Article Highlights from the December issue of The American Naturalist:
For the complete table of contents for the December issue, go to www.journals.uchicago.edu/an.
Columbia River Salmon are Adapting to Climate Change
Sockeye salmon are evolving through natural selection to deal with a warming climate, according to a study by researchers at the National Oceanic and Atmospheric Administration. In recent decades, scientists have observed that salmon in the Columbia River are starting their migration earlier in the year. The fish now migrate upstream an average of 10 days earlier than they did in the 1940s. Researchers knew that the change was associated with warming water temperatures, but an important question remained. Is this a behavioral response in reaction to warmer water, or are the fish evolving modified behavior through mortality and natural selection? Using 60 years of water temperature records and data on salmon mortality during migration, researchers led by Dr. Lisa Crozier have determined that the latter has played an important role. According to their model, up to two thirds of the 10-day advance in spawning is explained by natural selection, with a behavioral response to changes in river flow explaining the rest. "Evidence of an evolutionary response in Columbia River sockeye salmon is good news, because it appeared to reduce their exposure to potentially lethal river temperatures in recent years," said Dr. Crozier. "This study gives managers insight into the multiple processes that help salmon persist in the face of a changing environment, and augments our toolbox for predicting how other species might respond to similar changes."
Lisa G. Crozier, Mark D. Scheuerell, Richard W. Zabel, "Using Time Series Analysis to Characterize Evolutionary and Plastic Responses to Environmental Change: A Case Study of a Shift toward Earlier Migration Date in Sockeye Salmon." http://www.jstor.org/stable/10.1086/662669
Predators Keep Local Frogs In Uniform
Peruvian poison dart frogs of the genus Ranitomeya are jewels of the rainforest, renowned for the diversity of vivid colors they display, which vary greatly from region to region. Obviously, these colors have not evolved for our amazement, but rather to warn predators that they will be greatly ill if they dare taste them. But how do predators keep track ofand learn to avoidso many color patterns. And why do poison-dart frogs maintain such a high diversity of color patterns? Researchers from the University of Montreal have recently showed that diversity in poison-dart frogs is maintained locally due to the predators avoiding only one color pattern and quickly eliminating all others. Using hundreds of life-sized clay models painted to resemble the distinct color patterns of poison dart frogs, the researchers found that avian predators avoided models with the local coloration, but attacked models with non-local colors. The results show that the local predators have come to recognize and avoid the local frogs. "Being exotic is, in this case, not advantageous at all, as the frogs' vivid coloration make them more easily detected by predators that have not learned to recognize them," said Dr. Chouteau. These results highlight the close relationship between the colorful amphibians and their predators, and demonstrate that the geographic diversity of color patterns is maintained by the learning experience of a distinct predator community.
Mathieu Chouteau, Bernard Angers, "The Role of Predators in Maintaining the Geographic Organization of Aposematic Signals." http://www.jstor.org/stable/10.1086/662667
Can sexual selection's bizarre creations sometimes set evolution on a path to novel survival strategies?
Living organisms pursue a dazzling diversity of ecological strategies for surviving in and extracting resources from their environments, but how does such diversity come about? Because natural selection is shortsighted, unable to see potentially advantageous strategies for which no variation is immediately available, it will tend to keep populations doing what they do, ecologically speaking. So how do novel ecological strategies evolve? Most attempts to resolve this long-standing evolutionary puzzle have invoked a stochastic evolutionary process, genetic drift, which can sometimes pull very small populations away from their local phenotypic optimum. But an article by (University of New South Wales) Russell Bonduriansky explains an alternative process capable of displacing populations from their ecological comfort-zone: sexual selection. Darwin famously proposed sexual selection as an explanation for the evolution of bizarre traits that often seem to hinder prospects for survival and foraging. Perhaps the perverse tendency for sexual selectionand its more recently identified corollary, sexual conflictto act at cross purposes to survival and foraging needs might also, in the evolutionary long run, facilitate ecological diversification. The author brings together theory and evidence to make the case that sexual selection and conflict could act as engines of ecological diversification. Bizarre traits that evolve under sexual selection can, on occasion, furnish preadaptations for novel ecological functionsand can evolve to be expressed in both sexes, a process termed ecological co-optation. A variety of examples that implicate this process are discussed, along with suggestions for future research.
Russell Bonduriansky, "Sexual Selection and Conflict as Engines of Ecological Diversification." http://www.jstor.org/stable/10.1086/662665
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