Leaf development and evolution

The number of publications on “leaf morphogenesis” has increased annually since the early 1990s, when the Arabidopsis ‘model plant’ concept began being applied to studies of mechanisms of leaf morphogenesis. Nearly 20 years have passed since then, and a great leap in the understanding of leaf organogenesis has been made. As a result, so-called evo/devo studies on leaf development have joined the trend in leaf morphogenesis/development studies in the latter part of the present decade. This article is a brief overview of the progress made in the research to date and an introduction to the articles that appear in this special issue.     

Genome evolution and the evolution of exon-shuffling--a review

Recent studies on the genomes of protists, plants, fungi and animals confirm that the increase in genome size and gene number in different eukaryotic lineages is paralleled by a general decrease in genome compactness and an increase in the number and size of introns. It may thus be predicted that exon-shuffling has become increasingly significant with the evolution of larger, less compact genomes. To test the validity of this prediction, we have analyzed the evolutionary distribution of modular proteins that have clearly evolved by intronic recombination. The results of this analysis indicate that modular multidomain proteins produced by exon-shuffling are restricted in their evolutionary distribution. Although such proteins are present in all major groups of metazoa from sponges to chordates, there is practically no evidence for the presence of related modular proteins in other groups of eukaryotes. The biological significance of this difference in the composition of the proteomes of animals, fungi, plants and protists is best appreciated when these modular proteins are classified with respect to their biological function. The majority of these proteins can be assigned to functional categories that are inextricably linked to multicellularity of animals, and are of absolute importance in permitting animals to function in an integrated fashion: constituents of the extracellular matrix, proteases involved in tissue remodelling processes, various proteins of body fluids, membrane-associated proteins mediating cell-cell and cell-matrix interactions, membrane associated receptor proteins regulating cell cell communications, etc. Although some basic types of modular proteins seem to be shared by all major groups of metazoa, there are also groups of modular proteins that appear to be restricted to certain evolutionary lineages. In summary, the results suggest that exon-shuffling acquired major significance at the time of metazoan radiation. It is interesting to note that the rise of exon-shuffling coincides with a spectacular burst of evolutionary creativity: the Big Bang of metazoan radiation. It seems probable that modular protein evolution by exon-shuffling has contributed significantly to this accelerated evolution of metazoa, since it facilitated the rapid construction of multidomain extracellular and cell surface proteins that are indispensable for multicellularity.     

Parasite evolution and extinctions

We examine the evolution of diseases that show the frequency‐dependent transmission process that is commonly applied to sexually and vector‐transmitted infections. As is commonly found, the basic reproductive ratio (R₀) of the parasite is maximized by evolution. This has important implications, as it implies that for a wide range of circumstances diseases that show frequency‐dependent transmission may be selected to evolve towards driving their hosts to extinction. This contrasts with the results obtained in spatially explicit models where although parasite‐driven host extinction may occur, it is unlikely to evolve. We further show that an evolutionary constraint between transmission and virulence is required for evolution to lead to an endemic coexistence of both the host and the disease. Furthermore, this constraint needs to be saturating, such that transmission is ‘bought’ at an increasing cost in terms of virulence, to avoid evolution to extinction.     

The structure of protein evolution and the evolution of protein structure

The observed distribution of protein structures can give us important clues about the underlying evolutionary process, imposing important constraints on possible models. The availability of results from an increasing number of genome projects has made the development of these models an active area of research. Models explaining the observed distribution of structures have focused on the inherent functional capabilities and structural properties of different folds and on the evolutionary dynamics. Increasingly, these elements are being combined.     

Language evolution and an emergent property

Much debate has been stimulated by the recent hypothesis that human language consists of a faculty that is shared with non-human animals (faculty of language in a broad sense; FLB) and a faculty that is specific to human language (faculty of language in a narrow sense; FLN). This hypothesis has encouraged a tendency to emphasize one component of FLN: the cognitive operation of recursion. In consequence, non-syntactical, yet unique, aspects of human language have been neglected. One of these properties consists of vocal learning that enables an abundance of learned syllables. I suggest that FLN is not an independent faculty, but an 'emergent' property, arising from interactions between several other non-syntactical subfaculties of FLB, including vocal learning ability.     

Genetic algorithms and evolution

The genetic algorithm (GA) as developed by Holland (1975, Adaptation in Natural and Artificial Systems. Ann Arbor: University of Michigan Press) is an optimization technique based on natural selection. We use a modified version of this technique to investigate which aspects of natural selection make it an efficient search procedure. Our main modification to Holland's GA is the subdividing of the population into semi-isolated demes. We consider two examples. One is a fitness landscape with many local optima. The other is a model of singing in birds that has been previously analysed using dynamic programming. Both examples have epistatic interactions. In the first example we show that the GA can find the global optimum and that its success is improved by subdividing the population. In the second example we show that GAs can evolve to the optimal policy found by dynamic programming.     

Cultural niche construction and human evolution

Organisms frequently choose, regulate, construct and destroy important components of their environments, in the process changing the selection pressures to which they and other organisms are exposed. We refer to these processes as niche construction. In humans, culture has greatly amplified our capacity for niche construction and our ability to modify selection pressures. We use gene‐culture coevolutionary models to explore the evolutionary consequences of culturally generated niche construction through human evolution. Our analysis suggests that where cultural traits are transmitted in an unbiased fashion from parent to offspring, cultural niche construction will have a similar effect to gene‐based niche construction. However, cultural transmission biases favouring particular cultural traits may either increase or reduce the range of parameter space over which niche construction has an impact, which means that niche construction with biased transmission will either have a much smaller or a much bigger effect than gene‐based niche construction. The analysis also reveals circumstances under which cultural transmission can overwhelm natural selection, accelerate the rate at which a favoured gene spreads, initiate novel evolutionary events and trigger hominid speciation. Because cultural processes typically operate faster than natural selection, cultural niche construction probably has more profound consequences than gene‐based niche construction, and is likely to have played an important role in human evolution.     

Problem-solving exercises and evolution teaching

It has been suggested that the work of Kammerer provides suitable material, in the form of case studies, on which to base discussions of Lamarckism versus Darwinism. A set of structured problems is described as an example of possible problem-solving exercises, and further experiments to extend Kammerer's work are outlined.     

The ecology and evolution of autotomy

Autotomy, the self‐induced loss of a body part, occurs throughout Animalia. A lizard dropping its tail to escape predation is an iconic example, however, autotomy occurs in a diversity of other organisms. Octopuses can release their arms, crabs can drop their claws, and bugs can amputate their legs. The diversity of organisms that can autotomize body parts has led to a wealth of research and several taxonomically focused reviews. These reviews have played a crucial role in advancing our understanding of autotomy within their respective groups. However, because of their taxonomic focus, these reviews are constrained in their ability to enhance our understanding of autotomy. Here, we aim to synthesize research on the ecology and evolution of autotomy throughout Animalia, building a unified framework on which future studies can expand. We found that the ability to drop an appendage has evolved multiple times throughout Animalia and that once autotomy has evolved, selection appears to act on the removable appendage to increase the efficacy and/or efficiency of autotomy. This could explain why some autotomizable body parts are so elaborate (e.g. brightly coloured). We also show that there are multiple benefits, and variable costs, associated with autotomy. Given this variation, we generate an economic theory of autotomy (modified from the economic theory of escape) which makes predictions about when an individual should resort to autotomy. Finally, we show that the loss of an autotomizable appendage can have numerous consequences on population and community dynamics. By taking this broad taxonomic approach, we identified patterns of autotomy that transcend specific lineages and highlight clear directions for future research.     

Experimental evolution: experimental evolution and evolvability

The suggestion that there are characteristics of living organisms that have evolved because they increase the rate of evolution is controversial and difficult to study. In this review, we examine the role that experimental evolution might play in resolving this issue. We focus on three areas in which experimental evolution has been used previously to examine questions of evolvability; the evolution of mutational supply, the evolution of genetic exchange and the evolution of genetic architecture. In each case, we summarize what studies of experimental evolution have told us so far and speculate on where progress might be made in the future. We show that, while experimental evolution has helped us to begin to understand the evolutionary dynamics of traits that affect evolvability, many interesting questions remain to be answered.     

Predation and primate evolution

This paper presents the results of a general review of predation on nonhuman primates as a selective force in primate evolution. Testable hypotheses derived from the literature on predation on primates, concerning sexual dimorphism, male defense, group size, solitaries, transfer, subgrouping, and sex ratio, were applied to the available data on populations with varying predation rates in search of significant correlations. All seven hypotheses were supported, indicating that predation is and has been an important determinant of primate evolutionary history. Suggestions for accumulating a larger and more accurate body of information on predation rates on primates are offered.     

Psoriasis: evolution and revolution

Psoriasis is a model disease in dermatology. It is a common disease that affects at least 2 to 3 % of the population. It is an illness characterized by an excessive reaction of the skin, in term of proinflammatory cytokines release, to no specific attacks: these attacks can be immunological, mechanical, metabolic, drug-induced or psychological. This excessive reaction is characterized by epidermal proliferation combined with incomplete terminal differentiation, as well as an inflammatory response responsible for the chronic nature of the lesions. The way to understand psoriasis is therefore to reach a better appreciation of the messages that enable the skin cells to initiate an inflammatory response, and by better understanding the way in which the inflammatory cells responsible for innate and acquired immune responses are capable of bringing about proliferation and abnormal epidermal differentiation. Taking an interest in psoriasis is therefore taking an interest in all facets of skin physiology and in all the ways the skin reacts to attacks from the environment. Every year for more than thirty years, more than 300 publications have endeavoured to explore one aspect or another of psoriasis from a clinical, epidemiological, physiopathological or therapeutic point of view. There is no new technique for observing the skin that has not been immediately applied to the study of psoriasis - which is privileged to enjoy the reflected progress made in dermatology. Nor has psoriasis remained untouched by whims of fashion, all manner of scenarios having been suggested to explain it, right from a scarring disease to an autoimmune illness through a genetic or psychosomatic disorder. Psoriasis is at the origin of a medical revolution mounted to supplement and enhance the effectiveness of evidence-based medicine ; it is the "patient-centred medicine". Psoriasis only exceptionally jeopardizes life. Conversely, it is a disease that does affect quality of life. The patient alone must be the judge of his or her quality of life, and it is therefore up to the patient, not the doctor, to gauge the severity of psoriasis and hence decide on reasonable therapeutic indications. Psoriasis, then, cannot be treated without placing the patient, not the illness, at the centre of therapeutic negotiations. The 20th century has seen the disease targeted by boundless efforts ; the 21st century will see the development of medical techniques that allow the patient, in all its complexity, to be positioned at the centre of therapeutic efforts. This revolution began in dermatology, centring around psoriasis, and is spreading progressively to all chronic disorders and all disciplines. New quite interesting therapeutic weapons are available from a few months making possible to better adjust the therapeutic strategies of psoriasis to the patients needs but they are expensive opening again the debates on the limit of the social solidarity.     

Culture and the evolution of obesity

Human predispositions to fatness and obesity are best understood in the context of cultural and biological evolution. Both genes and cultural traits that were adaptive in the context of past food scarcities play a role today in the etiology of maladaptive adult obesity. The etiology of obesity must account for the social distribution of the condition with regard to gender, ethnicity, social class, and economic modernization. This distribution, which has changed throughout history, undoubtedly involves cultural factors. A model of culture is presented that has advantages over an undifferentiated concept of the “environment” for hypothesis generation. Cultural predispositions to obesity are found in the productive economy, the mode of reproduction, social structure, and cultural beliefs about food and ideal body size. Cross-cultural comparison can contribute to an understanding of the prevalence of obesity in some modern affluent societies.     

The evolution of concepts on the evolution of endothermy in birds and mammals

Warm-blooded animals, mammals and birds, are unique not because they are endothermic in the strict sense of the term but because they use an extravagant economy: they have high energy budgets and spend a large part of their energy resources on basic maintenance. Although several advantages of endothermy are easy to indicate, mechanisms behind evolution of such a wasteful life strategy remain unclear and have been subject to intensive debate. For two decades, the aerobic capacity model has been widely recognized as a promising hypothesis and has catalyzed a new direction in ecological and evolutionary physiology--the study of correlated evolution of behavioral and morphophysiological traits. Recently, two alternative models have been proposed, both of which see evolution of high metabolic rates in birds and mammals as an element in evolution of intensive parental care. Unlike previous models, which treated individuals as static objects of fixed properties, the parental care models explicitly incorporate life histories into a evolutionary-physiology research program. The aim of this article was to outline the process of evolution of major concepts in the field, which reflects development of the paradigm of modern evolutionary physiology.     

Human evolution

The origin, history, and singularity of our species has fascinated storytellers, philosophers and scientists throughout, and doubtless before, recorded history. Anthropology, the modern-era discipline that deals with these issues, is a notoriously contentious field, perhaps because the topic at hand – the nature of our own species – is one that is difficult or impossible to approach in an unbiased way. Recently, molecular genetics has increasingly contributed to this field. Here, I briefly discuss three areas where I believe molecular studies are likely to be of decisive importance in the future. These concern the questions of where and when our species originated, what the genetic background for characters that differ between us and apes is, and how the phenotypic traits that vary among human groups have evolved.     

Human evolution

The origin, history, and singularity of our species has fascinated storytellers, philosophers and scientists throughout, and doubtless before, recorded history. Anthropology, the modern-era discipline that deals with these issues, is a notoriously contentious field, perhaps because the topic at hand – the nature of our own species – is one that is difficult or impossible to approach in an unbiased way. Recently, molecular genetics has increasingly contributed to this field. Here, I briefly discuss three areas where I believe molecular studies are likely to be of decisive importance in the future. These concern the questions of where and when our species originated, what the genetic background for characters that differ between us and apes is, and how the phenotypic traits that vary among human groups have evolved.     

Human evolution

The origin, history, and singularity of our species has fascinated storytellers, philosophers and scientists throughout, and doubtless before, recorded history. Anthropology, the modern-era discipline that deals with these issues, is a notoriously contentious field, perhaps because the topic at hand – the nature of our own species – is one that is difficult or impossible to approach in an unbiased way. Recently, molecular genetics has increasingly contributed to this field. Here, I briefly discuss three areas where I believe molecular studies are likely to be of decisive importance in the future. These concern the questions of where and when our species originated, what the genetic background for characters that differ between us and apes is, and how the phenotypic traits that vary among human groups have evolved.     

Mosaic evolution,preadaptation, and the evolution of evolvability in apes

A major goal in postsynthesis evolutionary biology has been to better understand how complex interactions between traits drive movement along and facilitate the formation of distinct evolutionary pathways. I present analyses of a character matrix sampled across the haplorrhine skeleton that revealed several modules of characters displaying distinct patterns in macroevolutionary disparity. Comparison of these patterns to those in neurological development showed that early ape evolution was characterized by an intense regime of evolutionary and developmental flexibility. Shifting and reduced constraint in apes was met with episodic bursts in phenotypic innovation that built a wide array of functional diversity over a foundation of shared developmental and anatomical structure. Shifts in modularity drove dramatic evolutionary changes across the ape body plan in two distinct ways: (1) an episode of relaxed integration early in hominoid evolution coincided with bursts in evolutionary rate across multiple character suites; (2) the formation of two new trait modules along the branch leading to chimps and humans preceded rapid and dramatic evolutionary shifts in the carpus and pelvis. Changes to the structure of evolutionary mosaicism may correspond to enhanced evolvability that has a “preadaptive” effect by catalyzing later episodes of dramatic morphological remodeling.     

Predictive adaptive responses and human evolution

The importance of a single genotype being able to produce different phenotypes in different environments (phenotypic plasticity) is widely recognized in evolutionary theory and its adaptive significance is clear. In most cases, the developing organism responds to an environmental cue by producing a selectively and immediately appropriate phenotype. One subset of phenotypic responses to environmental stimuli, however, does not necessarily provide an immediate selective advantage. Rather, these kinds of responses, which we call 'predictive adaptive responses' (PARs), act primarily to improve fitness at a later stage of development. We argue that PARs have had an important role in human evolution, and that their recognition and interpretation has major significance for public health.