Yoke mushrooms
The division of living beings into systematics is a continuous subject of research. Different systematic classifications exist side by side and one after the other. The taxon treated here has become obsolete due to new research or is not part of the group systematics presented in the German-language Wikipedia.
The yoke mushrooms , zygomycetes or zygomycota formed a division within the realm of mushrooms until 2007 . They are named after the yoke-like structures that occur during sexual reproduction .
Whether the yoke mushrooms form a natural group is controversial. It may be a paraphyletic taxon ; it then does not include all descendants of their last common ancestor. As far as we know today, the closest relatives of the yoke mushrooms are either the potty mushrooms (Chytridiomycota) or the dikaryomycota group formed by the sac fungi (Ascomycota) and the mushrooms (Basidiomycota).
construction
Like most fungi, the yoke fungi form a branched mycelium made of microscopic threads, the hyphae , which spreads in the soil or in or on another substrate or - in the case of parasitic species - grows into host organisms. In contrast to the mushrooms and ashlar mushrooms , the hyphae of the yoke mushrooms are mostly not divided into cells by dividing walls ( septa ), but polynuclear ( coenocytic ). Only the reproductive serving sporangia are separated by septa. The mycelium is often anchored in the substrate or on the host via numerous rhizoids . These in turn can be connected to one another by running hyphae.
ecology
Yoke fungi live both saprobionic , i.e. on dead plant or animal remains, seeds or fruits , and parasitic . The saprobiontic species feed on substances absorbed from the environment, breaking down macromolecules using secreted enzymes . The hosts of the parasitic species can be animals , plants or other fungi.
A highly developed and very special form of parasitism is fusion parasitism of the Mucorales species, the victims of which are fungi of the same order.
The fungi of the species Zoophagus tentaclum represent a particularly interesting case : Without exaggeration, they can be described as carnivorous fungi . To do this, they form small loops consisting of hyphae in which, for example, roundworms can get caught. The noose is tightened by contact stimuli, prevents the prey from escaping and then slowly grows into the victim, which is now decomposed by powerful enzymes from the inside, like the fungus. Other types of mushrooms use sticky structures to catch prey. Due to the frequent occurrence in nitrogen-poor soils, it is likely that, as with most carnivorous plants, the prey is caught less for the production of metabolic energy and more to balance the nitrogen balance.
In addition, some yoke fungi enter into symbiotic communities with plants, they act as mycorrhizae . This means that they help the plant at its roots to absorb nutrients from the soil and, in return, receive photosynthesis products such as high-energy carbohydrates from them. In addition, mycorrhizae often repel other fungi that could attack their host plant as parasites. The above-described catching of plant-damaging roundworms can also serve this function.
distribution
Almost without exception, yoke mushrooms live on the land. They can be found in the soils of all continents with the possible exception of Antarctica . Parasitic species are naturally limited to the range of their host.
Reproduction
Yoke fungi can reproduce asexually as well as sexually. With the exception of the zygospores that occur during sexual reproduction, they are haploid , i.e. they only have a single set of chromosomes .
During asexual reproduction, spores are formed in specialized structures, the sporangia, which are spread individually by the wind or animal carriers , sometimes also literally shot off as a spore package . Under suitable conditions, an individual that is genetically identical to the original organism develops from them. The asexual reproductive structures, also called anamorphs , are extremely diverse within the yoke mushrooms.
In contrast, sexual reproduction, in which the genetic information of two organisms recombines , is relatively uniform. The two individuals must, however , belong to a different mating type , a kind of “mushroom sex”, which can usually not be determined externally and is therefore not referred to as male or female, but simply as a plus or minus type. This reproductive mechanism is known as heterothallia . In the yoke fungi, however, the mechanism of homothallia also occurs.
The process known as conjugation is initiated by messenger substances called pheromones . Yoke-like bridges now form between the hyphae involved: For this purpose, special structures, the gametangia , grow out of both cell threads and towards each other. If they touch, they surprisingly grow away from each other, but only to meet each other all the more securely by turning the loop. Only then does a swelling occur on the contact surface , then the dividing wall dissolves there and plasmogamy occurs , i.e. the cytoplasmic components of the gametangia flow together, while the numerous cell nuclei originally contained in them remain separated from one another for the time being.
The swelling is now encapsulated from the gametangia by two partition walls and develops into the zygospore characteristic of the yoke fungus, a spherical, thick-walled black spore container well-protected against adverse environmental influences. The name zygospore for this structure is a bit misleading as it is actually not a spore in the strict sense. This zygospore is initially still connected to the "parent organisms" through the former gametangia, now known as suspensors . The sexual reproductive structures consisting of suspensors and zygospore are called teleomorphs , in contrast to the anamorphs mentioned above .
Within the zygospore, nuclear fusion (karyogamy) finally takes place between two nuclei, which, however, is almost always followed immediately by meiosis , so that the diploid state, characterized by two complete sets of chromosomes, only lasts extremely briefly in the life cycle of the yoke fungi. The newly created haploid daughter nuclei are now "packed" with a little cell plasma as haploid sex spores and released under suitable environmental conditions.
Systematics
Phylogenetic studies have shown that the yoke mushrooms are not a natural family group. Therefore, the yoke mushrooms were abandoned as a taxon - possibly temporarily - in 2007 , and their orders were divided into several departments and sub-departments. Compare the systematics of mushrooms .
The approximately 1000 known species are divided into two classes , which are further subdivided into twelve orders :
- The Zygomycetes are the larger of the two classes with eight orders:
- Basidiobolales
- Dimargaritales
- Endogonal
- The Kickxellales , named after the mycologist Kickx, show a property that is unusual for yoke fungi, septate hyphae. Their asexual reproductive devices, the anamorphs, are in part highly complex.
- Mortierellales
- The Mucorales are almost exclusively saprobionts, so they live on dead material. They also include the common bread mold ( Rhizopus stolonifer ), which not only affects bread, but also fruits such as strawberries as cotton rot , and other Rhizopus species as well as Mucor species and the genus Absidia . A particularly interesting group form the Hutwerfer ( Pilobolus ) that can and reproduction spores targeted more than two meters wide shoot in the direction of sunlight to have an effective feature photoreceptor system.
- The zoopagales also mostly live as parasites; here the hosts are mostly amoebas , roundworms or other protists and small animals, but other fungi are also among their victims. The above mentioned "carnivorous" species Zoophagus tentaclum belongs to this order.
- The Trichomycetes live almost all commensal , which rarely is without effect on the host organism, as well as parasites inside the body of arthropods (Arthropoda) as insects (Insecta), millipedes (Myriapoda) or crustaceans (Crustacea). They have four orders and seven families:
- The Harpellales ,
- the Asellariales and
- the Eccrinales are considered to be closely related.
- The Amoebidiales , on the other hand, form a rather obscure and controversial group.
Individual evidence
- ^ TY James et al .: Reconstructing the early evolution of Fungi using a six-gene phylogeny . In: Nature , Volume 443, October 19, 2006, pp. 818-822, doi: 10.1038 / nature05110 .
- ↑ DS Hibbett et al .: A higher-level phylogenetic classification of the Fungi. (PDF; 1.3 MB) In: Mycological Research , Volume 111, No. 5, May 2007, pp. 509-547, doi: 10.1016 / j.mycres.2007.03.004 .
- ^ Mold fungus specialist center: Absidia - mold genus .
