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Impolite Science News

Why ants favour turning left when entering unknown spaces; detecting breast cancer through changes in bodily zinc levels; evening primroses help us to understand why sex is good for us 


An exploring ant encounters an unknown branching nest site  .Image: Edmund Hunt

 

Are Rock Ants Lefties?

 

New research from the University of Bristol has found that the majority of rock ants instinctively go left when entering unknown spaces.

 

Scientists carried out a study using the ant species Temnothorax albipennis, recreating typical ant environments in the lab. PhD student Edmund Hunt, who led the research, told Impolite Science: “They are small ants so they’re easy to keep in the lab. We can replicate their home environment (usually rock crevices) easily with two microscope slides and a cardboard perimeter.”

 

Hunt and his colleagues studied how these ants explore nest cavities and negotiate through branching mazes and found they were significantly more likely to turn left than right when exploring new nests.  Such left bias was also present when the ants were put in branching mazes, though this bias was initially obscured by wall-following behaviour. This seems to happen with most of the ants individually and is reflected at a colony level.

 

“The ants may be using their left eye to detect predators and their right to navigate,” says Hunt. “Also, their world is maze-like and consistently turning one way is a very good strategy to search and exit mazes.”

 

Brain lateralisation – how the brain functions using its left and right hemispheres – is present in all vertebrates and there is now an increasing amount of evidence for it in the behaviour of invertebrates. This type of regional specialisation is highly useful, as it allows animals to carry out two tasks simultaneously without decreasing their efficiency. For instance, studies on fish and lizards have revealed a right eye/left hemisphere bias for identifying prey, and a left eye/right hemisphere bias for predator detection and escape.

 

But why left and not right? “There’s no advantage to left versus right, it would seem to be incidental,” Hunt says. “But in the case of these ants, it may have an adaptive use, for example for exploring maze-like environments.” It has been reported that some tree ant colonies prefer to go right.

 

Behavioural lateralisation in invertebrates is an important field of study because it may provide insights into the early origins of lateralisation seen in a diversity of organisms, the researchers say. They suggest the turning bias may be the result of an evolutionary interplay between vision, exploration and migration factors.

 

‘Ants show a leftward turning bias when exploring unknown nest sites’ by Hunt ER, O’Shea-Wheller T, Albery GF, Bridger TH, Gumn M and Franks NR was published in Biology Letters.

 

http://rsbl.royalsocietypublishing.org/content/10/12/20140945

 

 

Researcher preparing trace element samples in a lab in the Department of Earth Sciences, University of Oxford

Image: University of Oxford, Earth Sciences Department

 

Could zinc levels be the key to earlier breast cancer diagnoses?

 

It may be possible to develop a simple blood test that, by detecting changes in the zinc in our bodies, could help to diagnose breast cancer earlier than current methods.

 

You may be surprised to hear that the key scientists involved in this study were actually geologists. The team, based at Oxford University, applied techniques normally used to analyse trace metal isotopes for studying climate change and planetary formation and applied them to how the human body processes metals. Isotopes are different forms of the same element that vary depending on the number of neutrons in their atomic nuclei.

 

Dr Fiona Larner, from Oxford’s Earth Science department, led the research. “Interdisciplinary studies are extremely useful, as the 'best tool for the job' may not be utilised by the field that would benefit from it,” she told Impolite Science. “There are a lot of opportunities for new discoveries by combining several fields of science and engineering.

 

“The methods used by earth scientists look at how different elements move around geological settings and help us understand the mechanisms involved. During these studies, it has been observed that biological interactions, such as those of plants and bacteria, induce similar measurable changes in the isotope composition. Other medical studies have focused on the principal element involved in the disease (eg calcium in osteoporosis); however, we thought that looking at a trace metal that is known to be altered in the disease, but is not the principal component, could still be useful in monitoring the disease and help us understand the processes behind that element's role.”

 

Larner’s team were able to show that changes in the isotopic composition of zinc, which can be detected in a person's breast tissue, could make it possible to identify a 'biomarker' (a measurable indicator) of early breast cancer. “Zinc has been linked to breast cancer for over a decade, but some of the processes involved were not fully understood,” says Larner. “The earth science methods are more sensitive [than clinical methods] in monitoring certain changes.”

 

The pilot study analysed zinc in the blood and blood serum of ten subjects (five breast cancer patients and five healthy controls) alongside a range of breast tissue samples from breast cancer patients. The researchers were able to show that they could detect key differences in zinc, caused when cancer subtly alters the way that cells process the metal.

 

“Our study also hints that copper may be useful, as a protein that binds both copper and zinc was an important part of the isotopic process. By looking at other metals in cell processes with isotopic methods, we can have a greater understanding of their metabolism in disease, and in relation to each other,” says Larner.

 

There is hope that less invasive methods than mammograms could be used to detect cancer in future. “If blood test screening became available, there is potential for it to be used to detect breast cancer earlier than currently possible,” says Larner, “But we have a lot more work to do before we know whether that is possible.”

 

The team is now developing a full-scale study to support its initial findings. “We have begun the search for the biomarker our study indicated was present,” says Larner.

 

The paper ‘Zinc isotopic compositions of breast cancer tissue' is published in the journal Metallomics.

 

 

Evening primrose (oenothera)

Photo c.c. Dr. Thomas G. Barnes, U.S. Fish and Wildlife Service

 

Evening primroses tell us sex is good for us

 

A genetic study on evening primroses has unlocked part of the mystery as to why sex is so common and favoured by evolution – species that have sex are healthier because they don't accumulate harmful mutations.

 

It has long been known that sex maintains genetic diversity and gives a greater chance of successful adaptations down the generations. Asexual populations, on the other hand, where each generation is effectively a clone of the last, are limited in their evolution.

 

Dr Jesse Hollister, in collaboration with other scientists around the world, completed the research while working at the University of Toronto. The team examined 30 pairs of species – one species in the pair reproduced sexually, the other asexually.

 

“We chose evening primroses for this study because, in this genus [Oenothera] consisting of over 200 species, about 30 per cent are functionally asexual,” Hollister explained to Impolite Science. “So, in around 70 per cent of the species, the maternal and paternal plants reshuffle their DNA in various ways prior to reproducing, allowing different combinations of genetic variants (genetic mutations) to be combined in each generation. In contrast, around 30 per cent of species pass their entire genome to offspring in a single linked block, which means that each generation will pass on all the mutations it inherited, as well as new mutations that arise in that generation. This difference in how mutations are inherited has been theorised to be vital to why sexual reproduction is favoured over asexual reproduction in most multicellular species. Most importantly for our study, the transitions to asexuality happened independently in different evening primrose species at different times in the past. This allowed us to infer what the effect of asexuality has been over time, by comparing young asexuals and old asexuals to their sexually reproducing sister species.

 

“The benefit of sexual reproduction is that, in general, it allows reshuffling of genetic variants, so that beneficial mutations (meaning beneficial genetic variants) can be separated from harmful mutations along the DNA molecule,” Hollister continues. “The result of this is that beneficial mutations can efficiently spread throughout populations, while harmful mutations are lost over time, as the most fit individuals (with the most beneficial mutations) produce more offspring each generation. In contrast, asexual species pass their DNA to offspring as a single linked block. This means that any harmful mutations that arise on a background that has beneficial mutations will tend to spread through the population because it is linked to the beneficial mutations. Likewise, beneficial mutations that arise on a genetic background that has harmful mutations will spread more slowly through the population (or not at all). This leads to a process, called ‘Muller's ratchet’, in which deleterious mutations build up over time within asexual populations, reducing their fitness and ability to compete. Compared to their sexual relatives, then, they may be more likely to go extinct.”

 

Hollister’s study confirmed this prediction. “We showed that evening primrose species that had reproduced asexually for longer had accumulated more harmful mutations compared to sexually reproducing species, while more recent asexual species carried only a modest increase in harmful mutations. From these comparisons, we could infer that asexual reproduction led to a buildup of harmful mutations over time. This means that asexual species may get worse at competing in the ecological arena over evolutionary time. So, our findings help explain why sexual reproduction appears to be the rule, and asexual reproduction the exception, among the majority of multicellular organisms.”

 

Hollister and colleagues will be following up on this work by looking into how long asexual evening primrose species tend to persist, and how transitions to asexuality affect mutations in different genes across the genome.

 

Journal Reference:

 

J. D. Hollister, S. Greiner, W. Wang, J. Wang, Y. Zhang, G. K.-S. Wong, S. I. Wright, M. T. J. Johnson. Recurrent loss of sex is associated with accumulation of deleterious mutations in Oenothera. Molecular Biology and Evolution, 2014; DOI: 10.1093/molbev/msu345
 

Sarah Barnett

About the Writer

Sarah is Impolite Conversation's science editor.

 

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