biologe

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Tag: Diptera

Round-leaved sundew: How a fly can die

The round-leaved sundew Drosera rotundifolia is a carnivorous plant. It digests mostly small arthropods in order to gain additional nitrogen on floor coverings with a lack of sufficiant mineral nutriment.

 

Sundew and its digestive secretions

 

Along the edges of the rounded leaves, tentacles are arranged, which produce sticky secretions, consisting of enzymes and formic acid. Attracted by a fragrant smell, small animals approach this deadly plant.

Please like my videos also on youtube, in case you like them. Copyrights Stefan F. Wirth

 

The secretions trap them finally to the leave. After some hours the tentacles move towards the leaf-inside due to growth „movements“, where digestive glands are located. Later even the whole leaf rolls that way that more glands get into a contact with the prey. The whole digestive procedure then needs several days. My video only shows the effect of sticky tentakles to a fly, which finally is unable to flee.

 

Fly on a sundew leaf, independent evolution of carnivorous plants

 

The fly specimen might have represented a too large prey, which is why it at first resisted against the slimy and sticky secretions. However later, its body is thus covered with threads of adhesive that it remains fixed to the sundew leaf. Carnivorous plants evolved several times independently within the Angiosperma. That means that pitcher plants, as for example Sarracenia or Nepenthes, systematically do not represent close relatives of the sundew or even between each other. Under comparable ecological conditions, selective pressures caused options for plants to enrich their nutrients by the ability to digest smaller animals using specific organs, usually being homologous to leaves. The way carnivorous traps develop, differs in the various groups of carnivorous plants.

 

Micro-habitats for mites or nematodes

 

Decaying remnants of partly digested arthropods can especially in Sarracenia or Nepenthes become micro-habitats, in which mites or nematodes might find suitable living conditions. Some of them can even be resistant against digestive enzymes of these plants. Whether microorganisms ,such as mites, also can occur on sundew, is unknown to me. Common inhabitants of pitchers of Sarracenia or Nepenthes are represented by mites of the Astigmata, e.g. of the family Histiostomatidae.

 

Distribution of the round-leaved sundew

 

The round-leaved sundew is native to the whole northern hemisphere in bogs and wetlands.

 

Copyrights for film and text: Stefan F. Wirth, October 2017/ November 2018

Microscopic wrack inhabitants: Mites (Ameronothridae), Protozoans, nematodes and Dipterans

Decomposing detritus (mostly dead algae debris) of marine organic material, laying onshore more or less close to the water line, containing seaweed or cadavers of aqatic animals, is named wrack. Wrack can appear under different kinds of ecological circumstances. In case, it would be in permanent contact with sea water, it might be mostly decomposed by marine organisms. But due to different reasons, wrack can land apart from a permanent sea water contact or even no sea water contact at all any more.

Here mostly terrestrial organisms with a tolerance for salty conditions would inhabit and decompose this piece of detritus. Sandhoppers (Cristacea) are known to switch between wracks of different conditions. They can for example carry mites or nematodes from one wrack habitat to another. Dead organic material generally always needs to be decomposed by living organisms, otherwise the whole ecological system would be harmed.

 

A specific kind of micro habitats

 

A small habitat, which would dry out after a while and thus exists only for a limited time, is called ephemere biochorion. Organisms being adapted to live there, must have adaptations, to leave their habitat by time to avoid desiccation. One option is a life strategy, which is named phoresy. Weaker organisms, unable to desperse themselves efficiently use other animals, such as winged insects, to take a ride on them to new habitats with suitable conditions for a development. Generally phoretic organisms can for example be represented by different groups of mites (e.g. Uropodida, Gamasina, Tarsenomidae, Scutacaridae, some Oribatida, Astigmata) and nematodes (Rhabditida).

 

Mites and nematodes

 

In case of wrack, decomposing close to the waterline, but without or only occasional water contact, Pellioditis marina (Nematoda, Rhabditida) is for example known as phoretic inhabitant along German coasts. Worldwide, crypitical sibling species of P. marina were meanwhile discovered. Depending on the exact situation of the wrack, also aquatic nematodes could appear there for a while. I couldn’t determine the nematode in my footage unfortunately at all, because I did not prepare slides of them enable a larger microscopic magnification. Phoretic mites can be associated with sand-hoppers (Amphipoda, Crustacea) and thus appear in wrack. Mites of the Histiostomatidae (Astigmata) were for example discovered in such a context by some researchers.

 

Mites of the Ameronothridae (Oribatida), sand-hoppers and dipterans

 

I so far never found them randomly, but also didn’t explicitely seek for histiostomatid species until now. My sample did not contain any Astigmata or I at least didn’t find them. Common inhabitants of decomposing wrack are oribatid mites of the Ameronothridae. This taxon with a worldwide distribution is charaterized by specific adaptations to deal as terrestrial organisms with (partly extreme) salty marine conditions. They are mostly algae feeders. Some species are known to appear in wrack. The sample, which I collected in context of the so called „Geo Tag der Natur 2018“ (Geo (journal) day of nature) in Norddeich Mole (East Frisian coast of Germany) contained many specimens (ca. 40, sample size of about 20×20 cm) of the Ameronothridae-species Ameronothrus sp.. My footage shows only one living specimen, as all had died until I began my filming activities.

Inhabitants of decomposing algae tissue along a beach at German North Sea, all copyrights Stefan F. Wirth

 

But I preserved several dead specimens for scientifc purposes. Ameronothridae might, according to literature, use phoresy via birds, but also might disperse themselves over smaller distances, due to their well developed cuticle, protecting against desiccation, and their rather fast locomotion abilities. Larvae of different species of flies (Diptera) developed inside my sample and hatched under my laboratory conditions after about two weeks. They intensively contributed to a fast decomposition of that organic marine tissue. Sand-hoppers were by the way not found at all.

 

Bacteria and protozoans

 

Bacteria are most important decomposers. But the function of protozoans (here e.g. Ciliata) in regard to the process of wrack degradation, which could still be isolated alive after about two weeks of decomposition,  is unknown to me. My sample was found almost on top of a dike, meters away from the highest tide in that area and consisted mostly of the seaweed Fucus vesiculosus.It also contained sea gull feathers.

 

Berlin/ Norddeich Mole June/August/November 2018 Copyrights Stefan F. Wirth