to a higher UV irradiance, and in a third we tested the effect of exposure duration on vitamin D concentrations in yellow mealworms.
This study shows that insects can synthesize vitamin D de novo and that the amounts depend on UVb irradiance and exposure duration.
Introduction Vitamin D metabolites perform a hormonal function in a wide variety of animal species 1 — 3. These animals can obtain vitamin D either by oral ingestion or via de novo synthesis 45. De novo synthesis requires exposure of a vitamin D precursor to ultraviolet light with a wavelength between and nm UVbfollowed by a temperature dependent step 67.
Humans, birds, reptiles, amphibians and fish can use both strategies, although de novo synthesis seems the primary route to acquire a sufficient vitamin D status 8 — Ergosterol is the primary vitamin D precursor in plants, yeasts and fungi, which UVb light converts to vitamin D2, whereas 7-dehydrocholesterol 7DHC is the precursor which forms vitamin D3 in vertebrates 12 The vertebrate liver hydroxylates either form of vitamin D to hydroxycholecalciferol 25 OH D which is the major circulating form of vitamin D