A zoo among the feathers
Birds are hosts to a wide variety of mites, most of them unknown to science
In late 2010, the chickens in the city of Bastos, in inland São Paulo State, developed an illness. Bastos is Brazil’s largest egg producer. The birds kept at farms began to lose feathers, stopped eating and spent the day scratching themselves. Egg production dropped considerably, and many chickens were killed to prevent the spread of contagion. The problem was later found to have been caused by a mite, but identifying it was not so simple, as the mite in question was unknown to science. To the veterinarians at the Biology Institute—an arm of the São Paulo State Department of Agriculture and Food Supply, which has a unit in the local municipality—this came as a surprise, since chickens are known for their importance to the economy, and chicken parasites have been widely studied. The mite in question was described in 2013 by Russian zoologist Sergey Mironov, and it was not just a new species, but also a new genus never before described. There were a few lingering questions, however: what was the natural host of Allopsoroptoides galli, and how did the arachnid infest the chickens?
The mystery was solved by biologist Fábio Akashi Hernandes of the Institute of Biosciences at São Paulo State University (Unesp) at Rio Claro. Hernandes and his team found the mite in the Guira Cuckoo (Guira guira), a bird that is fairly common throughout much of Brazil, as the researcher notes in a paper published in December 2014 in Parasitology Research. According to Hernandes, A. galli lives in perfect harmony with its natural host and the seven or eight other species of mites that inhabit the bird’s plumage. All except one of these species, unknown until then, are now being described.
“Unlike the situation with the chickens in Bastos, most feather mites are not harmful to their hosts,” Hernandes explains. Recent research studies have shown that healthy birds carry more of these microscopic arachnids than do sick birds. “This lends support to the idea that feather mites are normally not parasitic, but rather have a neutral or beneficial effect on birds,” says Heather Proctor, a zoologist at the University of Alberta, Canada, and one of the world’s leading experts on mites. Mites normally feed on excess oil produced in the plumage, thus preventing the proliferation of bacteria harmful to the host.
The case that occurred in the egg capital, as the city is known, is a rare instance of mites transferring from wild populations to domestic hosts. The principal scenario for the “contamination” is the fact that the chickens in Bastos live in free-range environments, where Guira Cuckoos and other birds move around freely looking for food and water.
The fact that a bird as common as the Guira Cuckoo has unknown mites gives an idea of the uncharted nature of this fauna, which is invisible to the naked eye. Mites—less well-known than ticks, their cousins in the subclass Acari—are usually a few hundred microns (thousandths of a millimeter) in length and live in the soil, on the ocean floor, on plants, in the living room rug, and even on human skin. Of the nearly one million mite species estimated to exist throughout the world, only 50,000 to 60,000 are known. Feather mites belong primarily to the superfamilies Analgoidea and Pterolichoidea, and fewer than 2,500 species have been described by taxonomists.
Brazil offers an entire universe of feathers waiting to be explored. In a 2011 research study, Hernandes, Proctor and Michel Valim, who is currently based at the Zoology Museum at the University of São Paulo, found 185 species of mites in 218 species of Brazilian birds, which represent a mere 12.4% of the country’s bird diversity, the second-largest in the world. On the basis of these numbers, they estimated that there are between 900 and 5,300 species of feather mites in Brazil. “I think the most likely figure is around 2,000,” Proctor says. In the world overall, they could number 10,000.
“In Brazil alone, there is material enough to study for another three lifetimes,” Hernandes jokes. To give an idea of the challenge involved in identifying Brazilian bird mites, he tells about the day when a student in his laboratory found a dead Common Waxbill (Estrilda astrild) on the university campus. It is an exotic bird of African origin, but quite common in Brazil. To their surprise, the researchers found seven mite species, “probably all of them new,” living in the bird’s plumage. The bird that holds the record for number of mite species is Aratinga holochlora, a Green Conure native to Mexico and Central America. In 1995, zoologist Tila Pérez of the National Autonomous University of Mexico identified 25 mite species on that bird.
To say that they live on feathers is a rather imprecise way to identify these creatures. “There are mites that live only on wing feathers, while others are specific to the feathers of the belly or back, or to the more delicate feathers of the neck; and some even live in the calamus, the part of the feather that inserts into the skin,” explains Hernandes, elaborating upon a specialization that goes far beyond bird species. Mite specialization can be seen under a microscope by observing their environment-adapted morphology. There are spurs for attaching onto wings, hooks at the joints to enable the mite to hold on in moments of turbulence, and even highly asymmetrical claws, which are common among mites that live on aquatic birds. The mite of the genus Michaelia, which spends its entire life on the Neotropic Cormorant (Phalacrocorax brasilianus), has a much bigger forelimb on one side than on the other, thought to enable it to accommodate to the flying and swimming lifestyle of the host bird. Another rather peculiar feature, unrelated to the host, involves distinctive sex organs such as that of Anisodiscus goodmani, in which the male genital apparatus is twice the size of its entire body.
In a research study begun in 2011 with master’s candidate Luiz Gustavo Pedroso and undergraduate student Matheus Gabriel as co-participants, Hernandes described several new species, and he plans to develop closer partnerships with institutes in other countries that use the more recent electron microscope technologies, such as the United States Department of Agriculture (USDA).
The scanning microscopes they use provide resolution that is impossible to achieve with optical instruments. “In images we took in March 2015, we were able to see details we had never dreamed of, such as structures of the mouth apparatus and the shape of the carapace and shields of mites,” he says. Another technology he expects to benefit from through partnership is the confocal laser scanning microscope, in which a laser beam scans the entire animal and generates a three-dimensional model.
Although he has no ready access to one of these instruments, Hernandes can count on the trained eyes of his team members. The 2014 paper reported another finding that gives an idea of just how invisible feather mites are. The plumage of the Guira Cuckoo contained several specimens of A. galli, the mite that terrorized the egg capital, inside the shell of an egg—a louse egg. It functioned as a spare carapace while its body was vulnerable during the molting process, when the animal sheds its covering to produce another, slightly larger one.
Diversity and taxonomy of feather mites (Arachnida: Acari: Astigmata) on birds of Brazil (No. 11/50145-0); Grant mechanism Young Investigators; Principal investigator Fábio Akashi Hernandes (IB-Unesp, Rio Claro); Investment R$346,193.00 (FAPESP).
HERNANDES, F. A. et al. From cuckoos to chickens: a caught-in-the-act case of host shift in feather mites (Arachnida: Acari: Psoroptoididae). Parasitology Research. V. 113, No. 12, p. 4355-61. December 2014.