Article Highlights from the November issue of The American Naturalist:
For the complete table of contents for the November issue, go to www.journals.uchicago.edu/an.
The singer not the song: Why some birds think simple songs are sexy
Female birds of several species prefer to mate with males who can perform elaborate songs with lots of sound variation, hence the evolution of complex calls like those of the lyrebird. But what about species that sing simple songs? Are the females of those species simply not as choosy? Not so, according to a new study by Gonalo Cardoso and Yang Hu. They studied several species of wood warblers, many of which sing songs consisting almost entirely of trillssimple repetitions of the same syllable. Those species that use mostly trills, the researchers found, tended to sing faster and modulate pitch more widely than the other species. Those warblers appear to use their simple songs to impress choosy ladies or to fight rivals, but they demonstrate their prowess with the quality of the performance, not the complexity of the song. "These simple songs are like a canvas on which vocal ability can be advertised and assessed easily," Dr. Cardoso said. "It's easier to identify the best athlete on a 100 meter run than on a gymnastics competition," he analogizes. The study suggests that mate choice can cut in two opposing ways, driving complex songs in some species and simple ones in others. Listen to the warbler's simple call here: http://www.allaboutbirds.org/guide/wilsons_warbler/id.
Gonalo C. Cardoso and Yang Hu, "Birdsong Performance and the Evolution of Simple (Rather than Elaborate) Sexual Signals"
How global warming could cause animals to shrink
A new study shows how global warming may cause the world's cold-blooded organisms to shrink in size. Most cold-blooded creatures are subject to what's known as the temperature-size rule, which describes how individuals of the same species tend to grow to smaller adult sizes when reared in warmer temperatures. Using 40 years of data on marine planktonic copepods, tiny crustaceans that are the main animal plankton in the world's oceans, researchers led by Andrew Hirst of Queen Mary University of London have confirmed the mechanism behind the rule. They found that warmer water causes copepods to grow faster, but also causes them to mature faster still. As a result, individuals end up with smaller body sizes when they reach full maturity. This is the first time this mechanism has been demonstrated in a large number of species, and it sheds important light on how cold-blooded creatures may be impacted as the world continues to warm.
Jack Forster, Andrew G. Hirst,and Guy Woodward, "Growth and Development Rates Have Different Thermal Responses"
How historic climate change drove modern species diversity
The lush tropical rainforests of northeastern Australia are home to the ornate nursery frog, a common terrestrial frog that thrives in warm, wet climates. But the climate in this region has not always been so hospitable, and a team of researchers led by biologist Conrad Hoskin wanted to see how historical climate change might have influenced the evolution of modern frog populations. Using paleoclimate data, the researchers show that during the last ice age, the present-day rainforest would have contracted substantially, with two small patches of forest isolated to the north and south of a larger central patch. If nursery frogs had been marooned in these peripheral patches with thousands of years to evolve in isolation, then genetic and phenotypic differences might be detectable in modern populations. And that's exactly what Hoskin and his team found. Using genetic profiling, the researchers found that modern nursery frogs come from three distinct lineages that correspond geographically with the ice age forest patterna large lineage living in the central part of the region, and two smaller lineages to the north and south. The lineages differ substantially in body size and each has a distinct mating call. They also don't seem to interbreed much, which means they likely now represent different species. "The research shows that climactic fluctuations can drive diversification, particularly where populations persist in tiny refugia peripheral to core refugial areas," Dr. Hoskin said.
Conrad J. Hoskin, Maria Tonione, Megan Higgie, Jason B. MacKenzie, Stephen E. Williams, Jeremy VanDerWal, and Craig Moritz, "Persistence in Peripheral Refugia Promotes Phenotypic Divergence and Speciation in a Rainforest Frog"
Hatching from a cold egg could lead to permanent problems
A cold start can mean a permanent setback for some birds, according to a study by Andreas Nord and Jan-ke Nilsson of Lund University in Sweden. The researchers studied blue tits, a small bird common across Europe, to see how incubation temperature influences a bird's development. Nord and Nilsson replaced eggs in natural nests with plaster ones. They brought the real eggs back to the lab, where they incubated them at different temperatures. Just before the eggs hatched, they were placed back in their nests for the mothers to raise, while Nord and Nilsson tracked growth and development of each hatchling. They found that the chicks incubated at lower temperatures were less likely to survive. Those that did survive tended to be smaller and develop more slowly. "Surprisingly, we found no indications of a recovery later in life," Nord said. "The effects of developmental temperature persisted even when the chicks were close to fully grown." The research shows just how delicate the incubation process can be as well as the dire consequences for chicks when mothers are unable to keep eggs at proper temperatures.
Andreas Nord and Jan-ke Nilsson, "Incubation Temperature Affects Growth and Energy Metabolism in Blue Tit Nestlings"
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