The Influence of the Environment on Shell Morphology and Calcification in Planktonic Foraminifera

Ein genaueres Verständnis darüber, auf welche Weise Umweltstress die Morphologie einer Population beeinflusst, könnte sich als wertvolles Werkzeug für die Rekonstruktion vergangener Stress-Intensitäten und Umweltbedingungen herausstellen. Insbesondere könnte es hilfreich sein, den Zustand einer Population (inkl. der Vorhersage von Aussterbeereignissen) zu bestimmen. Morphometrische Studien eignen sich hier besser als Populations-Dynamik Ansätze, da letztere von den natürlicherweise großen Schwankungen der Populationsgröße beeinflusst werden. Kalzitisches marines Mikroplankton (z.B. planktonische Foraminiferen) sind ein ideales Modellsystem für solche Studien, da sie in hohen Häufigkeiten im fossilen Befund erhalten bleiben und ihre gekammerte Schale eine Rekonstruktion der gesamten Ontogenie zulässt. Ihr hervorragendes Fossilisationspotential erlaubt außerdem natürliche Experimente auf ökologisch wirksamen Zeitskalen zu untersuchen, die nicht im Labor simuliert werden könnten. Planktonische Foraminiferen werden bereits häufig für geochemische und Populations-Studien verwendet, um vergangene Umweltbedingungen zu rekonstruieren. Ihre Schalen-Morphologie und -Kalzifikation wurden jedoch bisher selten untersucht, obwohl sie potentiell nützlich sind um vergangene Umweltbedingungen und Foraminiferen-Phylogenie zu rekonstruieren und rezente Ökosysteme zu monitorieren. Durch ihren hohen Anteil an der weltweiten Karbonat-Produktion könnte eine umweltbedingte Änderung ihrer Schalen-Kalzifikation zudem das ozeanische Karbonatsystem stören. Diese Studie versucht daher den Einfluss von Umweltänderungen (inkl. Stress) auf die Biometrie von Foraminiferen zu untersuchen. Zu diesem Zweck wurden mehrere Foraminiferen-Arten aus zwei pleistozänen Sedimentkernen und einer Sediment-Fallenserie bezüglich des Umwelteinflusses auf deren Morphologie und Schalen-Kalzifikation untersucht. Die Kalzifikations-Intensität (Menge an vorhandenem Kalzit) ist generell positiv mit der Karbonat-Sättigung des Meerwassers korreliert. Unter konstanter Karbonat-Sättigung zeigen sich jedoch außerdem Spezies-spezifische Einflüsse von Temperatur und Produktivität auf die Kalzifikations-Intensität der Schalen, welche den Einfluss der Karbonat-Sättigung auf diesen Parameter vermutlich zu jeder Zeit modifizieren. Kryptische Speziation stellt zudem ein signifikantes Problem für Kalzifikationsstudien dar, da die Schalen-Kalzifikation auch zw. kryptischen Spezies die traditionell oft zusammengefasst wurden deutlich unterschiedlich ist. Die Schalen-Größe war in keinem Fall mit der Spezies-Häufigkeit korreliert, was man erwartet hätte, wenn Letztere ein Maß für optimale Umweltbedingungen wäre. Zudem zeigt auch die Schalen-Kalzifikation unterschiedliche Korrelationen mit der Spezies-Häufigkeit, so dass entweder die Spezies-Häufigkeit kein brauchbarer Indikator für optimale Umweltbedingungen ist, oder dass optimale Bedingungen die Schalen-Biometrie von Foraminiferen nicht einheitlich beeinflussen. Andere morphologische Parameter zeigten charakteristische Änderungen welche auf Umwelt-Stress zurückzuführen sind. Diese Trends resultierten sämtlich in deutlichen Änderungen der Populations-Morphologie, ausgelöst durch selektive Prozesse, im Rahmen ökologisch relevanter Zeit-Skalen. Nahezu lethale Stress-Intensitäten resultierten hierbei in einer Populations-Morphologie, die deutlich von der einer weniger gestressten Population abwich. Diese Studie konnte zeigen, dass Foraminiferen-Biometrie (trotz ihrer uni-zellulären Organisationsstufe) komplex auf Umweltänderungen reagiert. Die beobachteten Reaktionen werden vom Zusammenspiel der abiotischen Umwelt, biotischer Stress-Reaktionen und kryptischer Diversität beeinflusst, so dass weitere Studien notwendig sind um diese Probleme zu minimieren.Understanding the effect of environmental stress on the morphology of a population can be developed into a versatile tool to reconstruct stress levels. Such knowledge could help to reconstruct past environments and to predict the state of a population, including future extinction. Especially for the latter aspect, morphometrics could be a valuable alternative for population-dynamics approaches, which suffer from the naturally high variability of population sizes. Calcitic marine microplankton, such as planktonic Foraminifera, offers an excellent model system for such studies. Planktonic Foraminifera occur in high abundances in the fossil record and their chambered shells allow the reconstruction of individual morphologies during their entire ontogeny. Their excellent fossilisation potential further allows to study natural experiments, which occurred over ecologically effective timescales that would have been impossible to simulate during laboratory experiments. Planktonic Foraminifera have already been broadly applied for geochemical and population studies to reconstruct past environments. Their morphology and shell calcification have in contrast been subject to comparably few studies so far. This is unfortunate, since both parameters could be useful for past environmental reconstructions, recent environmental monitoring, and phylogenetic research. Since planktonic Foraminifera have a large share on the worldwide marine calcite deposition, environmentally induced changes in their shell calcification could furthermore significantly influence the oceanic carbon pump. This study therefore aims at a better understanding of the influence of changing environments, including results of environmental stress, on the biometry of planktonic Foraminifera. For this purpose, several foraminiferal species were investigated within three selected environmental settings: two Pleistocene sediment cores and one sediment trap series. The shell calcification intensity and morphology have been investigated in light of their relation to environmental forcing and biological stress. The shell calcification intensity (amount of calcite present in the adult shell) shows signs of a universal positive correlation with carbonate saturation of the sea water. When the carbonate saturation is kept nearly constant, however, it is evident that shell calcification intensity is also influenced by other factors like temperature and productivity. Those secondary influences act species-specific and are presumably able to mediate or modify the effects of carbonate saturation. It could further be shown that cryptic speciation is a severe problem for calcification studies, because shell calcification is already significantly different between pseudo-cryptic species that have been commonly pooled together in the past. Shell size was in no case related to species abundance, what would have been expected under the assumption that species are most abundant under optimal environmental conditions. Together with the fact that shell calcification intensity is also variably correlated to species abundance, this implies that either species abundance is no versatile proxy for optimal growth conditions, or that optimal conditions are not uniformly related to biometric traits. Other phenotypic traits were observed to show characteristic deviations in relationship to environmental stress. The observed trends all led to a clear change in population morphology over ecologically relevant timescales as result of natural selective patterns. In a community which is exposed to near-lethal stress levels, this can culminate in a unique morphology that is clearly different from that of a less stressed population. The obtained results imply that foraminiferal biometry, despite their unicellular level of organisation, reacts in complex ways toward changes in the environmental setting. Those reactions are complicated by the interplay of abiotic (environment) and biotic (stress) factors and the presence of hidden diversity. Further research is needed to minimize those problems

Community- and population-level response of marine plankton to stress exposure: learning from the past

The effects of stress exposure in marine plankton are difficult to assess directly, because it is hard to replicate realistic conditions in laboratory experiments and because the physiological changes and adaptations in response to stress exposure occur over times scales that cannot be covered by direct observations. A viable alternative is provided by studies of marine microfossils. Census counts of microfossil assemblages allow reconstructions of community-level changes, whilst biometric studies provide information on the reaction of populations to different levels of stres

Genetic and morphometric evidence for parallel evolution of the Globigerinella calida morphotype

Molecular genetic investigations of the highly abundant extant planktonic foraminifera plexus Globigerinella siphonifera/Globigerinella calida have recently shown this group to be the genetically most diverse one within planktonic foraminifera, separating it into 12 distinct genetic types belonging to three main genetic lineages. Independently, several morphological or physiological variants have been described within the group, but the correlation between the high genetic diversity and the phenotypic variability remains unclear. In this study, we combine genetic data with morphometric analyses of shell shape and porosity of genotyped individuals of the different genetic lineages. Our morphometric measurements suggest a differentiation of three morphotypes within the plexus, two of which possess the elongated chambers described as a typical trait of G. calida. These two morphotypes with elongated chambers are associated with two distinct genetic lineages. The G. calida morphology therefore appears to have evolved twice in parallel. Unexpectedly, we show that the two morphotypes with elongated chambers can be separated from each other by characters seen in the lateral view of their shells. This implies that the taxonomy of the extant members of the genus Globigerinella should be revised. A comparison with the original descriptions and type specimens of members of the genus shows that two genetic types of one major lineage correspond to G. calida. The second group with elongated chambers is associated with a recently diverged genetic type and we propose to reinstate the name Globigerinella radians for this distinct form. The remaining nine of the 12 genetic types correspond to the G. siphonifera morphology, and in the absence of evidence for morphological differentiation, they form a paraphyletic morpho-taxon. Our results highlight the prevalence of parallelism in the evolution of shell morphology in planktonic foraminifera even at the lowest level of relatedness represented by genetic types

Phylogeography of the tropical planktonic foraminifera lineage Globigerinella reveals isolation inconsistent with passive dispersal by ocean currents

Morphologically defined species of marine plankton often harbor a considerable level of cryptic diversity. Since many morphospecies show cosmopolitan distribution, an understanding of biogeographic and evolutionary processes at the level of genetic diversity requires global sampling. We use a database of 387 single-specimen sequences of the SSU rDNA of the planktonic foraminifera Globigerinella as a model to assess the biogeographic and phylogenetic distributions of cryptic diversity in marine microplankton on a global scale. Our data confirm the existence of multiple, well isolated genetic lineages. An analysis of their abundance and distribution indicates that our sampling is likely to approximate the actual total diversity. Unexpectedly, we observe an uneven allocation of cryptic diversity among the phylogenetic lineages. We show that this pattern is neither an artifact of sampling intensity nor a function of lineage age. Instead, we argue that it reflects an ongoing speciation process in one of the three major lineages. Surprisingly, four of the six genetic types in the hyperdiverse lineage are biogeographically restricted to the Indopacific. Their mutual co-occurrence and their hierarchical phylogenetic structure provide no evidence for an origin through sudden habitat fragmentation and their limitation to the Indopacific challenges the view of a global gene flow within the warm-water provinces. This phenomenon shows that passive dispersal is not sufficient to describe the distribution of plankton diversity. Rather, these organisms show differentiated distribution patterns shaped by species interactions and reflecting phylogenetic contingency with unique histories of diversification rates

Comments on the geological map of the Breitenberg area (Northern Calcareous Alps, Austria)

During two fieldtrips in June–July 2008 and June 2009 the geological structure of an 8 km2 large area between the Breitenberg and the St Wolfgangsee (Austria, Northern Calcareous Alps) was surveyed. The area—belonging to the Osterhorn Clod, a part of the Austroalpine—comprises mainly calcareous lithologies of Upper Triassic to Lower Cretaceous ages. The lithologies clearly show a general deepening of the basin throughout the Mesozoic. The lagoonal back reef sediments of the Triassic are overlain by basin-and-swell limestones of a moderate water depth of the Lower Jurassic and distal sediments of a deep basin of the Upper Jurassic/Lower Cretacoeus. The mapping area is characterised by a division into two parts, seperated by a major fault in between: (a) A northeastern part, in which folded Upper Jurassic and Lower Cretaceous sediments predominate, and (b) a southwestern part, comprising a large syncline of Triassic and Lower Jurassic deposits in the majority. The small scale tectonism mainly comprises brittle, rather than ductile deformation. Clefts and slickensides were used for a basical palaeostress analysis. Two deformation events could be reconstructed: (a) a N–S to NNE–SSW shortening that is responsible for most of the folding and faulting and (b) an E–W to ESE–WNW shortening that occured later at least in the northern mapping area and folded the fold axis of the first event. The fielddata were compiled into a geological map and cross sections of the Breitenberg and the northerly adjacent area

Calcareous Dinoflagellate Cysts from the Upper Hauterivian of the Clay Pit Frielingen (NW Germany) and their Palaeoecological Implications

25 samples of the clay pit Frielingen (Upper Hauterivian, North-West German Basin) were investigated concerning their assemblage of calcareous dinoflagellate cysts (3196 cysts altogether). Proportions of taxa, character traits of Obliquipithonelloideae, and the results of some statistical approaches were investigated throughout a succession of the Simbirskites discofalctus zone, which has already been well studied concerning both sedimentological and palaeontological features. The investigation revealed that the general transgressive trend during that time interval, that was already known (Haq et al. 1987, Lutat 1996, Mutterlose 1991) must be modified for the Frielingen area. The thick dark bed 118 seems to comprise a regressive time interval with considerably higher sea surface temperatures. The general sea surface temperature could be reconstructed as well: it shows three intervals of general cooling, interupted by intervals with rising sea surface temperatures. One distintcly warmer interval, in which bed 118 was deposited, represents a dark bed, that is commonly interpreted as being indicative for cooler surface waters (Mutterlose and Ruffell 1999). It is therefore necessary that the interpretation of dark-light-rhythms of Northern Germany concerning the palaeoenvironment is not to strictly simplified. Factors other than sea surface temperature seem to be important as well. The species Pirumella edgarii, as was found out, seems to favour time intervals with higher sediment input. A possibly newly discovered species (Orthopithonelloidea incertae sedis) might be indicative for rather similar conditions