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PNAS Papers Present Analysis of Koala Retrovirus Transmission, Dementia Metabolites, Tree Growth-Defense Trade-Offs

Editor's Note: Some of the articles described below are not yet available at the PNAS site, but they are scheduled to be posted this week.

In a study slated to appear in PNAS this week, researchers from the University of Queensland describe how the koala retrovirus is passed among koalas. By sequencing more than 100 captive koalas of known pedigrees, the researchers found that the virus appears to largely be passed from mother to offspring — possibly via infected milk — with few instances of transmission between adult koalas. According to the researchers, this finding suggests various strategies to prevent the virus's spread, including breeding programs and antiretroviral treatment of mothers during the breeding season. "While substantial research is needed to demonstrate safety and effectiveness, this presents a potentially important conservation strategy for koala populations severely affected by disease and currently in rapid decline," they add.

A team of researchers in Japan has identified groups of metabolites that could be used to diagnose or treat different types of dementia, including Alzheimer's disease. For their new study, they collected blood samples from dementia patients as well as from healthy elderly and healthy young individuals for metabolomic analysis. Through their liquid chromatography-mass spectroscopy-based analysis, the researchers uncovered 33 metabolites that they classified into five subgroups that differed between individuals with dementia and healthy elderly individuals . In particular, they report that compounds from group A may act as neurotoxins and are increased in those with dementia, while compounds from the other groups, which may be protective or supportive, decline in dementia. "Our results suggest that detailed molecular diagnosis of dementia is now possible," they say.

A University of Wisconsin–Madison team explores genetic growth–defense trade-offs among the trembling aspen (Populus tremuloides). The group followed the trees for five years to find that high competition led to decreased survival of trees with slow-growing genotypes versus fast-growing genotypes, while low competition led to increased survivorship of all growth genotypes. At the same time, high competition was linked to low survivorship for well-defended genotypes. "We found that a genetically fixed growth–defense trade-off coupled with high levels of competition led to simultaneous selection for genotypes with both high growth rates and low herbivore defense levels," the researchers write, noting that their findings also "help explain nonintuitive patterns of defense allocation across populations where herbivory is not the principal selective force."