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How cells control the overall size and growth of membrane-bound organelles is an important unanswered question of cell biology. Fission yeast cells maintain a nuclear size proportional to cellular size, resulting in a constant ratio between nuclear and cellular volumes (N/C ratio). We have conducted a genome-wide visual screen of a fission yeast gene deletion collection for viable mutants altered in their N/C ratio, and have found that defects in both nucleocytoplasmic mRNA transport and lipid synthesis alter the N/C ratio. Perturbing nuclear mRNA export results in accumulation of both mRNA and protein within the nucleus, and leads to an increase in the N/C ratio which is dependent on new membrane synthesis. Disruption of lipid synthesis dysregulates nuclear membrane growth and results in an enlarged N/C ratio. We propose that both properly regulated nucleocytoplasmic transport and nuclear membrane growth are central to the control of nuclear growth and size.

Cyclin-dependent kinases (CDKs) lie at the heart of eukaryotic cell cycle control, with different cyclin–CDK complexes initiating DNA replication (S-CDKs) and mitosis (M-CDKs) 1 , 2 . However, the principles on which cyclin–CDK complexes organize the temporal order of cell cycle events are contentious 3 . One model proposes that S-CDKs and M-CDKs are functionally specialized, with substantially different substrate specificities to execute different cell cycle events 4 – 6 . A second model proposes that S-CDKs and M-CDKs are redundant with each other, with both acting as sources of overall CDK activity 7 , 8 . In this model, increasing CDK activity, rather than CDK substrate specificity, orders cell cycle events 9 , 10 . Here we reconcile these two views of core cell cycle control. Using phosphoproteomic assays of in vivo CDK activity in fission yeast, we find that S-CDK and M-CDK substrate specificities are remarkably similar, showing that S-CDKs and M-CDKs are not completely specialized for S phase and mitosis alone. Normally, S-CDK cannot drive mitosis but can do so when protein phosphatase 1 is removed from the centrosome. Thus, increasing S-CDK activity in vivo is sufficient to overcome substrate specificity differences between S-CDK and M-CDK, and allows S-CDK to carry out M-CDK function. Therefore, we unite the two opposing views of cell cycle control, showing that the core cell cycle engine is largely based on a quantitative increase in CDK activity through the cell cycle, combined with minor and surmountable qualitative differences in catalytic specialization of S-CDKs and M-CDKs. The core cell cycle is largely driven by increasing total CDK activity together with minor differences in the substrate specificity of the CDKs initiating DNA replication and mitosis.

Intraspecific genetic diversity across a species' geographic range is relevant to adaptive potential and long‐term population persistence, and identifying genetically distinct groups within species can direct management decisions focused on conserving species‐level genetic diversity. Comparative phylogeography using whole genome techniques allows for investigation of whether co‐distributed species exhibit shared spatial genetic differentiation at fine spatial scales, thereby facilitating a comparative approach to both landscape and conservation genetics. By sequencing over 900 low‐coverage whole genomes, we evaluated the concordance of genetic structure and diversity from 12 co‐occurring species of migratory birds whose breeding ranges span adjacent North American ecogeographic regions: the vast boreal forest belt and the temperate montane Appalachian forests. We detected concordant phylogeographic patterns in 11 of 12 species wherein populations from the southern Appalachians were genetically distinct from boreal belt populations. Our results reveal that small populations persisting in the southern Appalachian Mountains consistently harbor genetic diversity that is subtly distinct from much larger, widespread boreal populations of the same species. However, in most species, levels of standing genetic diversity were not significantly different between Appalachian and boreal populations despite the drastic difference in geographic extent of these populations. We found no evidence for shared signatures of selection across the genome, suggesting that the concordance of spatial genetic structure across species emerges from species‐specific patterns of molecular divergence across the genome rather than parallel patterns of selection. Conservation of the Appalachian ecosystem would likely support maintenance of distinct genetic diversity in several migratory avian species with widespread distributions.

[EN]The functions of cohesin are central to genome integrity, chromosome organization and transcription regulation through its prevention of premature sister-chromatid separation and the formation of DNA loops. The loading of cohesin onto chromatin depends on the Scc2-Scc4 complex; however, little is known about how it stimulates the cohesion-loading activity. Here we determine the large 'hook' structure of Scc2 responsible for catalysing cohesin loading. We identify key Scc2 surfaces that are crucial for cohesin loading in vivo. With the aid of previously determined structures and homology modelling, we derive a pseudo-atomic structure of the full-length Scc2-Scc4 complex. Finally, using recombinantly purified Scc2-Scc4 and cohesin, we performed crosslinking mass spectrometry and interaction assays that suggest Scc2-Scc4 uses its modular structure to make multiple contacts with cohesin.

Competitive diversification, that is, when increasing intraspecific competition promotes population niche expansion, is commonly invoked in evolutionary studies and currently plays a central role in how we conceptualize the process of adaptive diversification. Despite the frequency with which this idea is cited, the empirical evidence for the process is somewhat limited, and the findings of these studies have yet to be weighed objectively through synthesis. Here, we sought to fill this gap by reviewing the existing literature and collecting the data necessary to assess the evidence for competition as a diversifying force. Additionally, we sought to test a more recent hypothesis, which suggests that competition can act to both promote and inhibit dietary diversification depending on the degree to which a consumer depletes its resources. The surprising result of this synthesis was that increasing competition did not have a mean positive effect on population‐level diet breadth or the degree of individual specialization. Instead, we found that increasing intraspecific competition had a restricting effect on population‐level diet breadth in as many cases as it had a diversifying effect. This wide disparity in the effect of competition on consumer diet variation was negatively related to a metric for consumer resource depletion. Altogether, these findings call into question a long‐standing assumption of basic evolutionary models and lend some support to recent theoretical predictions. Specifically, these findings support the idea that competition is primarily diversifying for species with a small effect (per unit biomass) on their resources and that resource depletion limits the diversifying effect of competition for consumers with larger ecological effects. Competitive diversification, that is, when increasing intraspecific competition promotes population‐level niche expansion, is commonly invoked in evolutionary studies, and currently plays a central role in how we conceptualize the process of adaptive diversification. Despite the frequency with which this idea is cited, the empirical evidence for the process is somewhat limited, and the findings of these studies have yet to be weighed objectively through synthesis. Here, we sought to fill this gap by reviewing the existing literature. Our results support the idea that competition is primarily diversifying for species with small ecological effects and that resource depletion tends to limit the diversifying effect of competition.

The long-held view that gamma delta (γδ) T cells in mice and humans are fundamentally dissimilar, as are γδ cells in blood and peripheral tissues, has been challenged by emerging evidence of the cells’ regulation by butyrophilin (BTN) and butyrophilin-like (BTNL) molecules. Thus, murine Btnl1 and the related gene, Skint1, mediate T cell receptor (TCR)-dependent selection of murine intraepithelial γδ T cell repertoires in gut and skin, respectively; BTNL3 and BTNL8 are TCR-dependent regulators of human gut γδ cells; and BTN3A1 is essential for TCR-dependent activation of human peripheral blood Vγ9Vδ2⁺ T cells. However, some observations concerning BTN/Btnl molecules continue to question the extent of mechanistic conservation. In particular, murine and human gut γδ cell regulation depends on pairings of Btnl1 and Btnl6 and BTNL3 and BTNL8, respectively, whereas blood γδ cells are reported to be regulated by BTN3A1 independent of other BTNs. Addressing this paradox, we show that BTN3A2 regulates the subcellular localization of BTN3A1, including functionally important associations with the endoplasmic reticulum (ER), and is specifically required for optimal BTN3A1-mediated activation of Vγ9Vδ2⁺ T cells. Evidence that BTNL3/BTNL8 and Btnl1/Btnl6 likewise associate with the ER reinforces the prospect of broadly conserved mechanisms underpinning the selection and activation of γδ cells in mice and humans, and in blood and extralymphoid sites.

Species introductions provide opportunities to quantify rates and patterns of evolutionary change in response to novel environments. Alewives (Alosa pseudoharengus) are native to the East Coast of North America where they ascend coastal rivers to spawn in lakes and then return to the ocean. Some populations have become landlocked within the last 350 years and diverged phenotypically from their ancestral marine population. More recently, alewives were introduced to the Laurentian Great Lakes (~150 years ago), but these populations have not been compared to East Coast anadromous and landlocked populations. We quantified 95 years of evolution in foraging traits and overall body shape of Great Lakes alewives and compared patterns of phenotypic evolution of Great Lakes alewives to East Coast anadromous and landlocked populations. Our results suggest that gill raker spacing in Great Lakes alewives has evolved in a dynamic pattern that is consistent with responses to strong but intermittent eco‐evolutionary feedbacks with zooplankton size. Following their initial colonization of Lakes Ontario and Michigan, dense alewife populations likely depleted large‐bodied zooplankton, which drove a decrease in alewife gill raker spacing. However, the introduction of large, non‐native zooplankton to the Great Lakes in later decades resulted in an increase in gill raker spacing, and present‐day Great Lakes alewives have gill raker spacing patterns that are similar to the ancestral East Coast anadromous population. Conversely, contemporary Great Lakes alewife populations possess a gape width consistent with East Coast landlocked populations. Body shape showed remarkable parallel evolution with East Coast landlocked populations, likely due to a shared response to the loss of long‐distance movement or migrations. Our results suggest the colonization of a new environment and cessation of migration can result in rapid parallel evolution in some traits, but contingency also plays a role, and a dynamic ecosystem can also yield novel trait combinations.

Understanding interactions between biota and the built environment is increasingly important as human modification of the landscape expands in extent and intensity. For migratory birds, collisions with lighted structures are a major cause of mortality, but the mechanisms behind these collisions are poorly understood. Using 40 years of collision records of passerine birds, we investigated the importance of species' behavioural ecologies in predicting rates of building collisions during nocturnal migration through Chicago, IL and Cleveland, OH, USA. We found that the use of nocturnal flight calls is an important predictor of collision risk in nocturnally migrating passerine birds. Species that produce flight calls during nocturnal migration tended to collide with buildings more than expected given their local abundance, whereas those that do not use such communication collided much less frequently. Our results suggest that a stronger attraction response to artificial light at night in species that produce flight calls may mediate these differences in collision rates. Nocturnal flight calls probably evolved to facilitate collective decision-making during navigation, but this same social behaviour may now exacerbate vulnerability to a widespread anthropogenic disturbance. Our results also suggest that social behaviour during migration may reflect poorly understood differences in navigational mechanisms across lineages of birds.

Sources of fisheries information outside of fishery-independent surveys (e.g. fishery-dependent data) are especially valuable for species that support productive fisheries and lack reliable biological information, such as the northern shortfin squid ( Illex illecebrosus ). Fishery-dependent data streams are available for most species, however collaboration with industry members is critical to ensure that these fishery-dependent data are collected, applied, and interpreted correctly. Despite the need for collaboration and the frequency that fishery data are used in scientific research, there is limited literature on the structure of interactions and knowledge sharing that inform the analysis and application of fishery data. Between 2019 and 2022, a group of researchers collaborated with members of the northern shortfin squid fishing industry to bring together research data sets and knowledge from harvesters and processors to better describe the fishery dynamics, distribution, life history, and oceanographic drivers of the species. The collaboration focused on developing custom standardized fishery catch per unit effort (CPUE) indices to provide indicators of population trends that accounted for the impacts of technical and economic aspects of harvesting, processing and marketing on fishing effort, selectivity and landings of northern shortfin squid. We describe the methods used to inform and interpret the CPUE analyses, focusing on novel structure of interactions we had with industry members, and suggest best practices for integrating industry knowledge into CPUE standardization. The information shared and research products produced through this science-industry research collaboration advanced understanding of northern shortfin squid population and fishery dynamics, and contributed directly to the 2022 stock assessment and management process. Given the complex and stochastic nature of the northern shortfin squid population and fishery, we found it critical to maintain open communication and trust with processors and harvesters, who have unique insight into the factors that may be driving changes in catch, landings, and productivity of the valuable resource species.

The latitudinal diversity gradient (LDG) is an established macroecological pattern, but is poorly studied in microbial organisms, particularly parasites. In this study, we tested whether latitude, elevation, and host species predicted patterns of prevalence, alpha diversity, and community turnover of hemosporidian parasites. We expected parasite diversity to decrease with latitude, alongside the diversity of their hosts and vectors. Similarly, we expected infection prevalence to decrease with latitude as vector abundances decrease. Lastly, we expected parasite community turnover to increase with latitudinal distance and to be higher between rather than within host species. We tested these hypotheses by screening blood and tissue samples of three closely related avian species in a clade of North American songbirds (Turdidae: Catharus, n = 466) across 17.5° of latitude. We used a nested PCR approach to identify parasites in hemosporidian genera that are transmitted by different dipteran vectors. Then, we implemented linear‐mixed effects and generalized dissimilarity models to evaluate the effects of latitude, elevation, and host species on parasite metrics. We found high diversity of hemosporidian parasites in Catharus thrushes (n = 44 lineages) but no evidence of latitudinal gradients in alpha diversity or prevalence. Parasites in the genus Leucocytozoon were most prevalent and lineage rich in this study system; however, there was limited turnover with latitude and host species. Contrastingly, Plasmodium parasites were less prevalent and diverse than Leucocytozoon parasites, yet communities turned over at a higher rate with latitude and host species. Leucocytozoon communities were skewed by the dominance of one or two highly prevalent lineages with broad latitudinal distributions. The few studies that evaluate the hemosporidian LDG do not find consistent patterns of prevalence and diversity, which makes it challenging to predict how they will respond to global climate change. Catharus thrushes are heavily infected by a diverse assemblage of hemosporidian parasites; however, these parasites did not follow a latitudinal diversity gradient or prevalence. Instead, we see high community turnover of Plasmodium communities with latitude and host species and moderate turnover of Leucocytozoon communities with latitude.