Search

The role of maternal tissue in embryogenesis remains enigmatic in many complex organisms. Here, we investigate the contribution of maternal tissue to apical–basal patterning in the kelp embryo. Focussing on Undaria pinnatifida, we studied the effects of detachment from the maternal tissue using microsurgery, staining of cell wall modifications, morphometric measurements, flow cytometry, genotyping and a modified kelp fertilisation protocol synchronising kelp embryogenesis. Detached embryos are rounder and often show aberrant morphologies. When a part of the oogonial cell wall remains attached to the zygote, the apical–basal patterning is rescued. Furthermore, the absence of contact with maternal tissue increases parthenogenesis, highlighting the critical role of maternal signals in the initial stages of development. These results show a key role for the connection to the maternal oogonial cell wall in apical–basal patterning in kelps. This observation is reminiscent of another brown alga, Fucus, where the cell wall directs the cell fate. Our findings suggest a conserved mechanism across phylogenetically distant oogamous lineages, where localised secretion of sulphated F2 fucans mediates the establishment of the apical–basal polarity. In this model, the maternal oogonial cell wall mediates basal cell fate determination by providing an extrinsic patterning cue to the future kelp embryo.

Kelp forests in the North Atlantic are at risk of decline at their warm temperature distribution margins due to anthropogenic temperature rise and more frequent marine heat waves. To investigate the thermal adaptation of the cold-temperate kelp Laminaria digitata, we sampled six populations, from the Arctic to Brittany (Spitsbergen, Tromsø, Bodø [all Norway], Helgoland [Germany], Roscoff and Quiberon [both France]), across the species’ entire distribution range, spanning 31.5° latitude and 12-13°C difference in mean summer sea surface temperature. We used pooled vegetative gametophytes derived from several sporophytes to approximate the genetic diversity of each location. Gametophytes were exposed to (sub-) lethal high (20-25°C) and (sub-) optimal low (0-15°C) temperature gradients in two full-factorial, common-garden experiments, subjecting subsets of populations from different origins to the same conditions. We assessed survival of gametophytes, their ability to develop microscopic sporophytes, and subsequent growth. We hypothesized that the thermal performance of gametophytes and microscopic sporophytes corresponds to their local long-term thermal history. Integrated gametophyte survival revealed a uniform upper survival temperature (UST) of 24°C among five tested populations (Tromsø to Quiberon). In contrast, following two weeks of thermal priming of gametophytes at 20-22°C, sporophyte formation at 15°C was significantly higher in southern populations (Quiberon and Roscoff) compared to the high-latitude population of Tromsø. Between 0-15°C, survival of the Arctic population (Spitsbergen) was negatively correlated with increasing temperatures, while the southernmost population (Quiberon) showed the opposite. Thus, responses of survival at low, and sporophyte formation at high temperatures, support the concept of local adaption. On the other hand, sporophyte formation between 0-15°C peaked at 6-9°C in the Quiberon and at 9-12°C in the Spitsbergen population. Sporo

Thermal characteristics of kelp species have been studied in many ways, but potentially persistent effects of temperature across generations are yet poorly understood. In this context, the effect of thermal priming on fertility and growth of the N-Atlantic kelp species Laminaria digitata was investigated within and across life cycle generations in a two-step common garden experiment. Using vegetative clonal gametophytes from cold (5°C) and warm (15°C) pre-experimental cultivation (3 years), we first quantified gametogenesis and recruitment over two weeks at a common temperature of 10°C. Then, recruited sporophytes were transferred to a temperature gradient spanning the tolerance range of the species from 0°C to 20°C. We hypothesized that a warm gametophyte preexperimental cultivation promotes performance of sporophytes at warm temperatures and vice versa. Interestingly, gametogenesis speed and sporophyte recruitment were higher in gametophytes following cold compared to warm pre-experimental cultivation, which indicates carry-over effects of temperature within the gametophyte generation. Compared to warm pre-experimental cultivation of gametophytes, a cold preexperimental cultivation enhanced growth of juvenile Laminaria digitata sporophytes by more than 69% at the extreme low and high temperatures of 0 and 20°C. This is the first evidence for a cross-generational effect between gametophyte parents and offspring sporophytes. As cold gametophyte cultivation increased the trait performance of gametogenesis, recruitment and thermal tolerance of juvenile sporophytes, priming of early life cycle stages may be used to increase resilience and productivity of kelps in marine forest restoration efforts and kelp mariculture.

Marine forests and kelps as their foundation species are threatened by ocean warming especially at the warm distributional edges. Previously identified genetic divergence and ecotypic differentiation within kelp species may allow to produce more resilient lineages by intraspecific outbreeding among populations. In a mechanistic investigation of heat stress, heterosis (hybrid vigour), and underlying gene expression patterns, we assessed the thermal performance of inbred (selfings) and outbred (reciprocal crosses) sporophytes of the N-Atlantic kelp Laminaria digitata among clonal isolates from two divergent populations; one from the temperate North Sea (Helgoland) and one from the Arctic (Spitsbergen). First, we investigated the upper thermal tolerance of microscopic sporophytes in a 14-day experiment applying sublethal to lethal 20–23°C. The upper survival temperature of microscopic sporophytes was lower for the inbred Arctic selfing (21°C) than for the temperate selfing and the reciprocal crosses (22°C). Only in the temperate selfing, 4.5% of sporophytes survived 23°C. We then subjected 4–7 cm long sporophytes to a control temperature (10°C), moderate (19°C) and sublethal to lethal heat stress (20.5°C) for 18 days to assess gene expression in addition to physiological parameters. Growth and optimum quantum yield decreased similarly in the reciprocal crosses and the temperate selfing at 19 and 20.5°C, while inbred Arctic sporophytes died within seven days at both 19 and 20.5°C. In response to 20.5°C, 252 genes were constitutively regulated across all surviving lineages, which we use to describe metabolic regulation patterns in response to heat stress in kelp. At sublethal 20.5°C, ca. 150 genes were differentially expressed by either crossed lineage in comparison to the temperate selfing, indicating that they maintained a growth response similar to the temperate selfing with differential metabolic regulation during sublethal heat stress. Subtle differences in physiolo

Two morphologically similar digitate kelp species, Laminaria digitata and Hedophyllum nigripes, co-occur along a shallow sublittoral depth gradient in the Arctic but, in contrast to L. digitata, very few ecophysiological data exist for H. nigripes. We investigated growth, survival, photosynthetic characteristics and carbon:nitrogen ratios of juvenile sporophytes, and recruitment and survival of gametophytes in genetically verified Arctic isolates of both species along temperature gradients (0–25 °C) over 14 days. Laminaria digitata gametophytes survived 23–24 °C, while sporophytes survived 21–22 °C. Hedophyllum nigripes had lower temperature affinities. Gametophytes survived 19–21 °C, while sporophytes survived 18 °C. Male gametophytes were more heat-tolerant than female gametophytes in both species. The pronounced cold adaption of H. nigripes compared to L. digitata also became apparent in different sporophyte growth optima (L. digitata: 15 °C; H. nigripes: 10 °C) and gametogenesis optima (L. digitata: 5–15 °C; H. nigripes: 0–10 °C).Higher carbon:nitrogen ratios in H. nigripes suggest an adaptation to nutrient poor Arctic conditions. The overall temperature performance of H. nigripes possibly restricts the species to Arctic–Sub-Arctic regions, while Arctic L. digitatabehaved similarly to cold-temperate populations. Our data suggest that a future increase in seawater temperatures may hamper the success of H. nigripes and favour L. digitata in Arctic environments.

Along temperate to polar rocky shorelines, large brown algae known as kelps form marine forests which provide a three-dimensional habitat for many associated species. Ocean warming is posing an increasing threat to kelps at their warm distributional edges and first range shifts have been recorded. For these sessile species unable to migrate, trait variability due to phenotypic plasticity and genetic variation is an important mechanism of response to environmental change. The aim of this thesis was to produce a comprehensive assessment of the variation and plasticity of thermal traits across populations and life cycle stages of a keystone marine forest species, the cold-temperate to Arctic kelp Laminaria digitata. Using physiological response parameters, population genetics and transcriptomics, I present evidence for four levels of thermal trait variability in a marine forest key species. I describe (1) genetic and physiological differentiation along the species' distribution range, (2) genetic variation for phenotypic plasticity among genotypes, (3) carry-over effects over reproduction and individual ontogeny, and (4) the production of new phenotypes by outbreeding among distant lineages. Integrating these responses into a framework of seasonal temperature variation and predictions of ocean warming showed that L. digitata, as a species with a cold-temperate thermal profile, is adapted well to the current conditions along its distributional range, but may not be equipped to respond to rapid climate change at its warm range edges. The concepts investigated in this thesis provide further insight into trait variability as a mechanism of marine forest resilience and offer intriguing features for mariculture and conservation efforts.

To understand the thermal plasticity of a coastal foundation species across its latitudinal distribution, we assess physiological responses to high temperature stress in the kelp Laminaria digitata in combination with population genetic characteristics and relate heat resilience to genetic features and phylogeography. We hypothesize that populations from Arctic and cold-temperate locations are less heat resilient than populations from warm distributional edges. Using meristems of natural L. digitata populations from six locations ranging between Kongsfjorden, Spitsbergen (79°N), and Quiberon, France (47°N), we performed a common-garden heat stress experi- ment applying 15°C to 23°C over eight days. We assessed growth, photosynthetic quantum yield, carbon and nitrogen storage, and xanthophyll pigment contents as response traits. Population connectivity and genetic diversity were analyzed with microsatellite markers. Results from the heat stress experiment suggest that the upper temperature limit of L. digitata is nearly identical across its distribution range, but subtle differences in growth and stress responses were revealed for three popu- lations from the species’ ecological range margins. Two populations at the species’ warm distribution limit showed higher temperature tolerance compared to other populations in growth at 19°C and recovery from 21°C (Quiberon, France), and pho- tosynthetic quantum yield and xanthophyll pigment responses at 23°C (Helgoland, Germany). In L. digitata from the northernmost population (Spitsbergen, Norway), quantum yield indicated the highest heat sensitivity. Microsatellite genotyping revealed all sampled populations to be genetically distinct, with a strong hierarchical structure between southern and northern clades. Genetic diversity was lowest in the isolated population of the North Sea island of Helgoland and highest in Roscoff in the English Channel. All together, these results support the hypothesis of moderate local differenti

Phenotypic plasticity (genotype × environment interaction) is an especially important means for sessile organisms to cope with environmental variation. While kelps, the globally most productive group of seaweeds, generally possess a wide thermal performance range, kelp populations at their warm distribution limits are threatened by ocean warming. Here, we investigated effects of temperature during ontogeny of the kelp Laminaria digitata across haploid gametophyte and diploid sporophyte life cycle stages in five distinct genetic lines. We hypothesized that thermal plasticity increases trait performance of juvenile sporophytes in experimental temperatures that match the temperature experienced during gametogenesis and recruitment, and that plasticity differs among genetic lines (genetic variation for plasticity). We applied a full-factorial experimental design to generate different temperature histories by applying 5 and 15°C during meiospore germination, gametogenesis of parental gametophytes and recruitment of offspring sporophytes (19–26 days), and juvenile sporophyte rearing (91–122 days). We then tested for thermal plasticity among temperature history treatments at 5 and 15°C in a final 12-day experiment assessing growth, the storage compound mannitol, carbon and nitrogen contents, and fluorometric responses in 3–4 month old sporophytes for five genetic lines. Our study provides evidence for the importance of cold temperatures at early development on later sporophyte performance of L. digitata. Gametogenesis and recruitment at 5°C promoted higher growth of offspring sporophytes across experimental temperatures. While photosynthetic capacity was higher at 15°C, carbon and nitrogen storage were higher at 5°C, both showing fast acclimation responses. We identified an important role of genetic variation for plasticity in shaping L. digitata’s thermal plasticity. Trait performance at 5 or 15°C (reaction norm slopes) differed among genetic lines, even showing opposite

In temperate and polar rocky coastal ecosystems, kelps form the base of complexly structured and highly diverse species associations. In recent years, kelp forests worldwide have faced extinction at their equatorward limits and models have predicted a poleward shift of kelp ecosystems during climate change. To gain an understanding of local thermal adaptation and response plasticity in a forest-forming kelp species, we assessed populations of Laminaria digitata along its entire European distribution range from Brittany to Spitsbergen for their capacity to withstand high temperature stress, and connected physiological results to population genetics. Although the overall heat response was similar across the distribution range, we identified subtle adaptions reflecting the long-term local temperature history in one northern and one southern population. Additionally, we investigated the potential role of transgenerational plasticity (TGP, i.e. effects of parental environment on offspring traits) as a means of fast response to a warming environment between haploid gametophyte parents and diploid sporophyte offspring of L. digitata. Our results show TGP for the first time in a kelp, in that not the 15°C, but the 5°C gametophyte parent treatment enhanced juvenile sporophyte offspring growth. In this talk, I will conceptualize the thermal response of L. digitata and discuss our results within the framework of global warming.

Transgenerational effects (effects of parental environment on offspring traits) have recently gained attention as a means of fast response to changing environmental conditions, e.g. under climate change. In temperate and polar rocky coastal ecosystems, kelps form the base of complexly structured and highly diverse species associations. This study investigates the potential for temperature-mediated transgenerational plasticity along the development from haploid parents (gametophytes) to their juvenile diploid offspring (sporophytes) in a geographically isolated population of the brown alga Laminaria digitata from the island of Helgoland (North Sea). We sampled spores from wild donor sporophytes, which we raised at 5 and 15 °C during gametogenesis, and reared the resulting young sporophytes for three months in a full-factorial split design while keeping genetic lineages separate. A concluding 12-day experiment on growth, biochemistry (carbon, mannitol content) and photosynthetic characteristics (maximum quantum yield Fv/Fm, maximum electron transport rate rETRmax) of five genetic lineages allowed for the separation of late temperature (12 day) responses, within-generation plasticity (early temperature) and transgenerational plasticity (gametogenesis temperature) in response to 5 and 15 °C. We observed significant two- and three-way interactions between gametogenesis temperature and early and late sporophyte temperatures for all parameters. While interactive effects between early and late experimental temperatures probably represent acclimation processes, interactions involving gametogenesis temperature indicate transgenerational effects. The direction of these effects differed between parameters. A main effect is that only with a history of 5 °C as gametogenesis and early temperature, sporophytes are growing faster at 5 than 15 °C over 12 days late temperature. According to our results, the temperature experienced by parents during gametogenesis influences temperature

Transgenerational effects (parent environment effects on offspring traits) have recently gained attention as a means of fast response to changing environmental conditions under climate change. In temperate and polar rocky coastal ecosystems, kelps form the base of complexly structured and highly diverse species associations. This study investigates the potential for temperature-related within-generation and transgenerational plasticity in a geographically isolated population of the brown alga Laminaria digitata from the island of Helgoland (North Sea). We obtained separate strains (genetic lines) from fertile field material and assessed sporophyte growth and gametogenesis at 5 and 15 °C. Rearing the resulting sporophytes in a full-factorial design at these two temperatures resulted in four temperature history treatments. A concluding experiment on growth, photosynthetic characteristics (Fv/Fm, rapid P-I curves, pigments) and storage compounds of five parental strains should allow for the separation of phenotypic plasticity from genetic effects in the response to 5 and 15 °C. Initial results indicate seasonality in the temperature response, with higher plasticity in material collected in spring than in summer. Gametogenesis was faster at 15 than at 5 °C, but recruitment was higher at 5 °C. A difference in morphology between sporophytes raised at 5 and 15 °C indicates that the temperature during growth had a stronger impact on morphology than the temperature during gametogenesis. Here we will show preliminary results of whether performance is related to genetic background or phenotypic plasticity among strains.

Die vorliegende Studie untersucht den Einfluss verschiedener Temperaturen auf das Wachstum und auf physiologische Parameter des BlasentangsFucus vesiculosusaus dem westlichen Baltikum (Kieler Förde). Auf 5 cm Länge zugeschnittene Proben wurden über 21 Tage in einem Temperaturgradienten von 5 bis 29 °C inkubiert, während alle anderen abiotischen Faktoren konstant gehalten wurden. In regelmäßigen Abständen wurde das Wachstum anhand der Parameter Länge, Fläche und Frischgewicht gemessen, zusätzlich wurden Photosynthesemessungen durchgeführt.In einer anschließenden Nachkultur über 10 Tage bei 16 °C wurde die Fähigkeit zur Erholung der Fucus-Stücke geprüft.Abschließende Analysen lieferten Erkenntnisse zu Chlorophyll-, Stickstoff-und Kohlenstoffgehalt der Proben vor und nach Ablauf des Experiments. Ziel dieser Arbeit war es, eine genaue Temperaturcharakteristik für Fucus vesiculosusausdem westlichen Baltikumzu ermitteln, mit besonderem Fokus auf der Reaktion bezüglich erhöhter Temperaturen und der oberen Überlebensgrenze. Anhand der gesammelten Daten zeigt sich ein deutlicher Einfluss der Temperatur auf das Wachstum von Fucus vesiculosus. Während das schnellste Wachstum bei 15 bis 20 °C stattfindet, ist die Alge bei 26 bis 27 °C stark gestresstbei geringen Wachstumsraten. 28 °C führen nach 2 Wochenzum Absterben von mehr als 50 % der Proben, 29 °C liefern diesen Effekt bereits nach 7 Tagen. 15 und 20 °C sorgen ebenfalls für eine konstante effektive Quantenausbeute über die Zeit, während sichbei den anderen Temperaturen negative Effekte zeigen. Das Optimum der relativen Elektronentransportrate in der Photosynthese liegt etwas über dem Wachstumsoptimum bei 20bis 26 °C, während das nichtphotochemische Quenching keine Temperatureffekte zeigt. Die Temperatur hat ebenfalls keinen Einfluss auf den Chlorophyllgehalt der Algen. Das Kohlenstoff-Stickstoff-Verhältnis liefert maximale Werte über einen weiten Temperaturbereich von 10 bis 27 °C.