biologe

Just another WordPress.com site

Kategorie: Uncategorized

Countryside of Berlin: urban green in a drone view (4K)

Many tourists from overseas use to visit European cities in a much too short time. For this reason they often miss an entire picture of for example the city Berlin, when inserting an only short interstop here. Especially winter tourists can experience the German capital as a sad a grey urban being with some architectural major sites and a remarkable party life only.

 

Climate and landscape types in Berlin

 

Berlin has a continental climate and shows a completely other face in summer. It’s a very green face. Not only is the center of the city then colorfully greened by numerous urban parks, which partly lay almost adjacent to each other, but also the outskirts, in major parts covered by forests and grasslands or fields, appear like green oases.

 

 

Countryside of Berlin as aerial videography, Copyrights Stefan F. Wirth, Berlin June 2019. Please give my video on youtube a like, in case you like it.

 

 

Lübarser Felder and surrounding

 

Lübarser Felder is an area of agriculture, being under the management of inhabitants of the adjacent village Lübars, which represents the only Berlin village that still practices agriculture. The village has a long history and still has architectural monuments, dating back to the 19th century. Lübarser Felder lay adjacent to a nature refuge area more in the north, consisting of different kinds of wetlands, such as bog meadows or lowland fens. Lake Köppcensee as part of that nature refuge area is visible from a bigger distance in one scene of my video.

 

Püttberge and surrounding

 

The sanddune-mounts Püttberge are located in the east of Berlin and belong to the nature refuge area Wilhelmshagen-Woltersdorfer Dünenzug. The area consists of sandy mounts, some of them reaching a height of up to 68 meters. They are part of the glacial valley of Berlin, which dates back to the Weichselian glaciation, which happend between 115,000 and 11,700 years ago and covered almost the whole Northern Europe. The dune elevations of Püttberge were formed due to windblown sand inside the glacial valley. My footage shows the Wilhelmshagen-Woltersdorfer Dünenzug in a greater distance seen from the edge of the whole area. Ecologically the Püttberge are characterized by numerous plants and animals, being typical for sanddune environments.

 

Lieper Bucht at river Havel

 

Lieper Bucht is a bathing beach area at river Havel, belonging to the Berlin city district Nikolassee in the South-West of Berlin. The adjacent forest area is the huge urban forest Grunewald. The riverside of Havel in Berlin is geologically charactrized as sandy with a tendency to the formation of dunes, being like Püttberge a relict of the Weichselian glaciation. Flora and fauna are correspondingly composed. Pine trees for example are typical representatives. The nearby Havel islands Lindwerder and Schwanenwerder are visibe in my footage.

 

Berlin, June 2019

Copyrights Stefan F. Wirth

Werbeanzeigen

Mite Histiostoma sp., putatively new species, from mud around ponds (Berlin) and its morphology

Gravel pit area „Im Jagen 86“ in Berlin as biotope

 

„Im Jagen 86“ is a former gravel pit area in the Berlin urban forest Grunewald. It today represents a dynamic biotope, consisting of different types of habitats: mud around ponds, sand dunes, dry grassland and forest. Since the early 2000th, its habitat composition partly changed remarkably. Out of several (smaller) ponds, only one bigger pond remained. All ponds originally were surrounded by sapropel, a habitat for different interesting organisms, such as beetles of Heterocerus, Elaphrus and Bembidion. The mite Histiostoma maritimum was commonly found phoreticaly on Heterocerus and Elaphrus. I additionally in those early 2000th described the new mite Histiostoma palustre from Hydrophilidae of Cercyon and Coelostoma, living inside the saporopel as well. Today only a few small areas with open sapropel exist. I so far did not look for Histiostoma maritimum again and don’t know, how common it still is. At least Heterocerus beetles are harder to find than in earlier years. I so far did not found Histiostoma palustre again.

 

Rearing conditions of a putatively new mite species

 

I collected new mud samples in March 2019 at different areas, but found developing histiostomatid mites in a sample from the edge between mud (sapropel) and mosses. It is a species I never found before there and which might represent a new species. Only females could be morphologically studied. Nymyphal stages (not deutonymphs) are only available as video footage. No males were found. I had added bigger potato pieces to stimulate microorganism growth as mite food into the soil sample (room temperature). After about one month, a few mites (females and proto/tritonymphs) developed on only one of these potato pieces and quickly died out shortly after my filming activities and after I could prepare a few females. I actually try to get them reared again. Due to the low temperatures in March, it is considered that these mites hibernate independently from insects in the substrate. No bigger insects could be found in the substrate, which might be the corresponding carriers. But different dipterans (e.g. Ceratopogonidae) developed, they had no mite deutonymphs after hatching in my sample.

 

 

 

 

Morphological reconstruction of females and important characters as well as behavioral observations

 

The females of Histiostoma sp. differ from other females, which I know, by the mosaic of the following characters: body conspicuously elongated with a distinctly big distance between hind ringorgans and anus, digitus fixus almost simple shaped, fringes or ridges on palparmembrane, 6 dorsal humps, unusually big copulation opening. Leg setation not yet studied. One pair of ventral setae hardly visible (not in the drawing). Nymphs were observed during burrowing activities (footage), females are may be also able to. Deutonymphs or males would be useful to decide, whether the species is new. Some species are only described by deutonymphs.

 

Berlin, March/ June 2019 All copyrights Stefan F. Wirth

Ancient villa of Pollius Felix in Sorrento/ Italy: a nature refuge

Ancient ruins around the Gulf of Naples

 

The area of the Gulf of Naples (Italy) is full of ancient Roman ruins. Besides famous excavation sites such as Pompeii or Herculaneum, also not so famous, but nevertheless very fascinating buildings from around the first century are preserved. An example is the (originally) huge villa of Pollius Felix nearby Sorrento.

 

Pollius Felix and his eccentric extended villa in Sorrento

 

Pollius Felix was a rich man and build several villas around the Gulf of Naples. But the one nearby Sorrento surely was his biggest and most eccentric domicil. He intended to unite the four elements water (sea), air, earth (rocks) and fire (artificial heating system? lava rocks?) in his architecture. Unfortunately only a part of the very extended villa is preserved. But impressively shows, how the Mediterranean Sea was made to a part of a private building. What the natives call „I Bagni della Regina Giovanna“ is a sea water bassin (may be of natural origin) that was connected via stairs and bridges with the ancient super house. A reconstruction of the whole villa by the way can be seen in the second floor of the Georges Vallet Archeological museum.

 

 

 

How to visit the ruins?

 

The ruins are accessible for free, but visitors need to have good walking and climbing conditions. First an about 20 minuts walk downwards to the sea through an old tight walkway is required. To access the major parts of the ruins themselves small pathways through mediterranean seaside vegetation is necessary. The sea water bassin can be reached via stairs. In summer, it is a popular place for (mostly native) swimmers.

 

Landscape and biodiversity

 

The whole area is covered with natural wild vegetation, private and non private gardens and olive groves. A remarkable biodiversity is present, and – depending from the season – alwas shows different faces. In spring, early summer and autumn, everything is greening and blooming, while in the hot summer season drought predominates. The area is a home for interesting Opiliones (harvestmen), Diplopodes, rose chafers, snails or lizards (Podarcis) and snakes (rarely). I visited „Villa Pollio Felice“ (also named Villa Limona) this time in spring/ early summer: April 2019. Unlike in autumn, when I mostl visited the Gulf of Naples in the past, different flowers covered the region. The most abundant species was Allium triquetrum, decorating lush meadows with their almost bell-shaped white blossoms.

 

Villa Pollio Felice/ Berlin April/June 2019 Copyrights Stefan F. Wirth

Pompeii, ancient Roman city under a dynamic sky

Ash layers preserved almost the entire city

 

The ancient Roman city Pompeii is famous for its incredible conservation status. Huge ash layers preserved all anorganic remnants of the city and its inhabitants. Also organic tissue persisted in partly remarkable conditions, but can not be compared with artefacts, which survived the destruction of the neighbour city Herculaneum. There lava rocks enabled an airtight seal and thus could shield decomposing microorganisms.

 

Well visible sky over the city of no roofs

 

Unlike Herculaneum, Pompeii is also famous as the city without roofs. And indeed, when walking through the vast excavated area of ancient ruins, no higher buildings are shading or obstruct a free view to the sky. Exactly these phenomina male sauntering through Pompeii so unique. The sky with its seasonal dynamics is from everywhere always well visible and due to in spring or in autumn sometimes rapidly changing weather conditions, a dramatic atmosphere based on powerfully moving cloud formations can occur.

 

 

 

 

Pompeii/ Berlin April/June 2019 Copyrights Stefan F. Wirth

Oribatida mites: Fast runners and slow crawlers

Microhabitats often consist of a complexity of organism species. Under suitable conditions, samples can be kept „alive“ for months and even for years by regularly adding moisture and organic tissue, in case of my sample of this footage: patato pieces.

 

 

Mites of the Oribatida and their different ways of locomotion. Copyrights: Stefan F. Wirth, Berlin April 2019. Please give the video a like on youtube too.

 

Soil samples from island Norderney

 

This soil sample was collected in summer 2018 on the North Sea island Usedom during my participation at the „Geo Tag der Natur“. It contained several specimens of the predatory chilopode Lithobius sp. and pieces of rotting wood, moss and forestground, everything collected under rotting treetrunks and tree branches. The samples additionally contained the carabid beetle Pterosticus cf. niger and ants of genus Lasius. Samples were collected in a small forest area with wetland aspects. The soil quality was rather moist.

 

Astigmatid mites

 

I later added potato pieces and regularly some water droplets to the sample with still living big arthropods/ insects. After some weeks, specimens of the astigmatid mite Acodyledon cf. schmitzi developed on dryer areas of the potato pieces. These mites were presumably phoretic associates of the carabid beetles. They died out after several months, after the sample had dried out a little bit and may be due to changes of the room temperature during winter time.

 

Oribatida

 

Now, almost a year later, the micro habitat is inhabited by mites of the Oribatida in greater numbers of specimens of at least three species: Nothrus sp. (genus not yet clarified), Nothrus palustris (already found for the first time shortly after the sample collection) and a species of Phthiracarida.

 

Locomotion and biodiversity

 

Purpose of the short film is to show different organisms, cultured after about a year in this sample: mites, nematodes, collembolans and microorganisms, fungae and bacteria. Of the bigger arthropods/insects, only one Lithobius species survived until now.  Also the diversity of ways of locomotion in different oribatid species is emphasized: There are slow crawlers (Nothrus) and fast runners (Phthiracarida).

 

Berlin, April 2019, Copyrights Stefan F. Wirth

Agriculture, natural countryside and stream pasture landscape north of Berlin

Berlin as a green city

 

 

Berlin, lake Köppchensee, March 2019. Copyrights Stefan F. Wirth.

 

Berlin is an unusually green metropolis. Besides numerous urban park landscapes and the huge forest area Grunewald, there is a unique countryside north of Berlin, including the area of the old village Lübars, being surrounded by numerous fields (Lübarser Felder) and a stream pasture landscape, named Tegeler Fließ, with bog meadows.

 

 

Nature sites Lübarser Felder, Arkenberge, Schönerlinder Teiche in 4K, copyrights Stefan F. Wirth. Please also like my video on Youtube.

 

Mounts Arkenberge and pondlandscape Schönerlinder Teiche

 

In the northeast, around the urban village Blankenfelde, the currently highest elevation of Berlin can be found, the Arkenberge. Originally, they represented a chain of smaller mounts as natural remnants of the Weichselian glacier. One of these mounts is especially conspicuous and is acually prepared to become accessible for people and forms with a height of 122 m over NHN the highest mountain of Berlin. It represents despite of its natural origin a rubble landfill site, which was formed beginning in 1984.
Adjacent to the Arkenberge, several wetland areas attract nature enthusiasts for hiking tours: the pond landscape „Schönerlinder Teiche“ (Brandenburg) and the lake Kiessee Arkenberge.

 

Mount Arkenberge with Kiessee Arkenberge, Berlin March 2019. Copyrights Stefan F. Wirth.

 

Mount Arkenberge, Berlin February/ March 2019. Copyrights Stefan F. Wirth

 

Eurasian blue tit at Schönerlinder Teiche (Wandlitz), February/ March 2019. Copyrights Stefan F. Wirth.

 

Ponds Schönerlinder Teiche (Wandlitz, Brandenburg), February/ March 2019. Copyrights Stefan F. Wirth.

 

Lowland area of the stream Tegeler Fließ as remnants of the Weichselian glacier and adjacent calcareous tufa area

 

The stream Tegeler Fließ is a wetland nature site with a high biodiversity of plants and animals. It is surrounded by different types of bog meadows. The Tegeler Fließ lowland is also a result of the last glacier period.

The stream lowland is additionally adjacent to a calcareous tufa area, which is well visible from top of the Arkenberge. Calcareous springs and calcareous tufas created here calcareous rush- marshes with an interesting biodiversity of for example species of mosses and snails.

 

Lake Köppchensee as part of the Tegeler Fließ lowland, March 2019. Copyrights Stefan F. Wirth.

 

Video footage and photos

 

The footage was captured from localities around the village Lübars in the area of Lübarser Felder and additionally around Arkenberge. Some above mentioned nature sites are only visible in a distance.

 

Berlin, March 2019, copyrights Stefan F. Wirth.

 

Late winter insect life: winter aconite blossoms and dipteran visitors

When do the first insect activities in the new year occur? Can insects be active in winter, even in the presence of snow? The answer is generally yes, different insect species even use to appear on warmer winter days on top of snow layers. Examples are the limoniid crane fly Chionea belgica, a wingless dipteran, which can be observed on milder winter days on snow surfaces along forest edges in Central Europe. Also the fly Trichocera hiemalis belongs to the winter crane flies (Trichoceridae) and can be characterized by a very well developed cold resistance. It appears on sunny winter days between branches of leafless trees in swarms around invading sunlight beams.

 

The winter aconite as an early blooming flower and its biology

 

But what about insects, visiting blooming flowers? This requires the existance of early blossoms, which can grow and bloom under winter conditions. A well known example is the winter aconite Eranthis hyemalis, which outlasts the summer period only by its underground tubers. Their conspicuous yellow blossoms belong to the first blooming flowers in the year. In Central Europe, they begin to grow under suitable conditions in mid February. They require milder temperatures, but even persist in case an unusual cold snap would happen. The blossoms open only at sunshine and thus close shortly after sunset. Opening and closing is a growth process, which depends on temperature conditions. Such a phenomenon is called thermonasty.

 

The winter aconite as a neophyte in Germany

 

In Central Europe, such as in Germany, E. hyemalis is a neophyte. It is originally native to Southern European areas, Turkey, South-East-France, Italy, Bulgaria and Hungary.

The species was introduced to Central Europe (and North America) as ornamental plant for gardens. It is proven that it was in Germany already cultivated since the 16th century. The German botanist, nature researcher and medical doctor Joachim Camerarius reared the winter agonite, which he brought from Italy, since 1588 in his backyards.

 

Common pollinating insects

 

Pollinating insects of E. hyemalis are flies, bumblebees and bees. To reach the nectar inside the blossoms requires a proboscis length of about two mm, which is mostly given in bumblebees and bees.

 

Flowerbed in Berlin urban park Schillerpark

 

I documented via my videography (4K) and photography a smaller area of winter aconites in front of a wall at urban park „Schillerpark“ (honoring the German poet Friedrich Schiller) in Berlin. The bright bricks of that wall reflected efficiently the solar warmth and thus created suitable conditions for a late winter flowerbed full of life.

 

Video with winter aconite blossoms and pollunating flies, copyrights Stefan F. Wirth.

 

Most abundant insects in that winter aconite bed

 

DSC03573bestsharpsignatur

Western honey bee, copyrights Stefan F. Wirth

 

The western honey bee Apis mellifera was often seen on blossoms, but unfortunately was not captured via video footage. Our honey bee hibernates in a so called winter clusters with lower temperatures and low activities in workers. Beginning in late winter/ early spring, workers increase the nest temperature due to body movements up to 35°C. This is exactly the body temperature, workers need to fly out and collect first nectar and pollen, for example from the winter agonite.

 

Drone fly on blossom of the winter aconite, copyrights Stefan F. Wirth

 

The drone fly Eristalis tenax belongs to the hoverflies (Syrphidae). Their larvae develop in watery environments, where they use their conspicuous snorkel tube to breath air at the water surface. Adults are typical blossom visitors, preferring Asteraceae and Apiaceae. Interesting highlight of their biology is the migratory behavior. These migratory insects form swarms, which cross the Alpes towards Southern European areas by using suitable wind conditions, where they finally hibernate and reproduce. The next generation returns the same way back. Not all individuals participate these migratory flights and would try to hibernate in Central Europe. Hibernating individuals are always females, which were fertilized prior to their winter diapause or their migration and which lay their eggs in the subsequent spring or in southern regions during winter. In Germany they only survive in greater numbers in milder winters, which they persist in temperature-stable hideways, such as gaps inside walls or wooden habitats. These specimen can be usually observed early in the year, beginning with March, when visiting blooming flowers. Their numerous very early appearance in mid February 2019 might be due to a very warm summer 2018 and a subsequent very mild winter in north-eastern Germany (Berlin). I have no comparative findings regarding the usual blooming time of the winter aconite and the abundance of drone flies there for Berlin or even this specific urban park. I also don’t know about indications that due to a global warming, as in some migratory birds, less specimens of the fly would migrate and more stay to hibernate here around.

The research station „Randecker Maar“ in the Swabian Jura records changes in migratory flights of birds and insects. They discovered a distinct decline of numbers of migrating drone flies and interpret it as a result of the increasing application of poisonous substances in the agricultural sector. Whether they additionally consider this being due to more individuals hibernating, where they are, based on generally warmer temperatures (global warming) is unknown to me.

 

Blow fly on blossom of the winter aconite, copyrights Stefan F. Wirth

 

The blow fly Calliphora vicina is a common blossom visitor in early spring and autumn. This fly, typically appearing in human settlements in Europe and the New World, is well adapted for an activity at lower temperatures (more than 13°C). While larvae develop in decomposing organic tissue (such as cadavers of animals), adults feed on nectar and pollen. They additionally incorprate saps from organic material with a strong odor.

C. vicina produces about five generation per year and throughout the year. The flies can even be active in winter, when temperatures reach a suitable level.

 

Other fly species were existant, but I did not determine them.

 

Time of footage and photo recording

 

Video footage and photos were recorded between 16 and 18 February 2019 in the urban park Schillerpark in Berlin.

 

Copyrights: Stefan F. Wirth, Berlin 2019.

Mite Histiostoma sachsi (Astigmata): Juvenile dispersal instar deutonymph and its orientation behavior

Some animals live in environments, where there is (almost) no light available. It makes no sense to see in the dark, but it is important for a specimen to know, where it actually is, where it is going to, whether there is enough food and what the conspecifics are doing. Predators need to be recognized in time, and a sexual partner must be found. There is also need for an efficient communication between specimens of a species. How can all this be performed by mites of the Astigmata, which usually live inside decomposing soil habitats in a more or less permanent darkness?

 

Olfactory sense organs in mites of the Histiostomatidae

 

Histiostoma sachsi (Histiostomatidae, Astigmata) is such a mite, living inside cow dung or compost. It might have a rudimentary ability for a light perception, but has not visible or functional eyes. It cannot produce any sounds. It can only feel and smell. Seemingly very limited abilities, but the contrary is fact: Due to evolution this mite is perfectly adapted to its life-style. It can feel objects by touching on them using its body setation (= body hairs). And it smells by means of very specialized body hairs, which are called solenidia and appear in different types, shapes and functions. These mites don’t smell on the level of us humans, which would be very insufficient. If at all, it should be compared with a dog. I am always fascinated when seeing blind dogs and how perfectly they can interact with their environment, despite their handicap. That’s may be how the efficiency of olfactory perception abilities of such a mite must be imagined. They do not only perceive scent particles from other animals, plants and soil components. Even olfactory signals from their conspecifics will be correctly and differentiatedly interpreted. And that not only marginally.  Olfactory signals represent indeed the major mode of their intraspecific communication.

 

Chemical communication of mites of the Histiostomatidae

 

Communication always requires contributions from both sides, a signal and an answer. These mites smell the signal of a conspecific using their solenidia, and they answer by the secretion of biochemical components. For these purposes, they possess a huge and complex gland system located on the upperside of their backs. Volatile excretions aggregate inside a big and rounded reservoir and finally leak to the outside via a pore, called oilgland opening. These gland systems are located symmetrically on both sides, each with one reservoir and one pore.

The meaning of the sent volatile message simply depends on the composition of the correspondingbiochemical components. Even diffferent stereochemical configurations of the same molecule can have different meanings. Citral for instance is a major component and has in different stereoisomers different functions. Such cummunicative volatile signals are usually named pheromones. And mites of the Histiostomatidae can indeed produce different kinds of pheromnes via the same gland system. Aggregation pheromones inform specimens about a suitable place to stay together with their conspecifics, for example due to a sufficient amount of food resources. Alarm pheromones solicit mites nearby to flee from an unpleasant situation. Sexual pheromones attract adult partners to each other in order to perform the mating procedure. But the gland secretions can even more. As allomones, they communicate with specimens of other species. They function as defenses against predators or other dangerous cohabitants.

 

Deutonymphs need to find a carrier for dispersal

 

Another form of communicative interspecific interactions is performed by a specific juvenile instar, the deutonymph. It looks morphologically quite different from all other instars (heteromorphic situation), does not need or possess a functional mouth, has a thicker cuticle as protection against drying out and a complex sucker organ on its underside in order to attach itself to an insect or another bigger arthropod. Deutonymphs of the astigmatid mites search for bigger carrier-arthropods to get carried from one habitat to another (dispersal strategy  is calledphoresy). While doing so, they again use their specifically modified leg setation (hairs) on the first pairs of legs to perceive scents for the detection of a suitable and passing by carrier. Basically it is still unknown, whether the term „communication“ is indeed appropriate in this context as we don’t know yet about a mutual interaction between deutonymphs and their carriers, before the phoretic ride begins.

 

 

Olfactory orientation of the deutonymph of Histiostoma sachsi, copyrights Stefan F. Wirth, February 2019.

 

Specific way of walking in deutonymphs

 

In detail, different kinds of behaviors can be observed in deutonymphs, when searching a carrier. The detailed behavioral patterns in this context can slightly differ between even closer related species. Deutonymphs of Histiostoma sachsi as all deutonymphs show a characteristic mode of walking, in which especially the first pair of legs plays an important role. During each step, performed by four pairs of legs, the first legs are lifted up much higher than all other hind legs. While doing so, they slightly tremble up and down. A behavior that mostly supports a better basic orientation inside a „jungle-„micro-landscape, being filled up with soil particles and decomposing plant tissues. But what H. sachsi deutonymphs additionally need in order to find their carriers is repeatedly to rest between the walking activities. Thus the first legs, which normally are still walking legs, are made free and that way available for the perception of carrier-scent-components only. These  namely are the legs that bear the highest densiy of solenidia.

 

Two different behavioral modes for an efficient orientation towards a carrier

 

Two different modes of resting with olfactory searching activities could be observed: In periodic intervals the deutonymph attached to the ground by using its sucking structures. They were then more or less laying on their entire undersides with only their forebodies slightly lifted up. By alternating moving the first legs up and down, olfactory information could be perceived from all directions without having the own body as a barrier to backwards. To improve its orientation situation, the deutonymph additionally turned on its own axis around, being stabilized by its sucking structures, which are flexible enough to follow these movements. When the deutonymph intended to continue its walk, it first needed to detach from the ground, which happened via muscle contractions that caused an abrupt detachment of the corresponding suckers. But main aim of the deutonymph is to find an elevated place, where the probability of a passing by carrier is especially high and from where a bigger insect (or other arthropod) can easier be ascended. There the second behavioral mode was performed. The deutonymph only fixed the edge of its hind body to the ground, again using the suckers on its underside, which are located close to this edge. This time the entire mite body stood in an upright position. The first legs again „waved“ alternating up and down and could under these especially elevated conditions even perceive scents from bigger distances. By occasionally slightly and alternating turning their upright bodies to both sides, olfactory information could be easier detected from all directions.

 

Carrier of H. sachsi still unknown

 

The frequency of such movements in mites increases typically as closer a suitable carrier approaches. But this was not yet observed or documented for Histiostoma sachsi. Its carrier inside the compost substrate is still unknown, which is why I so far could’t perform corresponding experiments. The species‘ describer, Scheucher (1957), found her mite specimens in cow dung and also didn’t identify the corresponding carriers there.

The observations presented in my video are part of my research project about morphologies and behaviors of deutonymphs in the Histiostomatidae.

 

Berlin, February 2019. All copyrights Stefan F. Wirth.

 

Arapaima gigas, einer der größten Süßwasserfische – doch was sind Fische eigentlich?

Sie sind beeindruckende Fische, nicht nur aufgrund ihrer Größe. Und doch kennen die meisten Menschen sie nur aus den Aquarienhäusern zoologischer Gärten. Arapaima gigas wird mindestens zwei Meter lang und erreicht in Ausnahmefällen sogar Längen von über drei Metern. Beheimatet ist die Art im Bereich des Amazonas-Beckens und ist in Peru, Brasilien und Guyana verbreitet.

 

Arapaima gigas, einer der größten bekannten Süßwasserfische aus dem Amazonas-Gebiet

 

Arapaima ist ein Räuber. Erwachsene Fische ernähren sich von anderen Fischen sowie Tieren in vergleichbarer Größe, wie zum Beispiel auch kleineren Säugern. Besonders auffällig sind die kräftig gestalteten großen Schuppen, die den Körper der Tiere umschließen. Sie dienen unter anderem als mechanischer Schutz gegen Angriffe durch Feinde. So können sie beispielsweise den Attacken der im selben Lebensraum beheimateten Piranhas, die zwar wesentlich kleiner sind, aber bekanntlich empfindliche Beißwerkzeuge besitzen, wirkungsvoll widerstehen. Das schützt Arapaima freilich nicht vor seinem größten Feind, dem Menschen. Er ist ein beliebter Speisefisch, der durch massenhafte Bejagung in seinem Bestand immer wieder gefährdet wird.

Arapaima gigas wird häufig als größter Süßwasserfisch der Welt bezeichnet. Dies basiert jedoch auf Übertreibungen. In Wahrheit befindet er sich in der Größenordnung des Europäischen Welses, dem größten europäischen Süßwasserfisch.

 

„Fische“ ist keine spezielle systematische Gruppierung

 

Ich verwendete bislang stets unkommentiert den Begriff „Fisch“. Was sind Fische eigentlich?Welche sogenannte Fische kennt man noch? Wie verhält es sich beispielsweise mit dem Bullenhai, der über drei Meter lang werden kann und neben marinen Habitaten auch im Süßwasser auftreten kann. Kann er als Gigant des Süßwassers mit dem Arapaima, dem Gigant aus dem Amazonas verglichen werden? Nach evolutionsbiologisch-systematischen (=phylogenetisch) Gesichtspunkten kann er das nicht. Der Begriff „Fisch“ bezeichnet nämlich keine spezielle, systematisch in sich geschlossene Gruppe. Stattdessen haben wir es mit einem deskriptiven Begriff zu tun, der alle Tiere umfasst, die in ihrer Gestalt ganz grundsätzlich eine gewisse Ähnlichkeit mit dem Goldfisch aufweisen.

Wenn wir außer Acht lassen, dass auch „Tintenfische“ und „Walfische“ nach demselben Muster benannt wurden, die bekanntlich zu den Mollusken und Säugetieren gehören, weist die Fischgestalt zumindest in den meisten Fällen auf eine irgendwie gestaltete Verwandtschaft hin. Jedoch sind Haie und Arapaima dennoch nicht sonderlich nahe miteinander verwandt.

 

Arapaima gigas im Aquarium des Zoos Berlin, ein gigantischer Süßwasserfisch, der regelmäßig atmosphärische Luft an der Wasseroberfläche aufnehmen muss. Copyrights Stefan F. Wirth

 

Bei den „Fischen“ handelt es sich nämlich um eine sogenannte paraphyletische Gruppe. Das heißt, sie umschließt zwar eine ihnen allen gemeinsame Stammart, jedoch keineswegs alle dazu gehörigen Tochtergruppen. Dazu würden nämlich auch alle Landwirbeltiere gehören. Eine vergleichbare paraphyletische Gruppe stellen beispielsweise die „Reptilien“ dar, zu denen Eidechsen/Schlangen, Schildkröten, Krokodile und alle Dinosaurier gehören. Da die Vögel aus den Dinosauriern hervorgingen, jedoch nicht zu den „Reptilien“ gezählt werden, haben wir es unter dieser Bezeichnung wieder mit einer Stammart und nur einem Teil aller Tochtergruppen zu tun, die allerdings im Stammbaum der Tiere nebeneinander stehen und daher näher miteinander verwandt sind, so wie auch bei den „Fischen“.

Im Falle der „Fische“ (paraphyletische Gruppen werden häufig in Anführungszeichen gesetzt) verhält es sich so, dass die verschiedenen als Fische bezeichneten Gruppen neben nur ihnen eigenen Merkmalen auch unterschiedliche Merkmale aufweisen, die auf eine Ahnenlinie hin zu den Wirbeltieren zurückgeführt werden müssen. Was unterscheidet also Knorpelfische (zum Beispiel Haie) und Strahlenflosser (Actinopterygii = echte Fische) voneinander? Eine Frage, die so in der modernen Systematik, die stets nach Gemeinsamkeiten sucht, eigentlich nicht gestellt wird. Richtiger ist es, zu fragen: Welche Merkmale teilen die Knorpelfische mit den Landwirbeltieren (z. B. knöcherner Schädel, Kiefer) und welche die Strahlenflosser (z.B. Lunge). Wenn man dennoch über Unterschiede sprechen möchte, ist festzustellen, dass Knorpelfische noch keine Lunge, die mit jener der Landwirbeltiere homolog ist, besitzen, Strahlenflosser aber schon. Die Lunge ist also auf der Ahnenlinie der Knorpelfische hin zu den Strahlenflossern evolviert. Anders als die „Fische“ sind die Strahlenflosser, die ich hier auch als echte Fische bezeichne, sehr wohl eine geschlossene systematische Einheit (=Monophylum), die auf Merkmale einer gemeinsamen Stammart zurückgeführt werden kann, die nur dieser Gruppe eigen sind. Ein Beispiel ist die namengebende Gestalt der Flossen, die durch Flossenstrahlen durchsetzt sind.

 

Zuerst gab es Lungen, aus denen Schwimmblasen evolvierten

 

Die Strahlenflosser (Actinopterygii), zu denen neben unzähligen Arten auch Arapaima gehört, besitzen also in der Tat ursprünglich paarige Lungen als Respirationsorgane. Diese sind demzufolge nicht erst vor dem Abzweig der Lungenfische entstanden, die als nächste Verwandte der Landwirbeltiere gelten. Die dortige Neuerung betrifft, anders als der Name Lungenfisch vermuten lässt, die Evolution eines Lungenkreislaufs, den es bei urtümlichen „Fischen“ mit Lunge noch nicht gegeben hat.

Aber besitzen echte Fische (Actinopteryii) nicht Schwimmblasen und atmen ausschließlich durch Kiemen? Mitnichten. Ursprüngliche Vertreter der echten Fische werden beispielsweise durch die Flösselhechte (Polypteriformes) representiert, die paarige sackförmige Lungen besitzen und neben der Kiemenatmung daher auch atmosphärische Luft veratmen können. Diese beeindruckenden Tiere können sich mithilfe ihrer Flossen nicht nur an Land fortbewegen, sondern lassen sich (es gibt Experimente an Senegal-Flösselhechten) auch unter vorwiegend terrestrischen Bedingungen in Terrarien halten.

Erst innerhalb der echten Fische ist die Schwimmblase entstanden, die sich durch Evolution aus den Lungen heraus bildete. Die fachgerechte Beschreibung lautet daher: Lunge und Schwimmblase sind einander homologe Organe. Innerhalb der Actinopterygii gibt es einen evolutiven Trend, demzufolge die Schwimmblase bei urtümlicheren Vertretern (noch) der Atmung dient, bei evolutiv weiter abgeleiteten Vertretern hingegen nur noch die Funktion der Austarierung im Wasser übernimmt.

Allerdings ist es innerhalb der echten Fische oftmals schwierig zu entschlüsseln und noch immer Gegenstand phylogenetischer Studien, ob die Lungenfunktion einer Schwimmblase einen Hinweis auf Urtümlichkeit darstellt, oder ob sekundär aus einer Schwimmblase mit Tarierfunktion erneut ein Atmungsorgan entstanden ist. In der Evolutionsbiologie werden im Übrigen unabhängige Entwicklungsschritte stets als Konvergenzen bezeichnet.

 

Arapaima gigas veratmet mithilfe seiner Schwimmblase atmosphärische Luft

 

Auch Arapaima gigas ist ein Luftatmer, der auf den Einsatz seines zusätzlichen Atmungsorgans in Form einer Schwimmblase sogar angewiesen ist. Er ist ein obligater Schwimmblasenatmer, der atmosphärische Luft an der Wasseroberfläche mithilfe seiner Mundöffnung aufnehmen muss. Dies wird als Anpassung an den häufig sauerstoffarmen Lebensraum der Tiere interpretiert, die sich häufig in Überflutungszonen des Amazonasbeckens aufhalten, wo wenig im Wasser gelöster Sauerstoff zur Verfügung steht. Der Literatur zufolge muss Arapaima gigas alle fünf bis fünfzehn Minuten die Wasseroberfläche aufsuchen, um dort mit seinem oberständigen Maul Luft einzuschnappen.

 

Berlin, Februar 2019, copyrights Stefan F. Wirth

Eudicella colmanti – Mating behavior of a colorful beetle

Rose chafers represent a group of colorful beetles, which taxonomically belong to the Scarabaeidae and thus are relatives of famous beetles such as Scarabaeus sacer, well known for rolling dung into balls and for being an important symbol for creation and the rising sun in the ancient Egyptian world. Even the stag beetles are more distant relatives of rose chafers.

 

Colorful and active during daytime

 

Unlike some related beetle clades, rose chafers are usually active during the day. This is also indicated by their very colorful bodies. Colors in insects can have different functions, but they usually all are optical signals, which require a visibility in the sun light. Greenish colors are common in rose chafer species and might have optical inner specific signal functions, but also might support an optical camouflage. This would also make sense in the preferred habitats of the adult beetles, which usually feed on softer parts of blossoms and on their pollen. But they also feed on fruits, whereby mostly liquids are incorporated as the chewing mouthparts are not very well developed.

 

Tropical rose chafer Eudicella colmanti during its copulation behavior, 4K videography, copyrights Stefan F. Wirth.

 

Tropical rose chafers from African countries

 

About 3000 species of rose chafers are known, of which most inhabit the tropical zones. The about 20 species of the genus Eudicella are more or less restricted to the African continent.

Eudicella colmanti is native to Gabun, Kamerun and Kongo, thus a species with a main distribution in Central Africa. But E. colmanti is like other species of this genus worldwide often kept in terraria, although species like E. smithi are more common inhabitants of this kind of artificial habitats. They all can be more or less easily reared.

 

Specific flying mode and copulation behavior

 

This is why I was able to study behavioral characters in detail. And rose chafers indeed show interesting behaviors. They for example perform a unique way of flying. It is a specific character of rose chafers (a so called apomorphy) that they fly with closed fore wings, which cannot be opened as in other beetles.

I documented in my video the mating behavior of a beetle couple. Interestingly this was not too difficult, although both genders can, when separated from each other, react to disturbances with a high agility.

 

Almost permanent copulation activities

 

But in the copulatory position, they accepted to be removed from their terrarium to the filming set and even stayed in position, when they were enlighted from different positions with very bright light beams. Please note the the female, which I observed regularly actively searching for a position underneath the male (behavior not clearly visible in my footage). But it also conspicuously never stopped feeding (on an apple) during the copulatory process (very well visible in my footage), obviously to obtain enough nutrients for the production of eggs. A copulation in my couple is not a unique event, but is repeated regularly and can take hours.

 

Phoretic mites

 

Both genders carried bigger numbers of mites. These were phoretic deutonymphs of the taxon Astigmata (Acariformes, Acaridae). As never determined the mite species, as it was not clear, whether it represented a natural associate of these tropical beetles, or whether it was a species native to Germany, which for example was carried into the terrarium via Drosophila flies.

Copyrights Stefan F. Wirth, Berlin March 2017/ February 2019