An uninvited guest

Frog breeds safely and undisturbed among leafcutter ants

Lithodytes lineatus breeds among leafcutter ants

Leafcutter ants ignore the frog Lithodytes lineatus when it breeds in their nests. They simply do not notice him, André Lima Barros and colleagues show, because the frog is chemically camouflaged.

Ants behave aggressively against intruders in their nests, but the South American Leptodactylid frog Lithodytes lineatus isn’t molested. In fact, he is at home in the huge colonies of leafcutter ants. Years ago, Andreas Schlüter reported that he had heard frog males calling from the interior of a leafcutter ant nest to attract females. Upon inspection of a nest, he found an adult frog within and numerous tadpoles swimming in a little pool. Obviously, the frogs breed in leafcutter nests.

It is clear why they willingly live there. Adult frogs, eggs and larvae are safe from predators, for the ants prevent these from entering the nest. Moreover, the nest has an agreeable humid microclimate.

But the question is why the ants, eager to evict all intruders from their nests, do tolerate these animals.

Now, André de Lima Barros and colleagues show that the frogs are chemically camouflaged. In their skin, they synthesize compounds which apparently imitate the odours with which the ants communicate. Since the ants rely on odour perception, the frogs go unnoticed: a good example of mimicry.

The researchers placed frogs of different species close to a nest entrance. When the experimental frog was a Lithodytes lineatus, the ants never attacked, but when it belonged to another species – either a species that is closely related to Lithodytes lineatus or a species that looks exactly the same as this frog – the ants became aggressive and bit the unwanted guest, that tried to escape quickly.

Next, the biologists prepared an extract from the skin of Lithodytes lineatus and coated a frog with it that normally would be chased away by the ants. Impregnated with skin extract of Lithodytes lineatus, the frog elicited no response.

So, Lithodytes lineatus can enter a leafcutter nest unharmed thanks to chemical camouflage. The uninvited guest is not a burden to the ants whatsoever, as he doesn’t touch the ants nor their brood. As he eats all sorts of other critters, such as assassin bugs and crickets, he may help the ants to keep the nest free of such enemies, in return for a safe place to breed.

Willy van Strien

Photo: Lithodytes lineatus, outside ant nest. Andrew Kay (via Flickr, Creative Commons CC BY-NC-SA 2.0)

De Lima Barros, A., J. L. López-Lozano & A. P. Lima, 2016. The frog Lithodytes lineatus (Anura: Leptodactylidae) uses chemical recognition to live in colonies of leaf-cutting ants of the genus Atta (Hymenoptera: Formicidae). Behavioral Ecology and Sociobiolology, October 20 online. Doi: 10.1007 / s00265-016-2223-y
Schlüter, A., P. & K. Löttker Mebert, 2009. Use of an active nest of the leaf cutter ant Atta cephalotes (Hymenoptera: Formicidae) as a breeding site of Lithodytes lineatus (Anura: Leptodactylidae). Herpetology Notes 2: 101-105.

Surprising and familiar

The pied butcherbird and the art of composing

pied butcherbird, male. V. Nunn

A clever composer is able to grip the audience with variations, but without presenting music that is a confusing chaos. The pied butcherbird masters that art too, as Eathan Janney and colleagues report.

A piece of music with more variety in it is more pleasing to listen to. But it should not be too surprising: the piece must remain recognizable as a unit. In order to maintain consistency, a composer will repeat parts of the music and take care that themes can be heard several times.

In this respect, the beautiful singing pied butcherbird can compete with a good composer, according to research done by Eathan Janney and colleagues.

The black and white bird, slightly smaller than a magpie, lives in Australia where it is the most accomplished song bird with a very complex song. The bird may sound like a flute, a cornet or organ; hence the name. Males can sing continuously for hours at night. Their song consists of hundreds of clear phrases which take about two and a half second. After each phrase they wait a few seconds before they proceed.

Janney wondered if they, just as composers, keep a balance between novelty and repetition. That would be important to prevent habituation in female listeners while at the same time the bird remains identifiable as an individual. He studied the nocturnal solo songs of 17 birds. He divided the phrases of each bird in types and investigated how often and in what order he sang each type. He also discerned motifs; a motif is a single tone or a group of a few tones (syllable) that often recurs. Several types of phrases may share a same motif. Finally, for each bird he investigated how he arranged his phrases and motifs. Was there any structure in the temporal patterning?

The singing of the birds is well organized, the analysis shows. Types of phrases and particularly motifs were regularly spaced in time. That regularity arises, as the researchers show, because a performing bird orders the different types of phrases in such a way, that each motif is heard at constant time intervals.

The birds differ greatly in the amount of variation in their song. Some birds have more types of phrases and more different motifs in their repertoire than others. The more variety, the greater the risk that the song as a whole will be incoherent. But, as it turns out, the birds with the most different phrases and motifs organized their song more strictly. The larger the repertoire is, the stronger the temporal regularity with which the motifs are repeated. The birds seem to actively maintain the balance between variety and regularity – just like a good composer.

Willy van Strien

Photograph: Pied butcherbird male. Vicki Nunn (Wikimedia Commons, Creative Commons CC BY-SA 4.0)

An accomplished performer can be heard on this video of the researchers
Hear another record of the song

Janney, E., H. Taylor, C. Scharff, D. Rothenberg, L.C. Parra & O. Tchernichovski, 2016. Temporal regularity increases with repertoire complexity in the Australian pied butcherbird’s song. Royal Society Open Science 3: 160357. Doi: 10.1098/rsos.160357

Fly trap

Parachute flower smells like a tasty bee in distress


Flowers of the African parachute plant are deceivers, as Annemarie Heiduk and colleagues show. The flowers mimic the smell of honeybees that are caught in the jaws of a spider. Their volatiles attract flies that feed on the fluids that such unhappy bees excrete. These flies pollinate the flowers.

Many plants have their flowers pollinated by insects. The insects take up pollen from one flower they visit and leave some of it on the pistil of the next flower, that can then grow seeds. And in return, most plants offer their pollinators nectar as a reward.

But not all plants are honest plants. Some lure their pollinators with false promises of a reward.

A sophisticated deceptive plant is the African parachute plant Ceropegia sandersonii, a climbing herb from southern Africa, as Annemarie Heiduk and colleagues reveal.
Its pollinators are Desmometopa-flies. They visit the flowers and disperse the pollen, but not voluntarily. The flower is a trap where they go into. Downward pointing hairs on the flower wall make it impossible for them to get out. Clumps of pollen (pollinaria) within the flower dislodge and stick to their mouthparts.

Only the next day, when the flower withers, the flies are able to escape, packed with pollen. In the flower that they enter next, they will deposit the pollinaria unwittingly on the right place.

The question arises: how is it that the flies can be tricked time and again? Now, Heiduk answered that question: the flower smells like their food.

The flies, especially the females, need protein and they derive it from honeybees. They can’t overpower a honeybee by themselves, as they are much smaller. But when a spider has caught one, they come and feed on the fluids that leak from the dying bee. They find such a bee as they detect compounds that are released from its mandible glands and sting glands when it tries to defend itself by biting or stabbing. Also, they detect the pheromones that the bee releases to alert conspecifics.

Heiduk analysed the blend of volatiles dispersed by the flowers of the parachute plant, and found that many components are identical to the compounds that are released by bees in agony. This blend of volatiles is unique among flowering plants, and clearly adapted to lure the flies. Upon detection, they approach the flower, expecting to find a helpless bee. They find nothing of the kind, however, but are imprisoned for a time and meanwhile serve the plant. For free.

Willy van Strien

Photograph: Ceropegia sandersonii. Alzheimer1 (via Flickr. Creative Commons BY-NC-SA 2.0)

Nasty video: a honeybee is hold by a spider and licked by Desmometopa-flies

Heiduk, A., I. Brake, M. von Tschirnhaus, M. Göhl, A. Jürgens, S.D. Johnson, U. Meve & S. Dötterl, 2016. Ceropegia sandersonii mimics attacked honeybees to attract kleptoparasitic bees for pollination. Current Biology, online October 6. Doi: 10.1016/j.cub.2016.07.085