Increasing Colony Size Research Articles

Social insect colonies are more likely to accept unrelated queens when they come with workers

Abstract Relatedness underlies the evolution of reproductive altruism, yet eusocial insect colonies occasionally accept unrelated reproductive queens. Why would workers living in colonies with related queens accept unrelated ones, when they do not gain indirect fitness through their reproduction? To understand this seemingly paradox, we investigated whether acceptance of unrelated queens by workers is an incidental phenomenon resulting from failure to recognize non-nestmate queens, or whether it is adaptively favored in contexts where cooperation is preferable to rejection. Our study system is the socially polymorphic Alpine silver ant, Formica selysi. Within populations, some colonies have a single queen, and others have multiple, sometimes unrelated, breeding queens. Social organization is determined by a supergene with two haplotypes. In a first experiment, we investigated whether the number of reproductive queens living in colonies affects the ability of workers at rejecting alien queens, as multiple matrilines within colonies could increase colony odor diversity and reduce workers’ recognition abilities. As workers rejected all alien queens, independently of the number of queens heading their colony, we then investigated whether their acceptance is flexible and favored in specific conditions. We found that workers frequently accepted alien queens when these queens came with a workforce. Our results show that workers flexibly adjust their acceptance of alien queens according to the situation. We discuss how this conditional acceptance of unrelated queens may be adaptive by providing benefits through increased colony size and/or genetic diversity, and by avoiding rejection costs linked to fighting.

Coverage Increases of Porites astreoides in Grenada Determined by Shifts in Size-Frequency Distribution

Despite coral community collapse, the mustard hill coral (Porites astreoides) is a species currently experiencing success throughout the Caribbean. The inshore reefs of Grenada were selected to study the influence of benthic factors on the abundance, size, and coverage of P. astreoides colonies. Surveys of reef communities along established 30 m transects were conducted at eight sites in 2014 and 2017 using a 0.5 m² quadrat. Coral Point Count was used to annotate the images, estimating the coverage of scleractinian corals, sponges, algae, and benthic substrates. Coverage, size, and abundance of P. astreoides colonies were quantified using the area measurement tool in ImageJ standardized against the quadrats. There were significant differences in benthic community assemblages between islands, selected sites, and between years. From 2014 to 2017 there was a significant decrease in the mean abundance of P. astreoides colonies and significant increases in mean colony size and coverage. The presence of P. astreoides colonies was significantly correlated with: rubble (−), sand (−); pavement (+); macroalgae (−); coralline algae (+); sponges (varying response); gorgonians (−); massive corals (+); and branching corals (−). P. astreoides follows similar recruitment patterns as other scleractinian corals. Observed changes in P. astreoides populations appear to indicate a recovery event following a disturbance, potentially tropical storm Chantal in 2013.

Colony expansions underlie the evolution of army ant mass raiding

The mass raids of army ants are an iconic collective phenomenon, in which many thousands of ants spontaneously leave their nest to hunt for food, mostly other arthropods. While the structure and ecology of these raids have been relatively well studied, how army ants evolved such complex cooperative behavior is not understood. Here, we show that army ant mass raiding has evolved from a different form of cooperative hunting called group raiding, in which a scout directs a small group of ants to a specific target through chemical communication. We describe the structure of group raids in the clonal raider ant, a close relative of army ants in the subfamily Dorylinae. We find evidence that the coarse structure of group raids and mass raids is highly conserved and that all doryline ants likely follow similar behavioral rules for raiding. We also find that the evolution of army ant mass raiding occurred concurrently with expansions in colony size. By experimentally increasing colony size in the clonal raider ant, we show that mass raiding gradually emerges from group raiding without altering individual behavioral rules. This suggests that increasing colony size can explain the evolution of army ant mass raids and supports the idea that complex social behaviors may evolve via mechanisms that need not alter the behavioral interaction rules that immediately underlie the collective behavior of interest.

Ecological stoichiometry of functional traits in a colonial harmful cyanobacterium

AbstractTrait‐based approaches provide a mechanistic framework crossing scales from cellular traits to community dynamics, while ecological stoichiometry applies first principles to understand how the balance of energy and elements shape ecological interactions. However, few studies have explicitly linked both frameworks. In this study, we tested the stoichiometric regulation of a number of carbon (C) based (e.g., extracellular polysaccharides and colony formation) and nitrogen (N) containing traits (i.e., chlorophyll a, phycocyanin, and gas vesicle content) in cyanobacteria in laboratory experiments and in the field. We exposed the cosmopolitan colony forming freshwater cyanobacterium Microcystis sp. in batch experiments to light, N and phosphorus (P) limitation, and enhanced CO2 levels, and assessed the regulation of these traits. Cyanobacterial traits followed stoichiometrically predictable patterns, where N containing traits increased with cellular N content, and decreased with increasing C : N ratios. C‐based traits increased with cellular C content and C : N ratios under nutrient, particularly N, limitation. The pattern of colony formation was confirmed with field data from Lake Taihu (China), showing an increase in colony size when N was limiting and N : P ratios were low. These findings demonstrate how an explicit coupling of trait‐based approaches to ecological stoichiometry can support our mechanistic understanding of responses of cyanobacteria toward shifts in resource availability.

Tissue fusion and enhanced genotypic diversity support the survival of Pocillopora acuta coral recruits under thermal stress

Scleractinian coral recruitment provides critical support for reef persistence under the threat of global climate change. The high mortality rates exhibited in early life history stages are further increased under thermal stress, compromising reef recruitment. Tissue fusion with neighboring recruits is one potential early life history strategy that has been shown to support recruit survival (particularly in brooding species) by promoting rapid increases in colony size and potential opportunities for enhanced intracolonial genetic diversity. However, tissue fusion also presents risks in the cost of growth and maintenance of relationships between genetically distinct individuals. Although fusion is one potential strategy for recruit survival, the effects of colony size and enhanced genetic diversity achieved through fusion on survival under ocean warming conditions are not well understood. Here we tested the effect of tissue fusion on Pocillopora acuta recruit survival under ambient and high temperature stress by manipulating the size and parental genotypic richness in fused recruits. We provided opportunities for tissue fusion in groups of recruits with enhanced parental genotypic richness (1–4 parent genotypes) and size (1–4 recruits) and tracked subsequent growth and survival (N = 137). Under ambient temperature (1–15 days post-settlement), fusion significantly increased survivorship regardless of parental genotypic richness, while negative competitive effects existed between closely settled, but unfused recruits. Under high temperature (+ 2.5 °C; 16–47 days post-settlement), the median survival of fused recruits was 5 days longer than individuals, with 1.5 days added to median survival when composed of multiple parental genotypes. These results demonstrate that tissue fusion during coral recruitment can improve survival and provides insights on early life history strategies to increase tolerance to ocean warming.

Contrary to vertebrates, less aggressive and more consistent individuals are common in disturbed habitats in the colonial spider Metabus gravidus (Araneae: Araneidae)

Abstract Habitat disturbance may affect average behavioural types and consistency/plasticity of behaviour. Studies with solitary vertebrates suggest that human-modified habitats may favour bolder, more aggressive and more plastic individuals. We evaluated whether wild colonial spiders, Metabus gravidus, vary in the magnitude, consistency and plasticity of boldness and aggressiveness between an undisturbed forest and an adjacent urban area in Monteverde, Costa Rica. Repeatability of aggressiveness was high at the disturbed site but moderate at the undisturbed site; repeatability of boldness was low at both sites. Individual and population plasticity was similar between sites for both behaviours. Aggressiveness decreases with increasing colony size at the disturbed site; this trend was not observed at the undisturbed site. Boldness did not change with colony size. In contrast to solitary animals, our results indicate that less aggressive and more consistent colonies may have an advantage living in human-disturbed habitats.

Optical backscattering and linear polarization properties of the colony forming cyanobacterium Microcystis.

Light scattering characteristics of the cyanobacterium Microcystis are investigated with numerical models for sphere aggregates. During summer bloom seasons, Microcystis is prevalent in many inland waters across the globe. Monitoring concentrations with remote sensing techniques requires knowledge of the inherent optical properties (IOPs), especially the backscattering properties of Microcystis cells and colonies in natural settings. In situ measurements in waters dominated by Microcystis blooms have previously detected extremely high backscattering ratios, i.e., bb/b>0.043 at 443 nm [1], the highest to our knowledge in the natural environment. These highbb/bvalues could hold promise as a diagnostic tool in identifying and monitoring Microcystis using optical approaches. However, it has been unclear how this type of optically 'soft' organic particle can generate such highbb/bvalues. In this study, the Multiple Sphere T-matrix (MSTM) model is used to calculate the IOPs of model colonies, including bb/b. Colony sizes in the model ranged from several cells to several hundred and both colony packing density and cell gas vacuole content were varied. Results are compared with model results for equivalent-volume spheres (EVS) and direct in situ measurements. Colony formation was required in the modeling to reproduce the high bb/bconsistent with in situ measurements. The combination of moderate to very dense colony (packing density >30%) and high gas vacuole content in individual cells (volume percentage >20%) was the most favorable condition leading to rapid increases in bb/bwith increasing number of cells Ncell of the colony. Significant linear correlations were observed betweenbb/b and Ncell1/3 for these colonies, wherebb/b increased beyond 0.04 once cell number reached about 1000 cells in the case with the most densely packed cells and highest gas vacuole content. Within commonly observed colony sizes (Ncell <106), colonies with high gas vacuole content exhibited bb/bvalues up to 0.055, consistent with direct measurements from Lake Erie. Polarized scattering was also of interest as a diagnostic tool, particularly with future Earth-orbiting polarimeters being deployed for the NASA Plankton, Aerosols, Cloud, ocean Ecosystem (PACE) mission. The Degree of Linear Polarization (DoLP), expressed by the ratio of two Mueller matrix elements-P12/P11, decreased with increasing colony cell number for Microcystis. Another ratio of two Mueller matrix elementsP22/P11, an index for nonsphericity, also decreased with increasing colony size. In addition to higher relative backscattering, greater colony packing density and larger gas vacuole sizes both led to lower DoLP peak magnitude and lowerP22/P11. An optical opposition feature due to constructive phase interference that was observed previously for cosmic dusts is also present for these modeled colonies, manifested by a narrow intensity peak and negative polarization dip near exact backscattering direction, gradually forming as colony size increases.

A mathematical model of the metastatic bottleneck predicts patient outcome and response to cancer treatment.

Metastases are the main reason for cancer-related deaths. Initiation of metastases, where newly seeded tumor cells expand into colonies, presents a tremendous bottleneck to metastasis formation. Despite its importance, a quantitative description of metastasis initiation and its clinical implications is lacking. Here, we set theoretical grounds for the metastatic bottleneck with a simple stochastic model. The model assumes that the proliferation-to-death rate ratio for the initiating metastatic cells increases when they are surrounded by more of their kind. For a total of 159,191 patients across 13 cancer types, we found that a single cell has an extremely low median probability of successful seeding of the order of 10−8. With increasing colony size, a sharp transition from very unlikely to very likely successful metastasis initiation occurs. The median metastatic bottleneck, defined as the critical colony size that marks this transition, was between 10 and 21 cells. We derived the probability of metastasis occurrence and patient outcome based on primary tumor size at diagnosis and tumor type. The model predicts that the efficacy of patient treatment depends on the primary tumor size but even more so on the severity of the metastatic bottleneck, which is estimated to largely vary between patients. We find that medical interventions aiming at tightening the bottleneck, such as immunotherapy, can be much more efficient than therapies that decrease overall tumor burden, such as chemotherapy.

Abstract 5675: Metastatic organ-specific changes in ERα and XPO1 signaling and metabolic adaptations dictate the therapy responses in endocrine resistant breast cancers

Abstract Introduction: Approximately 70% of human breast cancers express estrogen receptor alpha (ERα), providing a potential for targeted endocrine therapy for patients. Unfortunately, 30-40% of ER+ patients still experience recurrence and metastasis with a 5-year relative overall survival rate of just 24%. The tumor microenvironment (TME) plays a key role in the behavior of cancer cells and their response to endocrine therapies. However, there is a critical need for relevant 3D models of different metastatic sites to use for studying the molecular mechanisms driving resistance in these tumor phenotypes. Methods: We established 3D cell culture systems in novel hydrogels derived from decellularized bone, lung and liver tissues - the major sites of metastasis of ER+ tumors, and compared with standard Matrigel culture. Endocrine responsive (MCF7 and T47D) and resistant (MCF7 and T47D cells with ESR1 Y537S or D538G mutations) breast cancer cell lines were treated with fulvestrant (FUL), tamoxifen (TAM) and palbociclib (PAL). Tumorigenicity was assessed using in vitro cell viability and colony formation assays and in vivo breast cancer cell line xenografts in athymic mice. ERα cistromes and transcriptomes were assessed using ChIP-Seq and RNA-Seq analysis. Metabolic changes were assessed using whole metabolite profiling by GC-MS, a Seahorse XF analyzer, and flux analysis with labeled glucose and glutamine. Results: We observed metastatic site-specific responses to each drug. For example, TAM blocked colony formation in Matrigel and lung hydrogel but increased colony formation in bone and liver hydrogels. FUL acted as an agonist and increased colony number and size in all three-tissue matrices, but not in Matrigel. PAL increased colony size and number in Matrigel and liver hydrogel but not in bone or lung hydrogel. Genome-wide ERα recruitment to chromatin was reduced in liver hydrogels, consistent with decreased clinical response to endocrine agents in patients with liver metastasis. We found that treatment with individual drugs activated novel metabolic pathways to increase survival in different metastatic sites. Using RNA-Seq analysis, we identified increased expression of nuclear export pathway components (XPO1, KPNA2, etc.) in various metastatic sites. Combining an FDA-approved XPO1 small molecule inhibitor, Selinexor (SEL) with the current therapies used for advanced breast cancers (FUL, TAM or PAL) decreased metabolic adaptations in response to individual drug treatments and prevented colony formation in hydrogels and tumor growth in xenograft models. Conclusions: Further developing and characterizing 3D metastatic site models will enable us to elucidate the underlying mechanisms of metastasis and resistance, and target these mechanisms with novel drug combinations in already metastasized patients. Targeting metastatic-site specific adaptations to regenerate new vulnerabilities in endocrine-resistant breast tumors is novel. Given the need for better strategies for improving therapy response of metastatic ER+ tumors, our findings show uncovering the role ERα-XPO1 crosstalk plays in metastatic breast cancer could lead to new combined therapies that reduce mortality. Citation Format: Qianying Zuo, Eylem Kulkoyluoglu Cotul, Ashlie Santaliz-Casiano, Ozan Berk Imir, Elif Tunc, Chengjian Mao, David J. Shapiro, Ben Ho Park, Yosef Landesman, Zeynep Madak-Erdogan. Metastatic organ-specific changes in ERα and XPO1 signaling and metabolic adaptations dictate the therapy responses in endocrine resistant breast cancers [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 5675.

Behavioral responses to colony-level properties affect disturbance resistance of red harvester ant colonies

Self-organizing biological systems, such as colonies of social insects, are characterized by their decentralized control and flexible responses to changing environments, often likened to swarm intelligence. Although decentralized control is well known to be a product of local interactions among agents, without the need for a bird’s-eye view, indirect knowledge of properties that indicate the current states of the entire system also helps each agent to respond to changes, thereby leading to a more adaptive system. In this study, we analyze the rules that govern workers’ behavioral responses to colony-level properties and assess whether they contribute to adaptive flexibility in social insect colonies. We focus on task allocation among red harvester ants (Pogonomyrmex barbatus) as a model system and develop an ordinary differential equation model to describe the system of task allocation among workers. We simulate 12 scenarios specifying how workers respond to changes in the colony-level properties of colony size and nutritional state. We found that when workers decrease their contact rates in response to increasing colony size, they enable achievement of a larger colony size, similar to that of P. barbatus colonies in nature, and when workers increase their foraging levels in response to decreasing colony-wide nutritional levels, they increase resilience to environmental disturbances. These negative feedback rules governing the response to colony-level properties are consistent with previous reports on ants and honeybees.

Loss of PTPRJ/DEP-1 enhances NF2/Merlin-dependent meningioma development

IntroductionMeningiomas are common tumors in adults, which develop from the meningeal coverings of the brain and spinal cord. Loss-of-function mutations or deletion of the NF2 gene, resulting in loss of the encoded Merlin protein, lead to Neurofibromatosis type 2 (NF2), but also cause the formation of sporadic meningiomas. It was shown that inactivation of Nf2 in mice caused meningioma formation. Another meningioma tumor-suppressor candidate is the receptor-like density-enhanced phosphatase-1 (DEP-1), encoded by PTPRJ. Loss of DEP-1 enhances meningioma cell motility in vitro and invasive growth in an orthotopic xenograft model. Ptprj-deficient mice develop normally and do not show spontaneous tumorigenesis. Another genetic lesion may be required to interact with DEP-1 loss in meningioma genesis. MethodsIn the present study we investigated in vitro and in vivo whether the losses of DEP-1 and Merlin/NF2 may have a combined effect. ResultsHuman meningioma cells deficient for DEP-1, Merlin/NF2 or both showed no statistically significant changes in cell proliferation, while DEP-1 or DEP1/NF2 deficiency led to moderately increased colony size in clonogenicity assays. In addition, the loss of any of the two genes was sufficient to induce a significant reduction of cell size (p < .05) and profound morphological changes. Most important, in Ptprj knockout mice Cre/lox mediated meningeal Nf2 knockout elicited a four-fold increased rate of meningioma formation within one year compared with mice with Ptprj wild type alleles (25% vs 6% tumor incidence). ConclusionsOur data suggest that loss of DEP-1 and Merlin/NF2 synergize during meningioma genesis.

Coral reef assessments based on cover alone mask active dynamics of coral communities

Coral reef communities are often studied by tracking the percentage (or fraction) of the reef covered by coral through time. However, coral community dynamics result, in part, from underlying colony-level growth and mortality, which in turn depend on characteristics of individual colonies, such as size, taxon, life history strategy, and morphology. Colonies are also subject to external disturbances that propel fission into smaller coral fragments and fusion where related fragments later fuse into contiguous colonies. To quantify how changes in coral growth through time depend on individual colony characteristics and colony fission and fusion processes, 4385 individual Caribbean coral colonies representing 4 dominant coral types (Madracis mirabilis, mounding coral species, Agaricia agaricites, and Millepora spp.) were tracked at 6 mo intervals for 4 yr. Despite overall stable percent coral cover, colonies belonging to different coral types experienced differential growth, shrinkage, mortality, fission, and fusion processes. All coral types displayed size-dependent allometric growth patterns whereby relative, or proportional, growth in colony area decreased with increasing colony size. The largest changes in relative colony growth resulted from colony fission or fusion with other colonies, which occurred in 16.4% of all monitored colonies. Colony longevity, or survival, increased significantly with increasing colony size for all hard-coral groups that did not experience fission, fusion, or a combination of these processes. Our findings illustrate the usefulness of a size- and life-history-dependent approach to coral demography that elucidates the factors driving community dynamics of colonial organisms, which are not captured by traditional approaches based on benthic cover alone.

Mineral iron dissolution in Trichodesmium colonies: The role of O2 and pH microenvironments

AbstractColonies of the N2‐fixing cyanobacterium Trichodesmium can harbor distinct chemical microenvironments that may assist the colonies in acquiring mineral iron from dust. Here, we characterized O2 and pH gradients in and around Trichodesmium colonies by microsensor measurements on &gt; 170 colonies collected in the Gulf of Eilat over ∼ 2 months. O2 concentrations and pH values in the center of single colonies decreased in the dark due to respiration, reaching minimum values of 70 μmol L−1 and 7.7, whereas in the light, O2 and pH increased due to photosynthesis, reaching maximum values of 410 μmol L−1 and 8.6. Addition of dust and bacteria and increasing colony size influenced O2 and pH levels in the colonies, yet values remained within the range observed in single natural colonies. However, lower values down to 60 μmol L−1 O2 and pH 7.5 were recorded in the dark in dense surface accumulations of Trichodesmium. Using radiolabelled ferrihydrite, we examined the effect of these conditions on mineral iron dissolution and availability to Trichodesmium. Dark‐incubated colonies did not acquire iron from ferrihydrite faster than light‐incubated colonies, indicating that the dark‐induced decrease in pH and O2 within single colonies is too small to significantly increase mineral iron bioavailability. Yet, ligand‐promoted dissolution of ferrihydrite, a mechanism likely applied by Trichodesmum for acquiring mineral iron, did increase at the lower pH levels observed in surface accumulations. Thus, Trichodesmium surface blooms in their final stage may harbor chemical conditions that enhance the dissolution and bioavailability of mineral iron to the associated microbial community.

Suppression of PRPF4 regulates pluripotency, proliferation, and differentiation in mouse embryonic stem cells.

Mouse embryonic stem cells (mESCs) are characterized by their self-renewal and pluripotency and are capable of differentiating into all three germ layers. For this reason, mESCs are considered a very important model for stem cell research and clinical applications in regenerative medicine. The pre-mRNA processing factor 4 (PRPF4) gene is known to have a major effect on pre-mRNA splicing and is also known to affect tissue differentiation during development. In this study, we investigated the effects of PRPF4 knockdown on mESCs. First, we allowed mESCs to differentiate naturally and observed a significant decrease in PRPF4 expression during the differentiation process. We then artificially induced the knockdown of PRPF4 in mESCs and observed the changes in the phenotype. When PRPF4 was knocked down, various genes involved in mESC pluripotency showed significantly decreased expression. In addition, mESC proliferation increased abnormally, accompanied by a significant increase in mESC colony size. The formation of mESC embryoid bodies and teratomas was delayed following PRPF4 knockdown. Based on these results, the reduced expression of PRPF4 affects mESC phenotypes and is a key factor in mESC. SIGNIFICANCE OF THE STUDY: Our results indicate that PRPF4 affects the properties of mESCs. Suppression of PRPF4 resulted in a decrease in pluripotency of mESC and promoted proliferation. In addition, suppression of PRPF4 also resulted in decreased apoptosis. Moreover, the inhibition of PRPF4 reduced the ability to differentiate and formation of teratoma in mESC. Our results demonstrated that PRPF4 is a key factor of controlling mESC abilities.

Movement of cyanobacterial colonies in a large, shallow and eutrophic lake: A review

Cyanobacterial blooms caused by lake eutrophication result in serious damage to lake ecosystem services, and cyanobacterial movement is the key to bloom formation. Cyanobacteria exist as unicellular organisms when under laboratory culture for long periods of time, and their movement is considered to be controlled by gas vesicles. However, recent studies have shown that colony formation has a decisive influence on cyanobacterial movement, and that buoyant cyanobacteria in natural waterbodies mostly exist as colony. Cyanobacterial colonies are formed by wrapping multiple cells in extracellular polysaccharides, which is primarily a result of fission proliferation or collision adhesion. When compared with unicellular cyanobacteria, active and passive movements of cyanobacterial colonies with larger size and buoyancy changed deeply, making it easier for colonies to float upwards toward the water surface, resulting in further formation of surface blooms. Active movement of a cyanobacterial colony refers to colony movement that is driven by effective buoyancy in a weak hydrodynamic environment. Active movement depends on three dynamic parameters of cyanobacterial colonies (density, shape and size) that are intrinsically linked, with colony size being most important. Early studies suggested that changes in cyanobacterial density are the result of cell metabolism and established formulas on the relationship between light and cell density based on laboratory experiments. However, these formulas cannot be used to describe the density of cyanobacterial colonies during severe blooms. Colony density is primarily affected by colony size and decreases with increasing colony size. Moreover, colony size is an important parameter for characterizing colony morphology. Therefore, colony size has an important influence on the effective buoyancy of a colony. Specifically, the floating rate of large colonies of cyanobacteria (100–425 μm) was 1475 times that of small colonies ( in Lake Taihu. Passive movement of a cyanobacterial colony refers to hydrodynamically dominant movement. In Lake Taihu, the passive movement of cyanobacterial colonies is mainly controlled by hydrodynamic vertical disturbances, which are dominated by wind waves, and hydrodynamic horizontal transport, which is dominated by lake currents. Wind waves are conducive to acceleration of the recovery of wintering cyanobacteria, alleviation of nutrient limitations during severe blooms and improvement of the absorption efficiency of cyanobacteria, while also directly affecting colony morphology. Studies have shown that appropriate disturbance of wind waves can enlarge colonies, while disturbances that are too strong can change the colony shape or disintegrate the colony. Moreover, strong turbulence dominated by wind waves can entrain buoyant colonies and disperse surface blooms. The ratio of turbulence intensity to upward-floating rate is a direct indicator of the occurrence of turbulence entrainment of buoyant colonies. Lake currents transport nutrients from inflows or sediments to cyanobacteria and cause horizontal redistribution of cyanobacterial colonies in lakes. It is generally believed that the prevailing southeast wind-induced currents cause colonies to accumulate and form severe cyanobacterial blooms in the northwestern area of Lake Taihu. However, recent studies have suggested that the migration of buoyant colonies with free-movement is primarily determined by wind fields rather than surface lake currents. Accordingly, it is debatable whether cyanobacterial migration models based on lake current models can be used to simulate algal patchiness drift and large-scale bloom formation. Therefore, further studies are required to conduct long-term field monitoring of colony dynamics parameters along with experiments and field observations investigating cyanobacterial colony movements to explore the temporal and spatial dynamics of field cyanobacterial colonies and their influencing mechanisms. It is also necessary to investigate movements of cyanobacterial colonies caused by wind drift, turbulence entrainment, wind waves-induced mass transfer, Langmuir circulation system transportation and other hydrodynamic processes in shallow lakes. Accordingly, the hydraulic removal and numerical models of cyanobacterial blooms can be developed to control cyanobacterial blooms in shallow lakes.

A more efficient conditional mouse model of Dravet syndrome: Implications for epigenetic selection and sex-dependent behaviors

BackgroundDravet Syndrome (DS) is an epileptic disorder characterized by spontaneous and thermally-induced seizures, hyperactivity, cognitive deficits, autistic-like behaviors, and Sudden Unexpected Death in Epilepsy (SUDEP). DS is caused by de novo loss-of-function mutations in the SCN1A gene. Selective loss of GABAergic interneuron excitability is the primary cause of the disease. Up to 60% of Scn1a+/− mice die from SUDEP before sexual maturity. New methodWe used Cre-Lox technology to conditionally delete Scn1a in all epiblast-derived somatic cells by crossing a floxed Scn1a mouse with a mouse expressing Cre under the Meox2 promoter. ResultsParental Scn1a flox (F) mice, parental Meox2 Cre+ mice, and their F/+:Meox2-Cre− offspring were phenotypically normal and did not prematurely die. In contrast, F/+:Meox2-Cre+ offspring recapitulated DS seizure and behavioral phenotypes. Unexpectedly, male F/+:Meox2-Cre+ mice demonstrated impaired social interaction, while females did not. Comparison with existing methodIn the previous models, colony maintenance required breeding SUDEP survivors, which greatly increased colony size required to sustain experimental animal production, and raised the concern that surviving breeders have epigenetic traits that impart new phenotypes to their offspring. Our method greatly facilitates breeding, recapitulates DS phenotypes, eliminates concerns about parents that are survivors, and provides initial evidence for unexpected sex-dependent social interaction impairment. ConclusionsWe introduce a more efficient mouse model of human DS that demonstrates an efficient breeding strategy free from potential inherited epigenetic changes and reveals an unexpected sex-specific impairment of social interaction in DS. This new model should have great value to investigators of DS.

Mutational and Selective Processes Involved in Evolution during Bacterial Range Expansions.

Bacterial populations have been shown to accumulate deleterious mutations during spatial expansions that overall decrease their fitness and ability to grow. However, it is unclear if and how they can respond to selection in face of this mutation load. We examine here if artificial selection can counteract the negative effects of range expansions. We examined the molecular evolution of 20 mutator lines selected for fast expansions (SEL) and compared them to 20 other mutator lines freely expanding without artificial selection (CONTROL). We find that the colony size of all 20 SEL lines have increased relative to the ancestral lines, unlike CONTROL lines, showing that enough beneficial mutations are produced during spatial expansions to counteract the negative effect of expansion load. Importantly, SEL and CONTROL lines have similar numbers of mutations indicating that they evolved for the same number of generations and that increased fitness is not due to a purging of deleterious mutations. We find that loss of function mutations better explain the increased colony size of SEL lines than nonsynonymous mutations or a combination of the two. Interestingly, most loss of function mutations are found in simple sequence repeats (SSRs) located in genes involved in gene regulation and gene expression. We postulate that such potentially reversible mutations could play a major role in the rapid adaptation of bacteria to changing environmental conditions by shutting down expensive genes and adjusting gene expression.

How bacterial cells and colonies move on solid substrates.

Many bacteria rely on active cell appendages, such as type IV pili, to move over substrates and interact with neighboring cells. Here, we study the motion of individual cells and bacterial colonies, mediated by the collective interactions of multiple pili. It was shown experimentally that the substrate motility of Neisseria gonorrhoeae cells can be described as a persistent random walk with a persistence length that exceeds the mean pili length. Moreover, the persistence length increases for a higher number of pili per cell. With the help of a simple, tractable stochastic model, we test whether a tug of war without directional memory can explain the persistent motion of single Neisseria gonorrhoeae cells. While persistent motion of single cells indeed emerges naturally in the model, a tug of war alone is not capable of explaining the motility of microcolonies, which becomes weaker with increasing colony size. We suggest sliding friction between the microcolonies and the substrate as the missing ingredient. While such friction almost does not affect the general mechanism of single cell motility, it has a strong effect on colony motility. We validate the theoretical predictions by using a three-dimensional computational model that includes explicit details of the pili dynamics, force generation, and geometry of cells.

Highlights of This Issue

The antidiabetic drug metformin has been shown to have anti-cancer properties that are poorly understood. Here, Hart and colleagues demonstrate that metformin inhibits the nuclear translocation and transcriptional activity of hypoxia-inducible factor (HIF)-1α and -2α. This in turn blocked the expression of sphingosine kinase 1 (SPHK1) and its target, sphingosine-1-phosphate (S1P), which are upregulated in ovarian cancer patients and are predictive of tumor aggressiveness and poor outcome. The authors suggest that patients with high SPHK1-S1P pathway activity may demonstrate considerable benefit from treatment with metformin.The epithelial-to-mesenchymal transition (EMT) is a critical step in the pathology and progression of cancer. In this study, Short and colleagues identify serine threonine kinase 17A (STK17A) as a key regulator of EMT in colorectal cancer. Loss of STK17A was associated with acquisition of a mesenchymal phenotype and increased invasive spread, whereas reactivation of STK17A signaling caused reversion to an epithelial phenotype and increased sensitivity to apoptotic signaling. Taken together, their data indicate a novel role for STK17A in controlling metastatic spread in colorectal cancer.Cisplatin therapy is a key component of the standard of care for pediatric osteosarcoma, but its potential to increase mutational burden in the tumor has yet to be defined. Here, Brady and colleagues demonstrate a unique mutational signature in metastatic samples from patients treated with cisplatin. The cisplatin signature accounted for greater than 40% of mutations in metastatic lesions and was associated with acquisition of putative driver mutations upon seeding of distant metastases. These data indicate widespread clonal heterogeneity in metastatic osteosarcoma, which could inform the optimal treatment of patients with recurrent disease.Ionizing radiation (IR) is a common treatment modality for many localized cancers, but its widespread genotoxic effects have the potential to induce tumorigenic mutations as well. Repullés and colleagues demonstrate that IR delivered to primary breast cells resulted in increased colony size and disrupted cellular polarity. Additionally, immortalized pre-malignant cells bearing hTERT and SV40 small and large T antigens displayed heightened sensitivity to radiation-induced cell transformation. Though cells from different donors displayed differential sensitivity to IR, these data imply that patients bearing premalignant genetic lesions may be at increased risk of developing oncogenic driver mutations in response to radiotherapy.

Strategies of the invasive tropical fire ant (Solenopsis geminata) to minimize inbreeding costs

How invasive species overcome challenges associated with low genetic diversity is unclear. Invasive ant populations with low genetic diversity sometimes produce sterile diploid males, which do not contribute to colony labour or reproductive output. We investigated how inbreeding affects colony founding and potential strategies to overcome its effects in the invasive tropical fire ant, Solenopsis geminata. Our genetic analyses of field samples revealed that 13–100% of males per colony (n = 8 males per 10 colonies) were diploid, and that all newly mated queens (n = 40) were single-mated. Our laboratory experiment in which we assigned newly mated queens to nests consisting of 1, 2, 3, or 5 queens (n = 95 ± 9 replicates) revealed that pleometrosis (queens founding their nest together) and diploid male larvae execution can compensate for diploid male load. The proportion of diploid male producing (DMP) colonies was 22.4%, and DMP colonies produced fewer pupae and adult workers than non-DMP colonies. Pleometrosis significantly increased colony size. Queens executed their diploid male larvae in 43.5% of the DMP colonies, and we hypothesize that cannibalism benefits incipient colonies because queens can redirect nutrients to worker brood. Pleometrosis and cannibalism of diploid male larvae represent strategies through which invasive ants can successfully establish despite high inbreeding.