Adaptive divergence across Southern Ocean gradients in the pelagic diatom Fragilariopsis kerguelensis.

The Southern Ocean is characterized by longitudinal water circulations crossed by strong latitudinal gradients. How this oceanographic background shapes planktonic populations is largely unknown, despite the significance of this region for global biogeochemical cycles. Here, we show, based on genomic, morphometric, ecophysiological and mating compatibility data, an example of ecotypic differentiation and speciation within an endemic pelagic inhabitant, the diatom Fragilariopsis kerguelensis. We discovered three genotypic variants, one present throughout the latitudinal transect sampled, the others restricted to the north and south, respectively. The latter two showed reciprocal monophyly across all three genomes and significant ecophysiological differences consistent with local adaptation, but produced viable offspring in laboratory crosses. The third group was also reproductively isolated from the latter two. We hypothesize that this pattern originated by an adaptive expansion accompanied by ecotypic divergence, followed by sympatric speciation.

Comparative analysis of bottom trawl and nanopore sequencing in fish biodiversity assessment: The sylt outer reef example.

The assessment of fish diversity is crucial for effective conservation and management strategies, especially in ecologically sensitive regions such as marine protected areas. This study contrasts the effectiveness of environmental DNA (eDNA) metabarcoding analysis employing Nanopore technology with compare beam trawl surveys at the Sylt Outer Reef, a Natura 2000 site in the North Sea, Germany. Out of the 17 fish species caught in a bottom trawl (using a 3m beam trawl), 14 were also identified through eDNA extracted from water samples. The three species not detected in the eDNA results were absent because they lacked representation in public DNA databases. The eDNA method detected twice as many fish species as the beam trawl, totalling 36 species, of which 14 were also detected by the trawl. Additionally, the selection of primers (Mifish) facilitated the identification of one marine mammal species, the harbour porpoise. In conclusion, the findings underscore the potential of eDNA coupled with MinION sequencing (Long read technology) as a robust tool for biodiversity assessment, surpassing traditional methods in detecting species richness.

Migration-related changes in gene expression in leg muscle of the Christmas Island red crab Gecarcoidea natalis: seasonal preparation for long-distance walking.

During their annual breeding migration the Christmas Island land crab Gecarcoidea natalis sustains locomotion aerobically for up to 12 h per day compared with just 10 min during the dry season when their muscles quickly become anaerobic. A seasonal transition to an endurance-muscle phenotype would thus seem essential for migrating crabs. The current study employed a gene discovery approach comparing two expressed sequence tag (EST) libraries, one each for leg muscle from dry (non-migrating) and wet season (migrating) crabs. The 14 most abundant transcripts differed in their representation between the two libraries. The abundances of transcripts of genes predicted to code for different proteins forming contractile muscle components, including actin, troponin and tropomyosin, were significantly different between seasons and thus between physiological states. The shift in the isoform composition of the contractile elements provided evidence for a switch from slow phasic (S1) to slow tonic (S2) fatigue-resistant muscle fibres. A tropomyosin (tm) transcript aligned with a tm isoform of lobster (tmS2), and semi-quantitative RT-PCR confirmed this isoform to be more abundant in the migrating crab muscle. Two LIM protein coding genes, a paxillin-like transcript (pax) and a muscle LIM protein (mlp), were relatively up-regulated in muscle of wet season crabs. These proteins have a fundamental role in muscle development and reconstruction, and their comparative up-regulation is consistent with a remodelling of leg muscle for migration in the wet season. Such a transition would result in an increased representation of aerobic endurance-type fibres concomitant with the greater aerobic exercise capacity of the migrating red crabs.

The adaptive significance of crustacean hyperglycaemic hormone (CHH) in daily and seasonal migratory activities of the Christmas Island red crab Gecarcoidea natalis.

The Christmas Island red crab Gecarcoidea natalis undergoes extreme changes in metabolic status, ranging from inactivity during the dry season, to a spectacular annual breeding migration at the start of the wet season. The dramatic change in metabolic physiology that this polarisation entails should be reflected in changes in endocrine physiology, particularly that of the crustacean hyperglycaemic hormone (CHH), of which we know relatively little. CHH levels were measured using a novel ultrasensitive time-resolved fluoroimmunoassay (TR-FIA), together with metabolites (glucose, lactate), in the field at several scales of temporal resolution, during migratory activities (wet season) and during the inactive fossorial phase (dry season). Release patterns of CHH were measured during extreme (forced) exercise, showing for the first time an unexpectedly rapid pulsatile release of this hormone. A seasonally dependent glucose-sensitive negative-feedback loop was identified that might be important in energy mobilisation during migration. Haemolymph lactate levels were strongly correlated with CHH levels in both field and experimental animals. During migration, CHH levels were lower than during the dry season and, during migration, daytime CHH levels (when most locomotor activity occurred) increased. However, the intense dawn activity in both dry and wet seasons was not always associated with repeatable hyperglycaemia or CHH release. The results obtained are discussed in relation to the life history and behaviour of G. natalis.