Shaken, not stirred

Olives are part of any good Greek salad – or Bulgarian shopska salad, or any other variation of the tomato-cucumber-olive salad that heralds summer. From fat, plump Kalamata, to the sort of sad, de-stoned kinds straggling at the back of your fridge, all types wriggle their way in.

Somewhat surprisingly, as researchers noted this week in PLOS One, a huge diversity exists not only on supermarket shelves, but also in Iranian olives. What’s more, this variation is separate from the large variation in olives that grow in the Mediterranean. To find out whether olive types in the two areas are related, the researchers looked at SSR markers, regions in the olive’s DNA in which short combinations of bases encoding information are repeated many times. Looking at the length of SSR markers in different varieties, the researchers work out which olive types are related and which aren’t. They find that olives in the Mediterranean and Iran probably separated early on in the olive’s history. Olives are cultivated only in a few regions of Iran, but the research shows that Iranian olive types vary greatly. Most of the diversityin Iran’s olive trees is actually found in patches of trees and small groves, abandoned from cultivation or remnants of a former cultivation as “holy trees”.

Olive trees in Cyprus.  (By Anna Anichkova (Own work) [CC-BY-SA-3.0 ], via Wikimedia Commons)

Olive trees in Cyprus.
(By Anna Anichkova (Own work) [CC-BY-SA-3.0 ], via Wikimedia Commons)

Why should we care? Iranian olive trees are not fickle: some survive at low temperatures nearly unheard of in the Mediterranean, others withstand over 40°C, while some grow at high altitudes and poor soil condition. In face of dwindling diversity, an unexpected source of genetic variation is rare and welcome news. A large pool of diversity seems like a good hedge of bets for an uncertain climatic future, but low numbers and threats to their environment endanger also this olive source. Thankfully, some Iranian olive trees bear large fruits, which bodes well for the summer salads of our future. For which a good recipe, as always, comes from smitten kitchen:

Original paper in PLOS One:


Need for speed – Drosophila antennae regulate flight speed

Just relying on their eyes is not enough for the fruitfly Drosophila when zooming to that pitiful last banana on your counter. Wind-sensing antennae allow fruitflies to fly at constant speed, even when winds change.

Characteristically, fruitflies straight flight bouts are punctuated by quick changes in direction. Flies tend fly straight at a constant speed, even when wind speeds change. This suggests that flies actively regulate their groundspeed. The visual information of just seeing your kitchen pass by isn’t fast enough for the fly. 50 to 100 milliseconds have passed by the time the image reaches the fly’s brain and is processed so that it can respond, which roughly equates to 10 to 20 wing beats between seeing and reacting.

Sensors on the antenna of flies measure the speed of passing air with a delay of only about 10 milliseconds. In a paper published this week in PNAS, researchers let flies with clipped antennae fly in a wind tunnel, and compared how they fared in short and rapid gusts of wind with flies with intact wings.  Flies react to wind in an unexpected way, in the same direction as air drag – in headwind gusts, flies slow down, while in tailwind gusts, they fly faster. But afterwards, flies with intact antennae quickly return back to a set groundspeed.  Flies without antennae return to their groundspeed more slowly, and in steady wind, the groundspeed of flies without antennae changes greatly.

Drosophila melanogaster - sensing airspeed with their antennae. By André Karwath aka Aka (Own work) [CC-BY-SA-2.5], via Wikimedia Commons

Drosophila melanogaster – sensing airspeed with their antennae.
By André Karwath aka Aka (Own work) [CC-BY-SA-2.5], via Wikimedia Commons

The researchers show that airspeed measured by the antennae is combined with what the fly sees to achieve a steady groundspeed. Visual information is a baseline to regulate groundspeed to a specific velocity, but it has a long delay. So if windspeed changes quickly, the visual information is not fast enough to adapt flight speed rapidly and reliable: By the time the fly is able to react, the wind might have already changed again, and the adaptation overshoots. Airspeed measurement by antennae has a short delay, and gives a robust input that makes speed changes less variable. Combining airspeed with visual information allows flies to fly at a stable groundspeed, and rapidly react to wind speed changes.

Feeling the air and seeing the kitchen pass by, flies adapt their speed to changing winds, helping them to home in on your lonely banana.

If you would like to give your banana a better fate than being fly fodder, I suggest smitten kitchen’s recipe for chocolate banana bread.