Altered interactions between cis-regulatory elements partially resolve BLADE-ON-PETIOLE genetic redundancy in Capsella rubella.

Duplicated genes are thought to follow one of three evolutionary trajectories that resolve their redundancy: neofunctionalization, subfunctionalization or pseudogenization. Differences in expression patterns have been documented for many duplicated gene pairs and interpreted as evidence of subfunctionalization and a loss of redundancy. However, little is known about the functional impact of such differences and about their molecular basis. Here, we investigate the genetic and molecular basis for the partial loss of redundancy between the two BLADE-ON-PETIOLE genes BOP1 and BOP2 in Red Shepherd's Purse (Capsella rubella) compared to Arabidopsis (Arabidopsis thaliana). While both genes remain almost fully redundant in A. thaliana, BOP1 in C. rubella can no longer ensure wild-type floral organ numbers and suppress bract formation, due to an altered expression pattern in the region of the cryptic bract primordium. We use two complementary approaches, transgenic rescue of A. thaliana atbop1 atbop2 double mutants and deletions in the endogenous AtBOP1 promoter, to demonstrate that several BOP1 promoter regions containing conserved non-coding sequences interact in a non-additive manner to control BOP1 expression in the bract primordium, and that changes in these interactions underlie the evolutionary divergence between C. rubella and A. thaliana BOP1 expression and activity. Similarly, altered interactions between cis-regulatory regions underlie the divergence in functional promoter architecture related to the control of floral organ abscission by BOP1. These findings highlight the complexity of promoter architecture in plants and suggest that changes in the interactions between cis-regulatory elements are key drivers for evolutionary divergence in gene expression and the loss of redundancy.

Dominant-negative chaperonin mutation ptCPN60α1S57F uncovers redundancy in chloroplast rRNA processing.

The biogenesis of functional forms of chloroplast ribosomal RNAs (rRNAs) is crucial for the translation of chloroplast mRNAs into polypeptides. However, the molecular mechanisms underlying the proper processing and maturation of chloroplast rRNA species are poorly understood. Through a genetic approach, we isolated and characterized an Arabidopsis mutant, α1-4, harboring a missense mutation in the plastid chaperonin-60α1 gene. Using allelism tests and transgenic manipulation, we determined functional redundancy among ptCPN60 subunits. The ptCPN60α1S57F mutation caused specific defects in the formation of chloroplast rRNA species, including 23S, 5S, and 4.5S rRNAs, but not 16S rRNAs. Allelism tests suggested that the dysfunctional ptCPN60α1S57F competes with other members of the ptCPN60 family. Indeed, overexpression of the ptCPN60α1S57F protein in wild-type plants mimicked the phenotypes observed in the α1-4 mutant, while increasing the endogenous transcriptional levels of ptCPN60α2, ß1, ß2, and ß3 in the α1-4 mutant partially mitigated the abnormal fragmentation processing of chloroplast 23S, 5S, and 4.5S rRNAs. Furthermore, we demonstrated functional redundancy between ptCPN60ß1 and ptCPN60ß2 in chloroplast rRNA processing through double-mutant analysis. Collectively, our data reveal a novel physiological role of ptCPN60 subunits in generating the functional rRNA species of the large 50S ribosomal subunit in Arabidopsis chloroplasts.

Retention of duplicated genes in evolution.

Gene duplication is a prevalent phenomenon across the tree of life. The processes that lead to the retention of duplicated genes are not well understood. Functional genomics approaches in model organisms, such as yeast, provide useful tools to test the mechanisms underlying retention with functional redundancy and divergence of duplicated genes, including fates associated with neofunctionalization, subfunctionalization, back-up compensation, and dosage amplification. Duplicated genes may also be retained as a consequence of structural and functional entanglement. Advances in human gene editing have enabled the interrogation of duplicated genes in the human genome, providing new tools to evaluate the relative contributions of each of these factors to duplicate gene retention and the evolution of genome structure.

A cofunctional grouping-based approach for non-redundant feature gene selection in unannotated single-cell RNA-seq analysis.

Feature gene selection has significant impact on the performance of cell clustering in single-cell RNA sequencing (scRNA-seq) analysis. A well-rounded feature selection (FS) method should consider relevance, redundancy and complementarity of the features. Yet most existing FS methods focus on gene relevance to the cell types but neglect redundancy and complementarity, which undermines the cell clustering performance. We develop a novel computational method GeneClust to select feature genes for scRNA-seq cell clustering. GeneClust groups genes based on their expression profiles, then selects genes with the aim of maximizing relevance, minimizing redundancy and preserving complementarity. It can work as a plug-in tool for FS with any existing cell clustering method. Extensive benchmark results demonstrate that GeneClust significantly improve the clustering performance. Moreover, GeneClust can group cofunctional genes in biological process and pathway into clusters, thus providing a means of investigating gene interactions and identifying potential genes relevant to biological characteristics of the dataset. GeneClust is freely available at https://github.com/ToryDeng/scGeneClust.

Plexin-B1 and Plexin-B2 play non-redundant roles in GABAergic synapse formation.

Synapse formation in the mammalian brain is a complex and dynamic process requiring coordinated function of dozens of molecular families such as cell adhesion molecules (CAMs) and ligand-receptor pairs (Ephs/Ephrins, Neuroligins/Neurexins, Semaphorins/Plexins). Due to the large number of molecular players and possible functional redundancies within gene families, it is challenging to determine the precise synaptogenic roles of individual molecules, which is key to understanding the consequences of mutations in these genes for brain function. Furthermore, few molecules are known to exclusively regulate either GABAergic or glutamatergic synapses, and cell and molecular mechanisms underlying GABAergic synapse formation in particular are not thoroughly understood. We previously demonstrated that Semaphorin-4D (Sema4D) regulates GABAergic synapse development in the mammalian hippocampus while having no effect on glutamatergic synapse development, and this effect occurs through binding to its high affinity receptor, Plexin-B1. In addition, we demonstrated that RNAi-mediated Plexin-B2 knock-down decreases GABAergic synapse density suggesting that both receptors function in this process. Here, we perform a structure-function study of the Plexin-B1 and Plexin-B2 receptors to identify the protein domains in each receptor which are required for its synaptogenic function. Further, we examine whether Plexin-B2 is required in the presynaptic neuron, the postsynaptic neuron, or both to regulate GABAergic synapse formation. Our data reveal that Plexin-B1 and Plexin-B2 function non-redundantly to regulate GABAergic synapse formation and suggest that the transmembrane domain may underlie functional distinctions. We also provide evidence that Plexin-B2 expression in presynaptic GABAergic interneurons, as well as postsynaptic pyramidal cells, regulates GABAergic synapse formation in hippocampus. These findings lay the groundwork for future investigations into the precise signaling pathways required for synapse formation downstream of Plexin-B receptor signaling.

The nonredundant nature of the Axin2 regulatory network in the canonical Wnt signaling pathway.

Axin is one of two essential scaffolds in the canonical Wnt pathway that converts signals at the plasma membrane to signals inhibiting the degradation of ß-catenin, leading to its accumulation and specific gene activation. In vertebrates, there are two forms of Axin, Axin1 and Axin2, which are similar at the protein level and genetically redundant. We show here that differential regulation of the two genes on the transcriptional and proteostatic level confers differential responsiveness that can be used in tissue-specific regulation. Such subtle features may distinguish other redundant gene pairs that are commonly found in vertebrates through gene knockout experiments.

Proprioceptive and Visual Feedback Responses in Macaques Exploit Goal Redundancy.

A common problem in motor control concerns how to generate patterns of muscle activity when there are redundant solutions to attain a behavioral goal. Optimal feedback control is a theory that has guided many behavioral studies exploring how the motor system incorporates task redundancy. This theory predicts that kinematic errors that deviate the limb should not be corrected if one can still attain the behavioral goal. Studies in humans demonstrate that the motor system can flexibly integrate visual and proprioceptive feedback of the limb with goal redundancy within 90 ms and 70 ms, respectively. Here, we show monkeys (Macaca mulatta) demonstrate similar abilities to exploit goal redundancy. We trained four male monkeys to reach for a goal that was either a narrow square or a wide, spatially redundant rectangle. Monkeys exhibited greater trial-by-trial variability when reaching to the wide goal consistent with exploiting goal redundancy. On random trials we jumped the visual feedback of the hand and found monkeys corrected for the jump when reaching to the narrow goal and largely ignored the jump when reaching for the wide goal. In a separate set of experiments, we applied mechanical loads to the arm of the monkey and found similar corrective responses based on goal shape. Muscle activity reflecting these different corrective responses were detected for the visual and mechanical perturbations starting at ∼90 and ∼70 ms, respectively. Thus, rapid motor responses in macaques can exploit goal redundancy similar to humans, creating a paradigm to study the neural basis of goal-directed motor action and motor redundancy.SIGNIFICANCE STATEMENT Moving in the world requires selecting from an infinite set of possible motor commands. Theories predict that motor commands are selected that exploit redundancies. Corrective responses in humans to either visual or proprioceptive disturbances of the limb can rapidly exploit redundant trajectories to a goal in <100 ms after a disturbance. However, uncovering the neural correlates generating these rapid motor corrections has been hampered by the absence of an animal model. We developed a behavioral paradigm in monkeys that incorporates redundancy in the form of the shape of the goal. Critically, monkeys exhibit corrective responses and timings similar to humans performing the same task. Our paradigm provides a model for investigating the neural correlates of sophisticated rapid motor corrections.

Landscape genomics reveals regions associated with adaptive phenotypic and genetic variation in Ethiopian indigenous chickens.

Climate change is a threat to sustainable livestock production and livelihoods in the tropics. It has adverse impacts on feed and water availability, disease prevalence, production, environmental temperature, and biodiversity. Unravelling the drivers of local adaptation and understanding the underlying genetic variation in random mating indigenous livestock populations informs the design of genetic improvement programmes that aim to increase productivity and resilience. In the present study, we combined environmental, genomic, and phenotypic information of Ethiopian indigenous chickens to investigate their environmental adaptability. Through a hybrid sampling strategy, we captured wide biological and ecological variabilities across the country. Our environmental dataset comprised mean values of 34 climatic, vegetation and soil variables collected over a thirty-year period for 260 geolocations. Our biological dataset included whole genome sequences and quantitative measurements (on eight traits) from 513 individuals, representing 26 chicken populations spread along 4 elevational gradients (6-7 populations per gradient). We performed signatures of selection analyses ([Formula: see text] and XP-EHH) to detect footprints of natural selection, and redundancy analyses (RDA) to determine genotype-environment and genotype-phenotype-associations. RDA identified 1909 outlier SNPs linked with six environmental predictors, which have the highest contributions as ecological drivers of adaptive phenotypic variation. The same method detected 2430 outlier SNPs that are associated with five traits. A large overlap has been observed between signatures of selection identified by[Formula: see text]and XP-EHH showing that both methods target similar selective sweep regions. Average genetic differences measured by [Formula: see text] are low between gradients, but XP-EHH signals are the strongest between agroecologies. Genes in the calcium signalling pathway, those associated with the hypoxia-inducible factor (HIF) transcription factors, and sports performance (GALNTL6) are under selection in high-altitude populations. Our study underscores the relevance of landscape genomics as a powerful interdisciplinary approach to dissect adaptive phenotypic and genetic variation in random mating indigenous livestock populations.

Changes in high-order interaction measures of synergy and redundancy during non-ordinary states of consciousness induced by meditation, hypnosis, and auto-induced cognitive trance.

High-order interactions are required across brain regions to accomplish specific cognitive functions. These functional interdependencies are reflected by synergistic information that can be obtained by combining the information from all the sources considered and redundant information (i.e., common information provided by all the sources). However, electroencephalogram (EEG) functional connectivity is limited to pairwise interactions thereby precluding the estimation of high-order interactions. In this multicentric study, we used measures of synergistic and redundant information to study in parallel the high-order interactions between five EEG electrodes during three non-ordinary states of consciousness (NSCs): Rajyoga meditation (RM), hypnosis, and auto-induced cognitive trance (AICT). We analyzed EEG data from 22 long-term Rajyoga meditators, nine volunteers undergoing hypnosis, and 21 practitioners of AICT. We here report the within-group changes in synergy and redundancy for each NSC in comparison with their respective baseline. During RM, synergy increased at the whole brain level in the delta and theta bands. Redundancy decreased in frontal, right central, and posterior electrodes in delta, and frontal, central, and posterior electrodes in beta1 and beta2 bands. During hypnosis, synergy decreased in mid-frontal, temporal, and mid-centro-parietal electrodes in the delta band. The decrease was also observed in the beta2 band in the left frontal and right parietal electrodes. During AICT, synergy decreased in delta and theta bands in left-frontal, right-frontocentral, and posterior electrodes. The decrease was also observed at the whole brain level in the alpha band. However, redundancy changes during hypnosis and AICT were not significant. The subjective reports of absorption and dissociation during hypnosis and AICT, as well as the mystical experience questionnaires during AICT, showed no correlation with the high-order measures. The proposed study is the first exploratory attempt to utilize the concepts of synergy and redundancy in NSCs. The differences in synergy and redundancy during different NSCs warrant further studies to relate the extracted measures with the phenomenology of the NSCs.

The PDE-Opathies: Diverse Phenotypes Produced by a Functionally Related Multigene Family.

The phosphodiesterase (PDE)-opathies, an expanding set of disorders caused by germline mutations in cyclic nucleotide PDEs, present an intriguing paradox. The enzymes encoded by the PDE family all hydrolyze cAMP and/or cGMP, but mutations in different family members produce very divergent phenotypes. Three interacting factors have been shown recently to contribute to this phenotypic diversity: (i) the 21 genes encode over 80 different isoforms, using alternative mRNA splicing and related mechanisms; (ii) the various isoforms have different regulatory mechanisms, mediated by their unique amino-terminal regulatory domains; (iii) the isoforms differ widely in their pattern of tissue expression. These mechanisms explain why many PDE-opathies are gain-of-function mutations and how they exemplify uniqueness and redundancy within a multigene family.

A Concept of Complementarity Between Complexity and Redundancy can Account for Kant's Biological Teleology and Unify Mechanistic and Finalistic Biology.

Over 160 years after Darwin and 70 years after the discovery of DNA, two fundamental questions of biology remain unanswered: What differentiates the living from the nonliving? How can mechanistic and finalistic or holistic biology be unified? Niels Bohr introduced a concept of complementarity in quantum physics and based on the paradox of light as a simultaneous wave and particle, conjectured that a similar concept might exist in biology that would solve the paradox of life originating from the nonliving. Bohr proposed that two mutually exclusive-independent observations may be necessary to explain a phenomenon and provided support to Immanuel Kant's idea that the "purposive" behaviour of organisms could only be explained in teleological terms and that mechanical and teleological approaches were necessary and complementary to explain biology. We present a concept of complementarity whereby biochemical pathways or cellular channels for the flow of information are simultaneously complex and redundant and complexity and redundancy complement each other. The postulates of biological complementarity are that (1) it was an essential condition in the origin of life; (2) it provided physiological flexibility that allowed organisms to mount self-protection response and complexity to evolve in the face of deleterious mutations before the evolution of bi-parental sex; (3) it laid the foundation for the evolution of a choice of response when confronted with threat; and (4) it applies to all levels of biological organizations and, thus, can serve as a basis for the unification of mechanistic and holistic biology. It is proposed that teleology is simultaneously constitutive and heuristic: constitutive because organisms' "purposive" behaviours are adaptive and are grounded in mechanism (complexity and redundancy), and heuristic because with our finite cognition and our goal-oriented (humans alone are aware of "tomorrow") and anthropomorphic pre-disposition, teleology will remain useful as a guide to our making sense of the world, even how to ask a meaningful question.

Small vessel disease and cognitive reserve oppositely modulate global network redundancy and cognitive function: A study in middle-to-old aged community participants.

Cerebral small vessel disease (SVD) can disrupt the global brain network and lead to cognitive impairment. Conversely, cognitive reserve (CR) can improve one's cognitive ability to handle damaging effects like SVD, partly by optimizing the brain network's organization. Understanding how SVD and CR collectively influence brain networks could be instrumental in preventing cognitive impairment. Recently, brain redundancy has emerged as a critical network protective metric, providing a nuanced perspective of changes in network organization. However, it remains unclear how SVD and CR affect global redundancy and subsequently cognitive function. Here, we included 121 community-dwelling participants who underwent neuropsychological assessments and a multimodal MRI examination. We visually examined common SVD imaging markers and assessed lifespan CR using the Cognitive Reserve Index Questionnaire. We quantified the global redundancy index (RI) based on the dynamic functional connectome. We then conducted multiple linear regressions to explore the specific cognitive domains related to RI and the associations of RI with SVD and CR. We also conducted mediation analyses to explore whether RI mediated the relationships between SVD, CR, and cognition. We found negative correlations of RI with the presence of microbleeds (MBs) and the SVD total score, and a positive correlation of RI with leisure activity-related CR (CRI-leisure). RI was positively correlated with memory and fully mediated the relationships between the MBs, CRI-leisure, and memory. Our study highlights the potential benefits of promoting leisure activities and keeping brain redundancy for memory preservation in older adults, especially those with SVD.

Study of two glycosyltransferases related to polysaccharide biosynthesis in Rhodococcus jostii RHA1.

The bacterial genus Rhodococcus comprises organisms performing oleaginous behaviors under certain growth conditions and ratios of carbon and nitrogen availability. Rhodococci are outstanding producers of biofuel precursors, where lipid and glycogen metabolisms are closely related. Thus, a better understanding of rhodococcal carbon partitioning requires identifying catalytic steps redirecting sugar moieties to storage molecules. Here, we analyzed two GT4 glycosyl-transferases from Rhodococcus jostii (RjoGlgAb and RjoGlgAc) annotated as α-glucan-α-1,4-glucosyl transferases, putatively involved in glycogen synthesis. Both enzymes were produced in Escherichia coli cells, purified to homogeneity, and kinetically characterized. RjoGlgAb and RjoGlgAc presented the "canonical" glycogen synthase activity and were actives as maltose-1P synthases, although to a different extent. Then, RjoGlgAc is a homologous enzyme to the mycobacterial GlgM, with similar kinetic behavior and glucosyl-donor preference. RjoGlgAc was two orders of magnitude more efficient to glucosylate glucose-1P than glycogen, also using glucosamine-1P as a catalytically efficient aglycon. Instead, RjoGlgAb exhibited both activities with similar kinetic efficiency and preference for short-branched α-1,4-glucans. Curiously, RjoGlgAb presented a super-oligomeric conformation (higher than 15 subunits), representing a novel enzyme with a unique structure-to-function relationship. Kinetic results presented herein constitute a hint to infer on polysaccharides biosynthesis in rhodococci from an enzymological point of view.

Difference in microbial community structure along a gradient of crater altitude: insights from the Nushan volcano.

The variation in the soil microbial community along the altitude gradient has been widely documented. However, the structure and function of the microbial communities distributed along the altitude gradient in the crater still need to be determined. We gathered soil specimens from different elevations within the Nushan volcano crater to bridge this knowledge gap. We investigated the microbial communities of bacteria and fungi in the soil. It is noteworthy that the microbial alpha diversity peaks in the middle of the crater. However, network analysis shows that bacterial (nodes 760 vs 613 vs 601) and fungal (nodes 328 vs 224 vs 400) communities are most stable at the bottom and top of the crater, respectively. Furthermore, the soil microbial network exhibited a decline, followed by an increase across varying altitudes. The core microorganisms displayed the highest correlation with pH and alkaline phosphatase (AP, as determined through redundancy analysis (RDA) and Mantel tests for correlation analysis. The fungal community has a higher number of core microorganisms, while the bacterial core microorganisms demonstrate greater susceptibility to environmental factors. In conclusion, we utilized Illumina sequencing techniques to assess the disparities in the structure and function of bacteria and fungi in the soil.IMPORTANCEThese findings serve as a foundation for future investigations on microbial communities present in volcanic soil.

Photostasis and photosynthetic adaptation to polar life.

Photostasis is the light-dependent maintenance of energy balance associated with cellular homeostasis in photoautotrophs. We review evidence that illustrates how photosynthetic adaptation in polar photoautrophs such as aquatic green algae, cyanobacteria, boreal conifers as well as terrestrial angiosperms exhibit an astonishing plasticity in structure and function of the photosynthetic apparatus. This plasticity contributes to the maintenance of photostasis, which is essential for the long-term survival in the seemingly inhospitable Antarctic and Arctic habitats. However, evidence indicates that polar photoautrophic species exhibit different functional solutions for the maintenance of photostasis. We suggest that this reflects, in part, the genetic diversity symbolized by inherent genetic redundancy characteristic of polar photoautotrophs which enhances their survival in a thermodynamically challenging environment.

Genomic architecture controls multivariate adaptation to climate change.

As climate change advances, environmental gradients may decouple, generating novel multivariate environments that stress wild populations. A commonly invoked mechanism of evolutionary rescue is adaptive gene flow tracking climate shifts, but gene flow from populations inhabiting similar conditions on one environmental axis could cause maladaptive introgression when populations are adapted to different environmental variables that do not shift together. Genomic architecture can play an important role in determining the effectiveness and relative magnitudes of adaptive gene flow and in situ adaptation. This may have direct consequences for how species respond to climate change but is often overlooked. Here, we simulated microevolutionary responses to environmental change under scenarios defined by variation in the polygenicity, linkage, and genetic redundancy of two independent traits, one of which is adapted to a gradient that shifts under climate change. We used these simulations to examine how genomic architecture influences evolutionary outcomes under climate change. We found that climate-tracking (up-gradient) gene flow, though present in all scenarios, was strongly constrained under scenarios of lower linkage and higher polygenicity and redundancy, suggesting in situ adaptation as the predominant mechanism of evolutionary rescue under these conditions. We also found that high polygenicity caused increased maladaptation and demographic decline, a concerning result given that many climate-adapted traits may be polygenic. Finally, in scenarios with high redundancy, we observed increased adaptive capacity. This finding adds to the growing recognition of the importance of redundancy in mediating in situ adaptive capacity and suggests opportunities for better understanding the climatic vulnerability of real populations.

Leveraging the redundancy of S-denitrosylases in response to S-nitrosylation of caspases: Experimental strategies and beyond.

Redox-based protein posttranslational modifications, such as S-nitrosylation of critical, active site cysteine thiols have garnered significant clinical attention and research interest, reasoning for one of the crucial biological implications of reactive messenger molecule, nitric oxide in the cellular repertoire. The stringency of the S-(de)nitrosylation-based redox switch governs the activity and contribution of several susceptible enzymes in signal transduction processes and diverse pathophysiological settings, thus establishing it as a transient yet reasonable, and regulated mechanism of NO adduction and release. Notably, endogenous proteases like cytosolic and mitochondrial caspases with a molecular weight ranging from 33 to 55 kDa are susceptible to performing this biochemistry in the presence of major oxidoreductases, which further unveils the enormous redox-mediated regulational control of caspases in the etiology of diseases. In addition to advancing the progress of the current state of understanding of 'redox biochemistry' in the field of medicine and enriching the existing dynamic S-nitrosoproteome, this review stands as a testament to an unprecedented shift in the underpinnings for redundancy and redox relay between the major redoxin/antioxidant systems, fine-tuning of which can command the apoptotic control of caspases at the face of nitro-oxidative stress. These intricate functional overlaps and cellular backups, supported rationally by kinetically favorable reaction mechanisms suggest the physiological relevance of identifying and involving such cognate substrates for cellular S-denitrosylases that can shed light on the bigger picture of extensively proposing targeted therapies and redox-based drug designing to potentially alleviate the side effects of NOx/ROS in disease pathogenesis.

Many-to-many mapping: A simulation study of how the number of traits and tasks affect the evolution of form and function.

Many-to-many mapping of form-to-function posits that multiple morphological and physiological traits affect the performance of multiple tasks in an organism, and that redundancy and multitasking occur simultaneously to shape the evolution of an organism's phenotype. Many-to-many mapping is expected to be ubiquitous in nature, yet little is known about how it influences the evolution of organismal phenotype. The F-matrix is a powerful tool to study these issues because it describes how multiple traits affect multiple tasks. We undertook a simulation study using the F-matrix to test how the number of traits and the number of tasks affect trait integration and evolvability, as well as the relationships among tasks. We found that as the number of traits and/or tasks increases, the relationships between the tasks and the integration between the traits become weaker, and that the evolvability of the traits increases, all resulting in a system that is freer to evolve. We also found that as the number of traits increases, performance tradeoffs tend to become weaker, but only to a point. Our work shows that it is important to consider not only multiple traits, but also the multitude of tasks that those traits carry out when studying form-function relationships. We suggest that evolution of these relationships follows functional lines of least resistance, which are less defined in more complex systems, resulting in a mechanism for diversification.

The north-south divide? Macroalgal functional trait diversity and redundancy varies with intertidal aspect.

BACKGROUND AND AIMS: Marine macroalgae ('seaweeds') are critical to coastal ecosystem structure and function, but also vulnerable to the many environmental changes associated with anthropogenic climate change (ACC). The local habitat conditions underpinning observed and predicted ACC-driven changes in intertidal macroalgal communities are complex and probably site-specific and operate in addition to more commonly reported regional factors such as sea surface temperatures. METHODS: We examined how the composition and functional trait expression of macroalgal communities in SW England varied with aspect (i.e. north-south orientation) at four sites with opposing Equator- (EF) and Pole-facing (PF) surfaces. Previous work at these sites had established that average annual (low tide) temperatures vary by 1.6 °C and that EF-surfaces experience six-fold more frequent extremes (i.e. >30 °C). KEY RESULTS: PF macroalgal communities were consistently more taxon rich; 11 taxa were unique to PF habitats, with only one restricted to EF. Likewise, functional richness and dispersion were greater on PF-surfaces (dominated by algae with traits linked to rapid resource capture and utilization, but low desiccation tolerance), although differences in both taxon and functional richness were probably driven by the fact that less diverse EF-surfaces were dominated by desiccation-tolerant fucoids. CONCLUSIONS: Although we cannot disentangle the influence of temperature variation on algal ecophysiology from the indirect effects of aspect on species interactions (niche pre-emption, competition, grazing, etc.), our study system provides an excellent model for understanding how environmental variation at local scales affects community composition and functioning. By virtue of enhanced taxonomic diversity, PF-aspects supported higher functional diversity and, consequently, greater effective functional redundancy. These differences may imbue PF-aspects with resilience against environmental perturbation, but if predicted increases in global temperatures are realized, some PF-sites may shift to a depauperate, desiccation-tolerant seaweed community with a concomitant loss of functional diversity and redundancy.

Functional compensation in a savanna scavenger community.

Functional redundancy, the potential for the functional role of one species to be fulfilled by another, is a key determinant of ecosystem viability. Scavenging transfers huge amount of energy through ecosystems and is, therefore, crucial for ecosystem viability and healthy ecosystem functioning. Despite this, relatively few studies have examined functional redundancy in scavenger communities. Moreover, the results of these studies are mixed and confined to a very limited range of habitat types and taxonomic groups. This study attempts to address this knowledge gap by conducting a field experiment in an undisturbed natural environment assessing functional roles and redundancy in vertebrate and invertebrate scavenging communities in a South African savanna. We used a large-scale field experiment to suppress ants in four 1 ha plots in a South African savanna and paired each with a control plot. We distributed three types of small food bait: carbohydrate, protein and seed, across the plots and excluded vertebrates from half the baits using cages. Using this combination of ant suppression and vertebrate exclusion, allowed us explore the contribution of non-ant invertebrates, ants and vertebrates in scavenging and also to determine whether either ants or vertebrates were able to compensate for the loss of one another. In this study, we found the invertebrate community carried out a larger proportion of overall scavenging services than vertebrates. Moreover, although scavenging was reduced when either invertebrates or vertebrates were absent, the presence of invertebrates better mitigated the functional loss of vertebrates than did the presence of vertebrates against the functional loss of invertebrates. There is a commonly held assumption that the functional role of vertebrate scavengers exceeds that of invertebrate scavengers; our results suggest that this is not true for small scavenging resources. Our study highlights the importance of invertebrates for securing healthy ecosystem functioning both now and into the future. We also build upon many previous studies which show that ants can have particularly large effects on ecosystem functioning. Importantly, our study suggests that scavenging in some ecosystems may be partly resilient to changes in the scavenging community, due to the potential for functional compensation by vertebrates and ants.