Heterokont Predator Develorapax marinus gen. et sp. nov. – A Model of the Ochrophyte Ancestor

Abstract

Heterotrophic lineages of Heterokonta (or stramenopiles), in contrast to a single monophyletic group of autotrophs, Ochrophyta, form several clades that independently branch off the heterokont stem lineage. The nearest neighbors of Ochrophyta in the phylogenetic tree appear to be almost exclusively bacterivorous, whereas the hypothesis of plastid acquisition by the ancestors of the ochrophyte lineage suggests an ability to engulf eukaryotic alga. In line with this hypothesis, the heterotrophic predator at the base of the ochrophyte lineage may be regarded as a model for the ochrophyte ancestor. Here, we present a new genus and species of marine free-living heterotrophic heterokont Develorapax marinus, which falls into an isolated heterokont cluster, along with the marine flagellate Developayella elegans, and is able to engulf eukaryotic cells. Together with environmental sequences D. marinus and D. elegans form a class-level clade Developea nom. nov. represented by species adapted to different environmental conditions and with a wide geographical distribution. The position of Developea among Heterokonta in large-scale phylogenetic tree is discussed. We propose that members of the Developea clade represent a model for transition from bacterivory to a predatory feeding mode by selection for larger prey. Presumably, such transition in the grazing strategy is possible in the presence of bacterial biofilms or aggregates expected in eutrophic environment, and has likely occurred in the ochrophyte ancestor.

Chimeric origins of ochrophytes and haptophytes revealed through an ancient plastid proteome

“…Because oomycetes are the sister-group of ochrophytes (Aleoshin et al, 2016; Derelle et al, 2016), this suggests that our dataset retains useful phylogenetic signal.…”

“…For the cryptomonad, haptophyte and dinotom sequences, as plastid-targeted proteins from these lineages may be identified using targeting predictors trained on diatoms such as HECTAR (Aleoshin et al, 2016) and ASAFind (Gruber et al, 2015; Gschloessl et al, 2008), each of the HPPGs initially generated was enriched with plastid-targeted sequences from each cryptomonad, haptophyte and dinotom sub-category identified by in silico prediction with these programmes (Table S2- sheet 1; Table S3- sheet 1 [Dorrell et al, 2016]).…”

“…The ochrophytes include the diatoms, which are major primary producers in the ocean (Bowler et al, 2010; Armbrust et al, 2004), multicellular kelps, which serve as spawning grounds for marine animals (Cock et al, 2010) and the pelagophytes, microscopic algae of which some are known to form harmful blooms (Gobler et al, 2011) (Figure 1, panel A; Figure 1—figure supplement 1). The stramenopiles also contain many aplastidic and non-photosynthetic lineages (e.g., oomycetes), which diverge at the base of the ochrophytes and play important roles as pathogens and in microbial food webs (Aleoshin et al, 2016; Derelle et al, 2016) (Figure 1—figure supplement 1).

10.7554/eLife.23717.003Figure 1.Procedure for identification of conserved plastid-targeted proteins in ochrophytes.(Panel A ) shows a schematic unrooted ochrophyte tree, with the three major ochrophyte lineages (chrysista, hypogyristea, and diatoms) denoted by different coloured labels.

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Genome size of chrysophytes varies with cell size and nutritional mode

“…As chrysophytes branch within the Ochrophyta, which comprise the phototrophic Stramenopiles, it is likely that mixotrophic and heterotrophic chrysophytes evolved from a phototrophic ancestor (Cavalier-Smith 1999;Aleoshin et al 2016). A further evidence for this hypothesis is that the Synurophytes, which consist of only phototrophic representatives, branch relatively basal in a phylogenetic tree.…”

Microbial Diversity in the Eukaryotic SAR Clade: Illuminating the Darkness Between Morphology and Molecular Data

“…Roughly 30 000 species are recognized in the Open Tree Taxonomy within the Stramenopila, but as many as 1 000 000 species have been estimated to exist, and most of the biodiversity is believed as yet to be unidentified. Recent reports have consistently unveiled novel clades using a variety of sequencing and taxonomic approaches and largely focusing on marine habitats . Despite their importance as primary producers (fixing a considerable amount of CO 2 ) and in other biogeochemical cycles (e.g., nitrogen and sulfur cycling), there remains a lack of molecular information for most stramenopiles lineages, resulting in poor support for phylogenetic relationships along the backbone of this massive clade …”