Australasian Science: Australia's authority on science since 1938


By Stephen Luntz

Brief bites of science news.

Pregnant Weight Gain Has Lasting Effects

The avoidance of excessive weight gain during pregnancy can have benefits for both mother and child, as well as improving the chances for a natural birth, Prof Lesley McCowan of the University of Auckland Department of Obstetrics and Gynaecology has confirmed. “Big babies become big children and big adults later on,” said McCowan. “If we can reduce that happening, we can have a big public health impact.”

In a study of almost 2000 women in Australia, New Zealand and Ireland, McCowan found 17.2% gained the recommended amount, 8.6% gained less and 74.3% put on more. Those in the last category had babies that were heavier at birth and more likely to be delivered by caesarean.

“Most women who gain too much weight are not able to lose that weight after pregnancy, and it puts those women on a trajectory to becoming obese,” McCowan said.

Stand Up for Your Health

Just sitting down for 4 hours per day is enough to increase the risk of heart disease, diabetes and even cancer. Emma George, a PhD student at the University of Western Sydney’s School of Science and Health, sorted more than 63,000 Australian men aged 45–64 according to the time they spent sitting. “The rates of chronic diseases reported by the participants exponentially increased in proportion with the amount of time the participants spent sitting down,” said George.

Disturbingly, the effects could not be removed by vigorous exercise after work, as the results were independent of body mass index and physical activity. “The results of this study suggest that there is potential for people to improve their overall health if they found more opportunities to move around during the day and reduce the amount of time spent sitting,” George said.

Fairy Wrens Sing True

Large male fairy wrens can reach the low notes that evade their smaller rivals, Dr Michelle Hall of the University of Melbourne Department of Zoology has revealed in PLoS ONE.

The finding may seem obvious – conveying size is a way to scare off rivals and possibly to win mates. “Surprisingly, there is very little evidence that the pitch of calls indicates body size differences within species, except in frogs,” Hall says. “This is the first time we have been able to show that song pitch indicates body size in song birds.”

Hall correlated the leg length of 45 male purple-crowned fairy wrens with the deepest pitch the birds issued, and found a relationship. While the complexity of the bird song makes it difficult to establish whether the average pitch of large individuals is lower, she found that the larger males could make their voices resonate when the need arose.

Stroke Risk from Cannabis Use

Cannabis users are twice as likely to suffer a stroke as young adults, according to Prof Alan Barber of the Centre for Brain Research at the University of Auckland.

The finding comes from urine tests of 160 ischaemic stroke and transient ischaemic attack patients, which were 2.3 times as likely to show evidence of cannabis in urine as a control group matched for age and sex. Previous studies have reported that ischaemic strokes are relatively common within hours of cannabis use.

“These patients usually had no other vascular risk factors apart from tobacco, alcohol and other drug usage,” said Barber. “It’s challenging to perform prospective studies involving illegal substances such as cannabis because questioning stroke and control patients about cannabis use is likely to obtain unreliable responses.”

While Barber warned that cannabis may be more dangerous than previously thought, he noted that all but one of the users also smoked tobacco.

Low Energy? Eat Fruit

Insufficient vitamin C intake can strip skeletal muscles of the vitamin and affect muscle function, leading to loss of energy, according to Prof Margreet Vissers of the University of Otago.

Vissers has previously demonstrated that mice absorb far less vitamin C from tablets than from kiwi fruit (AS, September 2011, p.10). For this study she fed men aged 18–35 either two kiwi fruit per day or half a kiwi fruit for 6 weeks. The latter group lost vitamin C from their skeletal muscles and with it feelings of energy. The work was published in The Journal of Clinical Nutrition.

“Many people think that all fruit and vegetables are equally able to supply vitamin C, but this is not the case. The levels in food vary hugely across the spectrum,” said Vissers.

Maternal Weight Linked to Arterial Thickening

Children of overweight and obese mothers are more likely to have thickened aorta at birth, a paper in Fetal and Neonatal Edition of Archives of Disease of Childhood reveals. Thickening of aorta, the body’s major artery, is associated with heart disease.

In a study of 23 newborn babies Dr Michael Skilton of Sydney University’s Boden Institute found that the internal aortal walls ranged from 0.65–0.97 mm thick and overweight mothers had children with walls 0.6 mm thicker on average.

"We already know that the children of overweight or obese mothers are more likely to become overweight and obese themselves, which will potentially increase their risk of heart attack and stroke in adulthood," said Skilton. "To our knowledge, this is the first study demonstrating that being an overweight or obese mother can itself potentially lead to poor health of the blood vessels, which is consistent with higher risk of heart disease and stroke in later life.”

CO2 Helps Wheat – to a Point

Increased carbon dioxide can help wheat cope with decreased water capacity, but only when the temperature effects are mild.

Eduadro Dias de Oliveira, a doctoral student at the University of Western Australia, placed wheat in tunnel houses with higher CO2 levels and compared growth when temperatures were raised by 2°C, 4°C and 6°C above ambient temperature.

For the smallest temperature increase the carbon dioxide increased the plants’ capacity to cope with drought conditions, de Oliveira reported in Functioning Plant Biology, with greater biomass and higher grain yield. However, at higher temperatures the effects were reversed.

Hormone Therapy and Breast Cancer Decline

A decline in Hormone Replacement Therapy (HRT) is not necessarily the reason for falling rates of breast cancer, a study in the Journal of Family Planning and Reproductive Health has concluded.

Three large studies published around the millennium linked HRT to breast cancer, and dissemination of these findings since 2002 led to a decrease in the use of HRT. Breast cancer reporting has also fallen in much of the developed world, and understandably these have been linked.

However, Em/Prof Henry Burger of the Monash Medical Centre was part of an international team reviewing the timing of these changes. The team reported: “The evidence to suggest a correlated decline in the incidence of breast cancer following a decline in the use of HRT has not adequately satisfied the criteria of time order, detection bias, confounding, statistical stability and strength of association, internal consistency, and external consistency; biological plausibility is difficult to assess.”

Eyes On Evolutionary History

Deep sea fish often have huge eyes to catch the faint luminescence produced by fellow creatures. However, a surprising study in PLoS ONE has found that eye size among lantern fish depends on genealogy rather than available light.

Ms Fanny de Busserolles, a PhD student at the University of WA's Oceans Institute and the School of Animal Biology, examined 237 specimens from 61 species. She found a great variation in the size of the eyes, and that this could not be explained by the depth at which the species lived or the strength of its bioluminescence.

"These results show that there is a lot more to learn and exciting results to discover from this extreme and mysterious environment that is the deep sea,” said de Busserolles.

Hi-Res Images Obtained of Wallaby Foetus

The first high-resolution video of a wallaby foetus has been made by a German/Australian collaboration.

Like other marsupials, most of the development of the tammar wallaby occurs in the pouch, but little has been known about what occurs beforehand as the wallaby foetus grows to the point where it can crawl to its new home.

Prof Marilyn Renfree of the University of Melbourne’s Zoology Department succeeded in imaging the foetus when it was just 1.5 mm long and following it until birth, including the creation of a detailed 3D reconstruction. Even at birth the wallaby weighs less than half a gram, but 3 days beforehand it can be seen making climbing movements as it prepares for the epic trek to the pouch.

Pacific Fisheries to Suffer

Pacific Island coral reef fisheries will decline by 20% by 2050 as a result of climate change, according to a report prepared for the Secretariat of the Pacific Community.

"Nowhere else do so many countries depend so heavily on fish and shellfish for food security, livelihoods, economic development and government revenue,” says Johanna Johnson of Southern Cross University’s National Marine Science Centre, who co-authored paper of the study’s findings in Nature Climate Change.

Skipjack tuna are another vital part of the region’s diet and are expected to move east, disrupting catches in the western Pacific. The report finds prospects for increased freshwater aquaculture on some Pacific Islands to address food insecurity.