New Worlds: Darwin’s finch and the evolution of smell

The similarity between bird song and human language makes birds a useful scientific model for probing how this ability developed.

By JUDY SIEGEL-ITZKOVICH
spring flowers 311 (photo credit: Ariel Jerozolimski)
spring flowers 311
(photo credit: Ariel Jerozolimski)
Smell and speech are completely different, but odor may play a role in avian communication, according to Weizmann Institute of Science researchers. Darwin’s finches – 14 related species of songbirds found on the Galapagos and Cocos Islands – will forever be enshrined in history for having planted the seeds of the theory of evolution. Today, exactly 150 years after Darwin’s famous book, finches can still teach us about evolution. An international group of researchers, among them Prof. Doron Lancet and Dr. Tsviya Olender of the Rehovot institute’s molecular genetics department, recently produced the full genome of the zebra finch and analyzed it. Their report, which appeared two weeks ago in Nature, is especially significant for what it reveals about the learning of language and speech. For the Weizmann scientists, however, the findings have provided an interesting twist on the evolution of the sense of smell.
Song birds – like humans – are capable of complex communication through sound. The similarity between bird song and human language makes birds a useful scientific model for probing how this ability developed, what neuronal mechanisms are required and which genes encode them. Significantly, the scientific team found that a large percentage of genes expressed in the finch brain are devoted to vocal communication. They also found that the expression levels of a number of genes, specifically those belonging to the important class of micro-RNAs, change after the bird is exposed to song. This implies that such genes might be involved in a bird’s ability to learn new tunes.
“The senses are sophisticated means of interacting with the environment. In our lab, we are primarily interested in smell,” says Olender, who joined the project along with Lancet in order to map the genes encoding smell receptors in the finch. In doing so, they were entering the fray on a long-standing debate over whether the sense of smell is important for birds. Some positive evidence exists: Homing pigeons have been shown to use smell to help them navigate. In contrast, a computer-aided analysis of the chicken genome had shown that out of 500 genes encoding smell receptors, a mere 70 produce active proteins. Lancet and Olender have now conducted a similar analysis of the zebra finch genome. Their findings revealed that while the finch has the same total number of smell genes, it possesses three times as many that are active: Around 200 of the finch’s genes can produce functional smell receptors. This figure supports the claim that some birds do rely on smell.
A comparison of the zebra finch genome to those of other birds sheds some light on how this sense evolved: Unlike mammals, in which all species share most of their smell receptor gene families, 95 percent of the receptors in the finches appear to belong to families unique to them. In other words, it is possible that each bird species evolved its own array of smell receptors. Lancet: “This finding suggests that smell may be involved in the unique communication among individuals within the species, on top of the messages they send through their songs.”  
AMPHIBIAN WARNING FOR QUAKES?
British scientists say they’ve discovered that common toads can detectearthquakes as many as several days in advance of any apparent seismicactivity. Researchers from the Open University in London, who publishedtheir findings recently in the Journal of Zoology,were quoted by UPI as saying they found 96 percent of male toads(Bufonidae) in a population abandoned their breedingsite five days before an earthquake struck L’Aquila in Italy last year.The breeding site was about 65 kilometers from the quake’s epicenter.
The scientists said the number of paired toads at the site also dropped to zero three days before the earthquake.
“Our study is one of the first to document animal behavior before,during and after an earthquake,” the study’s lead author, Rachel Grant,said. “Our findings suggest that toads are able to detect pre-seismiccues, such as the release of gases and charged particles.”
The researchers did not explain where the females went and whether themale toads’ sudden departure could have been circumstantial.