The evolution of plant sexual diversity

Charles Darwin recognized that flowering plants have an unrivalled diversity of sexual systems. Determining the ecological and genetic factors that govern sexual diversification in plants is today a central problem in evolutionary biology. The integration of phylogenetic, ecological and population-genetic studies have provided new insights into the selective mechanisms that are responsible for major evolutionary transitions between reproductive modes.     

Four Darwinian themes on the origin,evolution and preservation of island life

Charles Darwin’s observations and insights continue to inspire nearly all scientists who are captivated by both the marvels and the perils of island life. Here I feature four themes inspired by Darwin’s singular insights: themes that may continue to provide valuable lessons for understanding the ecological and evolutionary development of insular biotas, and for conserving the natural character and evolutionary potential of all species restricted to isolated ecosystems (natural or anthropogenic).     

Ecological drivers of the Ediacaran-Cambrian diversification of Metazoa

Organismal modifications to their physical and chemical environment play a significant role in structuring many modern ecosystems, and experimental evidence suggests that such behavior can increase diversity. Despite the important role such activities play in connecting ecology and evolution, less is known of the macroevolutionary impact of such influences, especially their role during major evolutionary transitions. The Ediacaran-Cambrian diversification of Metazoa encompassed the appearance and early diversification of virtually all major clades of marine animals and the establishment of metazoan-dominated ecosystems. Here we assess the role of positive ecological feedbacks using a new compilation of the first occurrences of all metazoan phyla, classes; orders and equivalent stem taxa, as well as data from a previously published compendium on fossils from the early to middle Cambrian of China. The results reveal relatively minor feedback during the Ediacaran, but a substantial increase during the Cambrian, principally through bioturbation and the appearance of a number of structural engineers, including sponges. Chemical modification of the environment through filtering and bioturbation seems to have had the largest impact. Data on taxic diversity is a poor proxy for abundance, or for the actual environmental impact of these activities, however. Future assessments of the influence of ecological feedbacks on this event will require standardized assessments of the abundance of taxa with different ecological roles.     

Paleontological Patterns, Macroecological Dynamics and the Evolutionary Process

Here we consider evolutionary patterns writ large in the fossil record. We argue that Darwin recognized but downgraded or de-emphasized several of these important patterns, and we consider what a renewed emphasis on these patterns can tell us about the evolutionary process. In particular, one of the key patterns we focus on is the role geographic isolation plays in fomenting evolutionary divergence; another one of the key patterns is stasis of species; the final pattern is turnovers, which exist at several hierarchical scales, including regional ecosystem replacement and pulses of speciation and extinction. We consider how each one of these patterns are related to the dynamic of changing ecological and environmental conditions over time and also investigate their significance in light of other concepts including punctuated equilibria and hierarchy theory. Ultimately, we tie each of these patterns into a framework involving macroecological dynamics and the important role environmental change plays in shaping evolution from the micro- to macroscale.     

Pacific walrus: Benthic bioturbator of Beringia

The dependency of walruses on sea ice as habitat, the extent of their feeding, their benthic bioturbation and consequent nutrient flux suggest that walruses play a major ecological role in Beringia. This suggestion is supported by several lines of evidence, accumulated during more than three decades of enquiry and leading to the hypothesis that positive feedbacks of walrus feeding strongly influence productivity and ecological function via benthic bioturbation and nutrient flux. Walruses annually consume an estimated 3 million metric tons of benthic biomass. Walrus prey species inhabit patches across the shelf according to sediment type and structure. Side-scan sonar and our calculations indicate that the area affected by walrus feeding is in the order of thousands of square kilometers per year. Annual to long-term walrus bioturbation results in significant, large-scale changes in sediment and biological-community structure, and magnifies nutrient flux from sediment pore water to the water column by about two orders of magnitude over wide areas. The combined effects of walrus feeding must be placed in the context of long-term, regional climate changes and responses. Should sea ice continue to move northward as a result of climate change, the walrus' ecological role could be diminished or lost, the benthic ecosystem could be fundamentally altered and native subsistence hunters would be deprived of important resources.     

Macroevolution of ecosystem engineering, niche construction and diversity

Organisms influence their environments through activities that range from bioturbation to modification of redox gradients and construction of structures. Some of these activities modify the selective regime of the builder (niche construction) and some influence the ecological success of other species (ecosystem engineering) as well as their evolutionary prospects. In this article, I argue that these processes produce effects that persist over geological time, modulating macroevolutionary patterns and diversity. Examples include greater sediment bioturbation and increased thickness and persistence of shell beds. The impact of these processes has been increasing over time, with recent communities encompassing greater ecosystem engineering than those of the early Phanaerozoic. Thus, positive feedback through environmentally mediated selection seems to have increasingly enhanced biodiversity through the Phanaerozoic.     

Engaging with Lyell: Alfred Russel Wallace’s Sarawak Law and Ternate papers as reactions to Charles Lyell’s Principles of Geology

Alfred Russel Wallace (1823–1913) and Charles Darwin (1809–1882) are honored as the founders of modern evolutionary biology. Accordingly, much attention has focused on their relationship, from their independent development of the principle of natural selection to the receipt by Darwin of Wallace’s essay from Ternate in the spring of 1858, and the subsequent reading of the Wallace and Darwin papers at the Linnean Society on 1 July 1858. In the events of 1858 Wallace and Darwin are typically seen as central players, with Darwin’s friends Charles Lyell (1797–1875) and Joseph Dalton Hooker (1817–1911) playing supporting roles. This narrative has resulted in an under-appreciation of a more central role for Charles Lyell as both Wallace’s inspiration and foil. The extensive anti-transmutation arguments in Lyell’s landmark Principles of Geology were taken as the definitive statement on the subject. Wallace, in his quest to solve the mystery of species origins, engaged with Lyell’s arguments in his private field notebooks in a way that is concordant with his engagement with Lyell in the 1855 and 1858 papers. I show that Lyell was the object of Wallace’s Sarawak Law and Ternate papers through a consideration of the circumstances that led Wallace to send his Ternate paper to Darwin, together with an analysis of the material that Wallace drew upon from the Principles. In this view Darwin was, ironically, intended for a supporting role in mediating Wallace’s attempted dialog with Lyell.     

Epigenetic mechanisms in the endosperm and their consequences for the evolution of flowering plants

The sudden rise of angiosperms to ecological dominance was an "abominable mystery" to Charles Darwin, and understanding the underlying evolutionary driving force has remained a scientific challenge since then. The recognition of polyploidization as an important factor for plant speciation is likely to hold a key to this mystery and we will discuss possible mechanisms underlying this phenomenon. Polyploidization raises an immediate reproductive barrier in the endosperm, pointing towards an important but greatly underestimated role of the endosperm in preventing interploidy hybridizations. Parent-of-origin-specific gene expression is largely restricted to the endosperm, providing an explanation for the dosage sensitivity of the endosperm. Here, we review epigenetic mechanisms causing endosperm dosage sensitivity, their possible consequences for raising interploidy and interspecies hybridization barriers and their impact on flowering plant evolution. This article is part of a Special Issue entitled: Epigenetic Control.     

Diversity Over Time

Temporal turnover is a fundamental feature of ecological communities. Darwin 1859 noted the ecological and evolutionary significance of turnover, Fisher and Preston acknowledged its role in their models of species abundance, while this ongoing and entirely natural rearrangement of species underpins key ecological concepts such as MacArthur and Wilson’s theory of island biogeography. However, the current focus on spatial patterns of diversity means that temporal changes are often overlooked. Here I argue that failure to take heed of the time frame over which data are collected can lead to both artefacts and artifictions. There are also deeper issues, such as the consequences for species richness estimation and rarefaction methods of a constantly changing community. Moreover, some of the confusion surrounding species abundance distributions may be resolved by taking account of time. A better appreciation of temporal turnover is essential for accurate diversity measurement and assessment, and, more importantly, will also lead to improved understanding of the processes that underpin community structure.     

Evolutionary ethics,Darwinian ethics and ethical naturalism

The relevance of evolutionary theory to ethics goes back to Darwin but until recently discussion employed evolutionary theory to justify ethical, social and political positions. Recently, evolutionary theory has been used to explain the existence of moral systems and moral propensities and, thereby, to provide a naturalistic basis for ethics. I argue that this approach has advanced our understanding of the basis of moral systems and moral propensities but does not as yet adequately incorporate the role of cognition in its account. Cognition has the effect of decoupling to some extent — though, of course, far from fully — human moral systems from their evolutionary origins. In an adequate account, evolutionary theory will play a crucial role but so also will our evolved cognitive abilities.     

New‐age ideas about age‐old sex: separating meiosis from mating could solve a century‐old conundrum

Ever since Darwin first addressed it, sexual reproduction reigns as the ‘queen’ of evolutionary questions. Multiple theories tried to explain how this apparently costly and cumbersome method has become the universal mode of eukaryote reproduction. Most theories stress the adaptive advantages of sex by generating variation, they fail however to explain the ubiquitous persistence of sexual reproduction also where adaptation is not an issue. I argue that the obstacle for comprehending the role of sex stems from the conceptual entanglement of two distinct processes – gamete production by meiosis and gamete fusion by mating (mixis). Meiosis is an ancient, highly rigid and evolutionary conserved process identical and ubiquitous in all eukaryotes. Mating, by contrast, shows tremendous evolutionary variability even in closely related clades and exhibits wonderful ecological adaptability. To appreciate the respective roles of these two processes, which are normally linked and alternating, we require cases where one takes place without the other. Such cases are rather common. The heteromorphic sex chromosomes Y and W, that do not undergo meiotic recombination are an evolutionary test case for demonstrating the role of meiosis. Substantial recent genomic evidence highlights the accelerated rates of change and attrition these chromosomes undergo in comparison to those of recombining autosomes. I thus propose that the most basic role of meiosis is conserving integrity of the genome. A reciprocal case of meiosis without bi‐parental mating, is presented by self‐fertilization, which is fairly common in flowering plants, as well as most types of apomixis. I argue that deconstructing sex into these two distinct processes – meiosis and mating – will greatly facilitate their analysis and promote our understanding of sexual reproduction.     

Celebrate Darwin Day, An Event for Education and Outreach in Evolutionary Biology

Darwin Day is an international celebration of Charles Darwin’s birthday, February 12, and is used as an occasion for education and outreach in evolutionary biology. I describe the history and structure of Darwin Day at the University of Tennessee, one of the oldest Darwin Day organizations in the world. I detail past events including speakers, themes, and advertising ideas that have worked for us and suggestions for getting a Darwin Day started. I encourage interested groups especially those at schools, museums, libraries, nature centers, and other institutions to adapt ideas from our organization to fit their own circumstances and to start planning their own Darwin Days for the celebration of Darwin’s 200th birthday in 2009.     

Towards a postmodern synthesis of evolutionary biology

In 2009, we are celebrating the 200th anniversary of Charles Darwin and the 150th jubilee of his masterpiece, the Origin of Species. Darwin constructed the first coherent and compelling narrative of biological evolution and thus founded evolutionary biology—and modern biology in general, remembering the famous dictum of Dobzhansky. It is, however, counter-productive, and ultimately, a disservice to Darwin’s legacy, to define modern evolutionary biology as neo-Darwinism. The current picture of evolution, informed by results of comparative genomics and systems biology, is by far more complex than that presented in the Origin of Species, so that Darwinian principles, including natural selection, are incorporated into the evolving new synthesis as important but certainly not all-embracing tenets. This expansion of evolutionary biology does not denigrate Darwin in the least but rather emphasizes the fertility of his ideas.     

Charles Darwin's views of classification in theory and practice

It has long been argued that Charles Darwin was the founder of the school of "evolutionary taxonomy" of the Modern Synthesis and, accordingly, that he recognized genealogy and similarity as dual, synergistic criteria for classification. This view is based on three questionable interpretations: first, of isolated passages in the 13th chapter of the Origin of Species; second, of one phrase in a letter that Darwin wrote about the work of an author he had partly misunderstood; and third, of his taxonomic practice in the barnacle monographs, which only implicitly embody his philosophy of classification, if at all. These works, seen in fuller context and with the perspective of extensive correspondence, are consistent with the view that Darwin advocated only genealogy as the basis of classification, and that similarity was merely a tool for discovering evolutionary relationships. Darwin was neither a Mayrian taxonomist nor a cladist, and he did not approach systematic issues in the same terms that we do in the late 20th century.     

Charles Darwin,embryology, evolution and skeletal plasticity

Darwin provided us with the theory of evolutionary change through natural selection. Just as important to the science of biology was Darwin’s recognition that all organisms could be classified and were related to one another because they arose from a single common universal ancestor – what we know as the universal tree of life (UtoL). All the features of the skeletal biology of fish therefore can be explained, both in an evolutionary framework (ultimate causation) and in the framework of development, growth and physiology (proximate causation). Neither approach is complete without the other. I will outline the elements of Darwin’s theories on evolution and classification and, as importantly, discuss what was missing from Darwin’s theories. An important class of evidence for evolution used by Darwin came from embryology, both comparative embryology and the existence of vestiges and atavisms. After discussing this evidence I examine some fundamental features of skeletal development and evolution These include: the presence of four skeletal systems in all vertebrates; the existence of two skeletons, one based on cartilage, the other on bone and dentine; the modular nature of skeletal development and evolution; and the plasticity of the skeleton in response to either genetic or environmental changes.     

The pollination niche and its role in the diversification and maintenance of the southern African flora

The flora of southern Africa has exceptional species richness and endemism, making it an ideal system for studying the patterns and processes of evolutionary diversification. Using a wealth of recent case studies, I examine the evidence for pollinator-driven diversification in this flora. Pollination systems, which represent available niches for ecological diversification, are characterized in southern Africa by a high level of ecological and evolutionary specialization on the part of plants, and, in some cases, by pollinators as well. These systems are asymmetric, with entire plant guilds commonly specialized for a particular pollinator species or functional type, resulting in obvious convergent floral evolution among guild members. Identified modes of plant lineage diversification involving adaptation to pollinators in these guilds include (i) shifts between pollination systems, (ii) divergent use of the same pollinator, (iii) coevolution, (iv) trait tracking, and (v) floral mimicry of different model species. Microevolutionary studies confirm that pollinator shifts can be precipitated when a plant species encounters a novel pollinator fauna on its range margin, and macroevolutionary studies confirm frequent pollinator shifts associated with lineage diversification. As Darwin first noted, evolutionary specialization for particular pollinators, when resulting in ecological dependency, may increase the risk of plant extinction. I thus also consider the evidence that disturbance provokes pollination failure in some southern African plants with specialized pollination systems.     

Environmental and temporal patterns in bioturbation in the Cambrian–Ordovician of Western Newfoundland

The early Paleozoic emergence of bioturbating (sediment-dwelling and -mixing) animals has long been assumed to have led to substantial changes in marine biogeochemistry, seafloor ecology, and the preservation potential of both sedimentary and fossil archives. However, the timing of the rise of bioturbation and environmental patterns in its expansion have long been subjects of debate—resolution of which has been hampered, in part, by a paucity of high-resolution bioturbation data or of systematic investigations of facies trends in lower Paleozoic bioturbation. To address these issues, we conducted an integrated sedimentological and ichnological characterization of the Cambrian–Ordovician Port au Port succession and Cow Head Group of western Newfoundland, encompassing over 350 meters of stratigraphy logged at the centimeter to decimeter scale. We find that, across a wide range of marine facies, bioturbation does not on average exceed moderate intensities—corroborating observations from other lower Paleozoic successions indicating that the early Paleozoic development of bioturbation was a protracted process. Moreover, bioturbation intensities in the Port au Port succession and Cow Head Group are commonly characterized by considerable variability at even fine scales of stratigraphic resolution and changes in bioturbation intensity correlate strongly with variability in sedimentary facies. We observe that facies recording nearshore depositional environments and carbonate-rich lithologies are each characterized by the highest intensities of both burrowing and sediment mixing. These data highlight the need for a high-resolution and facies-specific approach to reconstructing the evolutionary history of bioturbation and suggest that average levels of bioturbation, although relatively low throughout this interval, increased notably earlier in nearshore marine settings.     

Charles Darwin and the problem of evolutionary progress

According to Ch. Darwin's evolutionary theory, evolutionary progress (interpreted as morpho-physiological progress or arogenesis in recent terminology) is one of logical results of natural selection. At the same time, natural selection does not hold any factors especially promoting evolutionary progress. Darwin emphasized that the pattern of evolutionary changes depends on organism nature more than on the pattern of environment changes. Arogenesis specificity is determined by organization of rigorous biological systems - integral organisms. Onward progressive development is determined by fundamental features of living organisms: metabolism and homeostasis. The concept of social Darwinism differs fundamentally from Darwin's ideas about the most important role of social instincts in progress of mankind. Competition and selection play secondary role in socio-cultural progress of human society.     

Why Darwin would have loved evolutionary game theory

Humans have marvelled at the fit of form and function, the way organisms'' traits seem remarkably suited to their lifestyles and ecologies. While natural selection provides the scientific basis for the fit of form and function, Darwin found certain adaptations vexing or particularly intriguing: sex ratios, sexual selection and altruism. The logic behind these adaptations resides in frequency-dependent selection where the value of a given heritable phenotype (i.e. strategy) to an individual depends upon the strategies of others. Game theory is a branch of mathematics that is uniquely suited to solving such puzzles. While game theoretic thinking enters into Darwin''s arguments and those of evolutionists through much of the twentieth century, the tools of evolutionary game theory were not available to Darwin or most evolutionists until the 1970s, and its full scope has only unfolded in the last three decades. As a consequence, game theory is applied and appreciated rather spottily. Game theory not only applies to matrix games and social games, it also applies to speciation, macroevolution and perhaps even to cancer. I assert that life and natural selection are a game, and that game theory is the appropriate logic for framing and understanding adaptations. Its scope can include behaviours within species, state-dependent strategies (such as male, female and so much more), speciation and coevolution, and expands beyond microevolution to macroevolution. Game theory clarifies aspects of ecological and evolutionary stability in ways useful to understanding eco-evolutionary dynamics, niche construction and ecosystem engineering. In short, I would like to think that Darwin would have found game theory uniquely useful for his theory of natural selection. Let us see why this is so.     

Darwin Day in deep time: promoting evolutionary science through paleontology

Charles Darwin’s birthday, February 12th, is an international celebration coined Darwin Day. During the week of his birthday, universities, museums, and science-oriented organizations worldwide host events that celebrate Darwin’s scientific achievements in evolutionary biology. The University of Tennessee, Knoxville (UT) has one of the longest running celebrations in the nation, with 2016 marking the 19th year. For 2016, the theme for our weeklong series of events was paleontology, chosen to celebrate new research in the field and to highlight the specific misconceptions of evolution within the context of geologic time. We provide insight into the workings of one of our largest and most successful Darwin Day celebration to date, so that other institutions might also be able to host their own rewarding Darwin Day events in the future.