Riboswitches are structured noncoding RNA domains that are typically found embedded in messenger RNAs, where they sense specific target molecules or elemental ions and regulate gene expression. These RNAs thus serve as genetic switches that can activate or repress gene expression in response to changing levels of their target ligand. To many observers, riboswitches might seem like rare oddities that are not as sophisticated as, or competitive with, the various protein factors that perform these same roles. However, as the number of experimentally validated riboswitch classes increases, and their true biochemical sophistication is recognized, it is becoming clearer that many species from all three domains of life entrust RNAs to make important chemical sensing and gene control decisions without the necessary participation of protein factors.

Interview with Alexis Maizel, who studies plant morphogenesis at Heidelberg University.

Steven Portugal introduces the Siamese fighting fish (Betta splendens).

Sala and Oakes introduce LIM domain proteins and discuss their roles in transcription, cytokinesis, adhesion, motility and mechanosignaling.

Sighs are a response to hypoxia, altered lung volume, and emotional state. A recent study employing in vivo physiology, optogenetics, chemoablation, and genetic silencing shows the importance of gastrin releasing peptide-expressing neurons in mediating sighs.

Cortical activity patterns occupy a small subset of possible network states. If this is due to intrinsic network properties, microstimulation of sensory cortex should evoke activity patterns resembling those observed during natural sensory input. Here, we use optical microstimulation of virally transfected layer 2/3 pyramidal neurons in the mouse primary vibrissal somatosensory cortex to compare artificially evoked activity with natural activity evoked by whisker touch and movement ("whisking"). We find that photostimulation engages touch- but not whisking-responsive neurons more than expected by chance. Neurons that respond to photostimulation and touch or to touch alone exhibit higher spontaneous pairwise correlations than purely photoresponsive neurons. Exposure to several days of simultaneous touch and optogenetic stimulation raises both overlap and spontaneous activity correlations among touch and photoresponsive neurons. We thus find that cortical microstimulation engages existing cortical representations and that repeated co-presentation of natural and artificial stimulation enhances this effect.

Animals use the geometry of their local environments to orient themselves during navigation. Single neurons in the rat postrhinal cortex (POR) appear to encode environmental geometry in an egocentric (self-centered) reference frame, such that they fire in response to the egocentric bearing and/or distance from the environment center or boundaries. One major issue is whether these neurons truly encode high-level global parameters, such as the bearing/distance of the environment centroid, or whether they are simply responsive to the bearings and distances of nearby walls. We recorded from POR neurons as rats foraged in environments with different geometric layouts and modeled their responses based on either global geometry (centroid) or local boundary encoding. POR neurons largely split into either centroid-encoding or local-boundary-encoding cells, with each group lying at one end of a continuum. We also found that distance-tuned cells tend to scale their linear tuning slopes in a very small environment, such that they lie somewhere between absolute and relative distance encoding. In addition, POR cells largely maintain their bearing preferences, but not their distance preferences, when exposed to different boundary types (opaque, transparent, drop edge), suggesting different driving forces behind the bearing and distance signals. Overall, the egocentric spatial correlates encoded by POR neurons comprise a largely robust and comprehensive representation of environmental geometry.

Exciting new research highlights how stigmatic receptors purposed for recognizing self-incompatible pollen interact with the FERONIA pathway to regulate stigmatic reactive oxygen species production to enforce a barrier against self-, intra- and interspecific pollen.

Although polyploidization is frequent in development, cancer, and evolution, impacts on animal metabolism are poorly understood. In Xenopus frogs, the number of genome copies (ploidy) varies across species and can be manipulated within a species. Here, we show that triploid tadpoles contain fewer, larger cells than diploids and consume oxygen at a lower rate. Drug treatments revealed that the major processes accounting for tadpole energy expenditure include cell proliferation, biosynthesis, and maintenance of plasma membrane potential. While inhibiting cell proliferation did not abolish the oxygen consumption difference between diploids and triploids, treatments that altered cellular biosynthesis or electrical potential did. Combining these results with a simple mathematical framework, we propose that the decrease in total cell surface area lowered production and activity of plasma membrane components including the Na+/K+ ATPase, reducing energy consumption in triploids. Comparison of Xenopus species that evolved through polyploidization revealed that metabolic differences emerged during development when cell size scaled with genome size. Thus, ploidy affects metabolism by altering the cell surface area to volume ratio in a multicellular organism.

Viruses are a vastly underestimated component of biodiversity that occur as diverse communities across hierarchical scales from the landscape level to individual hosts. The integration of community ecology with disease biology is a powerful, novel approach that can yield unprecedented insights into the abiotic and biotic drivers of pathogen community assembly. Here, we sampled wild plant populations to characterize and analyze the diversity and co-occurrence structure of within-host virus communities and their predictors. Our results show that these virus communities are characterized by diverse, non-random coinfections. Using a novel graphical network modeling framework, we demonstrate how environmental heterogeneity influences the network of virus taxa and how the virus co-occurrence patterns can be attributed to non-random, direct statistical virus-virus associations. Moreover, we show that environmental heterogeneity changed virus association networks, especially through their indirect effects. Our results highlight a previously underestimated mechanism of how environmental variability can influence disease risks by changing associations between viruses that are conditional on their environment.

Recurrent connectivity between excitatory neurons and the strength of feedback from inhibitory neurons are critical determinants of the dynamics and computational properties of neuronal circuits. Toward a better understanding of these circuit properties in regions CA1 and CA3 of the hippocampus, we performed optogenetic manipulations combined with large-scale unit recordings in rats under anesthesia and in quiet waking, using photoinhibition and photoexcitation with different light-sensitive opsins. In both regions, we saw striking paradoxical responses: subsets of cells increased firing during photoinhibition, while other cells decreased firing during photoexcitation. These paradoxical responses were more prominent in CA3 than in CA1, but, notably, CA1 interneurons showed increased firing in response to photoinhibition of CA3. These observations were recapitulated in simulations where we modeled both CA1 and CA3 as inhibition-stabilized networks in which strong recurrent excitation is balanced by feedback inhibition. To directly test the inhibition-stabilized model, we performed large-scale photoinhibition directed at (GAD-Cre) inhibitory cells and found that interneurons in both regions increased firing when photoinhibited, as predicted. Our results highlight the often-paradoxical circuit dynamics that are evidenced during optogenetic manipulations and indicate that, contrary to long-standing dogma, both CA1 and CA3 hippocampal regions display strongly recurrent excitation, which is stabilized through inhibition.

The Na+ channels that are important for action potentials show rapid inactivation, a state in which they do not conduct, although the membrane potential remains depolarized.1,2 Rapid inactivation is a determinant of millisecond-scale phenomena, such as spike shape and refractory period. Na+ channels also inactivate orders of magnitude more slowly, and this slow inactivation has impacts on excitability over much longer timescales than those of a single spike or a single inter-spike interval.3,4,5,6,7,8,9,10 Here, we focus on the contribution of slow inactivation to the resilience of axonal excitability11,12 when ion channels are unevenly distributed along the axon. We study models in which the voltage-gated Na+ and K+ channels are unevenly distributed along axons with different variances, capturing the heterogeneity that biological axons display.13,14 In the absence of slow inactivation, many conductance distributions result in spontaneous tonic activity. Faithful axonal propagation is achieved with the introduction of Na+ channel slow inactivation. This "normalization" effect depends on relations between the kinetics of slow inactivation and the firing frequency. Consequently, neurons with characteristically different firing frequencies will need to implement different sets of channel properties to achieve resilience. The results of this study demonstrate the importance of the intrinsic biophysical properties of ion channels in normalizing axonal function.

Selective attention1 is characterized by alternating states associated with either attentional sampling or attentional shifting, helping to prevent functional conflicts by isolating function-specific neural activity in time.2,3,4,5 We hypothesized that such rhythmic temporal coordination might also help to prevent representational conflicts during working memory.6 Multiple items can be simultaneously held in working memory, and these items can be represented by overlapping neural populations.7,8,9 Traditional theories propose that the short-term storage of to-be-remembered items occurs through persistent neural activity,10,11,12 but when neurons are simultaneously representing multiple items, persistent activity creates a potential for representational conflicts. In comparison, more recent, "activity-silent" theories of working memory propose that synaptic changes also contribute to short-term storage of to-be-remembered items.13,14,15,16 Transient bursts in neural activity,17 rather than persistent activity, could serve to occasionally refresh these synaptic changes. Here, we used EEG and response times to test whether rhythmic temporal coordination helps to isolate neural activity associated with different to-be-remembered items, thereby helping to prevent representational conflicts. Consistent with this hypothesis, we report that the relative strength of different item representations alternates over time as a function of the frequency-specific phase. Although RTs were linked to theta (∼6 Hz) and beta (∼25 Hz) phases during a memory delay, the relative strength of item representations only alternated as a function of the beta phase. The present findings (1) are consistent with rhythmic temporal coordination being a general mechanism for preventing functional or representational conflicts during cognitive processes and (2) inform models describing the role of oscillatory dynamics in organizing working memory.13,18,19,20,21.

The postembryonic formation of lateral roots (LRs) starts in internal root tissue, the pericycle. An important question of LR development is how the connection of the primary root vasculature with that of the emerging LR is established and whether the pericycle and/or other cell types direct this process. Here, using clonal analysis and time-lapse experiments, we show that both the procambium and pericycle of the primary root (PR) affect the LR vascular connectivity in a coordinated manner. We show that during LR formation, procambial derivates switch their identity and become precursors of xylem cells. These cells, together with the pericycle-origin xylem, participate in the formation of what we call a "xylem bridge" (XB), which establishes the xylem connection between the PR and the nascent LR. If the parental protoxylem cell fails to differentiate, XB is still sometimes formed but via a connection with metaxylem cells, highlighting that this process has some plasticity. Using mutant analyses, we show that the early specification of XB cells is determined by CLASS III HOMEODOMAIN-LEUCINE ZIPPER (HD-ZIP III) transcription factors (TFs). Subsequent XB cell differentiation is marked by the deposition of secondary cell walls (SCWs) in spiral and reticulate/scalariform patterns, which is dependent on the VASCULAR-RELATED NAC-DOMAIN (VND) TFs. XB elements were also observed in Solanum lycopersicum, suggesting that this mechanism may be more widely conserved in plants. Together, our results suggest that plants maintain vascular procambium activity, which safeguards the functionality of newly established lateral organs by assuring the continuity of the xylem strands throughout the root system.

The leaf epidermis is the outermost cell layer forming the interface between plants and the atmosphere that must both provide a robust barrier against (a)biotic stressors and facilitate carbon dioxide uptake and leaf transpiration.1 To achieve these opposing requirements, the plant epidermis developed a wide range of specialized cell types such as stomata and hair cells. Although factors forming these individual cell types are known,2,3,4,5 it is poorly understood how their number and size are coordinated. Here, we identified a role for BdPRX76/BdPOX, a class III peroxidase, in regulating hair cell and stomatal size in the model grass Brachypodium distachyon. In bdpox mutants, prickle hair cells were smaller and stomata were longer. Because stomatal density remained unchanged, the negative correlation between stomatal size and density was disrupted in bdpox and resulted in higher stomatal conductance and lower intrinsic water-use efficiency. BdPOX was exclusively expressed in hair cells, suggesting that BdPOX cell-autonomously promotes hair cell size and indirectly restricts stomatal length. Cell-wall autofluorescence and lignin stainings indicated a role for BdPOX in the lignification or crosslinking of related phenolic compounds at the hair cell base. Ectopic expression of BdPOX in the stomatal lineage increased phenolic autofluorescence in guard cell (GC) walls and restricted stomatal elongation in bdpox. Together, we highlight a developmental interplay between hair cells and stomata that optimizes epidermal functionality. We propose that cell-type-specific changes disrupt this interplay and lead to compensatory developmental defects in other epidermal cell types.

Organ loss occurs frequently during plant and animal evolution. Sometimes, non-functional organs are retained through evolution. Vestigial organs are defined as genetically determined structures that have lost their ancestral (or salient) function.1,2,3 Duckweeds, an aquatic monocot family, exhibit both these characteristics. They possess a uniquely simple body plan, variably across five genera, two of which are rootless. Due to the existence of closely related species with a wide diversity in rooting strategies, duckweed roots represent a powerful system for investigating vestigiality. To explore this, we employed a panel of physiological, ionomic, and transcriptomic analyses, with the main goal of elucidating the extent of vestigiality in duckweed roots. We uncovered a progressive reduction in root anatomy as genera diverge and revealed that the root has lost its salient ancestral function as an organ required for supplying nutrients to the plant. Accompanying this, nutrient transporter expression patterns have lost the stereotypical root biased localization observed in other plant species. While other examples of organ loss such as limbs in reptiles4 or eyes in cavefish5 frequently display a binary of presence/absence, duckweeds provide a unique snapshot of an organ with varying degrees of vestigialization in closely related neighbors and thus provide a unique resource for exploration of how organs behave at different stages along the process of loss.

Computational models and in vivo studies in rodents suggest that the emergence of gamma activity (40-140 Hz) during memory encoding and retrieval is coupled to opposed-phase states of the underlying hippocampal theta rhythm (4-9 Hz).1,2,3,4,5,6,7,8,9,10 However, direct evidence for whether human hippocampal gamma-modulated oscillatory activity in memory processes is coupled to opposed-phase states of the ongoing theta rhythm remains elusive. Here, we recorded local field potentials (LFPs) directly from the hippocampus of 10 patients with epilepsy, using depth electrodes. We used a memory encoding and retrieval task whereby trial unique sequences of pictures depicting real-life episodes were presented, and 24 h later, participants were asked to recall them upon the appearance of the first picture of the encoded episodic sequence. We found theta-to-gamma cross-frequency coupling that was specific to the hippocampus during both the encoding and retrieval of episodic memories. We also revealed that gamma was coupled to opposing theta phases during both encoding and recall processes. Additionally, we observed that the degree of theta-gamma phase opposition between encoding and recall was associated with participants' memory performance, so gamma power was modulated by theta phase for both remembered and forgotten trials, although only for remembered trials the dominant theta phase was different for encoding and recall trials. The current results offer direct empirical evidence in support of hippocampal theta-gamma phase opposition models in human long-term memory and provide fundamental insights into mechanistic predictions derived from computational and animal work, thereby contributing to establishing similarities and differences across species.

Gleadow et al. introduce the food crop cassava.

Vivek V. Venkataraman introduces gelada monkeys.

In the early 19th century, long before the discovery of the dinosaurs, scientists and the public alike were faced with the realization that strange beasts, wholly extinct, were once populating Earth's ancient oceans. In no small part, this realization was through the discovery of the first plesiosaurs (and ichthyosaurs) along the Dorset coast of England in the seaside town of Lyme Regis. There was this large marine reptile resembling a large sea turtle, but with four evenly shaped flippers and looking as though a large snake had been pulled through its carapace. It was soon to be named scientifically Plesiosaurus, in reference to its greater similarity to living reptiles than the Ichthyosaurus (Figure 1). While the Ichthyosaurus was relatively easily understood as a fish-shaped reptile descended from land-living ancestors, the Plesiosaurus was beyond comprehension, even though incomplete skeletons had been unearthed already in the early 18th century. Plesiosaurs seemed so alien that the first complete skeleton, discovered by the famed Mary Anning a little more than 200 years ago (Figure 1A), was considered a fake by the leading anatomist of the day, the Baron Georges Cuvier in Paris. Only study of the original specimen convinced him of the authenticity of this animal but reinforced his seminal insight that there is extinction.

Lyu et al. respond to the letter from Lentini and Reinius.

In a heterogeneous and changing environment, oviposition site selection strongly affects the survival and fitness of the offspring.1,2 Similarly, competition between larvae affects their prospects.3 However, little is known about the involvement of pheromones in regulating these processes.4,5,6,7,8 Here, we show that mated females of Drosophila melanogaster prefer to lay eggs on substrates containing extracts of conspecific larvae. After analyzing these extracts chemically, we test each compound in an oviposition assay and find that mated females display a dose-dependent preference to lay eggs on substrates spiked with (Z)-9-octadecenoic acid ethyl ester (OE). This egg-laying preference relies on gustatory receptor Gr32a and tarsal sensory neurons expressing this receptor. The concentration of OE also regulates larval place choice in a dose-dependent manner. Physiologically, OE activates female tarsal Gr32a+ neurons. In conclusion, our results reveal a cross-generation communication strategy essential for oviposition site selection and regulation of larval density.

Courtship has evolved to achieve reproductive success in animal species. However, whether courtship itself has a positive value remains unclear. In the present work, we report that courtship is innately rewarding and can induce the expression of appetitive short-term memory (STM) and long-term memory (LTM) in Drosophila melanogaster males. Activation of male-specific P1 neurons is sufficient to mimic courtship-induced preference and memory performance. Surprisingly, P1 neurons functionally connect to a large proportion of dopaminergic neurons (DANs) in the protocerebral anterior medial (PAM) cluster. The acquisition of STM and LTM depends on two distinct subsets of PAM DANs that convey the courtship-reward signal to the restricted regions of the mushroom body (MB) γ and α/β lobes through two dopamine receptors, D1-like Dop1R1 and D2-like Dop2R. Furthermore, the retrieval of STM stored in the MB α'/β' lobes and LTM stored in the MB α/β lobe relies on two distinct MB output neurons. Finally, LTM consolidation requires two subsets of PAM DANs projecting to the MB α/β lobe and corresponding MB output neurons. Taken together, our findings demonstrate that courtship is a potent rewarding stimulus and reveal the underlying neural circuit mechanisms linking courtship and reward in Drosophila males.

The subcellular positioning of synapses and their specialized molecular compositions form the fundamental basis of neural circuits. Like chemical synapses, electrical synapses are constructed from an assortment of adhesion, scaffolding, and regulatory molecules, yet little is known about how these molecules localize to specific neuronal compartments. Here, we investigate the relationship between the autism- and epilepsy-associated gene Neurobeachin, the neuronal gap junction channel-forming Connexins, and the electrical synapse scaffold ZO1. Using the zebrafish Mauthner circuit, we find Neurobeachin localizes to the electrical synapse independently of ZO1 and Connexins. By contrast, we show Neurobeachin is required postsynaptically for the robust localization of ZO1 and Connexins. We demonstrate that Neurobeachin binds ZO1 but not Connexins. Finally, we find Neurobeachin is required to restrict electrical postsynaptic proteins to dendrites, but not electrical presynaptic proteins to axons. Together, the results reveal an expanded understanding of electrical synapse molecular complexity and the hierarchical interactions required to build neuronal gap junctions. Further, these findings provide novel insight into the mechanisms by which neurons compartmentalize the localization of electrical synapse proteins and provide a cell biological mechanism for the subcellular specificity of electrical synapse formation and function.

Goal-directed navigation relies on both coarse and fine-grained coding of spatial distance between the current position of a navigating subject and a goal destination. However, the neural signatures underlying goal distance coding remain poorly understood. Using intracranial EEG recordings from the hippocampus of drug-resistant epilepsy patients who performed a virtual spatial navigation task, we found that the right hippocampal theta power was significantly modulated by goal distance and decreased with goal proximity. This modulation varied along the hippocampal longitudinal axis such that theta power in the posterior hippocampus decreased more strongly with goal proximity. Similarly, neural timescale, reflecting the duration across which information can be maintained, increased gradually from the posterior to anterior hippocampus. Taken together, this study provides empirical evidence for multi-scale spatial representations of goal distance in the human hippocampus and links the hippocampal processing of spatial information to its intrinsic temporal dynamics.

We investigated whether early visual input is essential for establishing the ability to use predictions in the control of actions and for perception. To successfully interact with objects, it is necessary to pre-program bodily actions such as grasping movements (feedforward control). Feedforward control requires a model for making predictions, which is typically shaped by previous sensory experience and interaction with the environment.1 Vision is the most crucial sense for establishing such predictions.2,3 We typically rely on visual estimations of the to-be-grasped object's size and weight in order to scale grip force and hand aperture accordingly.4,5,6 Size-weight expectations play a role also for perception, as evident in the size-weight illusion (SWI), in which the smaller of two equal-weight objects is misjudged to be heavier.7,8 Here, we investigated predictions for action and perception by testing the development of feedforward controlled grasping and of the SWI in young individuals surgically treated for congenital cataracts several years after birth. Surprisingly, what typically developing individuals do easily within the first years of life, namely to adeptly grasp new objects based on visually predicted properties, cataract-treated individuals did not learn after years of visual experience. Contrary, the SWI exhibited significant development. Even though the two tasks differ in substantial ways, these results may suggest a potential dissociation in using visual experience to make predictions about an object's features for perception or action. What seems a very simple task-picking up small objects-is in truth a highly complex computation that necessitates early structured visual input to develop.

Cytoplasmic stress granules (SGs) are phase-separated membrane-less organelles that form in response to various stress stimuli. SGs are mainly composed of non-canonical stalled 48S preinitiation complexes. In addition, many other proteins also accumulate into SGs, but the list is still incomplete. SG assembly suppresses apoptosis and promotes cell survival under stress. Furthermore, hyperformation of SGs is frequently observed in various human cancers and accelerates tumor development and progression by reducing stress-induced damage of cancer cells. Therefore, they are of clinical importance. However, the precise mechanism underlying SG-mediated inhibition of apoptosis remains ill-defined. Here, using a proximity-labeling proteomic approach, we comprehensively analyzed SG-resident proteins and identified the executioner caspases, caspase-3 and -7, as SG components. We demonstrate that accumulation of caspase-3/7 into SGs is mediated by evolutionarily conserved amino acid residues within their large catalytic domains and inhibits caspase activities and consequent apoptosis induced by various stresses. Expression of an SG-localization-deficient caspase-3 mutant in cells largely counteracted the anti-apoptotic effect of SGs, whereas enforced relocalization of the caspase-3 mutant to SGs restored it. Thus, SG-mediated sequestration of executioner caspases is a mechanism underlying the broad cytoprotective function of SGs. Furthermore, using a mouse xenograft tumor model, we show that this mechanism prevents cancer cells from apoptosis in tumor tissues, thereby promoting cancer progression. Our results reveal the functional crosstalk between SG-mediated cell survival and caspase-mediated cell death signaling pathways and delineate a molecular mechanism that dictates cell-fate decisions under stress and promotes tumorigenesis.

Multidisciplinary evidence suggests that the control of voluntary action arbitrates between two major forms of behavioral processing: cognitively guided (or goal directed) and autonomously guided (or habitual). Brain-state irregularities affecting the striatum-such as aging-commonly shift control toward the latter, although the responsible neural mechanisms remain unknown. Combining instrumental conditioning with cell-specific mapping and chemogenetics in striatal neurons, we explored strategies that invigorate goal-directed capacity in aged mice. We found that, under conditions favoring goal-directed control, aged animals resiliently expressed autonomously guided behavior, a response that was underpinned by a characteristic one-to-one functional engagement of the two main neuronal populations in the striatum-D1- and D2-dopamine receptor-expressing spiny projection neurons (SPNs). Chemogenetically induced desensitization of D2-SPN signaling in aged transgenic mice recapitulated the striatal plasticity state observed in young mice, an effect that shifted behavior toward vigorous, goal-directed action. Our findings contribute to the understanding of the neural bases of behavioral control and propose neural system interventions that enhance cognitive functioning in habit-prone brains.

Many marine mammal populations are recovering after long eras of exploitation.1,2 To what degree density-dependent body size declines in recovering species reflect a general response to increased resource competition is unknown. We examined skull size (as a proxy for body size), skull morphology, and foraging dynamics of the top marine predator, the California sea lion (Zalophus californianus), which have been steadily increasing over the last few decades and have approached or reached their carrying capacity in southern California.3 We show that, contrary to predictions, male California sea lions increased rather than decreased their average body size over a 46-year (1962-2008) recovery period. Larger males had proportionally longer oral cavities and more powerful bite strength, and their foraging niche expanded. Females between 1983 and 2007 maintained stable skull dimensions, but their isotopic niche was broader than contemporary males. Increased male body size is compatible with an intensification of density-dependent sexual selection for larger and more competitive individuals concurrent with an expanding foraging niche. High foraging variability among females would explain their body size stability during decades of population recovery. We demonstrate that body size reduction is not the universal response to population recovery in marine mammals and show that selective ecological dynamics could contribute to protecting populations against the increased density-dependent intraspecific competition. However, prey shifts associated with climate change will likely prevent California sea lions (and other marine mammals) from attaining these ecological dynamics, augmenting their vulnerability to resource competition and diminishing their capacity to overcome it.

Increased human activities caused the isolation of populations in many species-often associated with genetic depletion and negative fitness effects. The effects of isolation are predicted by theory, but long-term data from natural populations are scarce. We show, with full genome sequences, that common voles (Microtus arvalis) in the Orkney archipelago have remained genetically isolated from conspecifics in continental Europe since their introduction by humans over 5,000 years ago. Modern Orkney vole populations are genetically highly differentiated from continental conspecifics as a result of genetic drift processes. Colonization likely started on the biggest Orkney island and vole populations on smaller islands were gradually split off, without signs of secondary admixture. Despite having large modern population sizes, Orkney voles are genetically depauperate and successive introductions to smaller islands resulted in further reduction of genetic diversity. We detected high levels of fixation of predicted deleterious variation compared with continental populations, particularly on smaller islands, yet the fitness effects realized in nature are unknown. Simulations showed that predominantly mildly deleterious mutations were fixed in populations, while highly deleterious mutations were purged early in the history of the Orkney population. Relaxation of selection overall due to benign environmental conditions on the islands and the effects of soft selection may have contributed to the repeated, successful establishment of Orkney voles despite potential fitness loss. Furthermore, the specific life history of these small mammals, resulting in relatively large population sizes, has probably been important for their long-term persistence in full isolation.

The human microbiome seeding starts at birth, when pioneer microbes are acquired mainly from the mother. Mode of delivery, antibiotic prophylaxis, and feeding method have been studied as modulators of mother-to-infant microbiome transmission, but other key influencing factors like modern westernized lifestyles with high hygienization, high-calorie diets, and urban settings, compared with non-westernized lifestyles have not been investigated yet. In this study, we explored the mother-infant sharing of characterized and uncharacterized microbiome members via strain-resolved metagenomics in a cohort of Ethiopian mothers and infants, and we compared them with four other cohorts with different lifestyles. The westernized and non-westernized newborns' microbiomes composition overlapped during the first months of life more than later in life, likely reflecting similar initial breast-milk-based diets. Ethiopian and other non-westernized infants shared a smaller fraction of the microbiome with their mothers than did most westernized populations, despite showing a higher microbiome diversity, and uncharacterized species represented a substantial fraction of those shared in the Ethiopian cohort. Moreover, we identified uncharacterized species belonging to the Selenomonadaceae and Prevotellaceae families specifically present and shared only in the Ethiopian cohort, and we showed that a locally produced fermented food, injera, can contribute to the higher diversity observed in the Ethiopian infants' gut with bacteria that are not part of the human microbiome but are acquired through fermented food consumption. Taken together, these findings highlight the fact that lifestyle can impact the gut microbiome composition not only through differences in diet, drug consumption, and environmental factors but also through its effect on mother-infant strain-sharing patterns.

The breathing rhythm serves as a reference that paces orofacial motor actions and orchestrates active sensing. Past work has reported that pacing occurs solely at a fixed phase relative to sniffing. We re-evaluated this constraint as a function of exploratory behavior. Allocentric and egocentric rotations of the head and the electromyogenic activity of the motoneurons for head and orofacial movements were recorded in free-ranging rats as they searched for food. We found that a change in state from foraging to rearing is accompanied by a large phase shift in muscular activation relative to sniffing, and a concurrent change in the frequency of sniffing, so that pacing now occurs at one of the two phases. Further, head turning is biased such that an animal gathers a novel sample of its environment upon inhalation. In total, the coordination of active sensing has a previously unrealized computational complexity. This can emerge from hindbrain circuits with fixed architecture and credible synaptic time delays.

Symbiosis between prokaryotes and microbial eukaryotes (protists) has broadly impacted both evolution and ecology. Endosymbiosis led to mitochondria and plastids, the latter spreading across the tree of eukaryotes by subsequent rounds of endosymbiosis. Present-day endosymbionts in protists remain both common and diverse, although what function they serve is often unknown. Here, we describe a highly complex community of endosymbionts and a bacteriophage (phage) within a single cryptomonad cell. Cryptomonads are a model for organelle evolution because their secondary plastid retains a relict endosymbiont nucleus, but only one previously unidentified Cryptomonas strain (SAG 25.80) is known to harbor bacterial endosymbionts. We carried out electron microscopy and FISH imaging as well as genomic sequencing on Cryptomonas SAG 25.80, which revealed a stable, complex community even after over 50 years in continuous cultivation. We identified the host strain as Cryptomonas gyropyrenoidosa, and sequenced genomes from its mitochondria, plastid, and nucleomorph (and partially its nucleus), as well as two symbionts, Megaira polyxenophila and Grellia numerosa, and one phage (MAnkyphage) infecting M. polyxenophila. Comparing closely related endosymbionts from other hosts revealed similar metabolic and genomic features, with the exception of abundant transposons and genome plasticity in M. polyxenophila from Cryptomonas. We found an abundance of eukaryote-interacting genes as well as many toxin-antitoxin systems, including in the MAnkyphage genome that also encodes several eukaryotic-like proteins. Overall, the Cryptomonas cell is an endosymbiotic conglomeration with seven distinct evolving genomes that all show evidence of inter-lineage conflict but nevertheless remain stable, even after more than 4,000 generations in culture.