Darwin's Observations Research Articles

Repeated evolution of a reproductive polyphenism in plants is strongly associated with bilateral flower symmetry

Polyphenisms are a special type of phenotypic plasticity in which the products of development are not continuous but instead are separate and distinct phenotypes produced in the same genetic background. One of the most widespread polyphenisms in the flowering plants is cleistogamy, in which the same individual plant produces both open, cross-pollinated flowers as well as highly reduced and closed, self-pollinated (cleistogamous) flowers.1-5 Cleistogamy is not a rare evolutionary phenomenon. It has evolved independently at least 41 times.1 But what favors the evolution of cleistogamy is still largely unknown.1 Darwin6 proposed a hypothesis that has never been properly tested. He observed that cleistogamy is more common in taxa with bilaterally symmetric (zygomorphic) flowers than in those with radially symmetric (actinomorphic) flowers. Moreover, Darwin suggested that cleistogamous flowers help to ensure pollination, which he postulated is less certain in zygomorphic taxa that rely on more specialized groups of pollinators. Here, we combined the largest datasets on floral symmetry and cleistogamy and used phylogenetic approaches to show that cleistogamy is indeed disproportionately associated with zygomorphic flowers and that zygomorphic species are more likely to evolve cleistogamy than actinomorphic species. We also show that zygomorphic species are less capable of autonomous open-flower self-pollination (lower autofertility), suggesting that selection of cleistogamy via reproductive assurance in zygomorphic taxa could help account for Darwin's observation. Our results provide support for the hypothesis that polyphenisms are favored when organisms encounter contrasting environments.

On the origins of observations of heterostyly in Primula.

In 1862, Charles Darwin published his landmark study on the different forms of flower in Primula; he coined the term distyly and subsequently expanded his studies to other species, including those with tristyly. Darwin is widely recognized as the first to study pin and thrum flowers in Primula, and to provide an explanation for the functional significance of the two floral morphs. Our laboratory is pursuing the genes that underpin floral heteromorphy in Primula, work influenced by Darwin's observations. One day, while appreciating a print of Primula vulgaris from William Curtis' Flora Londinensis, I was struck by the fact that I was looking at images of dimorphic Primula flowers captured in a late-1700s copper-plate engraving that predated Darwin's observations by over 70 yr. This realization triggered a journey into archives of botanical texts, herbals and florilegia from the 16(th) to 19(th) Centuries, and correspondence archives, in search of earlier documents that could have influenced Darwin and the origins of an idea. Darwin was not the first to observe floral heteromorphy in Primula, but he was the first to realize the significance of the two floral morphs. Darwin's insight and exposition of purpose have underpinned all consequent work on the subject.

The politics of becoming different: Rethinking evolution through population genetics

Recent ‘new materialist’ readings of evolution by such feminists as Elizabeth Grosz, Claire Colebrook, Luciana Parisi, Susan Oyama and Myra Hird have provided important insights on the openness of evolutionary processes and the emergence of difference by focusing on evolution as a temporal dynamic. Building on Darwin's observations on geographical variation, this article highlights the importance of viewing evolution as not only temporal but also spatial. For this purpose, the article turns to population genetics and its practice of mapping the early human diaspora. The article identifies a spatiotemporal dynamic of evolutionary emergence that posits gender, sexuality and race as ontologically mutually constitutive, as well as shows that such ontology is inseparable from the techniques and technologies that study it. The article argues that this mutual embeddedness of ontology and epistemology provides a site where both the limits and potential of evolutionary emergence may be examined and negotiated.

First steps in studying the origins of secondary woodiness inBegonia(Begoniaceae): combining anatomy, phylogenetics, and stem transcriptomics

Since Darwin's observation that secondary woodiness is common on islands, the evolution of woody plants from herbaceous ancestors has been documented in numerous angiosperm groups. However, the evolutionary processes that give rise to this phenomenon are poorly understood. To begin addressing this we have used a range of approaches to study the anatomical and genetic changes associated with the evolution and development of secondary woodiness in a tractable group. Begonia is a large, mainly herbaceous, pantropical genus that shows multiple shifts towards secondarily woody species inhabiting mainly tropical montane areas throughout the world. Molecular phylogenies, including only a sample of the woody species in Begonia, indicated at least eight instances of a herbaceous–woody transition within the genus. Wood anatomical observations of the five woody species studied revealed protracted juvenilism that further support the secondary derived origin of wood within Begonia. To identify potential genes involved in shifts towards secondary woodiness, stem transcriptomes of wood development in B. burbidgei were analysed and compared with available transcriptome datasets for the non-woody B. venustra, B. conchifolia, and Arabidopsis, and with transcriptome datasets for wood development in Populus. Results identified a number of potential regulatory genes as well as variation in expression of key biosynthetic enzymes. © 2015 The Authors. Biological Journal of the Linnean Society published by John Wiley & Sons Ltd on behalf of Linnean Society of London, Biological Journal of the Linnean Society, 2015, ●●, ●●–●●.

From so simple a beginning

I am neither a Darwinian demagogue, nor an Intelligent Design orator. But like any other scientist, I take as common sense Charles Darwin's observation: It is not the strongest of the species that survives, nor the most intelligent, but the one most responsive to change. Nevertheless, a recent news article from Nature, Korea surrenders to creationist demands, has ignited fresh debate. Although the article simply reports on the scientific world's concern about the process of deleting some examples of evolution from South Korean high school textbooks, members of the public are awkwardly arguing with each other on the subject of evolution, based on their religious faith or scientific belief.

Darwinian Thinking: 150 Years after The Origin

hypothesis that adaptive divergence leads to speciation and to the evolution of traits and behaviors that influence the prospects for species coexistence. A key issue here is the role of character displacement in the origin and mainte- nance of diversity. Pfennig and Pfennig find substantial evidence that character displacement plays an important role in the evolution of species interactions and identify a number of additional areas that Darwin had not con- sidered, including sexual selection and phenotypic plas- ticity. Their paper clearly illustrates how Darwin's original observations continue to shape our thinking on the in- terface between ecology, behavior, and evolution. Of the many insightful observations presented in The Origin, perhaps none is more remarkable than Darwin's discussion of the evolution of hybrid sterility. He under- stood that sterility could not have evolved as an adaptation of individual species and that interactions in the hybrids stemming from the contributions of each parent caused incompatibilities, but without today's specific knowledge of genetics, he was unable to reach a satisfactory expla- nation. Presgraves (2010) reviews this topic in detail, in- cluding an historical perspective on the contributions by Darwin, Muller, and Dobzhansky to the problem. He also provides an overview of the recent advances in our un- derstanding of the genetic mechanisms that contribute to the evolution of hybrid incompatibilities. This includes evidence that genetic conflict, and not adaptive divergence, may be a primary cause of hybrid sterility and inviability. Darwin considered multiple sources of evidence to gain support for his theory of natural selection, including the evolution of both living and extinct organisms. Hunt (2010) describes Darwin's attempts to use the fossil record to test the hypothesis that evolution by natural selection is a gradual process. Darwin argued at the time that the record was too incomplete to provide an adequate test. Hunt reviews the current paleontological record and con- cludes that over short periods, rates of morphological evo- lution are sometimes considerably faster than Darwin had proposed. Sticklebacks provide a particularly illustrative case, where a nearly continuous record extending over the last 10 million years shows that most phenotypic evolution occurred over a brief period of approximately 1,000 gen- erations. Moreover, for a wide variety of organisms and

From Energy Gradient and Natural Selection to Biodiversity and Stability of Ecosystems

The purpose of this paper is to incorporate well-established ecological principles into a foodweb model consisting of four trophic levels --- abiotic resources, plants, herbivores, and carnivores. The underlining principles include Kimura's neutral theory of genetic evolution, Liebig's Law of the Minimum for plant growth, Holling's functionals for herbivore foraging and carnivore predation, the One-Life Rule for all organisms, and Lotka-Volterra's model for intra- and interspecific competitions. Numerical simulations of the model led to the following statistical findings: (a) particular foodwebs can give contradicting observations on biodiversity and productivity, in particular, all known functional forms -- - positive, negative, sigmoidal, and unimodal correlations are present in the model; (b) drifting stable equilibria should be expected for ecosystems regardless of their size; (c) resource abundance and specific competitions are the main determining factors for biodiversity, with intraspecific competition enhancing diversity while interspecific competition impeding diversity; (d) endangered species are expected always and loss in lower trophic endangered species are expected at trophication, i.e. the establishment of a higher trophic level of a community. These findings may shed lights on some ongoing debates on biodiversity. In particular, finding (a) implies that the diversity vs. ecosystems functioning debate is most likely the result of incompatible particular observations each cannot be generalized. In particular, general causality should not be expected between diversity and productivity. Finding (b) does not support May's theory that large ecosystems are inherently unstable nor Eton's theory that stability requires diversity. However, it lends a strong support to the energetic theory for the latitudinal diversity gradient. Finding (c) supports Darwin's observation on the effect of interspecific competition on diversity. Finding (d) implies that loss of diversity is inevitable with the appearance of a super species like the human race. Our method and result also suggest that although the evolution of particular species cannot be predicted, some general statistic patterns appear to persist. In addition to the aforementioned findings, these persisting patterns include: the trophic succession, the trophic biomass separation in orders of magnitude, the upper bounds in biodiversity in relationship to the intensities of specific competitions despite the enormous possible number of species allowed by genetic mutations.

Darwin's Flinch: Sensation Theatre and Scientific Looking in 1872

Abstract This article explores the relationship between Darwin's The Expression of the Emotions in Man and Animals (London: Murray, 1872) and the debates surrounding audiences of sensation theatre. It takes as its starting point a flinch performed by Darwin in a self-experiment at London Zoological Gardens. Darwin's flinch combined the act of scientific observation with a self-consciously staged emotional gesture. In the 1860s and early 1870s, the passionate and demonstrative audiences of sensation plays were similarly understood to watch themselves feeling. In this economy of emotional surfaces, actors and audience were caught up in unsettling relations between outwards expression and the remote landscape of interior feeling. Entangled in this theatrical instability, Darwin's scientific observation reflected broader cultural concerns about the reliability of the emotional body. Thus the article offers Darwin's Expression as an unusual but nonetheless suggestive artefact of theatrical spectatorship in 1872, while also contributing to recent debates about the history of objectivity and its supposedly unemotional and restrained scientific observer. It argues that the technique of self-conscious emotional spectatorship, shared by Darwin and theatre audiences, constituted a distinctive model of late Victorian emotion and visuality, in which communities of spectators were also spectators of themselves.

Sarcophilia, cremation and Sir Henry Thompson (1820–1904)

Sarcophilia, a neologism for an attachment to human remains, is set in a review of the history of the disposal of the dead. The ancient practice of cremation was relaunched late in the 19th century by the urological surgeon cum social reformer Sir Henry Thompson. He was stimulated by Edwin Chadwick and Charles Dickens, and by Charles Darwin's observations on the earthworm. Sarcophilia is the reason for the controversial Human Tissue Act of 2004.

Darwin on island plants

Islands played a key role in Charles Darwin's observations and experiments on plant dispersal. By means of these experiments, he expunged the old idea that a given species could originate at multiple times and in multiple places. More importantly, by seeing the capabilities for dispersal of plant seeds, fruits and branches, he was able to develop ideas of how plants reach islands and thus he is one of the founders of plant biogeography. For facts regarding floristic distribution of plants, Darwin relied on other workers, most notably Sir Joseph Dalton Hooker. Among his insights were the differences between oceanic and continental islands on a floristic basis, ideas on how age of island and distance from mainland areas influenced composition of island floras, the nature of endemism on islands and the role islands and archipelagos served as stepping stones in dispersal. Ingenious at proposing hypotheses, but always respectful of facts, Darwin sought explanations for plant adaptations on islands at a time when knowledge of island botany was little more than floristic in nature. These explanations are compared with selected recent works in island botany.

Re-contemplate an entangled bank:The Power of Movement in Plantsrevisited

We review the ways in which two of Charles Darwin's lesser known works, The Movement and Habit of Twining Plants and The Power of Movement in Plants, stimulated 20th and 21st century research findings and philosophies. The legacy of Darwin's work permeates research on plant movement. For example, Darwin's demonstration that coleoptiles and roots fail to bend in response to light or gravity if their tips are removed helped researchers work toward the discovery of auxin and other plant hormones. Darwin's methodical observations on vine twining directions and circumnutation foreshadowed the recent discovery that 92% of vines twine in right-handed helices, regardless of their location on the planet. Finally, Darwin's observation of the similarity between plant responses to stimuli and the responses of lower animals foreshadowed the current debate over whether plants have `behaviour'. Thus, even Darwin's lesser-known works continue to influence research in the present day.

Endless forms most beautiful1

Beautiful form rather than efficient cause is the crucial category for understanding living processes, especially evolution. Drawing on the fields of non-equilibrium thermodynamics and citing Darwin's own observations, the author proposes a new understanding of form that corresponds to the dynamism present in living forms and overcomes the limitations of other metaphysical notions of form. Form as beautiful “dynamic form” promises an enriched empiricism, which not only can speak “correctly” about nature but also “well” of nature. In other words, an enriched empiricism of beautiful dynamic forms allows for a fruitful dialogue between science and theology. It avoids theological explanations that call for special divine intervention in the world of Nature which threaten the dignity and self-integrity of Creation. It opens up a view, however, of a divine “milieu,” a divine “Openness,” that providentially calls for beautiful dynamic forms to emerge and entangle through the evolutionary process of nature.

‘Marks of extreme violence': Charles Darwin's geological observations at St Jago (São Tiago), Cape Verde islands

Abstract The first stop on Charles Darwin's famous voyage around the world in HMS Beagle was at Porto Praya (Praia), the principal town on the island of St Jago (São Tiago) in the Cape Verde archipelago. From 16 January to 8 February 1832, Darwin enjoyed his first substantive opportunity to study the natural history of an exotic place. Darwin himself regarded this occasion as a significant turning point in his life because, according to his autobiography, it was here that he decided to research and publish a book on the geology of the places visited on the voyage. He also recalled that it was here, the very first port call, that convinced him of the ‘wonderful superiority’ of Charles Lyell's uniformitarian geology over the doctrine of successive cataclysms that he had been taught in England. Later commentators have generally accepted this account, which is significant for understanding the intellectual background to the Origin of Species , at face value. In this paper we reconstruct some of Darwin's observations at St Jago based on his contemporaneous notes and diary, and in the light of our own visit made in January 2002. We find little evidence to substantiate the claim that he interpreted the geology in Lyellian terms at the time. Instead, he formulated a theory involving a great cataclysm to explain the dramatic scenery in the island's interior. He speculated that a torrent of water had carved the main valleys of the island, leaving deposits of diluvium in their beds. It is indisputable that Darwin came to embrace gradualist thinking enthusiastically during the voyage. Some of his observations made on St Jago, especially relating to uplift of the coast, were instrumental in this change of view, but the conversion was gradual, not sudden. His later published works make no mention of his original catastrophist interpretations.

Song and the limbic brain: a new function for the bird's own song.

The neurobiological investigation of the avian song system has largely focused on the unique neural features of vocal control systems that contribute to learned motor patterns in songbirds. The role of emotion has been disregarded in developing a theory of song learning and performance. Here we review emerging evidence in support of Darwin's observation that vocal communication is emotional expression. We propose that neural pathways mediating emotional state remained integrated with the vocal control system as forebrain vocal control pathways evolved to support learned communication patterns. Vocalizations are therefore both a motor component of an emotional state and can influence emotional state via sensory feedback during vocal production. By acknowledging the importance of emotion in vocal communication, we are proposing that the song system and limbic brain are functionally linked in the production and reception of song.

Suffering, weeping and other preoccupations: Darwin's observations and our present-day

Suffering, weeping and other preoccupations: Darwin's observations and our present-day

The Role of Geitonogamy in the Gradual Evolution towards Dioecy in Cosexual Plants

We present a model for the gradual evolution towards dioecy in cosexual plants with geitonogamous selfing. We show how geitonogamous selfing (i.e. transfer of pollen between flowers on the same plant) can facilitate the evolution of dioecy (i.e. separate male and female individuals) in cosexual plants (i.e. both sexual functions on the same plant). We study the effect of parameters such as inbreeding depression, the attraction costs per flower, and the total amount of resources available per plant. We also consider different flower architectures (limited versus unlimited potential number of seeds per flower) and pollination biologies (biotic versus abiotic). We find that (1) if there is no maximum to the number of seeds per flower, then cosexuality is evolutionarily stable whenever the inbreeding depression is less than one-half. With abiotic pollination and an inbreeding depression greater than one-half, dioecy evolves via evolutionary branching, that is, through the gradual differentiation towards male and female plants, but only after the population has first evolved to a cosexual strategy with an intermediate sex ratio. The evolution of dioecy requires higher levels of inbreeding depression if pollination is by insects, but is facilitated by increasing the total amount of resources available per plant. (2) If the potential number of seeds per flower is limited, we get basically the same results as with an unlimited seed number per flower, but the outcome now also depends on the attraction costs per flower. With high attraction costs, the population can evolve to gynodioecy (females and cosexuals in the same population). Further increasing inbreeding depression leads to dioecy. Our results give a possible explanation of Darwin's observation that dioecy is more common in plant species with abiotic pollination and in large species with many flowers such as trees.

Speciation versus phenotypic plasticity in coral inhabiting barnacles: Darwin's observations in an ecological context.

Speciation and phenotypic plasticity are two extreme strategic modes enabling a given taxon to populate a broad ecological niche. One of the organismal models which stimulated Darwin's ideas on speciation was the Cirripedia (barnacles), to which he dedicated a large monograph. In several cases, including the coral-inhabiting barnacle genera Savignium and Cantellius (formerly Pyrgoma and Creusia, respectively), Darwin assigned barnacle specimens to morphological "varieties" (as opposed to species) within a genus. Despite having been the subject of taxonomic investigations and revisions ever since, the significance of these varieties has never been examined with respect to host-associated speciation processes. Here we provide evidence from molecular (12S mt rDNA sequences) and micromorphological (SEM) studies, suggesting that these closely related barnacle genera utilize opposite strategies for populating a suite of live-coral substrates. Cantellius demonstrates a relatively low genetic variability, despite inhabiting a wide range of corals. The species C. pallidus alone was found on three coral families, belonging to distinct higher-order classification units. In contrast, Savignium barnacles exhibit large between- and within-species variations with respect to both micromorphology and DNA sequences, with S. dentatum "varieties" clustering phylogenetically according to their coral host species (all of which are members of a single family). Thus, whereas Savignium seems to have undergone intense host-associated speciation over a relatively narrow taxonomic range of hosts, Cantellius shows phenotypic plasticity over a much larger range. This dichotomy correlates with differences in life-history parameters between these barnacle taxa, including host-infestation characteristics, reproductive strategies, and larval trophic type.

CRYPTIC SEXUAL SELECTION-MORE CONTROL ISSUES

Identifying the evolutionary processes that cause genetic and phenotypic divergence among species is one of the fundamental goals of evolutionary biologists. Darwin (1871) first pointed out that male traits such as plumage coloration, which he hypothesized to influence sexual selection, rapidly diverge among closely related species. In an earlier book (Sexual Selection and Animal Genitalia, Eberhard 1985), William Eberhard extended Darwin's observation by showing that male genitalia diverge very rapidly among closely related species which have internal fertilization but not among those with external fertilization. Eberhard hypothesized that the rapid divergence in male genitalia was driven by the process of choice. Traditionally, the term female has been used to describe a process whereby females differentially mate with some males among a pool of potential mates. The term was coined by Randy Thornhill (Thornhill 1983) to describe events occurring after the onset of copulation that determine the extent to which a makes use of a male's sperm. Eberhard's new book (Female Control: Sexual Selection by Cryptic Female Choice) focuses on cryptic choice and its importance to the process of sexual selection. Eberhard states in his first chapter that, despite the potential significance of cryptic choice, this topic has been essentially ignored in the major texts on sexual selection that have appeared since the publication of his earlier book. The aim of the new book is to clarify why cryptic choice can no longer be ignored. For a synopsis of much of the book, complete with references, a recent TREE article (Eberhard and Cordero 1995) reviews many of the major topics. Eberhard begins by defining cryptic choice and argues for its potentially broad application. He defends his focus on the opportunity forfemale-controlled sexual selection as a response to, in his view, the long-standing bias in the opposite direction. For example, he contrasts the phrase, and the direction of research on sperm competition, with the dearth of work on sperm screening. He then discusses in detail twenty different mechanisms which could result in cryptic choice. The traits proposed to underlie cryptic choice can be summarized as: variation in copulation quality, mechanical and chemical interactions between mates, transport

An ethologist aboard hms beagle: The young darwin's observations on animal behavior

Darwin's notes from the Beagle period abound with observations on animal behavior. Although in places anecdotal and anthropomorphic, they include many detailed, lively comments of the activities of birds, reptiles, mammals, crustacea, insects, and other invertebrates. In his comparative approach, belief in the importance of heredity, an understanding that behavior might be of assistance in taxonomy, and that it was linked with both the organism's morphology and habitat, and his attempts at experiments, Charles Darwin in his early and mid-twenties was using techniques and concepts that were to be of great significance in his later work.

Blushing as a function of audience size.

Almost no experimental analysis of blushing has been done since Darwin's observations in 1872. Forty-eight college women watched a videotape intended to elicit blushing, and a videotape not intended to elicit blushing, but elicit physiological responses. A subject was alone, or with one or four persons present. Blushing, which was measured directly with a photoplethysmograph probe on the cheek, was greater during the blushing than nonblushing stimulation. Blushing increased as audience size increased from one to four, but not from zero to one. Audience size and kind of stimulation interacted statistically. Similar results were obtained with ear coloration, cheek temperature, and skin conductance responses, although confidence levels were lower. Cheek coloration and temperature were significantly correlated during nonblushing stimulation, and the zero and one audience conditions, but not during the four audience condition, when blushing was greatest. These results may be placed within the context of emotional effects of audience size generally, including stuttering and speech disturbance, disruption of learning, and self-reported tension.