How cuckoo is that? Many species of cuckoos are parasitic — that is, they lay their eggs in other birds’ nests, letting the host parents feed and raise the next generation of cuckoos. Michael Sorenson, a CAS associate professor of biology and an expert on avian genetics, recently collaborated with Robert Payne, curator of birds and a professor of zoology at the University of Michigan, to try to better understand the evolutionary origins of this behavior.
Sorenson and Payne sequenced about 2,000 base pairs of mitochondrial DNA from every known species of cuckoo, using the genetic similarities and differences to reconstruct the bird’s family tree. To obtain genetic material from the many rare, endangered, or inaccessible species, Sorenson extracted DNA from the feathers of museum specimens collected and stuffed by ornithologists 50 to 100 years ago. The genetic analysis, the largest and most comprehensive ever done for a large family of birds, resulted in a well-defined family tree, showing clear relationships among cuckoo species, genera, and subfamilies.
The genetic analysis revealed that contrary to previous assumptions not two but three groups of cuckoos had independently evolved parasitic behavior, each with its own distinct characteristics. In one group, the Old World parasitic cuckoos, comprising 52 species descended from a single common ancestor, the newly hatched and still-blind cuckoo chick takes over by pushing the eggs of the host bird out of the nest. In a second Old World group of four species in the genus Clamator, cuckoo chicks are reared along with the young of the host species. And in the third, a South American group of three species, the cuckoo chick kills the host young directly by biting and stabbing them with sharp hooks on its beak.
Among Payne’s findings are that the brains of all three groups of parasitic cuckoos are smaller than those of other species. “Because parasitic cuckoos don’t build nests, don’t incubate eggs, and don’t feed young,” says Sorenson, “perhaps natural selection has let their brain size decline a bit after they became parasitic.” He also surmises, “Because a cuckoo female does not expend any time or energy in incubating eggs or rearing young, she can and does invest more in producing and laying eggs, typically putting one egg in each of a large number of host nests. Presumably this is the basic advantage of parasitism and begs the question of why more birds don’t take this easy way out!”
The research on cuckoos is in the chapter “A molecular genetic analysis of cuckoo phylogeny,” in Payne’s book Bird Families of the World: Cuckoos, recently published by Oxford University Press.
Spring fever and summer travel. Spring has finally arrived in New England, and with summer not too far behind, the thoughts of students and faculty turn to — well, travel. But to get to destinations like Paris, Rome, and Mombai it is necessary to spend long hours in crowded airplanes breathing recirculated air and to deal with apprehensions about picking up a cold or worse. According to SPH Professor David Ozonoff and Assistant Professor Lewis Pepper, the likelihood of getting sick from airplane air is open to question.
“Large commercial aircraft typically recirculate about 50 percent of cabin air, passing it first through high-efficiency particulate air (HEPA) filters,” they say. However, “only 85 percent of commercial airliners that carry more than 100 passengers in the current U.S. fleet and recirculate cabin air are equipped with them,” and although HEPA filters are believed to effectively filter out viruses, there is insufficient data to support that hypothesis.
Published reports of contagious diseases transmitted during air travel are, in fact, uncommon, and because of the way air is recirculated (across the airplane rather than from front to back), the risk is generally considered to be confined to passengers within two rows of one another. However, the authors point out, on an Air China flight in 2003, cases of SARS occurred in as many as 25 passengers scattered throughout almost the entire length of the coach cabin.
Moreover, from the standpoint of network theory and the small-world phenomenon — also known as six degrees of separation — frequent travel by passengers and airline personnel between population centers is likely to influence the ease and speed with which disease is spread. Ozonoff and Pepper propose that interdisciplinary teams of ventilation and infectious disease experts, mathematicians, and others are necessary to determine where preventive measures can be applied most effectively to prevent global epidemics.
As for summer vacation plans, the authors recommend good personal hygiene — wash your hands frequently, especially before eating, cover your nose and mouth while sneezing or coughing, and wash your hands after to protect others.
The editorial by Ozonoff and Pepper was published in the March 12, 2005, issue of the British medical journal Lancet.
Briefs" is written by Joan Schwartz in the Office of the Provost. To read
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