Costs of memory: lessons from 'mini' brains

Variation in learning and memory abilities among closely related species, or even among populations of the same species, has opened research into the relationship between cognition, ecological context and the fitness costs, and benefits of learning and memory. Such research programmes have long been dominated by vertebrate studies and by the assumption of a relationship between cognitive abilities, brain size and metabolic costs. Research on these 'large brained' organisms has provided important insights into the understanding of cognitive functions and their adaptive value. In the present review, we discuss some aspects of the fitness costs of learning and memory by focusing on 'mini-brain' studies. Research on learning and memory in insects has challenged some traditional positions and is pushing the boundaries of our understanding of the evolution of learning and memory.     

The diversity of aging models

Most of the signalling pathways involved in aging regulation have been recently found well conserved at various levels throughout the evolution. Taking this into account, a diversity of model organisms, including worms, rodents, and lemurs as well, allows to address different questions: how to understand the interactions between genetic and environmental factors while challenging theories of aging, to preserve hearing integrity, to fight against senescence of neural stem cells, or to explore brain fitness from gene expression to cognitive and social behavior? Here are the main issues that can be considered, stressing the complementarities of the models. The differentiation of aging physiological aspects from those induced by age-related pathologies will also be specified. By emphasizing recent ability of technologies to promote new aging insights, we discuss towards a better understanding of mechanisms governing aging.     

Trends in flower symmetry evolution revealed through phylogenetic and developmental genetic advances

A striking aspect of flowering plant (angiosperm) diversity is variation in flower symmetry. From an ancestral form of radial symmetry (polysymmetry, actinomorphy), multiple evolutionary transitions have contributed to instances of non-radial forms, including bilateral symmetry (monosymmetry, zygomorphy) and asymmetry. Advances in flowering plant molecular phylogenetic research and studies of character evolution as well as detailed flower developmental genetic studies in a few model species (e.g. Antirrhinum majus, snapdragon) have provided a foundation for deep insights into flower symmetry evolution. From phylogenetic studies, we have a better understanding of where during flowering plant diversification transitions from radial to bilateral flower symmetry (and back to radial symmetry) have occurred. From developmental studies, we know that a genetic programme largely dependent on the functional action of the CYCLOIDEA gene is necessary for differentiation along the snapdragon dorsoventral flower axis. Bringing these two lines of inquiry together has provided surprising insights into both the parallel recruitment of a CYC-dependent developmental programme during independent transitions to bilateral flower symmetry, and the modifications to this programme in transitions back to radial flower symmetry, during flowering plant evolution.     

Autosomal recessive primary microcephaly (MCPH): a review of clinical, molecular, and evolutionary findings

Autosomal recessive primary microcephaly (MCPH) is a neurodevelopmental disorder. It is characterized by two principal features, microcephaly present at birth and nonprogressive mental retardation. The microcephaly is the consequence of a small but architecturally normal brain, and it is the cerebral cortex that shows the greatest size reduction. There are at least seven MCPH loci, and four of the genes have been identified: MCPH1, encoding Microcephalin; MCPH3, encoding CDK5RAP2; MCPH5, encoding ASPM; and MCPH6, encoding CENPJ. These findings are starting to have an impact on the clinical management of families affected with MCPH. Present data suggest that MCPH is the consequence of deficient neurogenesis within the neurogenic epithelium. Evolutionary interest in MCPH has been sparked by the suggestion that changes in the MCPH genes might also be responsible for the increase in brain size during human evolution. Indeed, evolutionary analyses of Microcephalin and ASPM reveal evidence for positive selection during human and great ape evolution. So an understanding of this rare genetic disorder may offer us significant insights into neurogenic mitosis and the evolution of the most striking differences between us and our closest living relatives: brain size and cognitive ability.     

Understanding vertebrate brain evolution

Four major questions can be asked about vertebrate brain evolution:1) What major changes have occurred in neural organization andfunction? 2) When did these changes occur? 3) By what mechanismsdid these changes occur? 4) Why did these changes occur? Comparativeneurobiologists have been very successful in recognizing majorchanges in brain structure. They have also made progress inunderstanding the functional significance of these changes,although this understanding is primarily limited to sensorycenters, rather than integrative or motor centers, because ofthe relative ease of manipulating the relevant stimuli. Althoughneuropaleontology continues to provide important insights intowhen changes occurred, this approach is generally limited torecognizing variation in overall brain size, and sometimes brainregions, as interpreted from the surface of an endocranial cast.In recent years, most new information regarding when neuralchanges occurred has been based on cladistical analysis of neuralfeatures in extant taxa. Historically, neurobiologists havemade little progress in understanding how and why brains evolve.The emerging field of evolutionary developmental biology appearsto be the most promising approach for revealing how changesin development and its processes produce neural changes, includingthe emergence of novel features. Why neural changes have occurredis the most difficult question and one that has been the mostignored, in large part because its investigation requires abroad interdisciplinary approach involving both behavior andecology.     

Human brain evolution: harnessing the genomics (r)evolution to link genes, cognition, and behavior

The evolution of the human brain has resulted in numerous specialized features including higher cognitive processes such as language. Knowledge of whole-genome sequence and structural variation via high-throughput sequencing technology provides an unprecedented opportunity to view human evolution at high resolution. However, phenotype discovery is a critical component of these endeavors and the use of nontraditional model organisms will also be critical for piecing together a complete picture. Ultimately, the union of developmental studies of the brain with studies of unique phenotypes in a myriad of species will result in a more thorough model of the groundwork the human brain was built upon. Furthermore, these integrative approaches should provide important insights into human diseases.     

Identifying innovation in laboratory studies of cultural evolution: rates of retention and measures of adaptation

In recent years, laboratory studies of cultural evolution have become increasingly prevalent as a means of identifying and understanding the effects of cultural transmission on the form and functionality of transmitted material. The datasets generated by these studies may provide insights into the conditions encouraging, or inhibiting, high rates of innovation, as well as the effect that this has on measures of adaptive cultural change. Here we review recent experimental studies of cultural evolution with a view to elucidating the role of innovation in generating observed trends. We first consider how tasks are presented to participants, and how the corresponding conceptualization of task success is likely to influence the degree of intent underlying any deviations from perfect reproduction. We then consider the measures of interest used by the researchers to track the changes that occur as a result of transmission, and how these are likely to be affected by differing rates of retention. We conclude that considering studies of cultural evolution from the perspective of innovation provides us with valuable insights that help to clarify important differences in research designs, which have implications for the likely effects of variation in retention rates on measures of cultural adaptation.     

Evolution of primary microcephaly genes and the enlargement of primate brains

Brain size, in relation to body size, has varied markedly during the evolution of mammals. In particular, a large cerebral cortex is a feature that distinguishes humans from our fellow primates. Such anatomical changes must have a basis in genetic alterations, but the molecular processes involved have yet to be defined. However, recent advances from the cloning of two human disease genes promise to make inroads in this important area. Microcephalin (MCPH1) and Abnormal spindle-like microcephaly associated (ASPM) are genes mutated in primary microcephaly, a human neurodevelopmental disorder. In this 'atavistic' condition, brain size is reduced in volume to a size comparable with that of early hominids. Hence, it has been proposed that these genes evolved adaptively with increasing primate brain size. Subsequent studies have lent weight to this hypothesis by showing that both genes have undergone positive selection during great ape evolution. Further functional characterisation of their proteins will contribute to an understanding of the molecular and evolutionary processes that have determined human brain size.     

Evolution of ASPM is associated with both increases and decreases in brain size in primates

A fundamental trend during primate evolution has been the expansion of brain size. However, this trend was reversed in the Callitrichidae (marmosets and tamarins), which have secondarily evolved smaller brains associated with a reduction in body size. The recent pursuit of the genetic basis of brain size evolution has largely focused on episodes of brain expansion, but new insights may be gained by investigating episodes of brain size reduction. Previous results suggest two genes (ASPM and CDK5RAP2) associated with microcephaly, a human neurodevelopmental disorder, may have an evolutionary function in primate brain expansion. Here we use new sequences encoding key functional domains from 12 species of callitrichids to show that positive selection has acted on ASPM across callitrichid evolution and the rate of ASPM evolution is significantly negatively correlated with callitrichid brain size, whereas the evolution of CDK5RAP2 shows no correlation with brain size. Our findings strongly suggest that ASPM has a previously unsuspected role in the evolution of small brains in primates. ASPM is therefore intimately linked to both evolutionary increases and decreases in brain size in anthropoids and is a key target for natural selection acting on brain size.     

Genomic insights into the marine sponge microbiome

Marine sponges (phylum Porifera) often contain dense and diverse microbial communities, which can constitute up to 35% of the sponge biomass. The genome of one sponge, Amphimedon queenslandica, was recently sequenced, and this has provided new insights into the origins of animal evolution. Complementary efforts to sequence the genomes of uncultivated sponge symbionts have yielded the first glimpse of how these intimate partnerships are formed. The remarkable microbial and chemical diversity of the sponge-microorganism association, coupled with its postulated antiquity, makes sponges important model systems for the study of metazoan host-microorganism interactions, and their evolution, as well as for enabling access to biotechnologically important symbiont-derived natural products. In this Review, we discuss our current understanding of the interactions between marine sponges and their microbial symbiotic consortia, and highlight recent insights into these relationships from genomic studies.     

Translation in chloroplasts

The discovery that chloroplasts have semi-autonomous genetic systems has led to many insights into the biogenesis of these organelles and their evolution from free-living photosynthetic bacteria. Recent developments of our understanding of the molecular mechanisms of translation in chloroplasts suggest selective pressures that have maintained the 100-200 genes of the ancestral endosymbiont in chloroplast genomes. The ability to introduce modified genes into chloroplast genomes by homologous recombination and the recent development of an in vitro chloroplast translation system have been exploited for analyses of the cis-acting requirements for chloroplast translation. Trans-acting translational factors have been identified by genetic and biochemical approaches. Several studies have suggested that chloroplast mRNAs are translated in association with membranes.     

综述:阿尔茨海默病的神经影像学研究进展

阿尔茨海默病(Alzheimer's disease,AD)是以记忆和其他高级认知功能下降为特征的神经退行性疾病．早期的神经影像学研究通常是探索AD患者局部脑区的结构和功能变化．随着多模态神经影像技术和人脑连接组学研究方法的发展,研究者已经能够考察AD患者脑结构和功能连接通路．采用这些方法,最近的研究已经发现,AD患者脑网络的连接强度、网络效率、模块化组织和核心脑区连接的下降,并发现这些变化与患者的记忆评分等密切相关．这些新方法和新技术的出现不仅提供了新颖的观点来解释AD病的脑区失连接病理生理机制,而且发现的AD异常脑连接模式可能作为敏感特征应用于AD早期辅助诊断的影像标记物研究．特别重要的是,研究表明,在AD患者脑神经网络出现的异常连接模式,在AD前期即轻度认知障碍期患者中也已出现,表明了将AD影像学研究的重点前移到AD前期这一可治疗阶段的重要性和迫切性．     

Brain evolution by brain pathway duplication

Understanding the mechanisms of evolution of brain pathways for complex behaviours is still in its infancy. Making further advances requires a deeper understanding of brain homologies, novelties and analogies. It also requires an understanding of how adaptive genetic modifications lead to restructuring of the brain. Recent advances in genomic and molecular biology techniques applied to brain research have provided exciting insights into how complex behaviours are shaped by selection of novel brain pathways and functions of the nervous system. Here, we review and further develop some insights to a new hypothesis on one mechanism that may contribute to nervous system evolution, in particular by brain pathway duplication. Like gene duplication, we propose that whole brain pathways can duplicate and the duplicated pathway diverge to take on new functions. We suggest that one mechanism of brain pathway duplication could be through gene duplication, although other mechanisms are possible. We focus on brain pathways for vocal learning and spoken language in song-learning birds and humans as example systems. This view presents a new framework for future research in our understanding of brain evolution and novel behavioural traits.     

The jewels of our genome: the search for the genomic changes underlying the evolutionarily unique capacities of the human brain

The recent publication of the initial sequence and analysis of the chimp genome allows us, for the first time, to compare our genome with that of our closest living evolutionary relative. With more primate genome sequences being pursued, and with other genome-wide, cross-species comparative techniques emerging, we are entering an era in which we will be able to carry out genomic comparisons of unprecedented scope and detail. These studies should yield a bounty of new insights about the genes and genomic features that are unique to our species as well as those that are unique to other primate lineages, and may begin to causally link some of these to lineage-specific phenotypic characteristics. The most intriguing potential of these new approaches will be in the area of evolutionary neurogenomics and in the possibility that the key human lineage–specific (HLS) genomic changes that underlie the evolution of the human brain will be identified. Such new knowledge should provide fresh insights into neuronal development and higher cognitive function and dysfunction, and may possibly uncover biological mechanisms for information storage, analysis, and retrieval never previously seen.     

Making new molecules - evolution of pathways for novel metabolites in plants

Plants have adapted to their environments by diversifying in various ways. This diversification is reflected at the phytochemical level in their production of numerous specialized secondary metabolites that provide protection against biotic and abiotic stresses. Plant speciation is therefore intimately linked to metabolic diversification, yet we do not currently have a deep understanding of how new metabolic pathways evolve. Recent evidence indicates that genes for individual secondary metabolic pathways can be either distributed throughout the genome or clustered, but the relative frequencies of these two pathway organizations remain to be established. While it is possible that clustering is a feature of pathways that have evolved in recent evolutionary time, the answer to this and how dispersed and clustered pathways may be related remain to be addressed. Recent advances enabled by genomics and systems biology are beginning to yield the first insights into network evolution in plant metabolism. This review focuses on recent progress in understanding the evolution of clustered and dispersed pathways for new secondary metabolites in plants.     

Hedgehog-Gli signalling and the growth of the brain

The development of the vertebrate brain involves the creation of many cell types in precise locations and at precise times, followed by the formation of functional connections. To generate its cells in the correct numbers, the brain has to produce many precursors during a limited period. How this is achieved remains unclear, although several cytokines have been implicated in the proliferation of neural precursors. Understanding this process will provide profound insights, not only into the formation of the mammalian brain during ontogeny, but also into brain evolution. Here we review the role of the Sonic hedgehog-Gli pathway in brain development. Specifically, we discuss the role of this pathway in the cerebellar and cerebral cortices, and address the implications of these findings for morphological plasticity. We also highlight future directions of research that could help to clarify the mechanisms and consequences of Sonic hedgehog signalling in the brain.     

Game-theoretical approaches to studying the evolution of biochemical systems

Evolutionary optimization has been successfully used to increase our understanding of key properties of biochemical systems. Traditional optimization is, however, often insufficient for gaining deeper insights into the evolution of such systems because usually there is a mutual relationship between the properties optimized by evolution and the properties of the environment. Thus, by evolving towards optimal properties, organisms change their environment, which in turn alters the optimum. Evolutionary game theory provides an appropriate framework for analyzing evolution in such 'dynamic fitness landscapes'. We therefore argue that it is a promising approach to studying the evolution of biochemical systems. Indeed, recent studies have applied evolutionary game theory to key issues in the evolution of energy metabolism.     

Advancing our understanding of the connectivity,evolution and management of marine lobsters through genetics

The genomic revolution has provided powerful insights into the biology and ecology of many non-model organisms. Genetic tools have been increasingly applied to marine lobster research in recent years and have improved our understanding of species delimitation and population connectivity. High resolution genomic markers are just beginning to be applied to lobsters and are now starting to revolutionise our understanding of fine spatial and temporal scales of population connectivity and adaptation to environmental conditions. Lobsters play an important role in the ecosystem and many species are commercially exploited but many aspects of their biology is still largely unknown. Genetics is a powerful tool that can further contribute to our understanding of their ecology and evolution and assist management. Here we illustrate how recent genetic advancements are (1) leading to a step change in our understanding of evolution and adaptation, (2) elucidating factors driving connectivity and recruitment, (3) revealing insights into ecological processes and can (4) potentially revolutionise management of this commercially important group. We discuss how improvements in sequencing technologies and statistical methods for genetic data analyses combined with increased sampling efforts and careful sampling design have transformed our understanding of lobsters biology in recent years. We also highlight possible future directions in the application of genomic tools to lobster research that can aid management, in particular, the close-kin-mark-recapture method. Finally, we identify gaps and challenges in lobster research, such as the lack of any reference genomes and predictions on how lobsters will respond to future environmental conditions.