Tag: Süddeutsche Zeitung

Fifteen shades of photoreceptor in a butterfly’s eye

Selected coverage: ABC, Christian Science Monitor, Science Magazine, Süddeutsche Zeitung

When researchers studied the eyes of Common Bluebottles, a species of swallowtail butterfly from Australasia, they were in for a surprise. These butterflies have large eyes and use their blue-green iridescent wings for visual communication – evidence that their vision must be excellent. Even so, no-one expected to find that Common Bluebottles (Graphium sarpedon) have at least 15 different classes of “photoreceptors” — light-detecting cells comparable to the rods and cones in the human eye. Previously, no insect was known to have more than nine.

“We have studied color vision in many insects for many years, and we knew that the number of photoreceptors varies greatly from species to species. But this discovery of 15 classes in one eye was really stunning,” says Kentaro Arikawa, Professor of Biology at Sokendai (the Graduate University for Advanced Studies), Hayama, Japan and lead author of the study.

Have multiple classes of photoreceptors is indispensable for seeing color. Each class is stimulated by light of some wavelengths, and less or not at all by other wavelengths. By comparing information received from the different photoreceptor classes, the brain is able to distinguish colors.

Through physiological, anatomical and molecular experiments, Arikawa and colleagues were able to determine that Common Bluebottles have 15 photoreceptor classes, one stimulated by ultraviolet light, another by violet, three stimulated by slightly different blue lights, one by blue-green, four by green lights, and five by red lights.

Why do Common Bluebottles need so many classes of photoreceptor? After all, many other insects have only three classes of photoreceptor and yet have excellent color vision. Likewise, humans have only three classes of cones, enough to distinguish millions of colors.

Arikawa and his colleagues believe that Common Bluebottles use only four classes of photoreceptor for routine color vision, and use the other eleven to detect very specific stimuli in the environment, for example fast-moving objects against the sky or colorful objects hidden among vegetation. A similar system is found in another butterfly previously studied by the same research group, the Asian swallowtail Papilio xuthus, which has six photoreceptors.

“Butterflies may have a slightly lower visual acuity than ourselves, but in many respects they enjoy a clear advantage over us: they have a very large visual field, a superior ability to pursue fast-moving objects and can even distinguish ultraviolet and polarized light. Isn’t it fascinating to imagine how these butterflies see their world?” says Arikawa.

The results are published in the open-access journal Frontiers in Ecology and Evolution.

EurekAlert! PR: http://www.eurekalert.org/pub_releases/2016-03/f-fso030116.php

Study: http://journal.frontiersin.org/article/10.3389/fevo.2016.00018/full

Do you have a sweet tooth? Honeybees have a sweet claw

Selected coverage: Discovery News, Yahoo, Süddeutsche Zeitung, RedOrbit

New research on the ability of honeybees to taste with claws on their forelegs reveals details on how this information is processed, according to a study published in the open-access journal, Frontiers in Behavioral Neuroscience.

Insects taste through sensilla, hair-like structures on the body that contain receptor nerve cells, each of which is sensitive to a particular substance. In many insects, for example the honeybee, sensilla are found on the mouthparts, antenna and the tarsi – the end part of the legs. Honeybees weigh information from both front tarsi to decide whether to feed, finds the latest study led by Dr. Gabriela de Brito Sanchez, researcher, University of Toulouse, and Dr. Martin Giurfa, Director of the Research Centre on Animal Cognition, University of Toulouse, France.

Hundreds of honeybees were included in the study. Sugary, bitter and salty solutions were applied to the tarsi of the forelegs to test if this stimulated the bees to extend or retract their tongue – reflex actions that indicate whether or not they like the taste and are preparing to drink. Results revealed that honeybee tarsi are highly sensitive to sugar: even dilute sucrose solutions prompted the bees to extend their tongue. Measurements of nerve cell activity showed that the part of the honeybee tarsus most sensitive to sugary tastes is the double claw at its end. Also, the segments of the tarsus before the claws, known as the tarsomeres, were found to be highly sensitive to saline solutions.

“Honeybees rely on their color vision, memory, and sense of smell and taste to find nectar and pollen in the ever-changing environment around the colony,” says Dr. Giurfa. “The high sensitivity to salts of the tarsomeres and to sugar of the tarsal claws is impressive given that each tarsus has fewer sensilla than the other sense organs. The claw’s sense of taste allows workers to detect nectar immediately when they land on flowers. Also, bees hovering over water ponds can promptly detect the presence of salts in water through the tarsomeres of their hanging legs.”

But what if honeybees receive contradictory information, for example, about tasty sucrose from the right foreleg, but about water or distasteful caffeine from the left? The central nervous system of honeybees weighs this information from both sides, but unequally: input from the side that is first to taste something tasty or distasteful counts for more. For example, if a bee first tasted sucrose on one side, she would typically extend her tongue and subsequently ignore less attractive tastes on the other. But if the order was reversed, she was around 50% less likely than normally to extend her tongue for sucrose.

EurekAlert! PR: http://www.eurekalert.org/pub_releases/2014-02/f-dyh013114.php

Study: http://journal.frontiersin.org/article/10.3389/fnbeh.2014.00025/full