Natural antioxidants give top barn swallows a leg on competitors
Natural Antioxidants Give Top Barn Swallows a Leg Up on Competitors, Says New CU Study. A new University of Colorado at Boulder study indicates North American barn swallows outperform their peers in reproduction — the “currency” of evolutionary change — by maintaining a positive balance of antioxidants commonly sold in health food stores. The study is the first to track concentrations of carotenoids, which are naturally occurring plant pigments, in a wild bird or animal species over the course of the grueling breeding season. Carotenoids can offer the benefits associated with over-the-counter nutritional supplements that protect cells from free radical damage, said CU-Boulder Assistant Professor Rebecca Safran. Since American barn swallows migrate thousands of miles to their breeding grounds annually and immediately commence courtship, nesting and reproductive activities, many lose significant amounts of weight and become physiologically compromised during the intense spring activities, said Safran, lead study author. But the new study indicates some individuals can bear such costs better than others, she said. While other studies have looked at carotenoid levels in captive birds at a single point in time, the new study
is the first to monitor carotenoids within wild individuals as they feed, mate, nest, and rear young, said Safran of CU-Boulder’s ecology and evolutionary biology department. “Our results indicate the concentrations of these molecules are highly variable within individuals over time,” she said. “The season-long balance, rather than a sample at a single point in time, indicates which birds are the top performers as parents and mates.” A paper on the subject appears in the Feb. 25 issue of PLoS One, a journal of the Public Library of Science. Co-authors on the study included Arizona State University Associate Professor Kevin McGraw, CU-Boulder doctoral students Matthew Wilkins and Joanna Hubbard and project volunteer Julie Marling. “By monitoring wild populations of barn swallows during the breeding season, we determined how individual birds managed their own health while enduring the costs of parental care,” said Safran. “Individuals who maintain a positive balance in their nutritional status through the breeding and nesting season are those with the greatest reproductive performance and tend to be darker in color and larger in body mass.” Safran and her team, which included dozens of CU-Boulder students and volunteers from the community, trapped scores of barn swallows with mist nets in rural sites around Boulder County, measuring and weighing them and taking blood and feather samples before releasing them back into the wild. Each bird was sampled between two and four times over the breeding season. The blood analysis tests took place in McGraw’s Arizona State University lab. The three carotenoids measured in the study — lutein, zeaxanthin and beta-cryptoxanthin
— all are antioxidants that are sold in health food stores around the world. The swallows obtain carotenoids from insects that feed on plants rich in the nutrients. Since the barn swallow reproductive season lasts about four months, it makes sense that individuals should be able to signal their abilities as parents and mates over time, rather than at the beginning of the season when pair formation takes place, she said. “The swallows that maintained high levels of carotenoids throughout the summer got more reproductive attempts and produced more offspring,” Safran said. Many of the high-quality barn swallow pairs, which weighed more than their peers during the breeding season, produced two clutches of eggs rather than one, producing a greater number of young that fledged, she said. “Nutritional status is a 24-hour game, because many nutrients don’t carry over beyond the next day,” she said. The “top” barn swallows appear to be very efficient at foraging and dealing with the costs of reproductive success on a day-by-day basis, which includes guarding the nest and feeding the young, both of which are physiologically taxing activities, Safran said. “Our findings in this study contradict the prevailing scientific views regarding the immense physiological costs of reproduction in birds,” Safran said. “While evolutionary theory says individuals that pay the greatest cost in parental care do so at the expense of self-preservation, we found some individuals are good at doing it all
–– maintaining their own nutritional status while bearing the costs of reproduction.” The researchers also found that barn swallows carrying more carotenoids had deeper red breasts – a sign of healthy, robust individuals – and that those individuals darker in color had greater circulating levels of carotenoids at the start of the breeding season. Previous studies by Safran and her colleagues suggest females are more attracted to males with deep red breasts and that they “cheat” less on their male partners than other females. The breast coloring appears to be an indication of status, performance, testosterone and nutrition, she said. The study was funded in part by the National Science Foundation, the Howard Hughes Medical Institute and CU-Boulder’s Undergraduate Research Opportunities Program and the Biosciences Undergraduate Research Skills and Training. Both CU-Boulder programs offer undergraduates hourly wages or stipends to work with faculty members on innovative research projects. “One of the most exciting things that I do in my job is train students both in the field and in the lab,” said Safran. “Because this work requires many hands, it would be impossible to do these kinds of studies without them.” A 2008 study by Safran and her colleagues showed the testosterone of male North American barn swallows skyrocketed early in the breeding season when their breast colors were artificially enhanced to the deep red most attractive to females. The birds likely had more testosterone
racing through their bodies because of amorous interactions with the opposite sex and more run-ins with competing males. – Researchers investigate bird’s ‘carotenoid circle of life’. – “What you see is what you get” often is the mantra in the highly competitive life of birds, as they use brilliant displays of color to woo females for mating. Now researchers are finding that carotenoids – the compounds responsible for amping up red, orange and yellow colors of birds – also may play a role in color perception and in a bird’s ability to reproduce, making it a cornerstone in birds’ vitality. These are among the findings presented by Kevin McGraw, an Arizona State University assistant professor in the School of Life Sciences, at the American Association for the Advancement of Science annual meeting in Chicago. McGraw presented his findings Feb. 13 during a special session on evolutionary biology, called “Beyond the beagle: evolutionary approaches to the study of social behavior.” “Carotenoids play fascinating and multifaceted roles in the lives of animals,” McGraw said. “For years, we have known that, as antioxidants, they boost human health and, as colorants, make birds colorful and sexually attractive. Now, we are blending as well as expanding these paradigms and studying how consumption of carotenoids can improve or ‘tune’ their color vision, promote the health of offspring as they develop in the egg, and possibly improve male sperm quality.
” McGraw presented his findings in the paper, “Carotenoids as narcissistic agents of color evolution: A bird’s eye view.” McGraw, a biochemical ecologist and evolutionary biologist who has studied diet, coloration and physiology in birds, led the work that included post-doctoral researcher Melissah Rowe and Ph.D. student, Matthew Toomey. Researchers have long thought that carotenoids – responsible for the orange color of carrots and the red of lobster – play an important role in the evolutionary lives of birds by providing them with health benefits and vibrant colors. Because these pigments are limited in the diet and for physiological purposes, their use in coloration provides “honest, accurate information” about the bird’s overall quality as a mate. McGraw’s new work expands the scope of research on carotenoids to include many other behavioral and physiological benefits they may provide, including superior color perception and gamete formation. “Like in humans, carotenoids are also deposited in the retina, where they may protect the eye from photodamage by the Sun. There also is evidence that they can shape how well colors can be discriminated visually,” McGraw explained. “Ultimately, we envision a model where the more carotenoids you eat, the better you can see color, the better mates you choose, and the redder the foods you choose, thus giving you even more carotenoids for health,
attractiveness and vision. In a sense it is a carotenoid circle of life.” McGraw and colleagues are studying a native Arizona desert songbird species (the house finch) as well as two widespread ducks (mallard and northern pintail) to better understand how carotenoids are allocated and prioritized among all of these diverse fitness (survival and reproduction) functions. “For decades, poultry scientists and human egg-consumers have been interested in the carotenoids that chicken hens put into their yellow egg yolks. We now know that these nutrients aid in the health, growth, and perhaps eventual coloration and mate quality of their offspring,” McGraw said. Carotenoids may also affect the male gametes, sperm. “Testes and seminal fluid can be enriched with carotenoids, preventing sperm cells from oxidative damage and resulting in greater fertilization ability of males,” McGraw explained. “If this is the case, carotenoids really could enhance nearly every life-stage and aspect of survival and reproduction in birds.” “We are proposing a positive fitness feedback loop for these ‘self-loving molecules,’ given how high carotenoid accumulation can improve one’s state and one’s interest in selecting carotenoid richness in mates and food. This provides a window into how major sexual selection models, such as sensory biases and assortative mating, may be explained by a common, nutritional and narcissistic currency,” McGraw added. sources: colorado.edu, physorg.com
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