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The patchy distribution of the ditch shrimp Palaemon varians (Palaemonidae) in small-scale habitats with low salinity may hint at isolation and fragmentation processes. In order to evaluate the extent to which gene flow barriers exist and salinity has an influence on this dispersal pattern, the genetic diversity and differentiation of Baltic and North Sea populations were investigated and set in context with sequence data from the Mediterranean Sea. Therefore, 133 sequences of a fragment of the cytochrome oxidase subunit 1 (COI) from 13 different populations from the Baltic Sea and North Sea were generated and complemented with publicly available sequences to estimate a haplotype network and calculate genetic differentiation and diversity. The results show that genetic differentiation correlates with geographic distance and the populations of the different basins are differentiated from each other. In contrast to the expectation, genetic differentiation was generally weak within basins. However, different clusters of differentiated populations could be revealed, indicating two migration events into the Baltic Sea.

Since its introduction in the 1960’s for aquaculture, the Pacific oyster Magallana gigas (Thunberg, 1793) has successfully spread along almost all European coasts with far-reaching consequences for marine ecosystems. Up to now, it has not been recorded from the Baltic Sea proper. This was considered a consequence of the low salinity conditions, which are not suitable for larval development. Here we report our first records of Pacific oysters in the German Baltic Sea, specifically in the Kiel Bight. We confirmed their species identification by genetic barcoding. We suggest that Pacific oysters were able to settle in the Baltic Sea proper due to unusually high salinities that prevailed since the summer of 2018. Should these conditions occur more frequently in the future, or M. gigas be able to adapt to lower salinities, oysters may become established in the Baltic Sea proper.

AimEnvironmental gradients have emerged as important barriers structuring populations and species distributions. We set out to test whether a strong salinity gradient from marine to brackish, represented in a marginal northern European sea, should be considered a diversification hotspot or a population sink, and to identify life history traits that correlate with either evolutionary trajectory.LocationThe Baltic Sea, the North Sea and their transition zone.MethodsWe accumulated mitochondrial cytochrome oxidase subunit 1 sequence data and data on the distribution, salinity tolerance and life history for 28 species belonging to the Cnidaria, Crustacea, Echinodermata, Mollusca, Polychaeta and Gastrotricha, including seven non-native species. We calculated measures of genetic diversity and differentiation across the environmental gradient, coalescent times and migration rates between North and Baltic Sea populations, and analysed correlations between genetic and life history data.ResultsThe majority of investigated species is either genetically differentiated and/or is adapted to the lower salinity conditions of the Baltic Sea. Moreover, the species exhibiting population structure have a range of patterns of genetic diversity in comparison to the North Sea, from lower in the Baltic Sea to higher in the Baltic Sea, or equally diverse in North and Baltic Sea.Main conclusionsOur results indicate that the Baltic Sea should be considered a diversification hotspot: The diversity of genetic patterns points towards independent trajectories in the Baltic compared to the North Sea. At the same time, we found limited evidence for the traditional scenario of the Baltic Sea as a population sink with lower diversity and strong gene flow. The North Sea - Baltic Sea region provides a unique setting to study evolutionary adaptation during colonization processes at different stages by jointly considering native and non-native species.

The Chinese mitten crab (Eriocheir sinensis) is a prominent aquatic invader with substantial negative economic and environmental impacts. The aim of the present study was to re-evaluate the genetic diversity of mitten crabs throughout their native and invaded ranges based on publicly available sequence data, and assess if multiple introductions or rapid adaptation could be responsible for biologically divergent mitten crabs in Northern Europe. We assembled available genetic data of a fragment of the mitochondrial cytochrome c oxidase subunit one gene (COI) for all species of the genusEriocheir. We applied phylogenetic and population genetic analyses to compare native and invasive populations, and to identify possible source populations. The phylogenetic reconstruction revealed that five COI sequences from Europe, morphologically identified as Chinese mitten crab, actually belong to the Japanese mitten crab (Eriocheir japonica), representing the first indication of its presence in European waters. All other COI sequences from Europe could unambiguously be assigned to the Chinese mitten crab. In some Northern German populations of Chinese mitten crabs, genetic diversity was surprisingly high, due to seven unique haplotypes encoding several amino acid substitutions. This diversity may reflect a cryptic introduction from an unsampled native location, or rapid adaptation in the invaded range. Based on the genetic diversity shared between native and introduced range, Feiyunjiang, a tributary of the Yangtze River, emerges as a plausible source population for the original introduction of Chinese mitten crabs to Europe. This study highlights the complex and dynamic invasion processes of mitten crabs in Europe. We urge to further monitor mitten crab invasions using genetic tools.

While equal ratios of males and females are normal, crustacean sex ratios are frequently biased. Here I review potential reasons for sex ratio biases in animals, and evaluate how likely they apply ...

Changing species assemblages represent major challenges to ecosystems around the world. Retracing these changes is limited by our knowledge of past biodiversity. Natural history collections represent archives of biodiversity and are therefore an unparalleled source to study biodiversity changes. In the present study, we tested the value of natural history collections for reconstructing changes in the abundance and presence of species over time. In total, we scrutinized 17 080 quality-checked records for 242 epibenthic invertebrate species from the North and Baltic Seas collected throughout the last 200 years. Our approaches identified eight previously reported species introductions, 10 range expansions, six of which are new to science, as well as the long-term decline of 51 marine invertebrate species. The cross-validation of our results with published accounts of endangered species and neozoa of the area confirmed the results for two of the approaches for 49 to 55% of the identified species, and contradicted our results for 9 to 10%. The results based on relative record trends were less validated. We conclude that, with the proper approaches, natural history collections are an unmatched resource for recovering early species introductions and declines.

Environmental gradients have emerged as important barriers to structuring populations and species distributions. We set out to test whether the strong salinity gradient from the marine North Sea to the brackish Baltic Sea in northern Europe represents an ecological and genetic break, and to identify life history traits that correlate with the strength of this break. We accumulated mitochondrial cytochrome oxidase subunit 1 sequence data, and data on the distribution, salinity tolerance, and life history for 28 species belonging to the Cnidaria, Crustacea, Echinodermata, Mollusca, Polychaeta, and Gastrotricha. We included seven non-native species covering a broad range of times since introduction, in order to gain insight into the pace of adaptation and differentiation. We calculated measures of genetic diversity and differentiation across the environmental gradient, coalescent times, and migration rates between North and Baltic Sea populations, and analyzed correlations between genetic and life history data. The majority of investigated species is either genetically differentiated and/or adapted to the lower salinity conditions of the Baltic Sea. Species exhibiting population structure have a range of patterns of genetic diversity in comparison with the North Sea, from lower in the Baltic Sea to higher in the Baltic Sea, or equally diverse in North and Baltic Sea. Two of the non-native species showed signs of genetic differentiation, their times since introduction to the Baltic Sea being about 80 and700 years, respectively. Our results indicate that the transition from North Sea to Baltic Sea represents a genetic and ecological break: The diversity of genetic patterns points toward independent trajectories in the Baltic compared with the North Sea, and ecological differences with regard to salinity tolerance are common. The North Sea-Baltic Sea region provides a unique setting to study evolutionary adaptation during colonization processes at different stages by jointly considering native and non-native species.

We present a comprehensive revision and synthesis of the higher-level classification of the barnacles (Crustacea: Thecostraca) to the genus level and including both extant and fossils forms. We provide estimates of the number of species in each group. Our classification scheme has been updated based on insights from recent phylogenetic studies and attempts to adjust the higher-level classifications to represent evolutionary lineages better, while documenting the evolutionary diversity of the barnacles. Except where specifically noted, recognized taxa down to family are argued to be monophyletic from molecular analysis and/or morphological data. Our resulting classification divides the Thecostraca into the subclasses Facetotecta, Ascothoracida and Cirripedia. The whole class now contains 14 orders, 65 families and 367 genera. We estimate that barnacles consist of 2116 species. The taxonomy is accompanied by a discussion of major morphological events in barnacle evolution and justifications for the various rearrangements we propose.

Background During the COVID-19 pandemic, supplies of personal protective equipment (PPE) have been limited and sold at increased cost. Prior to the pandemic, we had initiated a project to improve PPE adherence and decrease cost by removing eligible patients from transmission based precautions (TBPs). At baseline, ordering providers are responsible for TBP utilization with orders through the electronic medical record. We observed that patients were in TBP when not indicated; remained in TBP beyond the appropriate time; and a reluctance on the part of providers to discontinue the orders. We tested the effect on TBP duration and PPE utilization house-wide through frequent review of TBP by a nurse educator with communication to providers of discontinuation opportunities. Methods From November 2019 to February 2020, all TBP orders in the pediatric intensive care unit (PICU) were reviewed intermittently. In March 2020, review was expanded to all inpatients with daily reviews in all units. Changes recommended and completed were tracked for all reviewed patients. We estimated cost of PPE in the PICU over time based on the number of patients in isolation and type of TBP utilized to determine whether our intervention resulted in reduced PPE use. Results Regular rounding in the PICU increased the proportion of patients in appropriate TBP and reduced the need to communicate with providers directly (33% vs 3% requiring intervention, Figure 1). Over the same time period, less PPE was used and PPE-related costs lowered (average total PPE cost $306.18 vs $95.15 per day, Figure 2). Less of an effect was seen when analyzing house-wide data. Figure 1 - P-chart of Percent Interventions Among Patients in TBP Figure 2 - X-chart of Total PPE Cost in the ICU Conclusion Isolation rounds is an effective means to ensure proper TBP adherence and manage PPE use appropriately. Additional study is needed to confirm a return on investment, to account for variation among units, and to sustain COVID-19-influenced gains beyond the pandemic. Disclosures All Authors: No reported disclosures

Genetic studies of introduced non-native species are a valuable tool to investigate invasion history and pathways, source populations and multiple introductions of alien species, as well as evolutionary genetic changes following establishment in a new environment. We used a set of nine polymorphic microsatellites to analyse the population genetic structure of the introduced Asian shore crabHemigrapsus takanoialong European coasts. Our dataset covered the complete known European range of the species, including the most recent records from Great Britain and the southwestern Baltic Sea. The results showed a similarly high genetic diversity ofH. takanoithroughout Europe, and no indication of genetic bottlenecks during secondary spread, even in the most recently established populations. Analyses for population structure along geographic regions gave support for a separation between the Bay of Seine populations (northern France) and all other populations. Genetic differentiation within the North and Baltic Seas was more subtle and patchy, hinting to potential unrecognised introduction events, dispersal barriers and anthropogenic vector activity. The populations from the Baltic Sea and Great Britain clustered with the Wadden Sea populations, suggesting secondary introductions from the southeastern North Sea as likely invasion pathways. In summary, we suggest that a combination of anthropogenic secondary spread and the species’ reproductive biology have prevented a loss of genetic diversity during its ongoing expansion. We argue that genetic data depicting population status shortly after an introduction event—like the British and Baltic Sea populations ofH. takanoi—may provide important baseline data for investigations of genetic changes during establishment and adaptation processes.

Crustacea display diverse life histories and occur in all marine habitats. This makes them particularly useful when thinking about how we can predict geographical distribution from life history and ecology. As would be expected from such diversity, crustaceans exhibit various population connectivity patterns, from panmictic, well-connected populations to small and isolated populations. Here we ask first what can be learned from exploring crustacean phylogeography and connectivity around well-understood vicariance events with known ages. We find that vicariance events are generally useful in calibrating molecular rates of evolution, but that there is substantial variation between taxa. This variation can be linked, on the one hand, to habitat differences (which determine when gene flow between populations actually ceased) and, on the other hand, to population size differences (which determine how fast genetic differences accumulate). In a few instances, populations must have diverged much earlier or later than the hypothesized vicariance event, providing evidence of earlier or later dispersal or more ancient separation. Second, we ask when comparative studies of multiple taxa show consistent results, predictable from their similar life history, and when not. For example, species that disperse little, such as brooding peracarids, have smaller, more isolated populations than species with planktonic larvae, such as decapods. Less consistent are the patterns across biogeographic breaks. While gene flow is clearly limited across such breaks in some species, other species do not seem to perceive them. This to-date-unexplained variation challenges our understanding of marine phylogeography.

Symbiotic relationships are often species specific, allowing symbionts to adapt to their host environments. Host generalists, on the other hand, have to cope with diverse environments. One coping strategy is phenotypic plasticity, defined by the presence of host-specific phenotypes in the absence of genetic differentiation. Recent work indicates that such host-specific phenotypic plasticity is present in the West Pacific lineage of the commensal barnacle Chelonibia testudinaria (Linnaeus, 1758). We investigated genetic and morphological host-specific structure in the genetically distinct Atlantic sister lineage of C. testudinaria. We collected adult C. testudinaria from loggerhead sea turtles, horseshoe crabs, and blue crabs along the eastern U.S. coast between Delaware and Florida and in the Gulf of Mexico off Mississippi. We find that shell morphology, especially shell thickness, is host specific and comparable in similar host species between the Atlantic and West Pacific lineages. We did not detect significant genetic differentiation related to host species when analyzing data from 11 nuclear microsatellite loci and mitochondrial sequence data, which is comparable to findings for the Pacific lineage. The most parsimonious explanation for these parallel patterns between distinct lineages of C. testudinaria is that C. testudinaria maintained phenotypic plasticity since the lineages diverged 4-5 mya.

Barnacles and their allies (Thecostraca) are a biologically diverse, monophyletic crustacean group, which includes both intensely studied taxa, such as the acorn and stalked barnacles, as well as cryptic taxa, for example, Facetotecta. Recent efforts have clarified phylogenetic relationships in many different parts of the barnacle tree, but the outcomes of these phylogenetic studies have not yet been combined into a single hypothesis for all barnacles. In the present study, we applied a new “synthesis” tree approach to estimate the first working Barnacle Tree of Life. Using this approach, we integrated phylogenetic hypotheses from 27 studies, which did not necessarily include the same taxa or used the same characters, with hierarchical taxonomic information for all recognized species. This first synthesis tree contains 2,070 barnacle species and subspecies, including 239 barnacle species with phylogenetic information and 198 undescribed or unidentified species. The tree had 442 bifurcating nodes, indicating that 79.3% of all nodes are still unresolved. We found that the acorn and stalked barnacles, the Thoracica, and the parasitic Rhizocephala have the largest amount of published phylogenetic information. About half of the thecostracan families for which phylogenetic information was available were polyphyletic. We queried publicly available geographic occurrence databases for the group, gaining a sense of geographic gaps and hotspots in our phylogenetic knowledge. Phylogenetic information is especially lacking for deep sea and Arctic taxa, but even coastal species are not fully incorporated into phylogenetic studies.

Male genitalia are extraordinarily diverse, and this diversity makes them valuable taxonomic and phylogenetic markers. Genitalia of true crabs (Brachyura) consist of two pairs of modified appendages, or gonopods. The first pair is tubular, and holds the second pair during copulation. Whether the second pair is shorter or longer than the first pair has important implications for copulation. Its length is often similar in closely related species, e.g. within genera and families, but is highly variable in the Brachyura at large. The genus Calappa Weber, 1795 contains species with long, short, and intermediate-length second gonopods, representing an unusually variable pattern. We investigated the evolution of the second gonopods in Calappa and other members of Calappidae. We assembled a molecular multi-locus phylogeny (mitochondrial marker: COI and 16S, nuclear marker: Enolase, H3 and 28S). Based on this phylogeny, long second gonopods are the ancestral state for Calappa as well as Calappidae in general. Short second gonopods evolved once, while intermediate-length second gonopods evolved independently at least four times. Scanning electron microscopic images of second gonopods of 22 species of Calappidae reveal that shortening of the second gonopod is always achieved by a shortening of the terminal segment. Congruently, taxon-specific structures at the tip of the terminal segment of the second gonopod, such as spines and pistil-like protrusions, are limited to long second gonopods. Based on current knowledge, a shortening of the second gonopod should be accompanied by extensive changes in the copulatory mechanism of males and females, including changes to the copulatory mechanism, mechanism of species recognition, targets of sexual selection, and the potential for sperm removal. Calappa therefore provides a vital example for the study of changes in copulatory mechanisms.

Dispersal and adaptation are the two primary mechanisms that set the range distributions for a population or species. As such, understanding how these mechanisms interact in marine organisms in particular – with capacity for long‐range dispersal and a poor understanding of what selective environments species are responding to – can provide useful insights for the exploration of biogeographic patterns. Previously, the barnacle Notochthamalus scabrosus has revealed two evolutionarily distinct lineages with a joint distribution that suggests an association with one of the two major biogeographic boundaries (~30°S) along the coast of Chile. However, spatial and genomic sampling of this system has been limited until now. We hypothesized that given the strong oceanographic and environmental shifts associated with the other major biogeographic boundary (~42°S) for Chilean coastal invertebrates, the southern mitochondrial lineage would dominate or go to fixation in locations further to the south. We also evaluated nuclear polymorphism data from 130 single nucleotide polymorphisms to evaluate the concordance of the signal from the nuclear genome with that of the mitochondrial sample. Through the application of standard population genetic approaches along with a Lagrangian ocean connectivity model, we describe the codistribution of these lineages through a simultaneous evaluation of coastal lineage frequencies, an approximation of larval behavior, and current‐driven dispersal. Our results show that this pattern could not persist without the two lineages having distinct environmental optima. We suggest that a more thorough integration of larval dynamics, explicit dispersal models, and near‐shore environmental analysis can explain much of the coastal biogeography of Chile.

Androdioecy is a sexual system characterized by the coexistence of hermaphrodites and males. It has evolved several times independently in ancestrally hermaphroditic barnacles. Life history and sex allocation theory suggest that dwarf males can occur in hermaphroditic populations with very small mating groups, low growth rates and high mortality rates. We tested these predictions in the androdioecious barnacle Chelonibia testudinaria (Linnaeus, 1758), an epibiont on loggerhead sea turtles, blue crabs, and horseshoe crabs. The potential number of mates is indeed very small on invertebrate hosts but larger on sea turtles. Growth rates are host-specific but comparable to those of other purely hermaphroditic barnacle species. The maximum age of hermaphrodites was less than three years, which is lower than in most purely hermaphroditic species. Our data suggest that small mating groups on some hosts and high mortality on all hosts contribute to the evolutionary origin and persistence of dwarf males.

Male True Crabs use two pairs of gonopods to deliver mating products during copulation. Commonly, the second pair is shorter than the first pair, and most research to date has focused on species with short second gonopods. We investigated male and female copulatory organs in Calappula saussurei and Calappa pelii, two species of box crabs (Calappidae) with second gonopods which are longer than the first pair. Scanning electron microscopy and histological cross sectioning show that the female copulatory system is unique in several aspects: the genital duct is part concave and part simple type. The seminal receptacle is divided into two chambers, a ventral chamber of ectodermal and mesodermal origin, and a dorsal chamber of ectodermal origin. This dorsal chamber is the location of spermatophore reception during copulation. A sperm plug closes the dorsal chamber off. We propose that long second gonopods deliver male mating products directly into the dorsal chamber. To date, spermatophore reception has been associated with the mesodermal tissue of the seminal receptacle. The copulatory system of box crabs with long second gonopods shows novel deviations from this general pattern.

Microsatellite markers remain an important tool for ecological and evolutionary research, but are unavailable for many non-model organisms. One such organism with rare ecological and evolutionary features is the epizoic barnacleChelonibia testudinaria(Linnaeus, 1758).Chelonibia testudinariaappears to be a host generalist, and has an unusual sexual system, androdioecy. Genetic studies on host specificity and mating behavior are impeded by the lack of fine-scale, highly variable markers, such as microsatellite markers. In the present study, we discovered thousands of new microsatellite loci from next-generation sequencing data, and characterized 12 loci thoroughly. We conclude that 11 of these loci will be useful markers in future ecological and evolutionary studies onC. testudinaria.

Microsatellite markers remain an important tool for ecological and evolutionary research, but are unavailable for many non-model organisms. One such organism with rare ecological and evolutionary features is the epizoic barnacle Chelonibia testudinaria (Linnaeus, 1758). Chelonibia testudinaria appears to be a host generalist, and has a unusual sexual system, androdioecy. Genetic studies on host specificity and mating behavior are impeded by the lack of fine-scale, highly variable markers. In the present study, we discovered thousands of new microsatellite loci from next-generation sequencing data, and characterized 12 loci thoroughly. We conclude that 11 of these loci will be useful markers in future ecological and evolutionary studies on C. testudinaria.

Predation on detritivores is expected to decelerate detritivore-mediated decomposition processes. In field mesocosms, we studied whether the decomposition of leaf and needle litter of live oak (Quercus virginiana) and loblolly pine (Pinus taeda), respectively, was affected by saltmarsh detritivores (Gastropoda: Littoraria irrorata and Melampus bidentatus) and predacious omnivores (Decapoda: Armases cinereum) and their interactions. Both crabs and snails alone increased decomposition (mass loss) rates of oak litter, while a combination of both resulted in the same mass loss as in animal-free controls, probably due to crabs feeding on snails rather than litter. Neither crabs nor snails alone affected mass loss of pine litter, but a combination of both significantly increased decomposition rates. Irrespective of the litter type, crabs significantly increased mortality of the snails but gained biomass only on pine litter and only when detritivorous snails were present. Our findings suggest that unidirectional facilitation of omnivorous semi-terrestrial crabs by their detritivorous prey (saltmarsh snails) promotes the decomposition of low-quality (pine) litter. On high-quality (oak) litter, by contrast, negative effects of the predator prevail, resulting in a drop of decomposition rates when crabs were present, probably owing to predation on detritivorous snails. Thus, the effects of predator/prey-interactions on decomposition processes are context-dependent and are controlled by resource quality.

A significant genetic cline has previously been identified along the Chilean coast in the barnacle Notochthamalus scabrosus. Samples from the previous study, spanning 800 km, were not able to show whether the southern lineage ultimately goes to fixation at higher latitudes. In addition to expanding the geographic sampling of this species, locations that were sampled approximately four to five generations ago were resampled for this study, enabling a temporal comparison of the location and strength of the observed cline. Here, we show that although the cline persists as expected, the tremendous changes in observed lineage frequencies near the clinal boundary are indicative of source-sink dynamics that may be associated with a codistributed biogeographic transition zone. We also find that the southern lineage does not increase in frequency in more southern populations, suggesting that this lineage is maintained through a combination of density-dependent interactions and a coastal fitness gradient.

Androdioecy was first described by Darwin in his seminal work on barnacle diversity; he identified males and hermaphrodites in the same reproductive population. Today, we realize that many androdioecious plants and animals share astonishing similarities, particularly with regard to their evolutionary history and mating system. Notably, these species were ancestrally dioecious, and their mating system has the following characteristics: hermaphrodites self-fertilize frequently, males are more successful in large mating groups, and males have a mating advantage. A male mating advantage makes androdioecy more likely to persist over evolutionary times. Androdioecious barnacles, however, appear to persist as an outlier with a different evolutionary trajectory: they originate from hermaphroditic species. Although sexual systems of androdioecious barnacles are known, no information on the mating system of androdioecious barnacles is available. This study assessed the mating system of the androdioecious barnacle Chelonibia testudinaria. In contrast to other androdioecious species, C. testudinaria does not self-fertilize, males do not have a mating advantage over hermaphrodites, and the average mating group is quite small, averaging only three individuals. Mating success is increased by proximity to the mate and penis length. Taken together, the mating system of C. testudinaria is unusual in comparison with other androdioecious plants and animals, and the lack of a male mating advantage suggests that the mating system alone does not provide an explanation for the maintenance of androdioecy in this species. Instead, we propose that sex-specific life history equalizes male and hermaphroditic overall fitness.

Male True Crabs use two pairs of gonopods to deliver mating products during copulation. Commonly, the second pair is shorter than the first pair, and most research to date has focused on species with short second gonopods. We investigated male and female copulatory organs in Calappula saussurei and Calappa pelii, two species of box crabs (Calappidae) with second gonopods which are longer than the first pair. Scanning electron microscopy and histological cross sectioning show that the female copulatory system is unique in several aspects: the genital duct is part concave and part simple type. The seminal receptacle is divided into two chambers, a ventral chamber of ectodermal and mesodermal origin, and a dorsal chamber of ectodermal origin. This dorsal chamber is the location of spermatophore reception during copulation. A sperm plug closes the dorsal chamber off. We propose that long second gonopods deliver male mating products directly into the dorsal chamber. To date, spermatophore reception has been associated with the mesodermal tissue of the seminal receptacle. The copulatory system of box crabs with long second gonopods shows novel deviations from this general pattern.