Why don't plants get sunburn?

Biologists have known about a mechanism that prevents excess sunlight from harming plants, but they haven't known much about its details. A plant can only use so much light energy to photosynthesise - excess energy is dissipated, by a little-known process. A recent paper identifies a protein, PsbS, as a key component of the plant's safety mechanism. 

Not all plants contain PsBs - they may still photosynthesise but lack protection from excess sunlight. The researchers used a mutant variety of Arabidopsis thaliana to show that plants which do not contain PsBs cannot dissipate excess light energy and the protein may thus be the key to the process.

Reference: Li, X.-P., Björkman, O. and Shih, C. 2000. A pigment-binding protein essential for regulation of photosynthetic light harvesting. Nature 403(6768):391 -395. 

Evolution - some bats got a second shot

However, recent DNA analysis has suggetsed that one family of microbats, including the horseshoe bat, is more closely related to, and has therefore probably evolved from, megabats. "It means either that echolocation evolved twice, or that it was lost by the megabats," says Michael Stanhope of the Queen's University of Belfast, who led the research. 

Reference: Nature 403(6768): 188.

Arms race shown in butterflies

Night-flying butterflies have ears, on the forewings of the insects, sensitive to ultrasound which bats use to navigate and locate their prey. The butterflies hear the bats coming and dart out of the way. Interestingly, butterflies evolved as 'day moths', probably as a response to night-time bat predation, since fossil records show that butterflies became daytime flyers at roughly the same time bats developed large ears and the ability to use echoes to locate their prey. Ears may be an alternative strategy to avoid bats.

The researchers, Dr Jayne Yack and Professor James Fullard, looked at one particular species in the family called Macrosoma heliconiaria which can be found on Barro Colorado Island, Panama. They have a very thin eardrum, stretched over an air-filled chamber. The eardrums vibrate when there is a burst of ultrasonic sound. These vibrations are detected by nerve cells packed into three little organs on the inside of the chambers. When exposed to simulated bat attacks in the form of intense bursts of ultrasonic noise the butterflies accelerated and went into steep dives or climbs, upward or downward loops, spirals and horizontal sweeps. 

"It's quite an unusual ear for insects," Professor Fullard says. "It resembles the moth ear, but it is certainly more complicated ... What we have here are a group of butterflies that moved into the night, or may be they are the remnants of the original insects. Maybe they had ears and the butterflies that didn't were pushed in to the daytime by bats."

Sticklebacks support Darwin

Populations which evolved, since Pleistocene times, under different ecological conditions were found to show different characteristics - "strong reproductive isolation" - whereas populations which evolved independently under similar ecological conditions lack isolation. This repeatable process strongly suggests that speciation is a process which produces organisms adapted to alternative environments. 

Reference: Science Volume 287, Number 5451, 14 Jan 2000, pp. 306 - 308; Natural Selection and Parallel Speciation in Sympatric Sticklebacks; Howard D. Rundle, * Laura Nagel, Janette Wenrick Boughman, Dolph Schluter 

Birds keep right

Stephen Lea of the University of Exeter has found that the birds can detect a 0.037-millimetre difference in the thickness of the two "valves" of a mussel shell. It's a tiny difference but it can save a bird 13 per cent of the effort needed to open a shell. Some 56 per cent of mussels have thinner right-hand valves, but the birds hammer the right-hand valves 72 per cent of the time. "If in doubt, they go right," says Lea.

Reference: New Scientist, 8 January 2000

Feel the quality, not the width

The phytoplankton which contains high concentrations of eicosapentaneoic acid, commonly known as an omega-3 fatty acid, support much higher zooplankton growth rates, even if the overall amount of phytoplankton is relatively low. 

"Phytoplankton that are more nutritious can have a major impact on the overall food web," said Michael Brett, assistant professor of civil and environmental engineering at the University of Washington. "What the study shows is that the rate at which zooplankton convert phytoplankton biomass to zooplankton biomass depends on the supply of this class of essential fatty acids. This gives us important insights into what may determine how energy moves through aquatic food webs." 

During their study the researchers fed Daphnia algae at various times of the year. During the summer, a type of phytoplankton poor in omega-3 fatty acids called cyanobacteria dominated the pond and the Daphnia suffered with an energy-conversion rate from plants to animal of 5 to 26 percent. During the winter and spring, however, diatoms dominated. Diatoms are rich in omega-3 fatty acids and, although the diatom concentration was lower than that of the summer phytoplankton, the Daphnia flourished with an energy-conversion rate of 50 to 65 percent. 

Those insights could help scientists predict biomass and energy flow rates in aquatic ecosystems, providing possible tools for fisheries managers.

Salt marshes contribute to the ozone hole

A recent study shows that CH3Br and CH3Cl are released to the atmosphere from all vegetation zones of two coastal salt marshes. If these measurements are typical of salt marshes globally, they suggest that such ecosystems, even though they constitute less than 0.1% of the global surface area, may produce roughly 10% of the total fluxes of atmospheric CH3Br and CH3Cl.

Reference: Robert C. Rhew, Benjamin R. Miller & Ray F. Weiss. Natural methyl bromide and methyl chloride emissions from coastal salt marshes. Nature 403, 292 - 295 (2000)

Raggy round the edges

Researchers in America have found that many threatened species are clinging on at the edges of their historical geographical ranges and not, as one might have expected, in the central regions which would historically have provided the most favourable habitat. This has important implications for conservation, which has in the past aimed to preserve core populations at the centre of a potentially endangered species' geographical range. 

The study uses results from 245 endangered or recently extinct species, of which just over half were birds and mammals, to show that , contrary to ecological expectations, 98% of these species maintained, or had maintained, populations on the edges of their previous ranges, and that for some these were the only populations left. Giant pandas and Tasmanian tigers, for example, both hung on in the extremities of their ranges long after the main populations had become extinct.

Reference: Channell, R. & Lomolino, M.V. Dynamic biogeography and conservation of endangered species. Nature 403, 84 (2000).