Foissner_Protist Diversity and Geographical Distribution_9048128005
213 pág.

Foissner_Protist Diversity and Geographical Distribution_9048128005

DisciplinaZoologia3.857 materiais33.003 seguidores
Pré-visualização50 páginas
be basal for the Physarales (Castillo et al. 1998). The tiny sporocarps, only
60 W. Foissner et al. (eds)
0.3\u20130.8 mm in total height, have been observed thus far almost exclusively in moist cham-
ber cultures, where they are rather conspicuous by having a silvery iridescent peridium. All
72 records of which we are aware were obtained from the bark of living trees or (less
frequently) shrubs. At least one distribution centre of the species seems to be represented by
the arid regions of the western United States (Colorado, New Mexico, Arizona and Utah),
although the species is present (albeit with a low frequency) in the less thoroughly studied
deserts of Central Asia (southern Russia, Kazakhstan and Mongolia). Fragmentary records
from other arid zones of the world (southern Spain, Tunesia and Oman) contribute to the
picture of a species apparently restricted to arid steppes and deserts, with a (possibly ques-
tionable) record from Myanmar (formerly Burma) as the only noticeable exception (Fig. 3).
Since arid habitats are generally understudied for myxomycetes, the distribution pattern
presented herein is certainly fragmentary, and more intense studies in shrub deserts or gal-
lery forests that occur along rivers in deserts and other arid areas will certainly add to the
number of localities from which the species is known.
Leocarpus fragilis (Dicks.) Rost. (Physarales), which produces calcareous, orange to red
sporocarps that resemble miniature grapes, is one of the most of all distinctive myxomyce-
tes. The species is frequently recorded by non-specialists for the group. The large and
robust, yellow phaneroplasmodium inhabits ground litter with an acidic pH (most often
between 4 and 6). Fruitings can consist of several thousand individual sporocarps. In dry
coniferous forests, exceedingly large mass fruitings can develop, and in 1993 one dry pine
plantation in eastern Germany (Brandenburg, Eggsdorf near Berlin) had an estimated den-
sity of 200\u2013400 fruitings per hectare. With a diameter of 12\u201314 \ufffdm, the spores are rela-
tively large for a myxomycete, which should decrease the probability of long-distance
dispersal, and local biotypes seem to exist. A form with spores in clusters of two has been
described as L. bisporus Nann.-Bremek. and Mitch. (Nannenga-Bremekamp 1989). Some
Fig. 2 World distribution map for Barbeyella minutissima Meyl., a myxomycete associated with montane
Picea and/or Abies forests. The encircled range indicates the European Alps, with numerous records of the
Protist Diversity and Geographical Distribution 61
specimens from South Africa have almost globose sporocarps, whereas the typical form is
egg-shaped (Schnittler, pers. observation of specimens from the Kew Botanical Garden,
London). The distribution map (Fig. 4) was developed from 1474 records. Regions with
many records were encircled with a line on the map. Two patterns seem evident when the
overall distribution is considered. First, L. fragilis rarely occurs in arctic regions but as a
litter-inhabiting species it can spread beyond the timberline. As such, its northern distribu-
tion may be limited more by climate than microhabitat availability. It is very common in
the temperate zone, but seems to be less common in southern temperate zones (e.g., in the
Mediterranean region or in the southeastern United States). The species appears to be
absent from highly arid regions (records from Israel and Spain are from the less arid parts
of these countries) and the humid tropics. However, disjunct occurrences in montane
regions are found farther southward (e.g., in the Canary Islands or the African Atlas Moun-
tains). Also, in fairly well studied tropical regions (e.g. Central America, Ecuador, Tanzania
and Taiwan), L. fragilis has not yet been found, except for a single record from the paramo
region of Costa Rica. As shown by a single record from southern Argentina (Tierra del
Fuego) and a few from South Africa and southern Australia, it reappears in temperate
regions of the southern hemisphere. In contrast to the statement in Martin and Alexopoulos
(1969) that L. fragilis is a cosmopolitan species, it seems to display a clear preference for
temperate zones.
Ceratiomyxa morchella Welden (Ceratiomyxales) was unknown to science until 1954.
The fruiting bodies are very evanescent and start to dissipate on the day following develop-
ment. However, fruitings of C. morchella are conspicuous, since the stalked, 2.5\u20134 mm
high fruiting bodies can occur in large developments. The stalk is translucent, colourless
and crowned by a pure white, globose head that resembles a miniature morel. The ovoid
spores, 9\u201311 £ 6\u20138 \ufffdm in diameter, are formed at the tip of 2\u201310 \ufffdm long stalks that cover
the white upper portion of the fruiting body like a covering of fur. According to studies by
Fig. 3 Distribution of Protophysarum phloiogenum M. Blackw. & Alexop., a species found almost exclu-
sively in arid environments
62 W. Foissner et al. (eds)
the authors in Costa Rica and Ecuador, C. morchella is strongly limited to decaying wood
with a very acidic pH, a rather rare microhabitat in tropical forests. Without exception, the
substrate upon which fruiting occurred for the more than 100 records considered herein
consisted of decorticated, moderately to strongly decayed wood of large diameter logs
with measured pH values between 3.0 and 4.5. This precludes any confusion with
C. sphaerosperma Boedijn, the second tropical species in the genus Ceratiomyxa, since the
latter is found exclusively upon substrates with a pH above 6.5 (up to 8), most often por-
tions of decaying of hard-shelled fruits. For C. morchella, fruitings with more than 10,000
individual fruiting bodies are not rare, and these typically cover the lower side of large,
fallen tree trunks that are kept above the ground by their root disk or other logs. The spores
are colourless and thin-walled. Lacking any UV-absorbing pigments, they may not be able
to survive the long periods of exposure to light that would be associated with long-distance
dispersal in the higher layers of the atmosphere. The preliminary map for C. morchella
(Fig. 5) was compiled from only 72 records, reXecting the fact that the slimy fruiting bodies
are diYcult to preserve as herbarium specimens. The northernmost records are from sub-
tropical Florida and tropical Mexico. The species is fairly common in the Caribbean region,
being known from Puerto Rico, Jamaica, St. Vincent and Trinidad. Records for Costa Rica
come from all parts of the country except the dry southwest and the highest mountains. It
was recorded twice during a survey in western Ecuador (Schnittler et al. 2002). The real
distribution centre of the species seems to be the Amazon Basin. In a study carried out in
the Yasuni National Park (eastern Ecuador) it was one of the most common species
(Schnittler, unpubl. data). Due to the paucity of records, it can not yet be determined if the
species commonly occurs only in the Paleotropics. The species is still unknown from tropi-
cal Africa, and there is only a single record from eastern Asia (New Guinea) mentioned in
the literature.
Fig. 4 World distribution map for Leocarpus fragilis (Dicks.) Rost., a temperate-zone myxomycete conWned
largely to the northern hemisphere. Encircled ranges in Europe and the United States depict regions with sev-
eral hundred records each
Protist Diversity and Geographical Distribution 63
Myxomycetes in the context of the current debate on protist distribution
On the whole, myxomycetes would seem to be rather opportunistic or \u201cfugitive\u201d organisms
(sensu Hutchinson 1951) in that they have a high reproductive potential, seem to possess
eVective dispersal mechanisms, and are characterized by rapid development. These proper-
ties allow them to exploit successfully habitat islands occurring both temporally and spa-
tially in nature. Although a particular habitat within which a species of myxomycete has
been established may persist for only a short period of