Unannotated Open Reading Frame in Saccharomyces cerevisiae Encodes Protein Localizing to the Endoplasmic Reticulum.

There are thousands of unannotated translated open reading frames (ORFs) in the Saccharomyces cerevisiae genome. Previous investigation into one such unannotated ORF, which was systemically labeled YGR016C-A based on its genomic coordinates, showed that replacing the ORF's ATG start codon with AAG led to a change in cellular fitness under different stress conditions (Wacholder et al., 2023). This suggested translation of YGR016C-A plays a role in cellular fitness. Here, we investigate Ygr016c-a's subcellular localization to gain insight into its cellular function. Computational prediction tools, co-expression analysis and fluorescence microscopy suggest that the Ygr016c-a protein localizes to the endoplasmic reticulum.

Endoscopic Management of a Chronic Gastrocutaneous Fistula after Bariatric Revisional Surgery Using a Novel Cardiac Septal Occluder.

Introduction: Endoscopic techniques are now considered the first-line approach for the management of bariatric surgery-related fistulas. The off-label use of cardiac septal defect occluders (CSDO) is an emerging technique that has demonstrated favorable outcomes for the closure of extravascular defects, including gastrointestinal (GI) disruptions. Previous case reports have reported similar results with the CSDO Amplatzer™ for the management of GI disruptions following bariatric surgery. However, the use of similar alternative devices for this purpose has not yet been described. Case Presentation: This case report presents the first reported use of the Occlutech® CSDO for the treatment of a chronic gastrocutaneous fistula after bariatric revisional surgery. Despite apparent initial success - no extravasation of contrast material through the device in the contrast study after the CSDO placement - fistula closure failed due to partial dislodgement of the device. The placement of a second device between the discs of the former one ultimately sealed the fistulous orifice. Discussion: In chronic GI fistulas, the mature tract is often not liable to the application of standard endoscopic methods, leading to failed closure attempts. A new application of Occlutech® CSDO can obviate the clinical burden of a high-risk laparotomy in these cases. Appropriate endoscopic equipment as well as the involvement of a multidisciplinary team are prime conditions to ensure successful patient outcomes.

Introdução: As técnicas endoscópicas são atualmente consideradas abordagens de primeira linha no manejo das fístulas associadas a cirurgia bariátrica. O uso off-label de dispositivos de oclusão do septo cardíaco (CSDO) é uma técnica nova que tem demonstrado resultados favoráveis no encerramento de defeitos extra-vasculares, incluindo fístulas gastrointestinais. Relatos de caso prévios reportaram resultados semelhantes com o CSDO Amplatzer ™ para o tratamento de fístulas gastrointestinais pós cirurgia bariátrica. No entanto, o uso de dispositivos alternativos semelhantes para esse fim ainda não foi descrito. Relato de Caso: Este relato de caso apresenta o primeiro uso reportado do CSDO Occlutech® para tratamento de fístula gastrocutânea crônica após cirurgia bariátrica revisional. Apesar do aparente sucesso inicial ­ nenhum extravasamento de contraste através do dispositivo na fluoroscopia após a colocação do CSDO, houve recorrência da drenagem fistulosa devido ao deslocamento parcial do dispositivo. A colocação de um segundo dispositivo entre os discos do primeiro acabou por encerrar o orifício fistuloso. Discussão: Nas fístulas gastrointestinais crônicas, o trajeto epitelizado muitas vezes não é passível de aplicação dos métodos endoscópicos tradicionais, levando a múltiplas tentativas fracassadas de encerramento. A nova aplicação de Occlutech® CSDO pode evitar o risco de uma laparotomia de alto risco nesses casos. Equipamentos endoscópicos adequados, bem como o envolvimento de equipe multidisciplinar são condições primordiais para garantir o sucesso do tratamento.

Past climate-driven range shifts structuring intraspecific biodiversity levels of the giant kelp (Macrocystis pyrifera) at global scales.

The paradigm of past climate-driven range shifts structuring the distribution of marine intraspecific biodiversity lacks replication in biological models exposed to comparable limiting conditions in independent regions. This may lead to confounding effects unlinked to climate drivers. We aim to fill in this gap by asking whether the global distribution of intraspecific biodiversity of giant kelp (Macrocystis pyrifera) is explained by past climate changes occurring across the two hemispheres. We compared the species' population genetic diversity and structure inferred with microsatellite markers, with range shifts and long-term refugial regions predicted with species distribution modelling (SDM) from the last glacial maximum (LGM) to the present. The broad antitropical distribution of Macrocystis pyrifera is composed by six significantly differentiated genetic groups, for which current genetic diversity levels match the expectations of past climate changes. Range shifts from the LGM to the present structured low latitude refugial regions where genetic relics with higher and unique diversity were found (particularly in the Channel Islands of California and in Peru), while post-glacial expansions following ~ 40% range contraction explained extensive regions with homogenous reduced diversity. The estimated effect of past climate-driven range shifts was comparable between hemispheres, largely demonstrating that the distribution of intraspecific marine biodiversity can be structured by comparable evolutionary forces across the global ocean. Additionally, the differentiation and endemicity of regional genetic groups, confers high conservation value to these localized intraspecific biodiversity hotspots of giant kelp forests.

A vast evolutionarily transient translatome contributes to phenotype and fitness.

Translation is the process by which ribosomes synthesize proteins. Ribosome profiling recently revealed that many short sequences previously thought to be noncoding are pervasively translated. To identify protein-coding genes in this noncanonical translatome, we combine an integrative framework for extremely sensitive ribosome profiling analysis, iRibo, with high-powered selection inferences tailored for short sequences. We construct a reference translatome for Saccharomyces cerevisiae comprising 5,400 canonical and almost 19,000 noncanonical translated elements. Only 14 noncanonical elements were evolving under detectable purifying selection. A representative subset of translated elements lacking signatures of selection demonstrated involvement in processes including DNA repair, stress response, and post-transcriptional regulation. Our results suggest that most translated elements are not conserved protein-coding genes and contribute to genotype-phenotype relationships through fast-evolving molecular mechanisms.

On the illusion of auxotrophy: met15Δ yeast cells can grow on inorganic sulfur, thanks to the previously uncharacterized homocysteine synthase Yll058w.

Organisms must either synthesize or assimilate essential organic compounds to survive. The homocysteine synthase Met15 has been considered essential for inorganic sulfur assimilation in yeast since its discovery in the 1970s. As a result, MET15 has served as a genetic marker for hundreds of experiments that play a foundational role in eukaryote genetics and systems biology. Nevertheless, we demonstrate here through structural and evolutionary modeling, in vitro kinetic assays, and genetic complementation, that an alternative homocysteine synthase encoded by the previously uncharacterized gene YLL058W enables cells lacking Met15 to assimilate enough inorganic sulfur for survival and proliferation. These cells however fail to grow in patches or liquid cultures unless provided with exogenous methionine or other organosulfurs. We show that this growth failure, which has historically justified the status of MET15 as a classic auxotrophic marker, is largely explained by toxic accumulation of the gas hydrogen sulfide because of a metabolic bottleneck. When patched or cultured with a hydrogen sulfide chelator, and when propagated as colony grids, cells without Met15 assimilate inorganic sulfur and grow, and cells with Met15 achieve even higher yields. Thus, Met15 is not essential for inorganic sulfur assimilation in yeast. Instead, MET15 is the first example of a yeast gene whose loss conditionally prevents growth in a manner that depends on local gas exchange. Our results have broad implications for investigations of sulfur metabolism, including studies of stress response, methionine restriction, and aging. More generally, our findings illustrate how unappreciated experimental variables can obfuscate biological discovery.

Isolated subcutaneous emphysema of the abdominal wall following endoscopic retrograde cholangiopancreatography.

Isolated subcutaneous emphysema without retroperitoneal perforation is a rare complication of endoscopic retrograde cholangiopancreatography (ERCP). We present the case of an 87-year-old female who developed extensive subcutaneous emphysema following ERCP for choledocholithiasis. Abdominal computed tomography showed air perfectly dissecting the abdominal wall muscle layers and no evidence of an air leak in the pleural, mediastinal, or peritoneal spaces.

Formulações do conceito de elaboração psíquica no pensamento freudiano: apontamentos para um debate / Concept of psychic elaboration in Freudian thought: notes for a debate / Formulations du concept d'élaboration psychique dans la pensée freudienne: notes pour un débat / Formulaciones del concepto de elaboración psíquica en el pensamiento freudiano: notas para un debate

Resumo Discutiremos sobre o desenvolvimento da clínica freudiana e os impasses que surgiram no percurso de Freud que levaram a diferentes formulações do que, aparentemente, seria um conceito único de elaboração psíquica. Nosso objetivo é situar as condições históricas, teóricas e técnicas que possibilitaram a emergência das diferentes formulações da elaboração psíquica no desenvolvimento da clínica freudiana, investigando seus desdobramentos e suas variações. A primeira formulação da elaboração psíquica, a elaboração associativa, relaciona-se a um processo intrapsíquico, definido como a capacidade do psiquismo para ligar afetos e representações. Já a segunda, a perlaboração, relaciona-se com a superação de resistências, em um processo transferencial e interpsíquico, uma vez que é pelas intervenções do analista que a perlaboração encontra chances de ocorrer como potencialidade. Por fim, apontaremos que a segunda formulação acarreta a primeira, pois é pela superação das resistências que a associação de uma representação ocorre.

Abstract This paper discusses the development of the Freudian clinic and the impasses in Freud's course that led to different formulations of what would apparently be a single concept of psychic elaboration. It seeks to situate the historical, theoretical, and technical conditions that enabled the emergence of different formulations of psychic elaboration during the development of the Freudian clinic, investigating its developments and variations. The first formulation of psychic elaboration, associative elaboration, is related to an intrapsychic process, defined as the psyche's ability to link affections and representations. The second, working-through, is related to overcoming resistance, in a transferential and interpsychic process, since it is through the analyst's interventions that working-through finds chances to occur as potentiality. Finally, the paper points out that the second formulation entails the first, since it is by overcoming resistances that the association of a representation occurs.

Résumé Cet article traite du développement de la clinique freudienne et des impasses du parcours de Freud qui ont conduit à différentes formulations de ce qui serait apparemment un concept unique d'élaboration psychique. L'objectif est de situer les conditions historiques, théoriques et techniques qui ont permis l'émergence de différentes formulations d'élaboration psychique au cours du développement de la clinique freudienne, en étudiant ses déroulements et ses variations. La première formulation de l'élaboration psychique, l'élaboration associative, est liée à un processus intrapsychique, défini comme la capacité du psychisme à relier les affections et les représentations. La seconde, la perlaboration, est liée au dépassement de la résistance, dans un processus transférentiel et interpsychique, puisque c'est à travers les interventions de l'analyste que la perlaboration trouve des chances de se produire comme potentialité. Enfin, l'article souligne que la seconde formulation entraîne la première, car c'est en surmontant la résistance que l'association d'une représentation se produit.

Resumen Discutiremos el desarrollo de la clínica freudiana y los callejones sin salida que surgieron en el camino de Freud y lo condujeron a diferentes formulaciones de lo que sería, aparentemente, un concepto único de elaboración psíquica. Nuestro objetivo es situar las condiciones históricas, teóricas y técnicas que hicieron posible el surgimiento de diferentes formulaciones de elaboración psíquica en el desarrollo de la clínica freudiana, investigando sus desarrollos y variaciones. La primera formulación de elaboración psíquica, la elaboración asociativa, está relacionada con un proceso intrapsíquico, definido como la capacidad de la psique para vincular afectos y representaciones. La segunda, la perlaboración, está relacionada con la superación de la resistencia, en un proceso transferencial e interpsíquico, ya que es a través de las intervenciones del analista que la perlaboración encuentra posibilidades de ocurrir como potencialidad. Finalmente, señalaremos que la segunda formulación produce la primera, porque al vencer la resistencia ocurre la asociación de una representación.

LI Detector: a framework for sensitive colony-based screens regardless of the distribution of fitness effects.

Microbial growth characteristics have long been used to investigate fundamental questions of biology. Colony-based high-throughput screens enable parallel fitness estimation of thousands of individual strains using colony growth as a proxy for fitness. However, fitness estimation is complicated by spatial biases affecting colony growth, including uneven nutrient distribution, agar surface irregularities, and batch effects. Analytical methods that have been developed to correct for these spatial biases rely on the following assumptions: (1) that fitness effects are normally distributed, and (2) that most genetic perturbations lead to minor changes in fitness. Although reasonable for many applications, these assumptions are not always warranted and can limit the ability to detect small fitness effects. Beneficial fitness effects, in particular, are notoriously difficult to detect under these assumptions. Here, we developed the linear interpolation-based detector (LI Detector) framework to enable sensitive colony-based screening without making prior assumptions about the underlying distribution of fitness effects. The LI Detector uses a grid of reference colonies to assign a relative fitness value to every colony on the plate. We show that the LI Detector is effective in correcting for spatial biases and equally sensitive toward increase and decrease in fitness. LI Detector offers a tunable system that allows the user to identify small fitness effects with unprecedented sensitivity and specificity. LI Detector can be utilized to develop and refine gene-gene and gene-environment interaction networks of colony-forming organisms, including yeast, by increasing the range of fitness effects that can be reliably detected.

De novo emergence of adaptive membrane proteins from thymine-rich genomic sequences.

Recent evidence demonstrates that novel protein-coding genes can arise de novo from non-genic loci. This evolutionary innovation is thought to be facilitated by the pervasive translation of non-genic transcripts, which exposes a reservoir of variable polypeptides to natural selection. Here, we systematically characterize how these de novo emerging coding sequences impact fitness in budding yeast. Disruption of emerging sequences is generally inconsequential for fitness in the laboratory and in natural populations. Overexpression of emerging sequences, however, is enriched in adaptive fitness effects compared to overexpression of established genes. We find that adaptive emerging sequences tend to encode putative transmembrane domains, and that thymine-rich intergenic regions harbor a widespread potential to produce transmembrane domains. These findings, together with in-depth examination of the de novo emerging YBR196C-A locus, suggest a novel evolutionary model whereby adaptive transmembrane polypeptides emerge de novo from thymine-rich non-genic regions and subsequently accumulate changes molded by natural selection.

Seascape genetics of the stalked kelp Pterygophora californica and comparative population genetics in the Santa Barbara Channel.

We conducted a population genetic analysis of the stalked kelp, Pterygophora californica, in the Santa Barbara Channel, California, USA. The results were compared with previous work on the genetic differentiation of giant kelp, Macrocystis pyrifera, in the same region. These two sympatric kelps not only share many life history and dispersal characteristics but also differ in that dislodged P. californica does not produce floating rafts with buoyant fertile sporophytes, commonly observed for M. pyrifera. We used a comparative population genetic approach with these two species to test the hypothesis that the ability to produce floating rafts increases the genetic connectivity among kelp patches in the Santa Barbara Channel. We quantified the association of habitat continuity and oceanographic distance with the genetic differentiation observed in stalked kelp, like previously conducted for giant kelp. We compared both overall (across all patches) and pairwise (between patches) genetic differentiation. We found that oceanographic transit time, habitat continuity, and geographic distance were all associated with genetic connectivity in P. californica, supporting similar previous findings for M. pyrifera. Controlling for differences in heterozygosity between kelp species using Jost's DEST , we showed that global differentiation and pairwise differentiation were similar among patches between the two kelp species, indicating that they have similar dispersal capabilities despite their differences in rafting ability. These results suggest that rafting sporophytes do not play a significant role in effective dispersal of M. pyrifera at ecologically relevant spatial and temporal scales.

Individual-based genetic analyses support asexual hydrochory dispersal in Zostera noltei.

Dispersal beyond the local patch in clonal plants was typically thought to result from sexual reproduction via seed dispersal. However, evidence for the separation, transport by water, and re-establishment of asexual propagules (asexual hydrochory) is mounting suggesting other important means of dispersal in aquatic plants. Using an unprecedented sampling size and microsatellite genetic identification, we describe the distribution of seagrass clones along tens of km within a coastal lagoon in Southern Portugal. Our spatially explicit individual-based sampling design covered 84 km2 and collected 3 185 Zostera noltei ramets from 803 sites. We estimated clone age, assuming rhizome elongation as the only mechanism of clone spread, and contrasted it with paleo-oceanographic sea level change. We also studied the association between a source of disturbance and the location of large clones. A total of 16 clones were sampled more than 10 times and the most abundant one was sampled 59 times. The largest distance between two samples from the same clone was 26.4 km and a total of 58 and 10 clones were sampled across more than 2 and 10 km, respectively. The number of extremely large clone sizes, and their old ages when assuming the rhizome elongation as the single causal mechanism, suggests other processes are behind the span of these clones. We discuss how the dispersal of vegetative fragments in a stepping-stone manner might have produced this pattern. We found higher probabilities to sample large clones away from the lagoon inlet, considered a source of disturbance. This study corroborates previous experiments on the success of transport and re-establishment of asexual fragments and supports the hypothesis that asexual hydrochory is responsible for the extent of these clones.

A multiplex culture system for the long-term growth of fission yeast cells.

Maintenance of long-term cultures of yeast cells is central to a broad range of investigations, from metabolic studies to laboratory evolution assays. However, repeated dilutions of batch cultures lead to variations in medium composition, with implications for cell physiology. In Saccharomyces cerevisiae, powerful miniaturized chemostat setups, or ministat arrays, have been shown to allow for constant dilution of multiple independent cultures. Here we set out to adapt these arrays for continuous culture of a morphologically and physiologically distinct yeast, the fission yeast Schizosaccharomyces pombe, with the goal of maintaining constant population density over time. First, we demonstrated that the original ministats are incompatible with growing fission yeast for more than a few generations, prompting us to modify different aspects of the system design. Next, we identified critical parameters for sustaining unbiased vegetative growth in these conditions. This requires deletion of the gsf2 flocculin-encoding gene, along with addition of galactose to the medium and lowering of the culture temperature. Importantly, we improved the flexibility of the ministats by developing a piezo-pump module for the independent regulation of the dilution rate of each culture. This made it possible to easily grow strains that have different generation times in the same assay. Our system therefore allows for maintaining multiple fission yeast cultures in exponential growth, adapting the dilution of each culture over time to keep constant population density for hundreds of generations. These multiplex culture systems open the door to a new range of long-term experiments using this model organism. © 2017 The Authors. Yeast published by John Wiley & Sons, Ltd.

Cryptic diversity, geographical endemism and allopolyploidy in NE Pacific seaweeds.

BACKGROUND: Molecular markers are revealing a much more diverse and evolutionarily complex picture of marine biodiversity than previously anticipated. Cryptic and/or endemic marine species are continually being found throughout the world oceans, predominantly in inconspicuous tropical groups but also in larger, canopy-forming taxa from well studied temperate regions. Interspecific hybridization has also been found to be prevalent in many marine groups, for instance within dense congeneric assemblages, with introgressive gene-flow being the most common outcome. Here, using a congeneric phylogeographic approach, we investigated two monotypic and geographically complementary sister genera of north-east Pacific intertidal seaweeds (Hesperophycus and Pelvetiopsis), for which preliminary molecular tests revealed unexpected conflicts consistent with unrecognized cryptic diversity and hybridization. RESULTS: The three recovered mtDNA clades did not match a priori species delimitations. H. californicus was congruent, whereas widespread P. limitata encompassed two additional narrow-endemic species from California - P. arborescens (here genetically confirmed) and P. hybrida sp. nov. The congruence between the genotypic clusters and the mtDNA clades was absolute. Fixed heterozygosity was apparent in a high proportion of loci in P. limitata and P. hybrida, with genetic analyses showing that the latter was composed of both H. californicus and P. arborescens genomes. All four inferred species could be distinguished based on their general morphology. CONCLUSIONS: This study confirmed additional diversity and reticulation within NE Pacific Hesperophycus/Pelvetiopsis, including the validity of the much endangered, modern climatic relict P. arborescens, and the identification of a new, stable allopolyploid species (P. hybrida) with clearly discernable ancestry (♀ H. californicus x ♂ P. arborescens), morphology, and geographical distribution. Allopolyploid speciation is otherwise completely unknown in brown seaweeds, and its unique occurrence within this genus (P. limitata possibly representing a second example) remains enigmatic. The taxonomic separation of Hesperophycus and Pelvetiopsis is not supported and the genera should be synonymized; we retain only the latter. The transitional coastline between Point Conception and Monterey Bay represented a diversity hotspot for the genus and the likely sites of extraordinary evolutionary events of allopolyploid speciation at sympatric range contact zones. This study pinpoints how much diversity (and evolutionary processes) potentially remains undiscovered even on a conspicuous seaweed genus from the well-studied Californian intertidal shores let alone in other, less studied marine groups and regions/depths.

Seascape drivers of Macrocystis pyrifera population genetic structure in the northeast Pacific.

At small spatial and temporal scales, genetic differentiation is largely controlled by constraints on gene flow, while genetic diversity across a species' distribution is shaped on longer temporal and spatial scales. We assess the hypothesis that oceanographic transport and other seascape features explain different scales of genetic structure of giant kelp, Macrocystis pyrifera. We followed a hierarchical approach to perform a microsatellite-based analysis of genetic differentiation in Macrocystis across its distribution in the northeast Pacific. We used seascape genetic approaches to identify large-scale biogeographic population clusters and investigate whether they could be explained by oceanographic transport and other environmental drivers. We then modelled population genetic differentiation within clusters as a function of oceanographic transport and other environmental factors. Five geographic clusters were identified: Alaska/Canada, central California, continental Santa Barbara, California Channel Islands and mainland southern California/Baja California peninsula. The strongest break occurred between central and southern California, with mainland Santa Barbara sites forming a transition zone between the two. Breaks between clusters corresponded approximately to previously identified biogeographic breaks, but were not solely explained by oceanographic transport. An isolation-by-environment (IBE) pattern was observed where the northern and southern Channel Islands clustered together, but not with closer mainland sites, despite the greater distance between them. The strongest environmental association with this IBE pattern was observed with light extinction coefficient, which extends suitable habitat to deeper areas. Within clusters, we found support for previous results showing that oceanographic connectivity plays an important role in the population genetic structure of Macrocystis in the Northern hemisphere.

Genes Left Behind: Climate Change Threatens Cryptic Genetic Diversity in the Canopy-Forming Seaweed Bifurcaria bifurcata.

The global redistribution of biodiversity will intensify in the coming decades of climate change, making projections of species range shifts and of associated genetic losses important components of conservation planning. Highly-structured marine species, notably brown seaweeds, often harbor unique genetic variation at warmer low-latitude rear edges and thus are of particular concern. Here, a combination of Ecological Niche Models (ENMs) and molecular data is used to forecast the potential near-future impacts of climate change for a warm-temperate, canopy forming seaweed, Bifurcaria bifurcata. ENMs for B. bifurcata were developed using marine and terrestrial climatic variables, and its range projected for 2040-50 and 2090-2100 under two greenhouse emission scenarios. Geographical patterns of genetic diversity were assessed by screening 18 populations spawning the entire distribution for two organelle genes and 6 microsatellite markers. The southern limit of B. bifurcata was predicted to shift northwards to central Morocco by the mid-century. By 2090-2100, depending on the emission scenario, it could either retreat further north to western Iberia or be relocated back to Western Sahara. At the opposing margin, B. bifurcata was predicted to expand its range to Scotland or even Norway. Microsatellite diversity and endemism were highest in Morocco, where a unique and very restricted lineage was also identified. Our results imply that B. bifurcata will maintain a relatively broad latitudinal distribution. Although its persistence is not threatened, the predicted extirpation of a unique southern lineage or even the entire Moroccan diversity hotspot will erase a rich evolutionary legacy and shrink global diversity to current (low) European levels. NW Africa and similarly understudied southern regions should receive added attention if expected range changes and diversity loss of warm-temperate species is not to occur unnoticed.

Reproductive strategies and isolation-by-demography in a marine clonal plant along an eutrophication gradient.

Genetic diversity in clonal organisms includes two distinct components, (i) the diversity of genotypes or clones (i.e. genotypic richness) in a population and (ii) that of the alleles (i.e. allelic and gene diversity within populations, and differentiation between populations). We investigated how population differentiation and genotypic components are associated across a gradient of eutrophication in a clonal marine plant. To that end, we combined direct measurements of sexual allocation (i.e. flower and seed counts) and genotypic analyses, which are used as an estimator of effective sexual reproduction across multiple generations. Genetic differentiation across sites was also modelled according to a hypothesis here defined as isolation-by-demography, in which we use population-specific factors, genotypic richness and eutrophication that are hypothesized to affect the source-sink dynamics and thus influence the genetic differentiation between a pair of populations. Eutrophic populations exhibited lower genotypic richness, in agreement with lower direct measurements of sexual allocation and contemporaneous gene flow. Genetic differentiation, while not explained by distance, was best predicted by genotypic richness and habitat quality. A multiple regression model using these two predictors was considered the best model (R(2) = 0.43). In this study, the relationship between environment and effective sexual-asexual balance is not simply (linearly) predicted by direct measurements of sexual allocation. Our results indicate that population-specific factors and the isolation-by-demography model should be used more often to understand genetic differentiation.

High and distinct range-edge genetic diversity despite local bottlenecks.

The genetic consequences of living on the edge of distributional ranges have been the subject of a largely unresolved debate. Populations occurring along persistent low latitude ranges (rear-edge) are expected to retain high and unique genetic diversity. In contrast, currently less favourable environmental conditions limiting population size at such range-edges may have caused genetic erosion that prevails over past historical effects, with potential consequences on reducing future adaptive capacity. The present study provides an empirical test of whether population declines towards a peripheral range might be reflected on decreasing diversity and increasing population isolation and differentiation. We compare population genetic differentiation and diversity with trends in abundance along a latitudinal gradient towards the peripheral distribution range of Saccorhiza polyschides, a large brown seaweed that is the main structural species of kelp forests in SW Europe. Signatures of recent bottleneck events were also evaluated to determine whether the recently recorded distributional shifts had a negative influence on effective population size. Our findings show decreasing population density and increasing spatial fragmentation and local extinctions towards the southern edge. Genetic data revealed two well supported groups with a central contact zone. As predicted, higher differentiation and signs of bottlenecks were found at the southern edge region. However, a decrease in genetic diversity associated with this pattern was not verified. Surprisingly, genetic diversity increased towards the edge despite bottlenecks and much lower densities, suggesting that extinctions and recolonizations have not strongly reduced diversity or that diversity might have been even higher there in the past, a process of shifting genetic baselines.