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By Stephen Luntz

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Multiple Sex Selection Strategies in Skinks
A species of Tasmanian lizard has evolved two separate mechanisms for choosing the sex of its offspring: one for high altitudes and one for sea level.

Snow skinks live in both the alpine and coastal regions of Tasmania. Studies of the coastal population concluded that they used temperature-dependent sex determination (TSD), a system common in reptiles. Females that basked in warm weather early in pregnancy produced mainly daughters, while those with fewer opportunities to sun themselves had sons.

This makes evolutionary sense. Larger females produce more offspring, so there is a benefit being born early in the breeding season in order to have grown more when it comes to mating time. But body size at breeding time does not confer an advantage for male skinks, which has led researchers to conclude that they don’t fight for mates.

However, an international team including Dr Erik Wapstra of the University of Tasmania found that skinks living in subalpine mountain areas behaved differently. Here mothers produced equal numbers of sons and daughters irrespective of the temperature conditions they were exposed to. High altitude skinks grow more slowly than their lowland cousins and take several years before they are ready to breed, by which time the benefits of a few extra weeks of life are wiped out.

“We don’t know how they turn sex selection on and off,” Wapstra says. “Presumably it is like the other forms of TSD, and temperature turns certain genes on. We understand TSD in some taxa, but not in others.”

After observing the effect in the field, and conducting computer modelling to show why the different strategies make sense, Wapstra confirmed the finding in the lab by exposing pregnant females to different amounts of basking heat from a sunlamp. Those collected at sea level adjusted the sex of their offspring, while those from the mountain did not.

The findings open up many lines of investigation. How many generations would it take for relocated skinks to change their selection methods? What would the offspring of cross-mated skinks do? Which system evolved first? Wapstra hopes to investigate at least some of these.

“More generally,” Wapstra notes, “the finding reveals that one of the most fundamental biological processes – that of sex determination – is more free to evolve within a species than previously thought”. He is interested in finding out how widespread such variation might be.

Global warming is likely to lead to an increase in the number of females at low altitude. In the short term this should be less of a problem than too many males. “Males are not the limiting resource,” Wapstra says.

The situation is different for New Zealand’s tuatara (AS, Jan/Feb 2009, p.4), where warmth produces males. However, over time too many females might lead to a population boom and bust.

The skinks are easy to study as they are small and short-lived. Wapstra hopes that further research will shed light on the evolutionary advantage of TSD in long-lived species such as crocodiles and turtles, where it appears to serve no purpose.

The research was published in Nature.

Mendel’s Gene Found
Scientists at New Zealand’s Plant and Food Research have characterised one of the seven pea genes studied by pioneering geneticist Gregor Mendel.

In the mid-19th century Mendel investigated the effects of hybridising peas with different characteristics, including seed and flower colour, plant height and the texture of seed pods. From his results he deduced the principles of recessive and dominant genes. Although his work was ignored at the time, its rediscovery formed the basis of 20th century genetics. However, the details of the genes responsible for the traits Mendel studied have remained a mystery until recently.

The gene described by Dr Roger Hellens of Plant and Food Research is the fourth of Mendel’s seven pea genes to be characterised at a molecular level. The gene controls whether flowers are coloured or white, the most famous of Mendel’s characteristics.

Pea flower colour is a result of pigment molecules known as anthocyanins. “By comparing the pea DNA sequences to those of other well-characterised plants, such as petunia, we have determined that Mendel’s gene is a transcription factor that controls the anthocyanin biosynthesis pathway,” Hellens says. “This transcription factor, when mutated, becomes inactive and anthocyanin is not produced, resulting in white flowers.”

The work was confirmed through the identification of rare forms of the relevant gene in exotic lines of peas, leading to publication in PLoS One.

Recycled Exhaust Heat Saves Fuel
Heat released in car exhaust gases can be captured and used to warm oil, reducing engine friction in the process. The result could reduce fuel consumption and pollution.

“A typical car engine releases about a third of the energy bound in fuel as exhaust waste gas. About another third is lost through heat transfer into the environment,” says Frank Will of Deakin University’s School of Engineering.

“Our system recovers and redirects some of this wasted heat and uses it to bring the engine oil up to its optimal operating temperature,” Will says. “This helps to reduce friction in the engine, which has the potential to reduce fuel consumption significantly.”

Will says the benefits vary “depending on how you drive,” but for typical journeys it is possible to reduce engine friction by 50% by increasing the oil temperature by about 30°C.

Several options have been designed to use the heat from exhaust gases to warm the oil before it enters the engine, with one version requiring just an additional hose and valve. “A more complex system requires a heat exchanger, but even the most expensive system shouldn’t cost more than $200.” Will claims this will deliver a 7% improvement in fuel economy, offering a far shorter payback period than buying a hybrid.

Moreover, Will’s idea is not in competition with other fuel-saving mechanisms. “Hybrids warm up the oil more slowly because they don’t run in idle, so there is an additional benefit there,” he says.

At the moment hybrids are also in danger of having water get into the oil, building up a dangerous sludge without frequent changes. Will says that the heat from exhaust gases vaporises the water, removing the problem. The idea is also theoretically applicable to motorbikes.

Since friction produces heat, reducing it means that less is available to warm the oil. However, Will says this is insignificant to operations as by far the bulk of the heat comes from combustion.

Will says there has been plenty of interest from car manufacturers, with some saying the benefits were so obvious they would incorporate it into their next set of engines. He is also working on a kit for retrofitting existing cars.

CO2 Won’t Boost Plant Growth
An ambitious experiment has undermined the idea that rising carbon dioxide levels will stimulate enough tree growth to bring global warming under control.

A favourite argument of those who oppose reducing emissions of greenhouse gases is that carbon dioxide is plant food, and higher levels will stimulate growth. On the one hand, optimists suggest that this could increase crop production. On the other hand, faster-growing trees could absorb so much carbon dioxide that they could mitigate the warming effect.

Experiments run on crops have produced mixed results. Plants grown in greenhouses with elevated CO2 levels do indeed grow much faster, provided they are supplied with plenty of water and other nutrients. However, under field conditions, where one or more nutrient may be in short supply, the benefits of carbon dioxide are more limited and in some cases there are serious negative effects (AS, Jan/Feb 2010, pp.31–33).

Prof Ross McMurtrie of the University of NSW School of Biological, Earth and Environmental Sciences is part of an international team exploring the other side of the question. A deciduous forest stand in Tennessee, Swedish conifers, and eucalypts at Hawkesbury near Sydney have been encased in transparent tents and exposed to varying levels of carbon dioxide to witness the effects on their growth.

Initially the signs from North America were promising. Trees exposed to 25% higher carbon dioxide levels – similar to predictions for 2050 – grew substantially faster and stored more carbon in their wood. However, a paper published in the Proceedings of the National Academy of Sciences found that the benefits don’t last. Once the first 6 years have passed the high carbon forest’s productivity declined, an effect that the researchers attribute to insufficient nitrogen in the soil.

“We’re going to have to learn not to trust in trees to remove as much carbon from the atmosphere as we had hoped,” McMurtrie says. The Hawkesbury work is less advanced, but appears likely to lead to similar results.

The findings are consistent with Liebig’s Law of the Minimum, a 19th century conclusion that growth in plants is limited not by total resources but by the resource in shortest supply. The consequence of this is that increasing a resource other than the most scarce one does not greatly increase growth.

Fish Net Protects Sleeping Fish from Parasites
Dr Lexa Grutter of the University of Queensland’s School of Biological Sciences has revolutionised our understanding of cleaner fish (see pp.38–39), and has now revealed what fish do at night when the cleaners are asleep and are not removing gnathiid isopods, which take blood and appear to transmit disease.

“Fish seek cleaner fish to remove these ‘marine mosquitoes’ during the day,” Grutter says. “At night, when cleaner fish sleep, mucous cocoons act like ‘mosquito nets’, allowing fish to sleep safely without being constantly bitten: a phenomenon new to science.”

The remarkable behaviour has been a source of wonderment for some time – guides on night dives like to point out examples of fish in these cocoons sleeping under ledges or in cracks in rocks. It has been suggested this was done to fend off attacks by eels, perhaps because the mucus tastes bad or hides the fish’s scent. However, evidence for the idea is weak.

Cleaner wrasse are one species that cocoon themselves, drawing Grutter’s attention. Honours student Jennifer Rumney collected coral parrotfish, kept them in tanks overnight and added parasites at midnight. Rumney compared the number of infestations for fish allowed to stay in their cocoon with those that had the mucus removed before the parasites were added.

The results were stark. More than 90% of the fish stripped of their mucus were attacked by gnathiids, as against 10% of those left in peace. The cocoon’s importance is revealed by the fact that some of the fish that had the cocoon removed simply made another one, even though the removal was done while they were asleep.

The mass of mucus required increases much more slowly than the size of the fish, so while it represents a significant energy burden on a small fish, production costs fall for larger individuals. On average Grutter estimates that the mucus represents 2.5% of the fish’s daily energy budget.

The mucus is produced in a gland below the gills and comes out through the mouth. Grutter thinks it is probably different from the mucus that covers parrotfish during the day, which at the very least is produced by a different gland.

The Seed for Speciation
Some orders of organisms are far more species-rich than others, and now scientists at the Australian National University think they know why – at least for birds.

“It has been shown before that species that accumulate more changes in their DNA tend to diversify more quickly,” says Dr Robert Lanfear of the Research School of Biology. “But is it changes in the DNA that cause speciation, or speciation that causes changes in the DNA?”

Another possibility is that a third factor is causing both. A study of plants reached the conclusion that available energy and water drove both speciation and mutation rates. However, Lanfear says his team checked everything they could think of that might have an influence in birds, including factors such as body size and sexual selection, and ruled these out.

Speciation might theoretically cause changes to accumulate in DNA, since it divides populations into smaller subgroups and neutral or mildly negative mutations are much more likely to become fixed in small populations. However, Lanfear says that no one can think of any reason why it would affect the underlying rate of mutation.

Using a study of a variety of genes in almost 200 species of birds, Lanfear and his colleagues examined the variation in DNA in cases where the changes do not affect the amino acid produced. “Selection is blind to these silent mutations so we can’t see how speciation could act on them,” he says. On the other hand it has been accepted for a while that the rate of silent mutations gives an indication of the overall mutation rate.

Lanfear found that mutation rates are indeed higher in species-rich suborders of birds such as songbirds, indicating that this is the driving factor. He says that “we have some idea” why some suborders of birds have faster rates of mutation, “but it’s hard to pin down”. The most likely candidate is the generation time, with species whose offspring are produced by younger parents having more mutations.

Although the idea that mutation rates drive speciation is more intuitively plausible to non-biologists, Lanfear says that many scientists had predicted the opposite.

Extinction Lurks on Small Reefs
Small and isolated reefs might be considered less prone to human disturbance since they are further from urban development and less attractive for fishing, yet, fish species on such reefs within the Great Barrier Reef system are more likely to be at risk of extinction, an Australian Institute of Marine Sciences (AIMS) study has found.

“Our results support the idea that small and isolated reefs are more susceptible to local species extinctions because of the tendency for their fish populations to be more variable,” says project leader Dr Camille Mellin of AIMS.

In work published in Ecology, Mellin found that the steady supply of immigrant fish on better-connected reefs helped maintain healthier populations. “If there is a disturbance to the population, such as a cyclone or coral bleaching, fish species on isolated reefs are much slower to recover,” Mellin says. “These populations are not as resilient to changes and are not easily replenished, increasing their probability of extinction.”

Although smaller populations tend to be more vulnerable to extinction, prior to this study it was thought this might be balanced by reduced human impacts.

Mellin notes that the team did not observe any cases of extinction, but was estimating future risk based on population size and variability.

The findings may have relevance for the placement of marine parks. “Our research suggests that conservation resources might be better allocated to the protection of large, connected habitats,” Mellin says. These reefs are more likely to act as source reefs for population replenishment on more isolated ones around them. However, Mellin says things are more complex than this, and she is planning to feed her work into another team that is optimising spatial arrangements for coral reef protection.

Although her work may appear to have parallels with recent research showing that reefs at the edges of climate zones are responsible for evolutionary change, Mellin does not believe there is a link. “We are studying populations at a decade scale. An evolutionary scale might take up to 100 generations, so we can’t draw any conclusions.”

Time to Bell the Cat?
Cat bells save birds, according to a study at the University of Otago study published in Wildlife Research.

Dr Yolanda van Heezik and colleagues placed belled collars on 37 cats and asked their owners to record the number of native birds they caught in 6 weeks. The collars were removed for a similar period. To eliminate seasonal influences the cats were split into two groups, half collared for each period.

The belled cats caught exactly half as many birds as cats that roamed without them. “This study shows it is worthwhile for domestic cats to wear bells, and would go some way towards reducing the huge numbers of native birds cats catch,” van Heezik says. “It won’t eliminate the problem completely, but it’s a start.”

Domestic cats are a problem for birds worldwide, but the issue is particularly acute for New Zealand’s avian-dominated ecosystem, with tens of thousands of native birds killed annually. Similar research in the Northern Hemisphere has produced conflicting results.

However, there is a downside to giving domestic felines a disadvantage in the hunting stakes. Cats catch far more rodents than birds, and belled collars caused an even more dramatic 61% reduction here.

But rats also pose a threat to birds. By reducing the number of rodents killed by cats it is possible that belled collars could lead to greater rat numbers – and therefore harm birds more than they help. Heezik says she’d like to study this further, but “a controlled study on all the cats in a neighbourhood would be hard to do”.

Not surprisingly, cats are not the most obedient research subjects. Of 45 cats initially enrolled in the program, three caught no prey, four had missing data (presumably due to human negligence) and one disappeared entirely during the study.

Beaks Bigger in the Tropics
A study of 214 species of birds has confirmed that those that live in warmer climates have bigger beaks. The researchers believe this is because beaks lose a lot of heat.

The 19th century observation known as Allen’s Rule holds that appendages are bigger in tropical areas. This was based on comparisons of related species, or even varieties within a species, across different climate zones. However, beak size and shape can primarily be explained through feeding requirements, with sexual selection a secondary consideration.

However, when Dr Glenn Tattersall of the Department of Biological Sciences at Ontario’s Brock University used an infrared camera to observe the heat given off by a toucan’s beak, he and Dr Matt Symonds of the University of Melbourne’s Department of Zoology wondered if such a substantial heat radiator would be an evolutionary hindrance in a colder climate.

Tattersall and Symonds drew on a collection of data on beak and body size for species in differing climate conditions. “Across all species there were strong links between bill length and both latitude, altitude and environmental temperature,” says Symonds. “Species that have to deal with colder temperatures have smaller bills.”

The finding raises the question of whether large beaks are an asset in warm climates, a drawback in the cold, or a bit of both. “We think it’s more likely that cold temperatures impose a constraint on the size of bird beaks,” says Tattersall. “It simply might be too much of a liability to carry around a big radiator of heat energy in a cold environment.”

Heat radiation occurs because beaks are remarkably vascularised, with large amounts of blood flowing close to the surface. The blood may be necessary to serve the nerve endings within the beak.

Were All Globular Clusters Once Dwarves?
The idea that globular clusters were once part of dwarf galaxies has taken a step further with modelling work conducted by Dr Kenji Bekki of the International Centre for Radio Astronomy Research.

In 2003 evidence emerged that Omega Centauri, the Milky Way’s largest globular cluster, might once have been the core of a dwarf galaxy 100–1000 times its current size (AS, Nov/Dec 2003, p.9). However, at the time it was thought that this was probably a unique situation among the clusters that circle our galaxy.

Last year Prof Duncan Forbes of Swinburne University proposed that around 25% of the galaxy’s globular clusters were once dwarf galaxies, with their outer stars stripped away by the Milky Way’s gravitational field to become part of the galaxy’s mainstream (AS, May 2010, p.5).

Bekki has modelled the interactions between globular clusters and galaxies, and proposed that all globular clusters were once at least 25 times larger, with the bulk of their mass having been tugged away over billions of years. He believes that larger clusters once represented the cores of dwarf galaxies, while smaller clusters once sat in the outskirts of these dwarves until the Milky Way’s galaxy separated them out.

Ryegrass Now Resistant
The discovery of ryegrass that is resistant to the herbicide paraquat is bad news for Australian farmers. “Annual ryegrass is the single most important weed affecting Australian cropping, and this discovery has major implications for Australian farmers,” says A/Prof Christopher Preston, who discovered the resistant ryegrass at two locations near Naracoorte in South Australia.

Paraquat is a “knockdown” herbicide used to kill weeds that appear before a crop. Like glyphosate it has very low soil activity, so it can be used to eliminate weeds with little effect on the harvest. With ryegrass resistance to glyphosate now widespread across Australia (AS, October 2008, p.6), the arrival of a dual-resistant weed is probably only a matter of time.

Preston says that no other effective herbicides with low soil activity are on the market. While chemical companies have put considerable effort into finding more, they have been unsuccessful so far. Ryegrass has also developed resistance to more selective herbicides.

While Preston advocates seasonal rotation of the herbicide used, he thinks farmers will need to concentrate more on integrated weed management practices, particularly preventing seeds from reaching the soil in the first place

Groundwater Yield at Risk
Groundwater yields are essential for rivers to continue flowing during droughts, and Dr David Rassam of CSIRO Water for a Healthy Country says we have been underestimating the damage done by drawing too much water from aquifers.

“Many rivers are highly dependent on ‘base flow’ from groundwater to keep running through dry times, and traditional ways of managing groundwater pumping follow a ‘safe yield’ approach, which balances the amount of water extracted with the amount known to be ‘recharging’ the aquifer,” Rassam says. Water permeates the bed of the stream from below, so some flow persists even after long periods without rain.

However, a study near Tarcutta, west of Canberra, demonstrated that these safe yields are an illusion. “We found that the impact on base flow of reducing recharge might be small at first, but that each subsequent reduction of recharge has a disproportionately large impact on base flow in the stream,” Rassam notes.

A 40% increase in groundwater pumping produced a 93% reduction in the base flow of the river. Rassam concludes that drying out “can happen much more easily than we previously thought”. As rains become more erratic, and public resistance to allocating water on the basis of science intensifies, the implications for local ecosystems are grim.

Krill Declining in Southern Ocean
Krill numbers appear to be declining in the Southern Ocean, although the scientist leading the study believes it is too early to say exactly what has been observed.

Since 1991 the Australian Antarctic Division (AAD) has been using continuous plankton recorders to monitor the Southern Ocean. “Since the project began in the early 1990s there have been significant changes in the composition of plankton in our samples,” says Dr Graham Hosie of the AAD. “We seem to be catching less krill in the plankton recorder. This could be the result of either a decline in numbers or a change in distribution.”

Krill are a prime source of food for many species higher up the food chain, so a decline could have severe consequences. However, Hosie notes that other species of zooplankton have become more common off the Antarctic Peninsula, leading to increasing numbers of fish. Some penguins have been observed shifting their diets from krill to fish.

Some smaller zooplankton seem to have become more common over the period, including one sudden and unexplained explosion where a species of foraminifera suddenly became ten times as common from waters south of Africa to those off New Zealand. “Samples were coming back as if full of grit,” Hosie says. Foraminifera have experienced a slow increase in the Northern Hemisphere, but nothing matching this spike.

Since we don’t know whether krill have actually become less common or have moved to places we are not sampling them, causes are hard to identify. However, climate change is a possible explanation for everything that has been observed, particularly off the Antarctic Peninsula, which has experienced some of the most rapid warming in the world.

Equivalent studies in the North Atlantic stretch back 80 years, making it easier to establish whether changes are cyclical. Hosie says in the late 1980s phytoplankton experienced dramatic changes there, with species that once bloomed in autumn and spring now blooming year-round.

“The changes have not been reversed. It could be climate or eutrophication from the rivers. This could lead to changes in fish species.

People may have to change their diets. Those are the sorts of changes we’re looking for and hoping not to find.”

Broadband Gap Closed
CSIRO has unveiled technology it hopes will fill the gap in the National Broadband Network between the fibre to be rolled out to most Australians and the satellite technology used for the most remote locations.

In between fibre and satellite technology, CSIRO’s Ngara system will use analogue TV channels to send and receive wireless broadband at a minimum of 12 Mbps per user to small clusters of homes.

“Someone who doesn’t live near the fibre network could get to it using our new wireless system,” CSIRO ICT Centre Director Dr Ian Oppermann said while launching a laboratory demonstration of the technology.

The closure of analogue TV stations will leave a legacy of broadcast towers with line-of-sight transmission to home aerials, and Ngara will put these to use.

Although similar such technologies have been developed elsewhere, Ngara packs three time as many bits of information into each 7 MHz-wide channel as any other technology in existence.

Ngara is uniquely suited to areas where the population is sparse but not so remote as to justify satellite technology. Field trials were scheduled to begin in Smithton before the end of 2010, but Oppermann says it will be 2 years before the technology is commercially available.

The challenge will be to make the cost of the transmission and reception boxes cheap enough to keep the technology viable, given that economies of scale in production may be limited. However, CSIRO hopes that the ready availability of well-placed transmission towers set up to broadcast at the right frequencies will keep costs low.