In This Issue
ECOLOGY
Invading is backbreaking work
The havoc that invasive species wreak on their newly adopted ecosystems has been well studied, but Gregory Brown et al. investigated the effects of widespread dispersal in new habitats on the invaders themselves. One of the most notorious invasive animal species, the cane toad, is suffering as a result of its march across Australia. Native to Central and South America, the large and highly toxic cane toads have spread rapidly across Australia since they were introduced in 1935. The authors found that the largest toads lived farthest from the center of the population and traveled the farthest each day. Within this boundary population, the researchers noticed that 10% of the larger toads had spinal arthritis. The researchers did not find arthritis in the smaller, nonboundary toads. The same characteristics that enable the cane toad to colonize new areas so rapidly also appear to predispose individuals to arthritis. Bigger, longer legs increase a larger toad's ability to seek out new territory but also put pressure on the body with every hop. The authors suggest that, with more energy going toward movement, less is put into the toad's immune system, which may predispose the toads to infection from soil bacteria that precipitate arthritis. — T.H.D.
Ventral view of fused vertebrae in adult cane toad.
Invasion, stress, and spinal arthritis in cane toads” by Gregory P. Brown, Cathy Shilton, Benjamin L. Phillips, and Richard Shine (see pages 17698–17700)
MICROBIOLOGY
An ocean bacterium with low diversity
Most of the genomes of oceanic bacteria have shown wide sequence variation based on geography and time. Jonathan Zehr et al. report that Crocosphaera watsonii, a tropical nitrogen-fixing cyanobacterium, defies this rule and shows extremely low genomic diversity in samples worldwide. The authors compared sequences from the laboratory-cultured strain, whose genome is fully sequenced, with large metagenomic samples taken from the subtropical North Pacific Ocean. They found sequence variation of <1% between the various samples and strains, even when intergenic regions were included. This finding contrasts with variation of 15% or more in other oceanic bacteria. The authors suggest that C. watsonii's many transposases may be responsible for maintaining genetic diversity through genomic rearrangements, given that the gene and genome sequences are highly conserved. Accumulating many DNA sequence mutations may not be the only way to colonize large swaths of the planet, according to the authors, and other strategies of evolution and adaptation can work as well, especially for rare organisms like C. watsonii. — P.D.
Fluorescence of natural photosynthetic pigment phycoerythrin in C. watsonii.
Low genomic diversity in tropical oceanic N2-fixing cyanobacteria” by Jonathan P. Zehr, Shellie R. Bench, Elizabeth A. Mondragon, Jay McCarren, and Edward F. DeLong (see pages 17807–17812)
NEUROSCIENCE
Understanding intent
Growing evidence suggests that the mirror neuron system is involved in understanding the intentions of others. That system suggests, for example, that watching a motor act activates the whole motor chain that forms the action, allowing the observer to understand the intention of the doer. Luigi Cattaneo et al. used muscle recordings to investigate this motor chain organi zation in typically developing children and in children with autism. The authors recorded data during observation and execution of two tasks: grasping an object with the intent to eat and with the intent to place the object into a container. When typically developing children watched others grasping food, their mouth muscle became active but similar activity did not occur in the autistic children. When children performed the task themselves, the mouth muscle became active upon grasping food in typically developing children but not until approaching the mouth in autistic children. These data show that typically developing children have a working action chain organization, which enables them to directly understand the doer's intention, whereas this mechanism is impaired in autistic children. Thus, autistic children cannot understand the intentions of others experientially, just cognitively. These findings may have important implications on how to focus autism rehabilitation. — T.H.D.
Experiment subject reaches for food.
Impairment of action chains in autism and its possible role in intention understanding” by Luigi Cattaneo, Maddalena Fabbri-Destro, Sonia Boria, Cinzia Pieraccini, Annalisa Monti, Giuseppe Cossu, and Giacomo Rizzolatti (see pages 17825–17830)
PHYSIOLOGY
New class of kidney hormones
For decades, it has been suspected that an unknown small molecule was acting along with other known hormones in regulating sodium and water excretion in the kidney. Christopher Cain et al. report that two molecules, xanthurenicacid 8-O-β-d-glucoside and xanthurenic acid 8-O-sulfate, are the long-sought human natriuretic hormones. The authors isolated the molecules from human urine, partially purified them via activity-guided fractionation, and identified them by using NMR-spectroscopic analyses of enriched active fractions. They found that the purified molecules caused sustained natriuresis in rats and inhibited sodium transport in frog skin. Because the molecules were active in amphibians and mammals, the authors say that this is likely an evolutionarily “old” signaling pathway. They suggest, based on their knowledge of the closely related molecule xanthurenic acid, which is suspected to be a part of many biological processes, that the two newfound molecules may affect sodium transport in other tissues and could possess other activities. — P.D.
Structure of xanthurenic acid 8-O-β-d-glucoside.
Identification of xanthurenic acid 8-O-β-d-glucoside and xanthurenic acid 8-O-sulfate as human natriuretic hormones” by Christopher D. Cain, Frank C. Schroeder, Stewart W. Shankel, Mark Mitchnick, Michael Schmertzler, and Neal S. Bricker (see pages 17873–17878)
