They mate only once in their lifetime and spend the rest of their yearlong life with their chosen mate and their family (of 60-70 offspring) in a single permanent burrow.  The isopod females initially dig the burrow and the males fight to win a particular female and a particular habitat.  Both parents take care of the brood, and all family members—young and old—continue to excavate and clean the burrow together.  Choosing where to establish a home is the responsibility of the female woodlouse (“desert isopod “) and under normal conditions, the largest males usually win the largest females.  However, what happens when there is a predator, such as an Israeli gold scorpion, living nearby? 

A study of this scenario was carried out in the Negev Desert, in southern Israel, by a Hebrew University of Jerusalem (HU) research team led by Professor Dror Hawlena and Dr. Viraj Torsekar.  They observed the mating behavior of male desert isopods in two locations – one close to the burrow of an Israeli gold scorpion (a risky area), and one further away (a safe area).  Their findings, recently published in Ecology, demonstrated the preference of large males for larger females in safe areas but less so for large females in risky areas.  “Using this manipulative field experiment, we found that desert isopods under risk of scorpion predation maintained ‘size assortative mating’, but that males that chose and fought over females were on average smaller for a given female size,” Torsekar explained.  Additionally, while bigger males stayed longer near safe burrows and won more male-male contests, fewer pairs were formed in risky sites.

The researchers also showed that the smaller males had often accepted second best and moved in with smaller females close to the lurking scorpion. Medium sized males chose between smaller females in safe places and larger female in risky places - demonstrating an equal fitness choice.

"This supported our novel hypothesis that the males anticipated the future risk of predation," noted Torsekar. The males seemed to incorporate information on the proximity of a predator when choosing a mate. They no longer made their selection based solely on the size of the female, although larger females do have larger broods.

It is hard work for the females to dig into the dry compacted soil of the desert, so they are always on the lookout for holes that can make life a little easier. The HU researchers dug holes in two groups, one near the burrow of an Israeli gold scorpion and one further away.  Female isopods readily adopted the holes and excavated full-size burrows. However, the study showed that fewer isopod pairs took up residence in burrows near predators, despite it being virtually free real estate.

It should be noted that the predatory behavior of scorpions is localized to the immediate vicinity around their burrows.  They don't go wandering off to look for prey but emerge only to attack prey that is detected by the vibrations isopods cause as they walk across the burrow roof.  However, it is known that the odor of the scorpion does alert isopods when they are near to its lair.

In courtship, once the females adopt a burrow, they are ready to admit a male. Peeping out from the top of the burrow, male and female encounter each other face-to-face - probably using the separation between the eyes of their prospective mate to assess size. Males compete furiously over the larger females, in hopes of producing a large brood.

"This information is crucial in predicting how the fear of a predator may affect prey population dynamics and evolutionary processes in the creation of new species," concluded Torsekar.

Now, research teams from TU Wien and from The Hebrew University of Jerusalem (HU) have found a surprising trick that allows a beam of light to be completely absorbed even in the thinnest of layers: They built a "light trap" around the thin layer using mirrors and lenses, in which the light beam is steered in a circle and then superimposed on itself – exactly in such a way that the beam of light blocks itself and can no longer leave the system. Thus, the light has no choice but to be absorbed by the thin layer – there is no other way out. This absorption-amplification method, which has now been presented in the scientific journal Science, is the result of a fruitful collaboration between the two teams: the approach was suggested by Prof. Ori Katz from The Hebrew University of Jerusalem and conceptualized with Prof. Stefan Rotter from TU Wien; the experiment was carried out in by the lab team in Jerusalem and the theoretical calculations came from the team in Vienna.

"Absorbing light is easy when it hits a solid object," shared Prof. Stefan Rotter from the Institute of Theoretical Physics at TU Wien. "A thick black wool jumper can easily absorb light. But in many technical applications, you only have a thin layer of material available and you want the light to be absorbed exactly in this layer."

There have already been attempts to improve the absorption of materials: For example, the material can be placed between two mirrors. The light is reflected back and forth between the two mirrors, passing through the material each time and thus having a greater chance of being absorbed. However, for this purpose, the mirrors must not be perfect – one of them must be partially transparent, otherwise the light cannot penetrate the area between the two mirrors at all. But this also means that whenever the light hits this partially transparent mirror, some of the light is lost.

To prevent this, it is possible to use the wave properties of light in a sophisticated way. “In our approach, we are able to cancel all back-reflections by wave interference”, noted HU’s Prof. Ori Katz. Helmut Hörner, from TU Wien, who dedicated his thesis to this topic explained, "in our method, too, the light first falls on a partially transparent mirror. If you simply send a laser beam onto this mirror, it is split into two parts: The larger part is reflected, a smaller part penetrates the mirror."

This part of the light beam that penetrates the mirror is now sent through the absorbing material layer and then returned to the partially transparent mirror with lenses and another mirror. “The crucial thing is that the length of this path and the position of the optical elements are adjusted in such a way that the returning light beam (and its multiple reflections between the mirrors) exactly cancels out the light beam reflected directly at the first mirror”, said Yevgeny Slobodkin and Gil Weinberg, HU graduate students who built the system in Jerusalem.

The two partial beams overlap in such a way that the light blocks itself, so to speak: although the partially transparent mirror alone would actually reflect a large part of the light, this reflection is rendered impossible by the other part of the beam travelling through the system before returning to the partially transparent mirror.

Therefore, the mirror, which used to be partially transparent, now becomes completely transparent for the incident laser beam. This creates a one-way street for the light: the light beam can enter the system, but then it can no longer escape because of the superposition of the reflected portion and the portion guided through the system in a circle. So the light has no choice but to be absorbed – the entire laser beam is swallowed up by a thin layer that would otherwise allow most of the beam to pass through.

"The system has to be tuned exactly to the wavelength you want to absorb," explained Rotter. "But apart from that, there are no limiting requirements. The laser beam doesn't have to have a specific shape, it can be more intense in some places than in others – almost perfect absorption is always achieved."

Not even air turbulence and temperature fluctuations can harm the mechanism, as was shown in experiments conducted at The Hebrew University in Jerusalem. This proves that it is a robust effect that promises a wide range of applications – for example, the presented mechanism could even be well suited to perfectly capture light signals that are distorted during transmission through the Earth's atmosphere. The new approach could also be of great practical use for optimally feeding light waves from weak light sources (such as distant stars) into a detector.

New research study led by the Hebrew University of Jerusalem (HU) and the Israel’s Agricultural Research Organization (Volcani Institute) details the success of a biological sensor for early detection of hidden disease in potato tubers, one of Israel’s chief export industries at 700,000 tons a year. 

Israeli farmers import European potatoes for planting in Israel.  However, a certain percentage of them carry disease within—either visibly or invisibly—that cause rot and significantly reduce the potato’s quality.  The Hebrew University-Volcani alliance is about to change that. They’ve developed a sensor that detects disease and can be used to inhibit the rot from growing and spreading. Their study, published in the upcoming edition of Talanta, was conducted by Dr. Dorin Harpaz and her PhD student Boris Veltman at HU’s Faculty of Agriculture, Food and Environment, under the supervision of Dr. Evgeni Eltzov of the Volcani Institute.  The team collaborated with the Volcani Institute’s Dr. Sarit Melamed and Dr. Zipora Tietel, as well as Dr. Leah Tsror from the Gilat Research Center.

The sensor relies on smart bioengineering and optics.  When the sensor is exposed to an infected potato, a bacterial compound within lights up—with the strength of the luminescence indicating the concentration and composition of the rot.  “The intensity of the light given off by the bacteria panel makes it possible to quickly and quantifiably analyze the characteristics of the disease, which the sensor can ‘smell,’ before the appearance of visible symptoms,” explained Eltzov. “The biosensor we developed will help identify diseased potatoes that do not yet have any external indications, and keep them away from healthy tubers, thus preventing the rot from developing or spreading to other healthy plants,” Harpaz added.

To form the bacteria panel, the team created a compound of four genetically-engineered bacteria that measure biological toxicity.  In this study, the biological sensor detected disease before there was any visible trace, and caused the optical sensor to shine twice as brightly as did the sensors in non-infected potatoes. Their capabilities were also demonstrated in a previous study that used the sensors to detect toxicity among artificial sweeteners in sport supplements. 

According to the researchers, early discovery of disease--before the potatoes are exported to foreign markets or replanted, offers a significant advantage to food growers. “The biological sensor can be used to quickly and economically identify hidden rot in potatoes, facilitate better post-harvest management, and reduce food wastage—particularly important given the current global food crisis,” concluded Harpaz.

The researchers looked at how a heterosexual couple's physiology and behavior adapt to each other during that first encounter.  The study was based on a speed-date experiment consisting of forty-six dates. Each date lasted 5 minutes during which the levels of physiological regulation of each partner were recorded with a band worn on the wrist. Behavioral movements, such as nodding, moving an arm, shifting a leg were also recorded in each partner during the date. After the encounter, the couple assessed the romantic interest and sexual attraction they felt for each other.  The study clearly showed that when couples synchronize their physiology with one another and adapt their behavioral movements to their partner during the date, they are romantically attracted to one another.  This research was recently published in Scientific Reports.

Intriguingly, the study also showed that the degree of synchrony affected men and women differently.  Although for both genders synchrony predicted attraction, women were more sexually attracted to men who showed a high level of synchrony – “super-synchronizers”; these men were highly desirable to female partners.

"Our research, " said Atzil, "demonstrates that behavioral and physiological synchrony can be a useful mechanism to attract a romantic partner. However, we still don’t know whether synchrony raises attraction or does the feeling of attraction generate the motivation to synchronize?”  An area of research that Atzil is planning to investigate.