Abstract
The genus Geolegnia represents a poorly documented group of saprolegnialean oomycetes isolated from soils as free-living organisms. Although it is morphologically similar to the facultative parasitic genus Leptolegnia, Geolegnia presents the uncommon property of having lost a flagellate stage in its lifecycle. Based on ITS and large subunit (LSU) rRNA sequence data, we show Geolegnia to be basal to Leptolegnia, and also introduce Geolegnia helicoides sp. nov. Using sequence data of Leptolegnia available in GenBank, supplemented by data derived from culture collections, we show that Geolegnia is nested within Leptolegnia, a genus characterised by its "conventional" biflagellate life cycle. The emergence of Geolegnia is therefore seen as a recent event, and we suggest here an evolutionary context where this loss might have been advantageous. Based on this study, Leptolegnia remains paraphyletic, awaiting the redefinition of genera in this complex.
Highlights
Oomycetes are a group of fungal-like heterokonts that are often associated with freshwater and terrestrial habitats, such as marginal sites around lakes, lagoons, streams, or isolated from seasonally or intermittently waterlogged soils, and marine environments (Lara & Belbahri 2011)
Of the Saprolegniales “galaxy” (Fuller & Jaworsky 1987). Members of this genus possess all characteristics of Leptolegnia, with the exception of the presence of flagella
As Geolegnia helicoides is nested within Leptolegnia, it can be deduced that it emerged from a Leptolegnia-like ancestor, and the loss of its flagella is certainly a recent evolutionary event
Summary
Oomycetes are a group of fungal-like heterokonts that are often associated with freshwater and terrestrial habitats, such as marginal sites around lakes, lagoons, streams, or isolated from seasonally or intermittently waterlogged soils, and marine environments (Lara & Belbahri 2011). There are many free-living species, others are plant pathogens (e.g. Phytophthora species), while others are animal parasites, including one species (Pythium insidiosum) infecting humans, and another (Saprolegnia parasitica) parasitising fish in fish farms The specificity of these parasites is considered to vary between groups, being maximal in the case of obligate parasitic species such as Peronospora, where particular strains may have a very limited host range (Goker et al 2007). Within Oomycetes, these losses have occurred several times; within basal genera, in Haptoglossa, one clade out of three comprises only organisms that produce non-flagellated (aplanosporic) zoospores (Hakariya et al 2009), and Chlamydiosporum aplanosporum has been reported to lack a flagellate stage (Glockling & Beakes 2000). In Peronosporales, Myzocytiopsis subliformis has aplanosporic zoospores (Glockling & Beakes 2000), as well as other obligately pathogenic clades such as Hyaloperonospora, Bremia, and most Peronospora species (Beakes et al 2012) All these taxa include only obligate parasites (Lara & Belbahri 2011),. We investigated the phylogenetic position of the genus based on a new species isolated from mosquito larvae living in the water-holding tanks supporting the plant Aechmea distichantha in a subtropical forest area of northern Argentina (Misiones Province)
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