Stylopage is a polytypic genus of predacious fungus in the order Zoopagales, within the subphylum Zoopagomycotina. All known species of Stylopage subsist on various species of amoebae or nematodes by trapping their prey, typically using an adhesive substance that coats their vegetative hyphae, and absorbing nutrients through the projection of a haustorium. 17 extant Stylopage species have been described thus far.
History and taxonomy Stylopage was first described in 1935 by Charles Drechsler, with the discovery and growth of three new species – S. haploe, S. araea, and S. lepte – on media that had been grown from decaying vegetable matter found in temperate woodlands near Washington, D.C. The genus name refers to the presence of conidia on long, rod-like fertile hyphae, as well as its predatory nature. Drechsler initially placed Stylopage within the now-defunct Phycomycetes. Upon discovery of further Stylopage species, Drechsler placed the genus within the newly created family, Zoopagaceae. Identification and description of further Stylopage species has largely been determined based on similarities in conidial morphology and observed predatory behaviour. Stylopage has been described as both a predator and an obligate parasite. Regardless, all known species of Stylopage exhibit predatory behaviour towards either amoebae or nematodes. Upon the reclassification of orders formerly belonging to Zygomycota, including Zoopagaceae, Stylopage and all other Zoopagales were placed within the subphylum Zoopagomycotina, under the new phylum Zoopagomycota. The Zoopagales have since been proven as a monophyletic order; within the Zoopagales, Stylopage forms a sister clade with Acaulopage, another predatory amoebophagous fungus. However, more recent phylogenetic tree reconstructions based on 18S rRNA phylogeny contend that Stylopage itself is not monophyletic, and that S. hadra forms a sister clade with Zoophagus spp., suggesting that similarities in conidial morphology are not enough to determine monophyly within Stylopage. These phylogenetic analyses also indicated that S. hadra conidia incorporate a bacterial endosymbiont also associated with Acaulopage tetraceros.
Geographical distribution and habitat Stylopage generally thrives in temperate, moist soils or decaying vegetation beds in temperate Northern Hemisphere regions. Since the discovery of the type specimens, multiple Stylopage species have been grown from soils across Eastern North America. Stylopage growth has been found as far west as Colorado, as far north as Michigan and Southern Ontario, and as far south as Florida. In addition, Stylopage can be found across Europe, with samples of multiple species collected from the United Kingdom, Ireland, and Germany. S. rhabdospora has also been cultured from samples obtained from the banks of the Sakawa River, in Japan. Drechsler initially reported that temperate, wet climates seem to promote the most growth of Stylopage species, and that North American summer temperatures were not conducive to its growth. Most samples of both nematophagous and amoebophagous species have been obtained from temperate riverbanks and forest floors, replete with rotting vegetation. More common species such as S. hadra and S. araea can be found ubiquitously in temperate Northern hemisphere leaf litter. Multiple Stylopage species have been reported from farmlands and agricultural soils in more tropical countries, albeit in areas and conditions with comparatively cooler climates. S. hadra, one of the most common nematophagous species, has been found in both Hawaii and India. S. leiohypha has also been found in India. Multiple Stylopage species have been reported from temperate mountain forest floors in Kenya. Interestingly, there is evidence that S. hadra can grow in agricultural soils with moderate levels (up to 1.8 mmol) of lead contamination. Animal dung has also been a highly fruitful area for Stylopage culture sources. S. anomala, S. cymosa, S. grandis, S. leiohypha, and S. hadra can all be found on horse or sheep dung sourced from temperate farmlands in the United Kingdom and Ireland. S. grandis has also been found on sheep dung from temperate Argentinian farming areas.
Morphology and growth Stylopage is characterized by sparsely-growing, dichotomously branching, aseptate vegetative hyphae. The genus is also distinguished from morphologically similar genera, such as Acaulopage, by its production of aseptate conidia on long, erect conidiophores. Vegetative hyphae are typically colourless or hyaline in appearance, although in some species, such as S. hadra, the adhesive substance used to constrain prey can cause the vegetative hyphae to appear golden-yellow under magnification. The size and shape of conidia, number of conidia per conidiophore, dimensions of hyphae, and presence or absence of zygospores all vary between species of Stylopage. Almost all species that produce multiple conidia per conidiophore do so successively - that is, after the production of one conidium, the conidiophore will branch out and continue elongating to produce another, often after previous conidia have detached.
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