The information continuum model of evolution

Most biologists agree that evolution is contingent on inherited information shaped by natural selection. This apparent consensus could be taken to indicate agreement on the forces shaping evolution, but vivid discussions reveal divergences on how evolution is perceived. The predominant Modern Synthesis (MS) paradigm holds the position that evolution occurs through random changes acting on genomic inheritance. However, studies from recent decades have revealed that evolutionary inheritance also includes DNA-methylation, RNA, symbionts, and culture, among other factors. This has fueled a demand of a broader evolutionary perspective, for example from the proponents of the Extended Evolutionary Synthesis (EES). Despite fundamental disagreements the different views agree that natural selection happens through dissimilar perpetuation of inheritable information. Yet, neither the MS, nor the ESS dwell extensively on the nature of hereditary information. We do - and conclude that information in and of itself is immaterial. We then argue that the quality upon which natural selection acts henceforth is also immaterial. Based on these notions, we arrive at the information-centric Information Continuum Model (ICM) of evolution. The ICM asserts that hereditary information is embedded in diverse physical forms (DNA, RNA, symbionts etc.) representing a continuum of evolutionary qualities, and that information may migrate between these physical forms. The ICM leaves theoretical exploration of evolution unrestricted by the limitations imposed by the individual physical forms wherein the hereditary information is embedded (e.g. genomes). ICM bestows us with a simple heuristic model that adds explanatory dimensions to be considered in the evolution of biological systems.publishedVersio

Production, mortality, and infectivity of planktonic larval sea lice, Lepeophtheirus salmonis (Krøyer, 1837): current knowledge and implications for epidemiological modelling

Current sea louse models attempt to estimate louse burdens on wild and cultured salmon by predicting the production and distribution of lice larvae and estimating the risk of transmission. While physical characteristics of water bodies and weather can be accurately modelled, many aspects of sea lice biology require further parameterization. The aims of this review are (i) to describe current knowledge regarding the production, mortality, and infectivity of planktonic sea lice larvae and (ii) to identify gaps in knowledge and suggest research approaches to filling them. Several major gaps are identified, and those likely to have the greatest impact on infection levels are (i) egg production, viability and hatching success, (ii) predation in plankton and (iii) copepodid infectivity profiles. A key problem identified in current parameter estimates is that they originate from a number of sources and have been determined using a variety of experimental approaches. This is a barrier to the provision of “best” or consensus estimates for use in modelling. Additional and more consistent data collection and experimentation will help to fill these gaps. Furthermore, coordinated international efforts are required to generate a more complete picture of sea louse infections across all regions experiencing problems with sea lice

Disentangling the key drivers of salmon louse Lepeophtheirus salmonis fecundity using multiyear field samples

Planktonic salmon louse Lepeophtheirus salmonis salmonis larvae produced at sal - mon farms spread to and infect both wild and farmed salmonids. Understanding and forecasting the production and distribution of these larval stages from farms is critical to aquaculture management. However, model forecasts are based on available data and therefore include parameters with limited empirical support. This investigation examined salmon louse fecundity with a focus on batch egg clutch size by collecting lice from farmed Atlantic salmon Salmo salar at multiple farms and from wild Atlantic salmon and sea trout S. trutta captured at field sites throughout Norway. The data were analyzed with mixed effects models and total length of female lice was identified as the primary determinant of clutch size. Further analysis revealed that female louse total length is partially explained by temperature at sampling. However, if the temperature at sampling is spatially or temporally disconnected from rearing temperature, it may not be possible to predict the total length of a louse using temperature. The fecundity investigation further found that 66% of female lice on farmed salmon were sexually mature, and 10% of these were not egg-bearing. In comparison, 73% of adult female lice on sea trout were sexually mature, and 40% of these were not egg-bearing. Our results indicate that salmon louse production forecasts would be improved by incorporating female louse sexual maturity and a clutch size parameter that is related to total length of female lice.publishedVersio

The effect of a warmer climate on the salmon lice infection pressure from Norwegian aquaculture

Climate change can hamper sustainable growth in the aquaculture industry by amplifying and adding to other environmental challenges. In Norway, salmon lice-induced mortality in wild salmonid populations is identified as a major risk factor for further expansion. Higher temperatures will induce increased production of salmon lice larvae, decreased developmental time from non-infective nauplii to infectious copepods, and higher infectivity of copepodids. In a warmer climate, a modelling exercise shows how these three factors lead to a significant increase in the infection pressure from farmed to wild salmonids, where the infectivity of copepodids is the term with the highest sensitivity to temperature changes. The total infection pressure gradually increases with increasing temperature, with an estimated twofold if the temperature increases from 9°C to 11°C. Thus, making it even harder to achieve a sustainable expansion of the industry with rising water temperature. This study demonstrates how bio-hydrodynamic models might be used to assess the combined effects of future warmer climate and infection pressure from salmon lice on wild salmonids. The results can be used as an early warning for the fish-farmers, conservation stakeholders and the management authorities, and serve as a tool to test mitigation strategies before implementation of new management plans.publishedVersio

Development of the salmon louse Lepeophtheirus salmonis parasitic stages in temperatures ranging from 3 to 24°C

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Parasite development affect dispersal dynamics; infectivity, activity and energetic status in cohorts of salmon louse copepodids

The salmon louse, Lepeophtheirus salmonis, is a parasitic copepod infecting wild and farmed salmonid fishes in the northern hemisphere. It has a direct lifecycle with a planktonic dispersal phase and an infective copepodid stage preceding five host bound stages. Several models predicting the dispersal of this ecologically and economically important pathogen have been developed, but none include variability in capability to infect. Therefore, the effect of age and temperature on infectivity and lipid metabolism was investigated experimentally using seven synchronized cohorts of copepodids at 5, 10 and 15 °C. In newly molted copepodids infectivity initially increase and then decrease with senescence. Within the experimental temperature range, peak infectivity was higher and occurred earlier at higher temperatures. While degree-days may serve as a useful crude descriptor of developmental age, it did not allow accurate prediction of infectivity peak timing and magnitude unless temperature was included as a separate factor in the derived infectivity model. Senescence was reflected in lipid store depletion and a temperature dependent variability in membrane lipid composition was evident. Interestingly, copepodids developing at 5 °C had approximately 50% less storage lipids when they molted into the parasitic stage than those developing at 10 and 15 °C. The declines in infectivity and storage energy were mirrored in decreasing copepodid swimming activity. When incorporating the copepodid infectivity results from this study into salmon louse dispersal model parameterization, the predictions suggest that earlier models may have underestimated the seasonal differences in salmon louse infection risk.publishedVersio

A trypsin-like protease with apparent dual function in early Lepeophtheirus salmonis (Krøyer) development

<p>Abstract</p> <p>Background</p> <p>Trypsin-like serine proteases are involved in a large number of processes including digestive degradation, regulation of developmental processes, yolk degradation and yolk degradome activation. Trypsin like peptidases considered to be involved in digestion have been characterized in <it>Lepeophtheirus salmonis</it>. During these studies a trypsin-like peptidase which differed in a number of traits were identified.</p> <p>Results</p> <p>An intronless trypsin-like serine peptidase (<it>LsTryp10</it>) from <it>L., salmonis </it>was identified and characterized. <it>LsTryp10 </it>mRNA is evenly distributed in the ovaries and oocytes, but is located along the ova periphery. LsTryp10 protein is deposited in the oocytes and all embryonic cells. <it>LsTryp10 </it>mRNA translation and concurrent degradation after fertilization was found in the embryos demonstrating that LsTryp10 protein is produced both by the embryo and maternally. The results furthermore indicate that LsTryp10 protein of maternal origin has a distribution pattern different to that of embryonic origin.</p> <p>Conclusion</p> <p>Based on present data and previous studies of peptidases in oocytes and embryos, we hypothesize that maternally deposited LsTryp10 protein is involved in regulation of the yolk degradome. The function of LsTryp10 produced by the embryonic cells remains unknown. To our knowledge a similar expression pattern has not previously been reported for any protease.</p

The effect of temperature on ability of Lepeophtheirus salmonis to infect and persist on Atlantic salmon

The salmon louse (Lepeophtheirus salmonis) is an ecologically and economically important parasite of salmonid fish. Temperature is a strong influencer of biological processes in salmon lice, with development rate increased at higher temperatures. The successful attachment of lice onto a host is also predicted to be influenced by temperature; however, the correlation of temperature with parasite survival is unknown. This study describes the effects of temperature on infection success, and survival on the host during development to the adult stage. To accurately describe infection dynamics with varying temperatures, infection success was recorded on Atlantic salmon (Salmo salar) between 2 and 10°C. Infection success ranged from 20% to 50% and was strongly correlated with temperature, with the highest success at 10°C. Parasite loss was monitored during development at eight temperatures with high loss of lice at 3 and 24°C, whilst no loss was recorded in the temperature range from 6 to 21°C. Sea temperatures thus have large effects on the outcome of salmon louse infections and should be taken into account in the management and risk assessment of this parasite. Improving understanding of the infection dynamics of salmon lice will facilitate epidemiological modelling efforts and efficiency of pest management strategies.publishedVersio

Comparison of visual and molecular taxonomic methods to identify ichthyoplankton in the North Sea

The North Sea is an important spawning and nursery ground for many demersal and pelagic fishes whose spawning areas are largely overlapping in time and space. This makes ichthyoplankton visual identification from the various species particularly challenging. Despite historically intensive research in the area, detailed information on spawning sites and times for many taxa, are incomplete. To update and detail the mapping of fish spawning performance and distribution in the central and northern regions of the North Sea, the performance of a visual method and a molecular taxonomic approach used for taxonomic classification of ichthyoplankton was evaluated. Samples of fish eggs and larvae were collected regularly and in parallel at different latitudinal locations from the central to the northern North Sea, including a sample with 78 larvae used for direct comparison between both methods. A total of 5332 individuals were inspected and 36 different species were identified. The visual processing identified 89% of the collected larvae to species level, however, for the eggs the taxonomic resolution was lower with only 5% identified to species level. In comparison to visual identification, molecular barcoding gave higher precision of identification for larvae and especially for the eggs. For the larvae, 98% were assigned to species level, and for the eggs 94% were assigned to species level. We find that molecular barcoding is more effective and precise in taxonomic identification of both eggs and larvae to species level. However, visual identification is still needed to provide information on the developmental stages.publishedVersio

The salmon louse Lepeophtheirus salmonis (Copepoda: Caligidae) life cycle has only two chalimus stages

Each year the salmon louse (Lepeophtheirus salmonis Krøyer, 1838) causes multi-million dollar commercial losses to the salmon farming industry world-wide, and strict lice control regimes have been put in place to reduce the release of salmon louse larvae from aquaculture facilities into the environment. For half a century, the Lepeophtheirus life cycle has been regarded as the only copepod life cycle including 8 post-nauplius instars as confirmed in four different species, including L. salmonis. Here we prove that the accepted life cycle of the salmon louse is wrong. By observations of chalimus larvae molting in incubators and by morphometric cluster analysis, we show that there are only two chalimus instars: chalimus 1 (comprising the former chalimus I and II stages which are not separated by a molt) and chalimus 2 (the former chalimus III and IV stages which are not separated by a molt). Consequently the salmon louse life cycle has only six post-nauplius instars, as in other genera of caligid sea lice and copepods in general. These findings are of fundamental importance in experimental studies as well as for interpretation of salmon louse biology and for control and management of this economically important parasite.publishedVersio