Osmoregulation in Barnacles: An Evolutionary Perspective of Potential Mechanisms and Future Research Directions

Measurement of protein concentration in bacteria and small organelles under a light transmission microscope

Protein concentration (PC) is an essential characteristic of cells and organelles; it determines the extent of macromolecular crowding effects and serves as a sensitive indicator of cellular health. A simple and direct way to quantify PC is provided by brightfield-based transport-of-intensity equation (TIE) imaging combined with volume measurements. However, since TIE is based on geometric optics, its applicability to micrometer-sized particles is not clear. Here, we show that TIE can be used on particles with sizes comparable to the wavelength. At the same time, we introduce a new ImageJ plugin that allows TIE image processing without resorting to advanced mathematical programs. To convert TIE data to PC, knowledge of particle volumes is essential. The volumes of bacteria or other isolated particles can be measured by displacement of an external absorbing dye ("transmission-through-dye" or TTD microscopy), and for spherical intracellular particles, volumes can be estimated from their diameters. We illustrate the use of TIE on Escherichia coli, mammalian nucleoli, and nucleolar fibrillar centers. The method is easy to use and achieves high spatial resolution.

Evolving views of ionic, osmotic and acid-base regulation in aquatic animals

The regulation of ionic, osmotic and acid-base (IOAB) conditions in biological fluids is among the most fundamental functions in all organisms; being surrounded by water uniquely shapes the IOAB regulatory strategies of water-breathing animals. Throughout its centennial history, Journal of Experimental Biology has established itself as a premier venue for publication of comparative, environmental and evolutionary studies on IOAB regulation. This Review provides a synopsis of IOAB regulation in aquatic animals, some of the most significant research milestones in the field, and evolving views about the underlying cellular mechanisms and their evolutionary implications. It also identifies promising areas for future research and proposes ideas for enhancing the impact of aquatic IOAB research.

Effects of low salinity stress on osmoregulation and gill transcriptome in different populations of mud crab Scylla paramamosain

Animals living in estuaries suffer from rapid and continuous salinity fluctuations, while the global warming and extreme precipitation aggravate this situation. Osmoregulation is important for estuarine animals adapt to salinity fluctuations. The present study investigated the effects of low salinity stress on osmoregulation and gill transcriptome in two populations of mud crab from Hangzhou Bay and Zhangzhou Bay of China, respectively. Crabs were transferred from salinity 25 ppt to 5 ppt for 96 h. Edematous swelling in gill filaments was caused by low salinity stress and was more serious in Zhangzhou Bay population. Gill Na⁺/K⁺-ATPase activity increased (p < 0.01) in both populations under the low salinity stress and was significantly higher (p < 0.01) in Hangzhou Bay population than in Zhangzhou Bay population. According to transcriptome analysis, there were 191 genes differentially expressed under the low salinity stress in gill tissue of both populations. Several ion transport and energy metabolism related pathways, as well as the arginine and proline metabolism pathway, were enriched by these genes. On the other hand, 272 genes were identified to differentially express between two populations under the low salinity stress, but not under the control salinity. The enrichment analysis showed that these genes were mainly related to ion transport, energy metabolism, osmolytes metabolism and methyltransferase activity. In conclusion, the present study suggested that mud crab exploited a combination of extracellular anisosmotic regulation and intracellular isosmotic regulation for osmoregulation under the low salinity stress. Hangzhou Bay population showed a greater osmoregulatory capacity, which is probably due to the enhanced ion transport, energy supply, and osmolytes regulation. Meanwhile, epigenetic modification might also contribute to an inherent osmoregulation ability for Hangzhou Bay population to response to salinity fluctuation rapidly.

A decade of progress in marine evolutionary biology

This article summarizes the Evolutionary Applications Special Issue, "A decade of progress in Marine Evolutionary Biology." The globally connected ocean, from its pelagic depths to its highly varied coastlines, inspired Charles Darwin to develop the theory of evolution during the voyage of the Beagle. As technology has developed, there has been a dramatic increase in our knowledge about life on our blue planet. This Special Issue, composed of 19 original papers and seven reviews, represents a small contribution to the larger picture of recent research in evolutionary biology, and how such advancements come about through the connection of researchers, their fields, and their knowledge. The first European network for marine evolutionary biology, the Linnaeus Centre for Marine Evolutionary Biology (CeMEB), was developed to study evolutionary processes in the marine environment under global change. Though hosted by the University of Gothenburg in Sweden, the network quickly grew to encompass researchers throughout Europe and beyond. Today, more than a decade after its foundation, CeMEB's focus on the evolutionary consequences of global change is more relevant than ever, and knowledge gained from marine evolution research is urgently needed in management and conservation. This Special Issue, organized and developed through the CeMEB network, contains contributions from all over the world and provides a snapshot of the current state of the field, thus forming an important basis for future research directions.

Ten years of marine evolutionary biology-Challenges and achievements of a multidisciplinary research initiative

The Centre for Marine Evolutionary Biology (CeMEB) at the University of Gothenburg, Sweden, was established in 2008 through a 10-year research grant of 8.7 m€ to a team of senior researchers. Today, CeMEB members have contributed >500 scientific publications, 30 PhD theses and have organised 75 meetings and courses, including 18 three-day meetings and four conferences. What are the footprints of CeMEB, and how will the centre continue to play a national and international role as an important node of marine evolutionary research? In this perspective article, we first look back over the 10 years of CeMEB activities and briefly survey some of the many achievements of CeMEB. We furthermore compare the initial goals, as formulated in the grant application, with what has been achieved, and discuss challenges and milestones along the way. Finally, we bring forward some general lessons that can be learnt from a research funding of this type, and we also look ahead, discussing how CeMEB's achievements and lessons can be used as a springboard to the future of marine evolutionary biology.

Ecological Load and Balancing Selection in Circumboreal Barnacles

Acorn barnacle adults experience environmental heterogeneity at various spatial scales of their circumboreal habitat, raising the question of how adaptation to high environmental variability is maintained in the face of strong juvenile dispersal and mortality. Here, we show that 4% of genes in the barnacle genome experience balancing selection across the entire range of the species. Many of these genes harbor mutations maintained across 2 My of evolution between the Pacific and Atlantic oceans. These genes are involved in ion regulation, pain reception, and heat tolerance, functions which are essential in highly variable ecosystems. The data also reveal complex population structure within and between basins, driven by the trans-Arctic interchange and the last glaciation. Divergence between Atlantic and Pacific populations is high, foreshadowing the onset of allopatric speciation, and suggesting that balancing selection is strong enough to maintain functional variation for millions of years in the face of complex demography.

Genomic Characterization of the Barnacle Balanus improvisus Reveals Extreme Nucleotide Diversity in Coding Regions

Barnacles are key marine crustaceans in several habitats, and they constitute a common practical problem by causing biofouling on man-made marine constructions and ships. Despite causing considerable ecological and economic impacts, there is a surprising void of basic genomic knowledge, and a barnacle reference genome is lacking. We here set out to characterize the genome of the bay barnacle Balanus improvisus (= Amphibalanus improvisus) based on short-read whole-genome sequencing and experimental genome size estimation. We show both experimentally (DNA staining and flow cytometry) and computationally (k-mer analysis) that B. improvisus has a haploid genome size of ~ 740 Mbp. A pilot genome assembly rendered a total assembly size of ~ 600 Mbp and was highly fragmented with an N50 of only 2.2 kbp. Further assembly-based and assembly-free analyses revealed that the very limited assembly contiguity is due to the B. improvisus genome having an extremely high nucleotide diversity (π) in coding regions (average π ≈ 5% and average π in fourfold degenerate sites ≈ 20%), and an overall high repeat content (at least 40%). We also report on high variation in the α-octopamine receptor OctA (average π = 3.6%), which might increase the risk that barnacle populations evolve resistance toward antifouling agents. The genomic features described here can help in planning for a future high-quality reference genome, which is urgently needed to properly explore and understand proteins of interest in barnacle biology and marine biotechnology and for developing better antifouling strategies.

The transcriptomic response of adult salmon lice (Lepeophtheirus salmonis) to reduced salinity

Salmon lice (Lepeophtheirus salmonis) are marine parasitic copepods living on salmonids and are challenging for salmon aquaculture. One of several treatment methods is the application of freshwater to the fish which can lead to lice loss. However, lab experiments have shown that salmon lice, acclimated to seawater, are capable of surviving for several weeks in freshwater, when attached to a host. If not attached to a host, they die within a few hours in freshwater but can survive a longer time in brackish water. The molecular mechanisms involved in the adaptation to low salinity of the louse have not been identified yet. In this study we incubated salmon lice, being attached to a host, or detached, in seawater, brackish water and freshwater for 4 h and 1 d, sampled the animals and used RNA-Seq to identify genes involved in these mechanisms. Freshwater incubation led to a much stronger regulatory response than brackish water and a longer incubation time gave a stronger effect than a short incubation. Among the most interesting genes, upregulated in low salinity water are in addition to several transporters, several enzymes involved in amino acid metabolism and especially in the proline biosynthesis. A strong upregulation of these enzymes might lead to an accumulation of proline which is known to be used as an osmolyte in other species. While the RNA-Seq experiment was performed with female samples, qPCR showed that at least 10 genes regulated in females, were also regulated in males.