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The present publication deals with recent palynological results of a relatively small interval of Muschelkalk and exposures of the overlying clay deposits in the Winterswijk quarries. For the first time the Lower Muschelkalk Member in the Netherlands could be independently dated as Bithynian (Anisian, Middle Triassic). Contrary to widely accepted opinions the overlying almost black clay deposit is not Liassic but Rhaetian in age and it is assigned to the Sleen Shale Formation. This marginal marine clay which pinches out to the south, is in turn overlain by a light gray, full-marine Lower-Oligocene clay of the Rupel Formation. An anomalous occurrence of Liassic clay is now attributed to subrosion of Röt salt followed by collapse of the overlying Muschelkalk, Rhaetian and Lias strata.

Summary The need for evolutionary studies on quantitative traits that integrate genetics is increasing. Studies on consistent individual differences in behavioural traits provide a good opportunity to do controlled experiments on the genetic mechanisms underlying the variation and covariation in complex behavioural traits. In this review we will highlight the contribution of genetic studies in animal personality research. We will start with reviewing the evidence that shows how much variation in animal personality traits is genetic, and connect this to knowledge from human personality studies. We will continue by considering the nature of that variation, its generation and maintenance. Finally we will point to further possibilities for studying the genetics of animal personalities. We will underline the importance of integrating both proximate and ultimate approaches when studying the evolution of animal personalities.

We analyzed fossil chironomids (nonbiting midges) and pollen in two lake-sediment records to reconstruct and quantify Holocene summer-temperature fluctuations in the European Alps. Chironomid and pollen records indicate five centennial-scale cooling episodes during the early- and mid-Holocene. The strongest temperature declines of ≈1°C are inferred at ≈10,700–10,500 and 8,200–7,600 calibrated 14 C years B.P., whereas other temperature fluctuations are of smaller amplitude. Two forcing mechanisms have been presented recently to explain centennial-scale climate variability in Europe during the early- and mid-Holocene, both involving changes in Atlantic thermohaline circulation. In the first mechanism, changes in meltwater flux from the North American continent to the North Atlantic are responsible for changes in the Atlantic thermohaline circulation, thereby affecting circum-Atlantic climate. In the second mechanism, solar variability is the cause of Holocene climatic fluctuations, possibly triggering changes in Atlantic thermohaline overturning. Within their dating uncertainty, the two major cooling periods in the European Alps are coeval with substantial changes in the routing of North American freshwater runoff to the North Atlantic, whereas quantitatively, our climatic reconstructions show a poor agreement with available records of past solar activity. Thus, our results suggest that, during the early- and mid-Holocene, freshwater-induced Atlantic circulation changes had stronger influence on Alpine summer temperatures than solar variability and that Holocene thermohaline circulation reductions have led to summer-temperature declines of up to 1°C in central Europe.

Within the framework of a palaeolimnological pilot study, the potential of sedimentary diatom assemblages for the reconstruction of the eutrophication history was studied in short sediment cores from five shallow lakes located in the Romanian Danube Delta. A total of 234 diatom taxa representing 57 genera could be identified but diatom assemblages are generally predominated by a few species only. Loss on ignition percentages, total diatom abundances and diatom downcore successions largely vary within the single sediment cores and between all five lakes. This suggests the presence of various lake environments within the Danube Delta, each characterized by lake-specific geomorphological, sedimentological, hydrological, and biological conditions. Highly variable depositional conditions are also confirmed by radiocesium measurements in two of the five cores suggesting distinct inter-lake differences in the sedimentation rate. Causes for the great intra-lake and inter-lake variability in diatom downcore successions are difficult to specify and may include changes in the physico-chemical conditions, aquatic vegetation cover, water depth, river influence, turbidity and inter-biotic interactions. However, based on this pilot study, it is likely that the spatial and temporal distribution of sedimentary diatom assemblages in Danube Delta lakes were not triggered by the trophic state. The delta lakes likely became meso- to eutrophic long before 1950, possibly during late-Holocene times.

The northwest Iberian ocean margin experiences seasonal upwelling of nutrient-rich water resulting in enhanced primary productivity. The quantitative organic-walled dinoflagellate cyst distribution and that of other palynomorphs has been determined in 37 box core-tops along three transects to trace the upwelling signal. Oligotrophic Impagidinium spp. represent the dominant offshore elements. Cysts of heterotrophic Protoperidinium spp. mainly occur in sediments of the seasonal upwelling area on the shelf and slope and show a sharp decrease offshore. The eutrophic autotrophic taxon Lingulodinium machaerophorum is also abundant in sediments of the seasonal upwelling area on the shelf and slope, and also decreases more offshore. Both relative as well as absolute numbers of these taxa may be used to trace the upwelling system despite potential taphonomic problems. Considering the overall similar environmental conditions with respect to the other two transects, the elevated palynomorph concentrations in the shielded Nazare Canyon samples may be seen to represent the actual fluxes of palynomorphs along the Iberian coast. If accepted, this would indicate a preservational and transport loss of cysts of an order of magnitude in other transects.

Stearoyl-CoA desaturase (SCD) in the bovine mammary gland introduces a cis-double bond at the ¿9 position in a wide range of fatty acids (FA). Several long-chain polyunsaturated fatty acids (PUFA) inhibit expression of SCD, but information on the effect of short-chain fatty acids on mammary SCD expression is scarce. We used a bovine mammary cell line (MAC-T) to assess the effect of acetic acid (Ac) and ß-hydroxybutyric acid (BHBA) in comparison with the effect of various long-chain fatty acids on the mRNA expression of the lipogenic enzymes SCD, acetyl-CoA carboxylase (ACACA), fatty acid synthase (FASN) and their associated gene regulatory proteins sterol regulatory element binding transcription factor 1 (SREBF1), insulin-induced gene 1 protein (INSIG1) and peroxisome proliferator-activated receptor alpha (PPARA)and peroxisome proliferator-activated receptor delta (PPARD) by quantitative real-time PCR. MAC-T cells were treated for 12 h without FA additions (CON) or with either 5 mM Ac, 5 mM BHBA, a combination of 5 mM Ac + 5 mM BHBA, 100 µM C16:0, 100 µM C18:0, 100 µM C18:1 cis-9, 100 µM C18:1 trans-11, 100 µM C18:2 cis-9,12 or 100 µM C18:3 cis-9,12,15. Compared with control, mRNA expression of SCD1 was increased by Ac (+61%) and reduced by C18:1 cis-9 (-61%), C18:2 cis-9,12 (-84%) and C18:3 cis-9,12,15 (-88%). In contrast to native bovine mammary gland tissue, MAC-T cells did not express SCD5. Expression of ACACA was increased by Ac (+44%) and reduced by C18:2 cis-9,12 (-48%) and C18:3 cis-9,12,15 (-49%). Compared with control, FASN expression was not significantly affected by the treatments. The mRNA level of SREBF1 was not affected by Ac or BHBA, but was reduced by C18:1 cis-9 (-44%), C18:1 trans-11 (-42%), C18:2 cis-9,12 (-62%) and C18:3 cis-9,12,15 (-68%) compared with control. Expression of INSIG1 was downregulated by C18:0 (-37%), C18:1 cis-9 (-63%), C18:1 trans-11 (-53%), C18:2 cis-9,12 (-81%) and C18:3 cis-9,12,15 (-91%). Both PPARA and PPARD expression were not significantly affected by the treatments. Our results show that Ac upregulated mRNA expression of SCD1 and ACACA in MAC-T cells. The opposite effect of the PUFA C18:2 cis-9,12 and C18:3 cis-9,12,15 on the these genes and the failure of Ac to mimic the PUFA-inhibited SREBF1 and INSIG1 mRNA expression, suggest that Ac can stimulate mammary lipogenesis via a transcriptional regulatory mechanism different from PUFA.

Stearoyl-CoA desaturase (SCD) is an important enzyme in the bovine mammary gland, where it inserts a cis-double bond at the ¿9 position in a wide range of fatty acids. Investigating SCD expression in the bovine mammary gland generally requires invasive biopsy to obtain mammary tissue. The aim of this study was to evaluate the use of milk somatic cells as a non-invasive alternative to biopsy for measuring mammary SCD expression in dairy cows. Both milk somatic cells and mammary tissue were collected from 14 Holstein-Friesian cows and used for analysis of SCD expression by real-time PCR. The SCD5 mRNA levels in mammary tissue compared with SCD1 were low, and for several milk somatic cell samples, SCD5 expression was even below the limit of detection. A significant relationship was found between SCD1 expression in milk somatic cells and in mammary tissue. In addition, SCD1 expression in milk somatic cells was significantly related to ¿9-desaturase indices in milk, which are commonly used as an indicator of SCD1 activity within the mammary gland. Our study showed that milk somatic cells can be used as a source of mRNA to study SCD1 expression in dairy cows, offering a non-invasive alternative to mammary tissue samples obtained by biopsy.

A comparative non-ruminant species view of the contribution of the large intestinal metabolism to inaccuracies in nitrogen and amino acid absorption measurements is provided to assess potential implications for the determination of crude protein/amino acid digestibility in adult humans consuming lower digestible protein sources. Most of the amino acids in the hindgut are constituents of the microorganisms and significant microbial metabolism of dietary and endogenous amino acids occurs. Bacterial metabolism of nitrogen-containing compounds leads to a significant disappearance of nitrogen in the large intestine. Literature data show that some 79 % of the nitrogen entering the large intestine of the horse is absorbed. For dogs, sows, and growing pigs these estimates are 49, 34 and 16 %, respectively. The coefficient of gut differentiation of humans compares closely to that of dogs while the coefficient of fermentation in humans is the lowest of all non-ruminant species and closest to that of cats and dogs. Large intestinal digesta transit times of humans compare closest to adult dogs. Significant amino acid metabolism has been shown to occur in the large intestine of the adult dog. Use of the growing pig as an animal model is likely to underestimate the fermentation of amino acids in the human large intestine. Based on the significant degree of fermentation of nitrogen-containing components in the large intestine of several non-ruminant species, it can be expected that determination of amino acid digestibility at a faecal level in humans consuming low quality proteins would not provide accurate estimates of the amino acids absorbed by the intestine.

Across vertebrates, spermatogenesis is under the endocrine control of two hormones, follicle-stimulating hormone (FSH) and androgens; the testicular production and secretion of the latter are controlled by luteinizing hormone. In fish, also the strong steroidogenic potency of Fsh should be taken into consideration indicating that a large part of Fsh action in fish spermatogenesis is mediated by androgens. In the studies encompassing this thesis, we aimed at elucidating the mechanisms, by which FSH and especially androgens regulate adult spermatogenesis with particular interest for the spermatogonial phase. Zebrafish was chosen as the experimental animal model. First, our studies identified 11-ketotestosterone (11-KT) as the main end product of the androgen synthesis pathway in zebrafish testis. Together with testosterone, 11-KT binds to and activates the zebrafish Ar at physiologically relevant concentrations. Subsequently, our developed experimental models revealed that all stages of spermatogenesis are dependent of androgens, and that the spermatogonial phase is particularly sensitive. In an in vitro model, an organ culture system for adult zebrafish testis, complete spermatogenesis was supported in the presence of 11-KT. Even more, a higher proportion of type A spermatogonia proliferated and differentiated to commit to the transformation process towards becoming spermatozoa. In contrast, in the absence of 11-KT spermatogenesis in the same testis culture system became depleted. This relates very well to the spontaneous and rapid downfall of the steroidogenic system under basal culture conditions. An in vivo model for oestrogen-induced androgen insufficiency revealed a marked inhibition of spermatogonial proliferation and differentiation, and germ cell depletion became more prominent with their progressive differentiation. The mechanism behind the inhibition of spermatogenesis in this in vivo model is negative oestrogenic feedback on the brain-pituitary system causing a reduction of expression of factors responsible for androgen synthesis, ultimately leading to reduced testicular androgen production. Sertoli cells express functional receptors for both FSH and androgens, in contrast to germ cells. We showed that zebrafish Sertoli cells contacting type A spermatogonia express high levels of ar transcript. It is thought that Sertoli cells mediate androgen or Fsh action by regulating the secretion of paracrine factors, which in turn influence spermatogonial differentiation. We showed that the gonad-specific fish representative of such a group of paracrine factors, the insulin-like growth factors (i.e. igf3), was highly expressed by zebrafish Sertoli cells contacting type A spermatogonia. Furthermore, its mRNA expression was positively modulated by both androgens as well as Fsh, for the latter independent of its steroidogenic potential. Studies on the action of a commercially available recombinant fish Igf protein (i.e. Igf1) on zebrafish spermatogenesis in vitro revealed a stimulatory effect on the proliferation of spermatogonia and their entrance into meiosis, and demonstrated the ability to enhance 11-KT-stimulated spermatogenesis. The present thesis expanded the knowledge on the sites of action and the mechanisms of endocrine control of adult fish spermatogenesis. In addition, novel experimental models to investigate the endocrine control of adult spermatogenesis were developed. Conclusively, zebrafish were proven to be an exciting animal model to investigate endocrine control mechanisms of the spermatogonial phase.

Across vertebrates, spermatogenesis is under the endocrine control of two hormones, follicle-stimulating hormone (FSH) and androgens; the testicular production and secretion of the latter are controlled by luteinizing hormone. In fish, also the strong steroidogenic potency of Fsh should be taken into consideration indicating that a large part of Fsh action in fish spermatogenesis is mediated by androgens. In the studies encompassing this thesis, we aimed at elucidating the mechanisms, by which FSH and especially androgens regulate adult spermatogenesis with particular interest for the spermatogonial phase. Zebrafish was chosen as the experimental animal model. First, our studies identified 11-ketotestosterone (11-KT) as the main end product of the androgen synthesis pathway in zebrafish testis. Together with testosterone, 11-KT binds to and activates the zebrafish Ar at physiologically relevant concentrations. Subsequently, our developed experimental models revealed that all stages of spermatogenesis are dependent of androgens, and that the spermatogonial phase is particularly sensitive. In an in vitro model, an organ culture system for adult zebrafish testis, complete spermatogenesis was supported in the presence of 11-KT. Even more, a higher proportion of type A spermatogonia proliferated and differentiated to commit to the transformation process towards becoming spermatozoa. In contrast, in the absence of 11-KT spermatogenesis in the same testis culture system became depleted. This relates very well to the spontaneous and rapid downfall of the steroidogenic system under basal culture conditions. An in vivo model for oestrogen-induced androgen insufficiency revealed a marked inhibition of spermatogonial proliferation and differentiation, and germ cell depletion became more prominent with their progressive differentiation. The mechanism behind the inhibition of spermatogenesis in this in vivo model is negative oestrogenic feedback on the brain-pituitary system causing a reduction of expression of factors responsible for androgen synthesis, ultimately leading to reduced testicular androgen production. Sertoli cells express functional receptors for both FSH and androgens, in contrast to germ cells. We showed that zebrafish Sertoli cells contacting type A spermatogonia express high levels of ar transcript. It is thought that Sertoli cells mediate androgen or Fsh action by regulating the secretion of paracrine factors, which in turn influence spermatogonial differentiation. We showed that the gonad-specific fish representative of such a group of paracrine factors, the insulin-like growth factors (i.e. igf3), was highly expressed by zebrafish Sertoli cells contacting type A spermatogonia. Furthermore, its mRNA expression was positively modulated by both androgens as well as Fsh, for the latter independent of its steroidogenic potential. Studies on the action of a commercially available recombinant fish Igf protein (i.e. Igf1) on zebrafish spermatogenesis in vitro revealed a stimulatory effect on the proliferation of spermatogonia and their entrance into meiosis, and demonstrated the ability to enhance 11-KT-stimulated spermatogenesis. The present thesis expanded the knowledge on the sites of action and the mechanisms of endocrine control of adult fish spermatogenesis. In addition, novel experimental models to investigate the endocrine control of adult spermatogenesis were developed. Conclusively, zebrafish were proven to be an exciting animal model to investigate endocrine control mechanisms of the spermatogonial phase.

Across vertebrates, spermatogenesis is under the endocrine control of two hormones, follicle-stimulating hormone (FSH) and androgens; the testicular production and secretion of the latter are controlled by luteinizing hormone. In fish, also the strong steroidogenic potency of Fsh should be taken into consideration indicating that a large part of Fsh action in fish spermatogenesis is mediated by androgens. In the studies encompassing this thesis, we aimed at elucidating the mechanisms, by which FSH and especially androgens regulate adult spermatogenesis with particular interest for the spermatogonial phase. Zebrafish was chosen as the experimental animal model. First, our studies identified 11-ketotestosterone (11-KT) as the main end product of the androgen synthesis pathway in zebrafish testis. Together with testosterone, 11-KT binds to and activates the zebrafish Ar at physiologically relevant concentrations. Subsequently, our developed experimental models revealed that all stages of spermatogenesis are dependent of androgens, and that the spermatogonial phase is particularly sensitive. In an in vitro model, an organ culture system for adult zebrafish testis, complete spermatogenesis was supported in the presence of 11-KT. Even more, a higher proportion of type A spermatogonia proliferated and differentiated to commit to the transformation process towards becoming spermatozoa. In contrast, in the absence of 11-KT spermatogenesis in the same testis culture system became depleted. This relates very well to the spontaneous and rapid downfall of the steroidogenic system under basal culture conditions. An in vivo model for oestrogen-induced androgen insufficiency revealed a marked inhibition of spermatogonial proliferation and differentiation, and germ cell depletion became more prominent with their progressive differentiation. The mechanism behind the inhibition of spermatogenesis in this in vivo model is negative oestrogenic feedback on the brain-pituitary system causing a reduction of expression of factors responsible for androgen synthesis, ultimately leading to reduced testicular androgen production. Sertoli cells express functional receptors for both FSH and androgens, in contrast to germ cells. We showed that zebrafish Sertoli cells contacting type A spermatogonia express high levels of ar transcript. It is thought that Sertoli cells mediate androgen or Fsh action by regulating the secretion of paracrine factors, which in turn influence spermatogonial differentiation. We showed that the gonad-specific fish representative of such a group of paracrine factors, the insulin-like growth factors (i.e. igf3), was highly expressed by zebrafish Sertoli cells contacting type A spermatogonia. Furthermore, its mRNA expression was positively modulated by both androgens as well as Fsh, for the latter independent of its steroidogenic potential. Studies on the action of a commercially available recombinant fish Igf protein (i.e. Igf1) on zebrafish spermatogenesis in vitro revealed a stimulatory effect on the proliferation of spermatogonia and their entrance into meiosis, and demonstrated the ability to enhance 11-KT-stimulated spermatogenesis. The present thesis expanded the knowledge on the sites of action and the mechanisms of endocrine control of adult fish spermatogenesis. In addition, novel experimental models to investigate the endocrine control of adult spermatogenesis were developed. Conclusively, zebrafish were proven to be an exciting animal model to investigate endocrine control mechanisms of the spermatogonial phase.

Puberty is the process by which a juvenile acquires for the first time the capacity to reproduce sexually, a critical basis for the conservation of a species. In general, the biological processes constituting the first gonadal maturation and the mechanisms involved in this process are similar among vertebrates. Internal and/or external signals trigger the secretion of gonadotropin-releasing hormone (Gnrh) by neurosecretory neurons in the ventral forebrain, and Gnrh stimulates the synthesis and secretion of two pituitary hormones, the gonadotropins known as follicle-stimulating hormone (Fsh) and luteinizing hormone (Lh). These two glycoproteins are the major hormones regulating the remarkable structural and functional changes occurring in the pubertal gonads during the activation of the two principal gonad tasks, the production of gametes and sex steroids. In context with the male-biased problems of precocious testis maturation in farmed cod, the present thesis focuses on male puberty. Pituitary fsh gene expression starts to increase at the beginning of testis development (proliferation of spermatogonia), followed by a slow elevation in testosterone plasma levels. With rapidly continuing spermatogenesis, which takes place in a peculiar spatio-temporal organization in the testicular lobes, high gonado-somatic indexes of up to 16 % are attained. Close to spawning, testosterone and 11-ketotestosterone, two potent ligands for the cod androgen receptor (Ar), peak in parallel with pituitary lh and testicular lhr (Lh receptor) gene expression, while fshr seems to be expressed in a constitutively manner in the cod testis. It is possible that attaining high plasma levels of potent androgens involves an auto-protective manner of androgen production, where weak Ar ligands, such as androstenedione and 11-ketoandrostenedione, are produced by the testis, thereby avoiding androgen-induced down-regulation of steroidogenic enzymes, while conversion to 17߭hydroxylated, potent androgens would occur in extra-gonadal tissues. After spawning, pituitary gonadotropin expression and androgens plasma levels decrease to basal levels, and only non-proliferating type A spermatogonia are present as germ cell population in the testis, conditions characterizing the spent condition. Like in many other teleost fish living at high latitudes, seasonally changing parameters are crucial environmental cues for cod. In this context, the present thesis also provides important information on the effects of constant light, a commonly used tool to prevent gonad maturation in cod farms, on the activity of the pituitary-testis axis. For instance, we found that even under constant light conditions, some males can escape the light-mediated inhibition and develop, associated with elevated pituitary lh and testicular ar expressions, spermatogenic activity including sperm production, albeit in a qualitatively and quantitatively compromised manner.

Puberty is the process by which a juvenile acquires for the first time the capacity to reproduce sexually, a critical basis for the conservation of a species. In general, the biological processes constituting the first gonadal maturation and the mechanisms involved in this process are similar among vertebrates. Internal and/or external signals trigger the secretion of gonadotropin-releasing hormone (Gnrh) by neurosecretory neurons in the ventral forebrain, and Gnrh stimulates the synthesis and secretion of two pituitary hormones, the gonadotropins known as follicle-stimulating hormone (Fsh) and luteinizing hormone (Lh). These two glycoproteins are the major hormones regulating the remarkable structural and functional changes occurring in the pubertal gonads during the activation of the two principal gonad tasks, the production of gametes and sex steroids. In context with the male-biased problems of precocious testis maturation in farmed cod, the present thesis focuses on male puberty. Pituitary fsh gene expression starts to increase at the beginning of testis development (proliferation of spermatogonia), followed by a slow elevation in testosterone plasma levels. With rapidly continuing spermatogenesis, which takes place in a peculiar spatio-temporal organization in the testicular lobes, high gonado-somatic indexes of up to 16 % are attained. Close to spawning, testosterone and 11-ketotestosterone, two potent ligands for the cod androgen receptor (Ar), peak in parallel with pituitary lh and testicular lhr (Lh receptor) gene expression, while fshr seems to be expressed in a constitutively manner in the cod testis. It is possible that attaining high plasma levels of potent androgens involves an auto-protective manner of androgen production, where weak Ar ligands, such as androstenedione and 11-ketoandrostenedione, are produced by the testis, thereby avoiding androgen-induced down-regulation of steroidogenic enzymes, while conversion to 17߭hydroxylated, potent androgens would occur in extra-gonadal tissues. After spawning, pituitary gonadotropin expression and androgens plasma levels decrease to basal levels, and only non-proliferating type A spermatogonia are present as germ cell population in the testis, conditions characterizing the spent condition. Like in many other teleost fish living at high latitudes, seasonally changing parameters are crucial environmental cues for cod. In this context, the present thesis also provides important information on the effects of constant light, a commonly used tool to prevent gonad maturation in cod farms, on the activity of the pituitary-testis axis. For instance, we found that even under constant light conditions, some males can escape the light-mediated inhibition and develop, associated with elevated pituitary lh and testicular ar expressions, spermatogenic activity including sperm production, albeit in a qualitatively and quantitatively compromised manner.

Puberty is the process by which a juvenile acquires for the first time the capacity to reproduce sexually, a critical basis for the conservation of a species. In general, the biological processes constituting the first gonadal maturation and the mechanisms involved in this process are similar among vertebrates. Internal and/or external signals trigger the secretion of gonadotropin-releasing hormone (Gnrh) by neurosecretory neurons in the ventral forebrain, and Gnrh stimulates the synthesis and secretion of two pituitary hormones, the gonadotropins known as follicle-stimulating hormone (Fsh) and luteinizing hormone (Lh). These two glycoproteins are the major hormones regulating the remarkable structural and functional changes occurring in the pubertal gonads during the activation of the two principal gonad tasks, the production of gametes and sex steroids. In context with the male-biased problems of precocious testis maturation in farmed cod, the present thesis focuses on male puberty. Pituitary fsh gene expression starts to increase at the beginning of testis development (proliferation of spermatogonia), followed by a slow elevation in testosterone plasma levels. With rapidly continuing spermatogenesis, which takes place in a peculiar spatio-temporal organization in the testicular lobes, high gonado-somatic indexes of up to 16 % are attained. Close to spawning, testosterone and 11-ketotestosterone, two potent ligands for the cod androgen receptor (Ar), peak in parallel with pituitary lh and testicular lhr (Lh receptor) gene expression, while fshr seems to be expressed in a constitutively manner in the cod testis. It is possible that attaining high plasma levels of potent androgens involves an auto-protective manner of androgen production, where weak Ar ligands, such as androstenedione and 11-ketoandrostenedione, are produced by the testis, thereby avoiding androgen-induced down-regulation of steroidogenic enzymes, while conversion to 17߭hydroxylated, potent androgens would occur in extra-gonadal tissues. After spawning, pituitary gonadotropin expression and androgens plasma levels decrease to basal levels, and only non-proliferating type A spermatogonia are present as germ cell population in the testis, conditions characterizing the spent condition. Like in many other teleost fish living at high latitudes, seasonally changing parameters are crucial environmental cues for cod. In this context, the present thesis also provides important information on the effects of constant light, a commonly used tool to prevent gonad maturation in cod farms, on the activity of the pituitary-testis axis. For instance, we found that even under constant light conditions, some males can escape the light-mediated inhibition and develop, associated with elevated pituitary lh and testicular ar expressions, spermatogenic activity including sperm production, albeit in a qualitatively and quantitatively compromised manner.

In the testis a complex process, called spermatogenesis, generates millions of spermatozoa per day. At the start of this process there are spermatogonial stem cells (SSCs) that have the ability to divide either into new stem cells (self-renewal) or daughter cells committed to develop into spermatozoa (differentiation). SSCs are the only cells among the adult stem cell systems capable of transmitting genetic information to future generations. This offers possibilities for in vitro SSC manipulation for instance with the goal of transferring relevant genes across bovine herds. As bovine species have a long generation interval, a system through which genes could be delivered to cattle through SSCs would prove effective and time-saving. SSCs and the first generations of differentiating spermatogonia are morphologically indistinguishable and are called type A spermatogonia. Therefore, we started with finding out at which age type A spermatogonia could be best isolated. We first investigated the onset of spermatogenesis in Brahman bulls, a widely used breed of Asian origin, and compared our results with the available information on European breeds. The best time to obtain A spermatogonia from European and Asian breeds was found to be the age period between the start of spermatogenesis (appearance of the first spermatogonia) to the age at which the first spermatocytes are formed. During this period the purity of the spermatogonia is optimal since no other differentiating germ cells have yet appeared. We then developed a culture system to propagate these A spermatogonia. Using StemPro medium and adding a number of growth factors we could successfully culture the cells for weeks. The usefulness of adding the growth factors GDNF, EGF, LIF and FGF2 was studied. Each of these growth factors was found to exert a specific effect on the culture. EGF, LIF and FGF2 specifically affected the somatic cells in culture while GDNF had a pronounced effect on the numbers of single type A spermatogonia, presumably SSCs. Overall the best results were obtained when the culture medium contained all four growth factors. A 365-fold increase in the numbers of A spermatogonia was found after 4 weeks of culture. To proof that GDNF actually stimulated the propagation of SSCs, a spermatogonial stem cell transplantation assay was carried out in which the cultured cells were transplanted into recipient mouse testes. The transplanted bovine SSCs colonized these testes and the extent of the colonization was taken as a measure of the numbers of bovine SSCs transplanted. A 10.000–fold increase in SSC numbers was found after a culture of 4.5 weeks. During culture in a liquid medium, many germ cells are lost during medium refreshments. To prevent this cell loss, we tested a semisolid culture medium (agar). Indeed, with an agar medium four times as many bovine spermatogonial colonies were able to grow. This indicates that it will be worthwhile to study the advantages of using an agar medium in further detail. In conclusion, we have developed a culture system for the propagation of bovine SSC which will allow further experimentation/manipulation and will eventually lead to more efficient ways of genetical improvement of cattle populations.

In the testis a complex process, called spermatogenesis, generates millions of spermatozoa per day. At the start of this process there are spermatogonial stem cells (SSCs) that have the ability to divide either into new stem cells (self-renewal) or daughter cells committed to develop into spermatozoa (differentiation). SSCs are the only cells among the adult stem cell systems capable of transmitting genetic information to future generations. This offers possibilities for in vitro SSC manipulation for instance with the goal of transferring relevant genes across bovine herds. As bovine species have a long generation interval, a system through which genes could be delivered to cattle through SSCs would prove effective and time-saving. SSCs and the first generations of differentiating spermatogonia are morphologically indistinguishable and are called type A spermatogonia. Therefore, we started with finding out at which age type A spermatogonia could be best isolated. We first investigated the onset of spermatogenesis in Brahman bulls, a widely used breed of Asian origin, and compared our results with the available information on European breeds. The best time to obtain A spermatogonia from European and Asian breeds was found to be the age period between the start of spermatogenesis (appearance of the first spermatogonia) to the age at which the first spermatocytes are formed. During this period the purity of the spermatogonia is optimal since no other differentiating germ cells have yet appeared. We then developed a culture system to propagate these A spermatogonia. Using StemPro medium and adding a number of growth factors we could successfully culture the cells for weeks. The usefulness of adding the growth factors GDNF, EGF, LIF and FGF2 was studied. Each of these growth factors was found to exert a specific effect on the culture. EGF, LIF and FGF2 specifically affected the somatic cells in culture while GDNF had a pronounced effect on the numbers of single type A spermatogonia, presumably SSCs. Overall the best results were obtained when the culture medium contained all four growth factors. A 365-fold increase in the numbers of A spermatogonia was found after 4 weeks of culture. To proof that GDNF actually stimulated the propagation of SSCs, a spermatogonial stem cell transplantation assay was carried out in which the cultured cells were transplanted into recipient mouse testes. The transplanted bovine SSCs colonized these testes and the extent of the colonization was taken as a measure of the numbers of bovine SSCs transplanted. A 10.000–fold increase in SSC numbers was found after a culture of 4.5 weeks. During culture in a liquid medium, many germ cells are lost during medium refreshments. To prevent this cell loss, we tested a semisolid culture medium (agar). Indeed, with an agar medium four times as many bovine spermatogonial colonies were able to grow. This indicates that it will be worthwhile to study the advantages of using an agar medium in further detail. In conclusion, we have developed a culture system for the propagation of bovine SSC which will allow further experimentation/manipulation and will eventually lead to more efficient ways of genetical improvement of cattle populations.

In the testis a complex process, called spermatogenesis, generates millions of spermatozoa per day. At the start of this process there are spermatogonial stem cells (SSCs) that have the ability to divide either into new stem cells (self-renewal) or daughter cells committed to develop into spermatozoa (differentiation). SSCs are the only cells among the adult stem cell systems capable of transmitting genetic information to future generations. This offers possibilities for in vitro SSC manipulation for instance with the goal of transferring relevant genes across bovine herds. As bovine species have a long generation interval, a system through which genes could be delivered to cattle through SSCs would prove effective and time-saving. SSCs and the first generations of differentiating spermatogonia are morphologically indistinguishable and are called type A spermatogonia. Therefore, we started with finding out at which age type A spermatogonia could be best isolated. We first investigated the onset of spermatogenesis in Brahman bulls, a widely used breed of Asian origin, and compared our results with the available information on European breeds. The best time to obtain A spermatogonia from European and Asian breeds was found to be the age period between the start of spermatogenesis (appearance of the first spermatogonia) to the age at which the first spermatocytes are formed. During this period the purity of the spermatogonia is optimal since no other differentiating germ cells have yet appeared. We then developed a culture system to propagate these A spermatogonia. Using StemPro medium and adding a number of growth factors we could successfully culture the cells for weeks. The usefulness of adding the growth factors GDNF, EGF, LIF and FGF2 was studied. Each of these growth factors was found to exert a specific effect on the culture. EGF, LIF and FGF2 specifically affected the somatic cells in culture while GDNF had a pronounced effect on the numbers of single type A spermatogonia, presumably SSCs. Overall the best results were obtained when the culture medium contained all four growth factors. A 365-fold increase in the numbers of A spermatogonia was found after 4 weeks of culture. To proof that GDNF actually stimulated the propagation of SSCs, a spermatogonial stem cell transplantation assay was carried out in which the cultured cells were transplanted into recipient mouse testes. The transplanted bovine SSCs colonized these testes and the extent of the colonization was taken as a measure of the numbers of bovine SSCs transplanted. A 10.000–fold increase in SSC numbers was found after a culture of 4.5 weeks. During culture in a liquid medium, many germ cells are lost during medium refreshments. To prevent this cell loss, we tested a semisolid culture medium (agar). Indeed, with an agar medium four times as many bovine spermatogonial colonies were able to grow. This indicates that it will be worthwhile to study the advantages of using an agar medium in further detail. In conclusion, we have developed a culture system for the propagation of bovine SSC which will allow further experimentation/manipulation and will eventually lead to more efficient ways of genetical improvement of cattle populations.

DNA double strand breaks (DSBs) are induced by ionizing radiation, and during meiotic recombination. DSBs are repaired via two main pathways, homologous recombination (HR) and non homologous end-joining (NHEJ). There are three main types of male germ cells, spermatogonia, spermatocytes and spermatids. Spermatogonia include stem cells and subsequent types of proliferating spermatogonia and express many DNA repair proteins including gamma-H2AX (a marker for DSBs) and p53 binding protein1 (53BP1) but not MDC1 (mediator of DNA damage checkpoint). MDC1 is an important protein that functions in both HR and NHEJ. In the lack of MDC1, spermatogonia differ from proliferating somatic cells, and this may explain why our studies revealed a slow and incomplete repair of DSBs in spermatogonia. In early spermatocytes (leptotene, zygotene and early pachytene stages of the meiotic prophase) during meiotic recombination DSB are induced. Our findings indicate that, the error prone repair via NHEJ does not take place in early spermatocytes, also not to repair radiation induced DSBs. First, these cells do not express 53BP1, an important protein in NHEJ. Second, this notion could be further established by studying the repair of recombination related DSBs and of DSBs induced by irradiation in scid mice (deficient for NHEJ) and in Rad54/Rad54B deficient mice, potentially deficient for HR. Repair of DSBs in early spermatocytes in scid mice was similar to that in wild type mice, however the repair was significantly lower in Rad54/Rad54B deficient mice. Hence, DSB repair in early spermatocytes is exclusively carried out through HR. In late spermatocytes (mid-pachytene through diplotene stages) all important repair proteins were found and using Rad54/Rad54B deficient mice, and scid mice, we could establish that both NHEJ and HR pathways are active in these cells, NHEJ probably being the most important. The meiotic divisions render round spermatids that elongate and transform into spermatozoa. In spermatids, HR is not possible as thy are haploid and earlier results indicate that in these cells DNA-PKcs, a protein indispensable for classical NHEJ, is not expressed or at very low levels. Nevertheless, after irradiation gamma-H2AX foci disappear in these cells indicating that these cells are capable of DSB repair. Using scid mice and mice in which PARP1 protein function was inhibited, we could establish that in spermatids some residual classical NHEJ takes place and that about half of the repair takes place through the recently discovered alternative pathway for NHEJ, involving the PARP1/XRCC1 proteins. Nevertheless, DSB repair in round spermatids is slow and incomplete. We also found that, in contrast to other somatic cells in the testis, Sertoli cells, the supporting somatic cells in the seminiferous epithelium, express several DNA repair proteins and repair DSBs, as shown by the in vivo disappearance of 53BP1 foci after irradiation and the results of the comet assay. This, together with our finding that adult Sertoli cells resume proliferation in culture indicates that adult Sertoli cells can no longer be regarded as a classical example of terminally differentiated cells that are no longer able to proliferate and do not repair DNA DSBs.

DNA double strand breaks (DSBs) are induced by ionizing radiation, and during meiotic recombination. DSBs are repaired via two main pathways, homologous recombination (HR) and non homologous end-joining (NHEJ). There are three main types of male germ cells, spermatogonia, spermatocytes and spermatids. Spermatogonia include stem cells and subsequent types of proliferating spermatogonia and express many DNA repair proteins including gamma-H2AX (a marker for DSBs) and p53 binding protein1 (53BP1) but not MDC1 (mediator of DNA damage checkpoint). MDC1 is an important protein that functions in both HR and NHEJ. In the lack of MDC1, spermatogonia differ from proliferating somatic cells, and this may explain why our studies revealed a slow and incomplete repair of DSBs in spermatogonia. In early spermatocytes (leptotene, zygotene and early pachytene stages of the meiotic prophase) during meiotic recombination DSB are induced. Our findings indicate that, the error prone repair via NHEJ does not take place in early spermatocytes, also not to repair radiation induced DSBs. First, these cells do not express 53BP1, an important protein in NHEJ. Second, this notion could be further established by studying the repair of recombination related DSBs and of DSBs induced by irradiation in scid mice (deficient for NHEJ) and in Rad54/Rad54B deficient mice, potentially deficient for HR. Repair of DSBs in early spermatocytes in scid mice was similar to that in wild type mice, however the repair was significantly lower in Rad54/Rad54B deficient mice. Hence, DSB repair in early spermatocytes is exclusively carried out through HR. In late spermatocytes (mid-pachytene through diplotene stages) all important repair proteins were found and using Rad54/Rad54B deficient mice, and scid mice, we could establish that both NHEJ and HR pathways are active in these cells, NHEJ probably being the most important. The meiotic divisions render round spermatids that elongate and transform into spermatozoa. In spermatids, HR is not possible as thy are haploid and earlier results indicate that in these cells DNA-PKcs, a protein indispensable for classical NHEJ, is not expressed or at very low levels. Nevertheless, after irradiation gamma-H2AX foci disappear in these cells indicating that these cells are capable of DSB repair. Using scid mice and mice in which PARP1 protein function was inhibited, we could establish that in spermatids some residual classical NHEJ takes place and that about half of the repair takes place through the recently discovered alternative pathway for NHEJ, involving the PARP1/XRCC1 proteins. Nevertheless, DSB repair in round spermatids is slow and incomplete. We also found that, in contrast to other somatic cells in the testis, Sertoli cells, the supporting somatic cells in the seminiferous epithelium, express several DNA repair proteins and repair DSBs, as shown by the in vivo disappearance of 53BP1 foci after irradiation and the results of the comet assay. This, together with our finding that adult Sertoli cells resume proliferation in culture indicates that adult Sertoli cells can no longer be regarded as a classical example of terminally differentiated cells that are no longer able to proliferate and do not repair DNA DSBs.

It was previously shown that administration of recombinant human Fms-like tyrosine kinase receptor-3 ligand (Flt3L) before allergen challenge of sensitized mice suppresses the cardinal features of asthma through unclear mechanisms. Here, we show that Flt3L dramatically alters the balance of conventional to plasmacytoid dendritic cells (pDCs) in the lung favoring the accumulation of pDCs. Selective removal of pDCs abolished the antiinflammatory effect of Flt3L, suggesting a regulatory role for these cells in ongoing asthmatic inflammation. In support, we found that immature pDCs are recruited to the lungs of allergen-challenged mice irrespective of Flt3L treatment. Selective removal of pDCs during allergen challenge enhanced airway inflammation, whereas adoptive transfer of cultured pDCs before allergen challenge suppressed inflammation. Experiments in which TLR9 agonist CpG motifs were administered in vitro or in vivo demonstrated that pDCs were antiinflammatory irrespective of their maturation state. These effects were mediated through programmed death-1/programmed death ligand 1 interactions, but not through ICOS ligand, IDO, or IFN-alpha. These findings suggest a specialized immunoregulatory role for pDCs in airway inflammation. Enhancing the antiinflammatory properties of pDCs could be employed as a novel strategy in asthma treatment.

It was previously shown that administration of recombinant human Fms-like tyrosine kinase receptor-3 ligand (Flt3L) before allergen challenge of sensitized mice suppresses the cardinal features of asthma through unclear mechanisms. Here, we show that Flt3L dramatically alters the balance of conventional to plasmacytoid dendritic cells (pDCs) in the lung favoring the accumulation of pDCs. Selective removal of pDCs abolished the antiinflammatory effect of Flt3L, suggesting a regulatory role for these cells in ongoing asthmatic inflammation. In support, we found that immature pDCs are recruited to the lungs of allergen-challenged mice irrespective of Flt3L treatment. Selective removal of pDCs during allergen challenge enhanced airway inflammation, whereas adoptive transfer of cultured pDCs before allergen challenge suppressed inflammation. Experiments in which TLR9 agonist CpG motifs were administered in vitro or in vivo demonstrated that pDCs were antiinflammatory irrespective of their maturation state. These effects were mediated through programmed death-1/programmed death ligand 1 interactions, but not through ICOS ligand, IDO, or IFN-alpha. These findings suggest a specialized immunoregulatory role for pDCs in airway inflammation. Enhancing the antiinflammatory properties of pDCs could be employed as a novel strategy in asthma treatment.

Ambiguous images are images that have multiple plausible perceptual interpretations. A human observer viewing an ambiguous image may perceive alternate interpretations in turn. One factor that affects perception of ambiguous images is prior exposure to identical or similar visual input. This thesis reports investigations into the influence of prior visual experience and perception on perception of ambiguous images.

Ambiguous images are images that have multiple plausible perceptual interpretations. A human observer viewing an ambiguous image may perceive alternate interpretations in turn. One factor that affects perception of ambiguous images is prior exposure to identical or similar visual input. This thesis reports investigations into the influence of prior visual experience and perception on perception of ambiguous images.

Ambiguous images are images that have multiple plausible perceptual interpretations. A human observer viewing an ambiguous image may perceive alternate interpretations in turn. One factor that affects perception of ambiguous images is prior exposure to identical or similar visual input. This thesis reports investigations into the influence of prior visual experience and perception on perception of ambiguous images.

The sensitivity of the present interglacial climate to the ongoing anthropogenic-driven increase of atmospheric greenhouse gas poses a fundamental concern to modern society. The Mediterranean region is responding with a distinct change towards drier and warmer conditions, which affects also the hydrography of the entire basin and is likely to continue in the near future. Notably, changes occurring in the atmosphere/sea surface are rapidly transferred to the deep sea via an effective thermohaline circulation, led by processes acting in the eastern Mediterranean. This thesis rises from the need to advance our understanding of the sensitivity of the eastern Mediterranean region to perturbations in the atmosphere/ocean system during interglacial periods. In addition, it exploits the sensitivity of the basin’s hydrography and climate to both high- to mid-latitude and tropical/subtropical systems in order to provide insights on large-scale teleconnections during periods of climate change. Investigations presented here specifically focus on the last two intervals of peak interglacial conditions, at times of substantial hydrological perturbations when extensive hydrographic changes led to the widespread deposition of organic-rich sediments (sapropels). Results for the last interglacial period indicate that ~124 ka BP, a large monsoon-fuelled freshwater injection along the North African margin substantially lowered the sea surface salinity (from 39 to 33 practical salinity units) in the Aegean Sea, a key site of deep-water overturning for the eastern Mediterranean. This change, in turn, triggered a rapid (~40 years) collapse of the Aegean deep-intermediate-water ventilation, promoting euxinic conditions – hostile to aerobic life – which expanded toward the photic layer within ~650 years, and subsequently propagated to the open eastern Mediterranean. Holocene Aegean records also reveal the occurrence of a monsoon-related freshwater disturbance – albeit far less intense – in the eastern Mediterranean during the early to middle Holocene interval of insolation/monsoon maximum (10 to 5.5 ka BP), which led to a less pronounced hydrographic response, with the “sole” stagnation of the deep-waters. Besides these dramatic changes in the basin’s hydrography that are mainly tied to monsoon-forced perturbations in the eastern Mediterranean freshwater budget, the regional climate in the past – as well as today – appears intimately linked to variations in the high latitude atmospheric forcing, which dominates the winter regime. Accordingly, eastern Mediterranean records are here exploited as invaluable archives of past variability in the meridional extent of high latitude atmospheric circulation, i.e., the atmospheric polar vortex. Specifically, early Holocene records from the Aegean Sea bear witnesses of a particularly sharp Aegean cooling event between 8.3 and 8.15 ka BP, embedded within an underlying cooling episode of 8.6-8.0 ka BP. In both timing and duration, this sharp event agrees with the so-called “8.2 event” reported from several records from the wider North Atlantic region, which has been related to a brief weakening of the Atlantic meridional overturning circulation. Taken together, these results point to the exceptional sensitivity of the eastern Mediterranean Sea interglacial climate to climate forcing, with rapid responses to climate forcing, and propagation of the signals through the water column down to the deep sea and, in turn, affecting the entire ecosystem.

The sensitivity of the present interglacial climate to the ongoing anthropogenic-driven increase of atmospheric greenhouse gas poses a fundamental concern to modern society. The Mediterranean region is responding with a distinct change towards drier and warmer conditions, which affects also the hydrography of the entire basin and is likely to continue in the near future. Notably, changes occurring in the atmosphere/sea surface are rapidly transferred to the deep sea via an effective thermohaline circulation, led by processes acting in the eastern Mediterranean. This thesis rises from the need to advance our understanding of the sensitivity of the eastern Mediterranean region to perturbations in the atmosphere/ocean system during interglacial periods. In addition, it exploits the sensitivity of the basin’s hydrography and climate to both high- to mid-latitude and tropical/subtropical systems in order to provide insights on large-scale teleconnections during periods of climate change. Investigations presented here specifically focus on the last two intervals of peak interglacial conditions, at times of substantial hydrological perturbations when extensive hydrographic changes led to the widespread deposition of organic-rich sediments (sapropels). Results for the last interglacial period indicate that ~124 ka BP, a large monsoon-fuelled freshwater injection along the North African margin substantially lowered the sea surface salinity (from 39 to 33 practical salinity units) in the Aegean Sea, a key site of deep-water overturning for the eastern Mediterranean. This change, in turn, triggered a rapid (~40 years) collapse of the Aegean deep-intermediate-water ventilation, promoting euxinic conditions – hostile to aerobic life – which expanded toward the photic layer within ~650 years, and subsequently propagated to the open eastern Mediterranean. Holocene Aegean records also reveal the occurrence of a monsoon-related freshwater disturbance – albeit far less intense – in the eastern Mediterranean during the early to middle Holocene interval of insolation/monsoon maximum (10 to 5.5 ka BP), which led to a less pronounced hydrographic response, with the “sole” stagnation of the deep-waters. Besides these dramatic changes in the basin’s hydrography that are mainly tied to monsoon-forced perturbations in the eastern Mediterranean freshwater budget, the regional climate in the past – as well as today – appears intimately linked to variations in the high latitude atmospheric forcing, which dominates the winter regime. Accordingly, eastern Mediterranean records are here exploited as invaluable archives of past variability in the meridional extent of high latitude atmospheric circulation, i.e., the atmospheric polar vortex. Specifically, early Holocene records from the Aegean Sea bear witnesses of a particularly sharp Aegean cooling event between 8.3 and 8.15 ka BP, embedded within an underlying cooling episode of 8.6-8.0 ka BP. In both timing and duration, this sharp event agrees with the so-called “8.2 event” reported from several records from the wider North Atlantic region, which has been related to a brief weakening of the Atlantic meridional overturning circulation. Taken together, these results point to the exceptional sensitivity of the eastern Mediterranean Sea interglacial climate to climate forcing, with rapid responses to climate forcing, and propagation of the signals through the water column down to the deep sea and, in turn, affecting the entire ecosystem.

The sensitivity of the present interglacial climate to the ongoing anthropogenic-driven increase of atmospheric greenhouse gas poses a fundamental concern to modern society. The Mediterranean region is responding with a distinct change towards drier and warmer conditions, which affects also the hydrography of the entire basin and is likely to continue in the near future. Notably, changes occurring in the atmosphere/sea surface are rapidly transferred to the deep sea via an effective thermohaline circulation, led by processes acting in the eastern Mediterranean. This thesis rises from the need to advance our understanding of the sensitivity of the eastern Mediterranean region to perturbations in the atmosphere/ocean system during interglacial periods. In addition, it exploits the sensitivity of the basin’s hydrography and climate to both high- to mid-latitude and tropical/subtropical systems in order to provide insights on large-scale teleconnections during periods of climate change. Investigations presented here specifically focus on the last two intervals of peak interglacial conditions, at times of substantial hydrological perturbations when extensive hydrographic changes led to the widespread deposition of organic-rich sediments (sapropels). Results for the last interglacial period indicate that ~124 ka BP, a large monsoon-fuelled freshwater injection along the North African margin substantially lowered the sea surface salinity (from 39 to 33 practical salinity units) in the Aegean Sea, a key site of deep-water overturning for the eastern Mediterranean. This change, in turn, triggered a rapid (~40 years) collapse of the Aegean deep-intermediate-water ventilation, promoting euxinic conditions – hostile to aerobic life – which expanded toward the photic layer within ~650 years, and subsequently propagated to the open eastern Mediterranean. Holocene Aegean records also reveal the occurrence of a monsoon-related freshwater disturbance – albeit far less intense – in the eastern Mediterranean during the early to middle Holocene interval of insolation/monsoon maximum (10 to 5.5 ka BP), which led to a less pronounced hydrographic response, with the “sole” stagnation of the deep-waters. Besides these dramatic changes in the basin’s hydrography that are mainly tied to monsoon-forced perturbations in the eastern Mediterranean freshwater budget, the regional climate in the past – as well as today – appears intimately linked to variations in the high latitude atmospheric forcing, which dominates the winter regime. Accordingly, eastern Mediterranean records are here exploited as invaluable archives of past variability in the meridional extent of high latitude atmospheric circulation, i.e., the atmospheric polar vortex. Specifically, early Holocene records from the Aegean Sea bear witnesses of a particularly sharp Aegean cooling event between 8.3 and 8.15 ka BP, embedded within an underlying cooling episode of 8.6-8.0 ka BP. In both timing and duration, this sharp event agrees with the so-called “8.2 event” reported from several records from the wider North Atlantic region, which has been related to a brief weakening of the Atlantic meridional overturning circulation. Taken together, these results point to the exceptional sensitivity of the eastern Mediterranean Sea interglacial climate to climate forcing, with rapid responses to climate forcing, and propagation of the signals through the water column down to the deep sea and, in turn, affecting the entire ecosystem.

We reconstruct the latest Paleocene and early Eocene (∼57-50 Ma) environmental trends in the Arctic Ocean and focus on the Paleocene-Eocene thermal maximum (PETM) (∼55 Ma), using strata recovered from the Lomonosov Ridge by the Integrated Ocean Drilling Program Expedition 302. The Lomonosov Ridge was still partially subaerial during the latest Paleocene and earliest Eocene and gradually subsided during the early Eocene. Organic dinoflagellate cyst (dinocyst) assemblages point to brackish and productive surface waters throughout the latest Paleocene and early Eocene. Dinocyst assemblages are cosmopolitan during this time interval, suggesting warm conditions, which is corroborated by TEX86′-reconstructed temperatures of 15°-18°C. Inorganic geochemistry generally reflects reducing conditions within the sediment and euxinic conditions during the upper lower Eocene. Spectral analysis reveals that the cyclicity, recorded in X-ray fluorescence scanning Fe data from close to Eocene thermal maximum 2 (∼53 Ma, presence confirmed by dinocyst stratigraphy), is related to precession. Within the lower part of the PETM, proxy records indicate enhanced weathering, runoff, anoxia, and productivity along with sea level rise. On the basis of total organic carbon content and variations in sediment accumulation rates, excess organic carbon burial in the Arctic Ocean appears to have contributed significantly to the sequestration of injected carbon during the PETM.

We reconstruct the latest Paleocene and early Eocene (∼57-50 Ma) environmental trends in the Arctic Ocean and focus on the Paleocene-Eocene thermal maximum (PETM) (∼55 Ma), using strata recovered from the Lomonosov Ridge by the Integrated Ocean Drilling Program Expedition 302. The Lomonosov Ridge was still partially subaerial during the latest Paleocene and earliest Eocene and gradually subsided during the early Eocene. Organic dinoflagellate cyst (dinocyst) assemblages point to brackish and productive surface waters throughout the latest Paleocene and early Eocene. Dinocyst assemblages are cosmopolitan during this time interval, suggesting warm conditions, which is corroborated by TEX86′-reconstructed temperatures of 15°-18°C. Inorganic geochemistry generally reflects reducing conditions within the sediment and euxinic conditions during the upper lower Eocene. Spectral analysis reveals that the cyclicity, recorded in X-ray fluorescence scanning Fe data from close to Eocene thermal maximum 2 (∼53 Ma, presence confirmed by dinocyst stratigraphy), is related to precession. Within the lower part of the PETM, proxy records indicate enhanced weathering, runoff, anoxia, and productivity along with sea level rise. On the basis of total organic carbon content and variations in sediment accumulation rates, excess organic carbon burial in the Arctic Ocean appears to have contributed significantly to the sequestration of injected carbon during the PETM.

We reconstruct the latest Paleocene and early Eocene (∼57-50 Ma) environmental trends in the Arctic Ocean and focus on the Paleocene-Eocene thermal maximum (PETM) (∼55 Ma), using strata recovered from the Lomonosov Ridge by the Integrated Ocean Drilling Program Expedition 302. The Lomonosov Ridge was still partially subaerial during the latest Paleocene and earliest Eocene and gradually subsided during the early Eocene. Organic dinoflagellate cyst (dinocyst) assemblages point to brackish and productive surface waters throughout the latest Paleocene and early Eocene. Dinocyst assemblages are cosmopolitan during this time interval, suggesting warm conditions, which is corroborated by TEX86′-reconstructed temperatures of 15°-18°C. Inorganic geochemistry generally reflects reducing conditions within the sediment and euxinic conditions during the upper lower Eocene. Spectral analysis reveals that the cyclicity, recorded in X-ray fluorescence scanning Fe data from close to Eocene thermal maximum 2 (∼53 Ma, presence confirmed by dinocyst stratigraphy), is related to precession. Within the lower part of the PETM, proxy records indicate enhanced weathering, runoff, anoxia, and productivity along with sea level rise. On the basis of total organic carbon content and variations in sediment accumulation rates, excess organic carbon burial in the Arctic Ocean appears to have contributed significantly to the sequestration of injected carbon during the PETM.

A study of upper Paleocene–lower Eocene (P–E) sediments deposited on the Lomonosov Ridge in the central Arctic Ocean reveals relatively high abundances of terrestrial biomarkers. These include dehydroabietane and simonellite derived from conifers (gymnosperms) and a tetra-aromatic triterpenoid derived from angiosperms. The relative percentage of the angiosperm biomarker of the summed angiosperm + conifer biomarkers was increased at the end of the Paleocene–Eocene thermal maximum (PETM), different when observed with pollen counts which showed a relative decrease in angiosperm pollen. Stable carbon isotopic analysis of these biomarkers shows that the negative carbon isotope excursion (CIE) during the PETM amounts to 3‰ for both conifer biomarkers, dehydroabietane and simonellite, comparable to the magnitude of the CIE inferred from marine carbonates, but significantly lower than the 4.5‰ of the terrestrial C29 n-alkane [M. Pagani, N. Pedentchouk, M. Huber, A. Sluijs, S. Schouten, H. Brinkhuis, J.S. Sinninghe Damste, G.R. Dickens, and the IODP Expedition 302 Expedition Scientists (2006), Arctic's hydrology during global warming at the Paleocene–Eocene thermal maximum. Nature, 442, 671–675.], which is a compound sourced by both conifers and angiosperms. Conspicuously, the angiosperm-sourced aromatic triterpane shows a much larger CIE of 6‰ and suggests that angiosperms increased in their carbon isotopic fractionation during the PETM. Our results thus indicate that the 4.5‰ C29 n-alkane CIE reported previously represents the average CIE of conifers and angiosperms at this site and suggest that the large and variable CIE observed in terrestrial records may be partly explained by the variable contributions of conifers and angiosperms. The differential response in isotopic fractionation of angiosperms and conifers points to different physiological responses of these vegetation types to the rise in temperature, humidity, and greenhouse gases during the PETM.