Molecular evidence for an independent origin of modern triserial planktonic foraminifera from benthic ancestors

Gallitellia vivans is the only Recent representative of the triserial planktonic foraminiferal family Guembelitriidae. The origin and evolution of this interesting albeit poorly known family are enigmatic. To elucidate the phylogenetic relationships between G. vivans and other planktonic foraminifera, we sequenced the small subunit ribosomal DNA (SSU rDNA) for comparison to our extensive database of planktonic and benthic species. Our analyses suggest that G. vivans represents a separate lineage of planktonic foraminifera, which branches close to the benthic rotaliids Stainforthia and Virgulinella. Both genera resemble Gallitellia in general morphological appearance, having elongate triserial tests at least in their early ontogenic stages. The divergence time of G. vivans is estimated at ca. 18 Ma (early Miocene), suggesting an origin independent from the Cretaceous and Paleogene triserial planktonic foraminifera. Our study thus indicates that modern triserial planktonic foraminifera are not related to the Cretaceous–Paleogene triserial species, and that the sporadic occurrences in the fossil record are not the result of poor preservation, but reflect multiple transitions from benthic to planktonic mode of life.     

Late Quaternary high uplift rates in northeastern Sicily: evidence from calcareous nannofossils and benthic and planktonic foraminifera

The northeastern part of Sicily is characterized by intense seismic activity. Several systems of faults have been recognized in Pliocene and Pleistocene sediments in the area and, in fact, estimates of uplift rates are among the highest recorded in Sicily and south Italy. We examined calcareous nannofossil and benthic and planktonic foraminifera assemblages from pelitic sediments of the Contrada Zura section (Barcellona Pozzo di Gotto Basin, Furnari village, Messina). The occurrence of Emiliania huxleyi, a coccolithophore species which appeared in the oceanic record about 270,000 years ago, is witness to the uniqueness of this outcrop, while the planktonic/benthic foraminifera ratio indicates a deep (slope) environment, in agreement with previous observations on macrobenthic and ostracod paleo-communities. Independently from the numerical estimate of the paleo-depth, there is little doubt that the occurrence of E. huxleyi in such sediments might be explained by exceptional uplift rates. Since resulting uplift rate estimates, between 3.2 and 5.5 mm/year, exceeded by far the regional, longer-term, vertical tectonic motion, we argue that a major contribution of coseismic displacement along active faults occurred in the Furnari area.     

Common evolutionary origin of planktonic and benthic nitrogen-fixing oscillatoriacean cyanobacteria from tropical oceans

The filamentous cyanobacteria belonging to the genus Hydrocoleum (Blennothrix) are among the most common mat-forming cyanobacteria in tropical oceans. We present here the evidence that these benthic cyanobacteria are morphologically and phylogenetically very close to the planktonic species of Trichodesmium. Genetic relationship was established independently with regard to sequences of the 16S rRNA gene, nifH gene, and phycocyanin and phycoerythrin intergenic spacers. The species of both genera formed a common distinct branch in phylogenetically reconstructed cyanobacterial trees, suggesting that the main constituents of cyanobacterial benthos and plankton have an early common origin and both represent major contributors to nitrogen budget of tropical oceans today as in the distant geological past.     

Molecular evidence for host-symbiont specificity in soritid foraminifera

Symbiosis between the dinoflagellate genus Symbiodinium and various invertebrates and protists is an ubiquitous phenomenon in shallow tropical and subtropical waters. Molecular studies undertaken on cnidarian symbionts revealed the presence of several distinctive lineages or subgeneric clades of Symbiodinium whose taxonomic level provides limited information about the specificity between invertebrate hosts and their symbionts. This contrasts with the finding of several Symbiodinium clades being present almost exclusively in foraminifera and belonging to the subfamily Soritinae. To test whether such specificity also exists at a lower taxonomic level within Soritinae, we obtained the SSU rDNA sequences from 159 soritid individuals collected in nine localities worldwide and representing all known morphospecies of this subfamily. For each individual, the symbionts were determined either by sequencing or by RFLP analysis. We distinguished 22 phylotypes of Soritinae in relation with a number of symbiont "groups" corresponding to 3 clades and 5 subclades of Symbiodinium. Among the 22 soritid phylotypes, 14 show strict symbiont specificity and only one was found to be a host for more than two "groups" of Symbiodinium. It is suggested that the strong host-symbiont specificity observed in Soritinae is a combined effect of a selective recognition mechanism, vertical transmission of symbionts, and biogeographical isolation.     

Basin-scale paleobiogeography and paleoecology: an example from Karpatian (Latest Burdigalian) benthic and planktonic foraminifera and calcareous nannofossils from the Central Paratethys

We present the paleobiogeography and ecology of benthic and planktonic foraminifera and calcareous nannoplankton during the Karpatian (Latest  Burdigalian) in the Austrian part of the Central Paratethys. Results are based on quantitative data of assemblages from the Molasse and Styrian Basins. Our data suggest that, although adjacent, the two basins underwent different paleoceanographic evolution during the Karpatian. Dysoxic bottom waters characterized the Molasse Basin, together with reducing environments, which produced the formation of pyritized levels. In the Styrian Basin, intense volcanic activity enriched surface waters in nutrient and produced strong primary productivity. Reduced planktonic foraminiferal abundance and dominance of agglutinated benthic forms in the Styrian Basin can be attributed to paleoceanographic conditions. The planktonic-depleted assemblages bias the paleodepth estimation by 100P(P + B) in the Styrian Basin and new tools for assessing paleodepth are needed. This study shows that paleobiogeography of foraminifera and calcareous nannoplankton is strictly related to local ecological conditions in enclosed basins and demonstrates that quantitative ecological studies are the best way to monitor the biogeographic evolution of enclosed basins.     

Paleoceanographic implications of smaller benthic and planktonic foraminifera from the Eocene Pazin Basin (Coastal Dinarides,Croatia)

Summary Smaller benthic and planktonic foraminifera from the clastic sediments of the Pazin Basin (Istria, Croatia) were studied in order to obtain more data about paleoceanographic conditions that existed in the Middle Eocene Dinaric foreland basin. The succession investigated corresponds to the Middle Eocene planktonic foraminiferal zones Globigerapsis kugleri/Morozovella aragonensis (P11), Morozovella lehneri (P12), and Globigerapsis beckmanni (P13). Benthic foraminiferal assemblages from the clastic succession are dominated by epifaunal trochospiral genera suggesting oligotrophic to mesotrophic conditions and moderately oxygenated bottom waters. Planktonic foraminiferal assemblages indicate mesotrophic to eutrophic conditions of the surface waters, with increased eutrophication in the upper part of the section. Water depth, based on the ratio between planktonic and epifaunal benthic foraminifera and on the recognized species of cosmopolitan benthic foraminifera, was estimated to have been between about 900 and 1200 m. The basin was elongated and open to marine currents on both sides allowing good circulation and ventilation of the bottom water.     

The recovery of benthic foraminifera and bacteria after disturbance: experimental evidence

In experiments with living meiofauna, sediment is often sieved prior to incubation. This is primarily to remove macrofauna and to increase reproducibility among replicates. At the onset of the experiment, the bacteria are severely disturbed. The effects of these disturbances are ill-known but might affect the outcome of the experimental meiofaunal and biogeochemical studies substantially.We compared the disturbance induced by sieving with the disturbance in microcosms from which meiofauna was removed by flushing with argon. Both experimental situations were compared with untreated cores and the field situation. Neither sieving nor flushing induced changes in the composition of the foraminiferal community compared with the natural situation; the four most abundant species found in the field remained dominant during the experiment. Sieving led to a pronounced disturbance in both bacterial as well as foraminiferal abundance patterns. The depth distribution of some species seems to be related to food, although bacteria might play a regulating role as well.     

A phylogeny of Cenozoic macroperforate planktonic foraminifera from fossil data

We present a complete phylogeny of macroperforate planktonic foraminifer species of the Cenozoic Era (∼65 million years ago to present). The phylogeny is developed from a large body of palaeontological work that details the evolutionary relationships and stratigraphic (time) distributions of species‐level taxa identified from morphology (‘morphospecies’). Morphospecies are assigned to morphogroups and ecogroups depending on test morphology and inferred habitat, respectively. Because gradual evolution is well documented in this clade, we have identified many instances of morphospecies intergrading over time, allowing us to eliminate ‘pseudospeciation’ and ‘pseudoextinction’ from the record and thereby permit the construction of a more natural phylogeny based on inferred biological lineages. Each cladogenetic event is determined as either budding or bifurcating depending on the pattern of morphological change at the time of branching. This lineage phylogeny provides palaeontologically calibrated ages for each divergence that are entirely independent of molecular data. The tree provides a model system for macroevolutionary studies in the fossil record addressing questions of speciation, extinction, and rates and patterns of evolution.     

Late Holocene deep-sea benthic foraminifera from the Sea of Marmara

The benthic foraminiferal assemblages of two cores from the late-Holocene, organic-carbon-rich and carbonate-poor, deep-sea sediments of the eastern depression of the Sea of Marmara have been studied. They were deposited under high level of primary productivity and poorly oxygenated bottom-water conditions; they show low diversity and are dominated by a group of species adapted to an infaunal life style with wide bathymetric distribution (ca. 70–2000 m) in the Mediterranean Sea. Oxygen deficiency down to about 0.5 ml/l does not seem adversely to affect the rate of reproduction of the dominant species belonging to Melonis, Chilostomella, buliminids, and bolivinitids. Their distribution is primarily controlled by substrate conditions.Faunal similarities with fossil assemblages in association with some late-Quaternary sapropels and related facies from the eastern Mediterranean basins suggest that they were deposited under palaeo-oceanographic conditions closely similar to those of the modern Sea of Marmara.     

Molecular evidence for the origin of plastids from a cyanobacterium-like ancestor

Summary The origin of plastids by either a single or multiple endosymbiotic event(s) and the nature of the progenitor(s) of plastids have been the subjects of much controversy. The sequence of the small subunit rRNA (Ssu rRNA) from the plastid of the chlorophyllc-containing algaCryptomonas is presented, allowing for the first time a comparison of this molecule from all of the major land plant and algal lineages. Using a distance matrix method, the phylogenetic relationships among representatives of these lineages have been inferred and the results indicate a common origin of plastids from a cyanobacterium-like ancestor. Within the plastid line of descent, there is a deep dichotomy between the chlorophyte/land plant lineage and the rhodophyte/chromophyte lineage, with the cyanelle ofCyanophora paradoxa forming the deepest branch in the latter group. Interestingly,Euglena gracilis and its colorless relativeAstasia longa are more related to the chromophytes than to the chlorophytes, raising once again the question of the origin of the euglenoid plastids.     

Multiple deep-water sources and trophic regimes in the latest Cretaceous deep sea: evidence from benthic foraminifera

Benthic foraminifera from 24 DSDP/ODP sites were investigated to assess their global horizontal and vertical distribution in the deep-sea environment at the end of the Cretaceous period. The samples analyzed are from the late Maastrichtian and within the planktic forammiferal Abathomphalus mayaroensis Zone from a wide range of oceans and paleolatitudes, including the low-latitude Sites 10 and 384 (Atlantic Ocean), 47, 171, 305, and 465 (Pacific Ocean), the mid-latitude Sites 20, 111, 356, 363, 516, 525, 527, 548, and 605 (Atlantic Ocean), 216, 217, and 758 (Indian Ocean), and the high-latitude Sites 208 (Pacific Ocean), 689, 698, 700, 738 and 750 (Southern Ocean).Correspondence analysis, based on the 75 most common taxa, shows a clear biogeographic trend along the first correspondence axis by arranging the sites in paleolatitudinal order. The assemblages from the Tethyan Realm (i.e., low latitudes) are marked by abundant heavily calcified buliminids (such as Bulimina incisa B. trinitatensis B. velascoensis, and Reussella szajnochae) and Aragonia spp., whereas high-latitude faunas are characterized by abundant Alabamina creta, Gyroidinoides quadratus, and Pullenia coryelli.The results indicate that the faunas at low and high latitudes, respectively, were influenced by quite different environmental conditions. This is based on the much higher abundance of infaunal morphotypes at low and mid latitudes compared to high latitudes, suggesting that the biogeographic trend found in the data set coincides with the trophic regime at the various sites. The results also provide support for the hypothesis that postulates two simultaneous sources and mechanisms for deep-water formation during the Late Cretaceous, including warm, saline deep water produced by evaporation at low (equatorial) latitudes in contrast to the formation of cold deep waters at high (southern) latitudes.     

Relative effect of taphonomy on calcification temperature estimates from fossil planktonic foraminifera

This paper explores the effects of preservation and taphonomy on the ultrastructure of recent and fossil (Quaternary and Neogene) Globigerinoides using scanning electron microscopy and thin section petrography. We show preservation states from: pristine (plankton tow) specimens that are “glassy”, have a microcrystalline test structure, and bear sharply defined interpore ridges with delicate spines; through core top and fossil specimens that have gametogenic calcite veneers of euhedral or lumpy deposits covering the interpore ridges and spine bases; to fossil material with extensive dissolution of the test wall and diagenetic calcite formed during shallow burial (less than 300 m below the sea floor). The latter produce a “grainy” texture to the test. Although we cannot unravel the precise effects of ecology and taphonomy on calcification temperature at every site, we show that for well-preserved fossil material with gametogenic calcite, temperature estimates are typically 2-3 °C cooler than modern sea surface, and are similar to those recorded using the δ¹⁸O of core top material from tropical latitudes. In contrast, at tropical sites with poor fossil preservation, estimates of calcification temperature are significantly cooler, sometimes by more than 10 °C than expected from present observations.     

Molecular evidence for a terrestrial origin of snakes

Biologists have debated the origin of snakes since the nineteenth century. One hypothesis suggests that snakes are most closely related to terrestrial lizards, and reduced their limbs on land. An alternative hypothesis proposes that snakes are most closely related to Cretaceous marine lizards, such as mosasaurs, and reduced their limbs in water. A presumed close relationship between living monitor lizards, believed to be close relatives of the extinct mosasaurs, and snakes has bolstered the marine origin hypothesis. Here, we show that DNA sequence evidence does not support a close relationship between snakes and monitor lizards, and thus supports a terrestrial origin of snakes.     

Late Quaternary deep and surface water mass evolution in the northeastern Indian Ocean inferred from carbon and oxygen isotopes of benthic and planktonic foraminifera

New planktonic and benthic foraminiferal stable isotope records from core YDY05 (northeastern Indian Ocean) provide new insights into paleoceanographic changes in the northeastern Indian Ocean since the last glacial period. The distinct δ¹⁸O decrease was observed since the beginning of the deglaciation to the mid-Holocene (∼8–6 kyr BP), possibly reflecting a reduction in surface salinity in the central Bay of Bengal (BoB) water, which probably resulted from strengthened precipitation, concurrent enhanced river discharge and rising sea-level, related to the intensification of Indian Summer Monsoon (ISM). Variations in benthic δ¹³C and δ¹³C_{Planktonic-Benthic} in our core site reflect significant variations in source water characteristics over the LGM-Holocene. The large δ¹³C_{Planktonic-Benthic} offset during the glacial period suggests a more sluggish deep water circulation, and lower δ¹³C_{Planktonic-Benthic} from the deglaciation to the Holocene suggests an enhanced deep water circulation in the central BoB. The drastic depletion in benthic δ¹³C during the glacial period suggests a significant reduction of North Atlantic Deep Water (NADW) intrusion and a progressive influx of Antarctic Bottom Water (AABW) and ¹²C-rich Circumpolar Deep Water (CDW) into the central BoB. In contrast, since the deglaciation, the central BoB experienced a drastically increased intrusion of better ventilated and ¹³C-rich NADW. The differences in benthic δ¹⁸O between the LGM section and the Holocene exceeds the ice volume effect by ∼0.5‰, providing further evidence that the deep water mass of the central BoB was influenced by the less dense NADW, instead of the AABW, since the last deglaciation.     

Morphology and microhabitat preferences of benthic foraminifera from the northwest Atlantic Ocean

The distribution of Rose Bengal stained calcareous benthic foraminifera was determined in six ☐ cores raised from water depths between 200 and 3000 m on the Nova Scotian continental margin and Gulf of Maine. The taxa can be separated into four microhabitats within the surficial sediments. Epifaunal taxa are generally found in the top cm, intermediate infaunal taxa are found from about 1 to 4 cm and deep infaunal taxa are found at > 4 cm sediment depth in at least one ☐ core. A fourth group, shallow infaunal taxa, is found in the top 2 cm and is inferred to be infaunal based on wall porosity characteristics and test shapes similar to infaunal taxa. The epifaunal, shallow infaunal and intermediate infaunal taxa maintain their positions within the sediments from core to core, whereas the deep infaunal taxa are found at progressively shallower sediment depths in cores within increasing organic carbon contents from shallower water depths.Each microhabitat category has distinct morphological characteristics. Epifaunal taxa have plano-covex or biconvex cross sections, trochospiral coiling and large pores absent or found on only one side. Shallow infaunal taxa have uniserial, triserial, or planispiral coiling, with surface ornamentation present on a number of taxa. The intermediate infaunal taxa have rounded peripheries, pores over the entire test and planispiral coiling, with the exception ofCibicidoides bradyi which has trochospiral coiling. The deep infaunal taxa have, in general, planispiral or triserial coiling with cylindrical or ovate shaped tests.     

Distribution and ecology of planktonic foraminifera from the seas around the Indonesian Archipelago

Planktonic foraminiferal assemblages in 50 core-top samples from the western and southern areas of the Indonesian Archipelago and 29 core tops retrieved northwest of Australia were grouped using cluster analysis. These assemblages make it possible to sub-divide the studied area in five provinces: 1/ the Banda/Java region (I); 2/ the Timor region (II); 3/ the Java upwelling region (III); 4/ the Indian monsoon Sumatra region (IV), and 5/ the NW Australia margin region (V). The foraminiferal assemblage groups reflect differences in sea-surface temperature, salinity, thermocline depth, and nutrient supply between these five provinces. These differences are related to surface circulation patterns. The carbonate dissolution is rather intense compared to that in other areas of the eastern Indian Ocean. Within the studied area, the strongest dissolution occurs in samples from the Java upwelling region, with the lysocline level rising above ∼2800 m. The increase in abundance of Globigerina bulloides at 10–8 ka BP in core SHI-9034 (the Java upwelling region) corresponds to the decrease in core SHI-9006 (the Banda/Java region) which indicates an intensification of upwelling in relation to a strengthened southeastern monsoon over the studied area.     

Molecular evidence from ascidians for the evolutionary origin of vertebrate cranial sensory placodes

Cranial sensory placodes are specialised areas of the head ectoderm of vertebrate embryos that contribute to the formation of the cranial sense organs and associated ganglia. Placodes are often considered a vertebrate innovation, and their evolution has been hypothesised as one key adaptation underlying the evolution of active predation by primitive vertebrates. Here, we review recent molecular evidence pertinent to understanding the evolutionary origin of placodes. The development of vertebrate placodes is regulated by numerous genes, including members of the Pax, Six, Eya, Fox, Phox, Neurogenin and Pou gene families. In the sea squirt Ciona intestinalis (a basal chordate and close relative of the vertebrates), orthologues of these genes are deployed in the development of the oral and atrial siphons, structures used for filter feeding by the sessile adult. Our interpretation of these findings is that vertebrate placodes and sea squirt siphon primordia have evolved from the same patches of specialised ectoderm present in the common ancestor of the chordates.     

Molecular evidence from Ciona intestinalis for the evolutionary origin of vertebrate sensory placodes

Cranial sensory placodes are focused areas of the head ectoderm of vertebrates that contribute to the development of the cranial sense organs and their associated ganglia. Placodes have long been considered a key character of vertebrates, and their evolution is proposed to have been essential for the evolution of an active predatory lifestyle by early vertebrates. Despite their importance for understanding vertebrate origins, the evolutionary origin of placodes has remained obscure. Here, we use a panel of molecular markers from the Six, Eya, Pax, Dach, FoxI, COE and POUIV gene families to examine the tunicate Ciona intestinalis for evidence of structures homologous to vertebrate placodes. Our results identify two domains of Ciona ectoderm that are marked by the genetic cascade that regulates vertebrate placode formation. The first is just anterior to the brain, and we suggest this territory is equivalent to the olfactory/adenohypophyseal placodes of vertebrates. The second is a bilateral domain adjacent to the posterior brain and includes cells fated to form the atrium and atrial siphon of adult Ciona. We show this bares most similarity to placodes fated to form the vertebrate acoustico-lateralis system. We interpret these data as support for the hypothesis that sensory placodes did not arise de novo in vertebrates, but evolved from pre-existing specialised areas of ectoderm that contributed to sensory organs in the common ancestor of vertebrates and tunicates.