Browsing by Author "Liesner, Daniel"
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- Heat stress responses and population genetics of the kelp Laminaria digitata (Phaeophyceae) across latitudes reveal differentiation among North Atlantic populationsPublication . Liesner, Daniel; Fouqueau, Louise; Valero, Myriam; Roleda, Michael Y.; Pearson, Gareth; Bischof, Kai; Valentin, Klaus; Bartsch, InkaTo 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 experiment 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 populations 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 photosynthetic 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 differentiation across L. digitata's European distribution, whereas effects are likely too weak to ameliorate the species' capacity to withstand ocean warming and marine heatwaves at the southern range edge.
- Increased heat resilience of intraspecific outbred compared to inbred lineages in the Kelp Laminaria digitata: physiology and transcriptomicsPublication . Liesner, Daniel; Pearson, Gareth Anthony; Bartsch, Inka; Rana, Shivani; Harms, Lars; Heinrich, Sandra; Bischof, Kai; Glöckner, Gernot; Valentin, KlausMarine 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 degrees C. The upper survival temperature of microscopic sporophytes was lower for the inbred Arctic selfing (21 degrees C) than for the temperate selfing and the reciprocal crosses (22 degrees C). Only in the temperate selfing, 4.5% of sporophytes survived 23 degrees C. We then subjected 4-7 cm long sporophytes to a control temperature (10 degrees C), moderate (19 degrees C) and sublethal to lethal heat stress (20.5 degrees 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 degrees C, while inbred Arctic sporophytes died within seven days at both 19 and 20.5 degrees C. In response to 20.5 degrees 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 degrees 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 physiology and the differential expression of nine genes between the reciprocal crosses at 20.5 degrees C indicate that female and male gametophytes may contribute differently to offspring traits. We consider potential inbreeding depression in the Spitsbergen selfing and quantify the better performance of both crosses using heterosis-related parameters. We discuss the potential and risks of outbreeding to produce more resilient crops for mariculture and marine forest restoration.