The evolution of early Foraminifera

Self Cite

256

259

Benthic foraminifers inhabit a wide range of aquatic environments including open marine, brackish, and freshwater environments. Here we show that several different and diverse foraminiferal groups (miliolids, rotaliids, textulariids) and Gromia , another taxon also belonging to Rhizaria, accumulate and respire nitrates through denitrification. The widespread occurrence among distantly related organisms suggests an ancient origin of the trait. The diverse metabolic capacity of these organisms, which enables them to respire with oxygen and nitrate and to sustain respiratory activity even when electron acceptors are absent from the environment, may be one of the reasons for their successful colonization of diverse marine sediment environments. The contribution of eukaryotes to the removal of fixed nitrogen by respiration may equal the importance of bacterial denitrification in ocean sediments.

Section: Resultsmentioning

confidence: 55%

Widespread occurrence of nitrate storage and denitrification among Foraminifera andGromiida

Piña-Ochoa

Høgslund

Geslin

et al. 2009

Self Cite

256

259

“…However, 24-n-propylidenecholesterol is also found in sponges as well as the foraminiferan Allogromia laticollaris (36), which is part of the "Monothalamid" clade thought to have Neoproterozoic origins (37,38). The late emergence of algal 24-n-propylidenecholesterol (24-npc) is also consistent with the geological record.…”

Section: Stramenopiles IImentioning

confidence: 56%

Sterol and genomic analyses validate the sponge biomarker hypothesis

Gold

Grabenstatter

Mendoza

et al. 2016

119

121

Molecular fossils (or biomarkers) are key to unraveling the deep history of eukaryotes, especially in the absence of traditional fossils. In this regard, the sterane 24-isopropylcholestane has been proposed as a molecular fossil for sponges, and could represent the oldest evidence for animal life. The sterane is found in rocks ∼650-540 million y old, and its sterol precursor (24-isopropylcholesterol, or 24-ipc) is synthesized today by certain sea sponges. However, 24-ipc is also produced in trace amounts by distantly related pelagophyte algae, whereas only a few close relatives of sponges have been assayed for sterols. In this study, we analyzed the sterol and gene repertoires of four taxa (Salpingoeca rosetta, Capsaspora owczarzaki, Sphaeroforma arctica, and Creolimax fragrantissima), which collectively represent the major living animal outgroups. We discovered that all four taxa lack C 30 sterols, including 24-ipc. By building phylogenetic trees for key enzymes in 24-ipc biosynthesis, we identified a candidate gene (carbon-24/28 sterol methyltransferase, or SMT) responsible for 24-ipc production. Our results suggest that pelagophytes and sponges independently evolved C 30 sterol biosynthesis through clade-specific SMT duplications. Using a molecular clock approach, we demonstrate that the relevant sponge SMT duplication event overlapped with the appearance of 24-isopropylcholestanes in the Neoproterozoic, but that the algal SMT duplication event occurred later in the Phanerozoic. Subsequently, pelagophyte algae and their relatives are an unlikely alternative to sponges as a source of Neoproterozoic 24-isopropylcholestanes, consistent with growing evidence that sponges evolved long before the Cambrian explosion ∼542 million y ago.sponges | Porifera | sterols | steranes | Amorphea

“…5 for a schematic overview), even though they 1) have a different calcification pathway, 2) do not form a monophyletic group (32), and 3) have evolved their pathways at periods with contrasting seawater chemistries (8,33). Calcification in foraminifera was likely invented before or during the Cambrian radiation, when miliolid and the agglutinating foraminifera separated from each other (32). The agglutinating foraminifera secrete an organic matrix holding together a suite of particles, silicates or carbonates, of various sizes and shapes.…”

Section: Discussionmentioning

confidence: 99%

“…The evolution of the miliolid calcification pathway puts an upper limit to the time calcification was invented. The test morphology of Cyclogyra planorbis represents that of the common miliolid (32,37) and agglutinating (38) ancestor, dating back to the Cambrian. Since this species elevates the pH during calcification (Fig.…”

Section: Discussionmentioning

confidence: 99%

Foraminifera promote calcification by elevating their intracellular pH

Nooijer

Toyofuku²,

Kitazato³

2009

310

262

Surface seawaters are supersaturated with respect to calcite, but high concentrations of magnesium prevent spontaneous nucleation and growth of crystals. Foraminifera are the most widespread group of calcifying organisms and generally produce calcite with a low Mg content, indicating that they actively remove Mg 2؉ from vacuolized seawater before calcite precipitation. However, one order of foraminifera has evolved a calcification pathway, by which it produces calcite with a very high Mg content, suggesting that these species do not alter the Mg/Ca ratio of vacuolized seawater considerably. The cellular mechanism that makes it possible to precipitate calcite at high Mg concentrations, however, has remained unknown. Here we demonstrate that they are able to elevate the pH at the site of calcification by at least one unit above seawater pH and, thereby, overcome precipitation-inhibition at ambient Mg concentrations. A similar result was obtained for species that precipitate calcite with a low Mg concentration, suggesting that elevating the pH at the site of calcification is a widespread strategy among foraminifera to promote calcite precipitation. Since the common ancestor of these two groups dates back to the Cambrian, our results would imply that this physiological mechanism has evolved over half a billion years ago. Since foraminifera rely on elevating the intracellular pH for their calcification, our results show that ongoing ocean acidification can result in a decrease of calcite production by these abundant calcifyers.benthic foraminifera ͉ foraminiferal evolution ͉ ocean acidification A large variety of organisms that form skeletons of calciumcarbonate have evolved over the last half billion years. Some groups precipitate predominantly aragonite, such as scleractinian corals (1) and calcareous chlorophytes (2), others mostly calcite, such as foraminifera (3), coccolithophores (4), and corraline Rhodophytes (2), and some a chimera of the two (5,6). The geological prevalence of the different groups is thought to be caused by successions in sea water chemistry: periods with relatively high Ca 2ϩ concentrations and low Mg 2ϩ concentrations (i.e., with low Mg/Ca ratios) have favored organisms precipitating calcite, while periods with relatively high Mg/Ca ratios (e.g., during the Neogene) have favored those forming aragonite (7-9). For foraminifera, the relation between ocean chemistry and their evolution is less clear (10) and possibly obscured by the existence of different calcification strategies in this group.Calcifying foraminifera are commonly divided into two groups according to their test (i.e., shell) structure: miliolid and hyaline. Miliolids precipitate calcite in the form of needles with a length of 2-3 m within cytoplasmic vesicles (11, 12) (see: 13 for the only known exception in this taxon). Before chamber formation, these needles accumulate in the cell and form a new chamber after simultaneous transport outside the test and assembly within an organic matrix (14). The needles forming the outer lay...