| 1. |
- Cavender, James C., et al.
(författare)
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New small dictyostelids from seasonal rainforests of Central America
- 2013
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Ingår i: Mycologia. - : Informa UK Limited. - 0027-5514 .- 1557-2536. ; 105:3, s. 610-635
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Tidskriftsartikel (refereegranskat)abstract
- Ten small dictyostelids isolated from samples collected from the surface humus layer of seasonal rainforests of Belize and Guatemala were studied morphologically, and nine were found to represent distinct species, all with an average height of < 2 mm (0.5-3.5 mm). Although their fruiting bodies (sorocarps) closely resemble one another, the nine species differ in their patterns of aggregation, stream pattern, branching development, formation of microcysts, spore shape, presence or absence of spore granules and their distribution, as well as in the shapes and behavior of their sorogens and myxamoebae. These stable morphological features were sufficient to recognize nine new species of small dictyostends, one with two varieties. SSU rDNA sequences were generated for all these new isolates, and phylogenetic analyses of these sequences show these new isolates belong to Dictyostelid group 3. As a result of this and other recent studies, the concept of what constitutes a species in the dictyostelids has become much more restricted and well defined, in as much as some of the morphological and behavioral patterns now being observed were overlooked in the past. The extent, flow direction and conformation of streaming within the group varies from simple aggregation mounds with no streams to short streams, to somewhat longer streams and finally to well developed streams. Each of these is characterized by a particular set of distinguishing features.
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| 2. |
- Fiz-Palacios, Omar, et al.
(författare)
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Did terrestrial diversification of amoebas (Amoebozoa) occur in synchrony with land plants?
- 2013
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Ingår i: PLOS ONE. - : Public Library of Science (PLoS). - 1932-6203. ; 8:9, s. e74374-
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Tidskriftsartikel (refereegranskat)abstract
- Evolution of lineage diversification through time is an active area of research where much progress has been made in the last decade. Contrary to the situation in animals and plants little is known about how diversification rates have evolved in most major groups of protist. This is mainly due to uncertainty about phylogenetic relationships, scarcity of the protist fossil record and the unknown diversity within these lineages. We have analyzed the evolutionary history of the supergroup Amoebozoa over the last 1000 million years using molecular dating and species number estimates. After an origin in the marine environment we have dated the colonization of terrestrial habitats by three distinct lineages of Amoebozoa: Dictyostelia, Myxogastria and Arcellinida. The common ancestor of the two sister taxa, Dictyostelia and Myxogastria, appears to have existed before the colonization of land by plants. In contrast Arcellinida seems to have diversify in synchrony with land plant radiation, and more specifically with that of mosses. Detection of acceleration of diversification rates in Myxogastria and Arcellinida points to a co-evolution within the terrestrial habitats, where land plants and the amoebozoans may have interacted during the evolution of these new ecosystems.
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| 3. |
- Perrigo, Allison, et al.
(författare)
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Diversity of dictyostelid social amoebae in high latitude habitats of Northern Sweden
- 2013
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Ingår i: Fungal diversity. - : Springer Science and Business Media LLC. - 1560-2745 .- 1878-9129. ; 58:1, s. 185-198
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Tidskriftsartikel (refereegranskat)abstract
- The dictyostelid social amoebae (Dictyostelia) occur in terrestrial habitats worldwide. It has been observed previously that their diversity decreases with increasing latitude and altitude. Here we look at dictyostelid diversity in the high latitude habitats of Northern Sweden. Dictyostelids were recovered from soil samples using traditional plating methods and then identified using morphological characters and molecular sequence (small subunit ribosomal RNA) data. In total, nine species were recovered, including two new species, described herein as Dictyostelium barbibulus and Polysphondylium fuscans. The species diversity found here is discussed in relation to previous findings in the area as well as other high-latitude studies, and biogeographical patterns are examined. The total number of species found in Northern Sweden is lower than the numbers recorded for regions further south in Europe, a finding consistent with a latitudinal gradient of species diversity. Our findings highlight the benefit of using molecular data for accurate species identification in Dictyostelia and the need for a continued sampling effort to better understand their diversity and distribution, especially in high latitude habitats.
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| 4. |
- Perrigo, Allison L
(författare)
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Diversity Underfoot : Systematics and Biogeography of the Dictyostelid Social Amoebae
- 2013
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Dictyostelids (Amoebozoa) are a group of social amoebae consisting of approximately 150 species, which are found in terrestrial habitats worldwide. They are divided into eight major clades based on molecular phylogeny, and within these clades are many species complexes. Some species are seemingly cosmopolitan in distribution, while others are geographically restricted. In this thesis dictyostelids were recovered from high latitude habitats (soils in Sweden and Iceland) as well as from the soles of shoes. Morphological characters and DNA sequence analyses were used to identify isolates that were recovered and delimit new species, as well as to investigate the monophyly of Dictyostelium aureostipes. Nine species were reported from Northern Sweden and four from Iceland. Among the isolates recorded in Sweden were two new species, described as D. barbibulus and Polysphondylium fuscans. P. fuscans was among the four species recovered from footwear, contributing evidence for anthropogenic transport of dictyostelids. Ecological patterns were assessed using linear regression and generalized linear models. The ecological analyses of dictyostelids recovered from Iceland indicate that these organisms are most frequently found in soils of near-neutral pH, but also exhibit a species richness peak in moderately acidic soils. These analyses indicate that in Iceland dictyostelid species richness decreases with altitude, and in the northern hemisphere the species richness increases with decreasing latitude. A three-region analysis of the D. aureostipes species complex indicated that this species is in fact made up of at least five phylogenetically distinct clades, and in light of this the group is in need of taxonomic revision. These results indicate that the dictyostelid species richness is higher than previously known, especially in high-latitude regions, and that even seemingly well-defined species may harbour cryptic diversity. Presently, species ranges may be expanding via anthropogenic dispersal but despite this, the dictyostelids are found to exhibit biogeographic trends well known from macroorganisms, such as a latitudinal gradient of species richness.
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| 5. |
- Romeralo, Maria, et al.
(författare)
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Analysis of phenotypic evolution in Dictyostelia highlights developmental plasticity as a likely consequence of colonial multicellularity
- 2013
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Ingår i: Proceedings of the Royal Society of London. Biological Sciences. - : The Royal Society. - 0962-8452 .- 1471-2954. ; 280:1764, s. 20130976-
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Tidskriftsartikel (refereegranskat)abstract
- Colony formation was the first step towards evolution of multicellularity in many macroscopic organisms. Dictyostelid social amoebas have used this strategy for over 600 Myr to form fruiting structures of increasing complexity. To understand in which order multicellular complexity evolved, we measured 24 phenotypic characters over 99 dictyostelid species. Using phylogenetic comparative methods, we show that the last common ancestor (LCA) of Dictyostelia probably erected small fruiting structures directly from aggregates. It secreted cAMP to coordinate fruiting body morphogenesis, and another compound to mediate aggregation. This phenotype persisted up to the LCAs of three of the four major groups of Dictyostelia. The group 4 LCA co-opted cAMP for aggregation and evolved much larger fruiting structures. However, it lost encystation, the survival strategy of solitary amoebas that is retained by many species in groups 1-3. Large structures, phototropism and a migrating intermediate 'slug' stage coevolved as evolutionary novelties within most groups. Overall, dictyostelids show considerable plasticity in the size and shape of multicellular structures, both within and between species. This probably reflects constraints placed by colonial life on developmental control mechanisms, which, depending on local cell density, need to direct from 10 to a million cells into forming a functional fructification.
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