Origins and Early Evolution of Predation

The Evolutionary Transition of the RNA World to Obcells to Cellular-Based Life

The obcell hypothesis is a proposed route for the RNA world to develop into a primitive cellular one. It posits that this transition began with the emergence of the proto-ribosome which enabled RNA to colonise the external surface of lipids by the synthesis of amphipathic peptidyl-RNAs. The obcell hypothesis also posits that the emergence of a predation-based ecosystem provided a selection mechanism for continued sophistication amongst early life forms. Here, I argue for this hypothesis owing to its significant explanatory power; it offers a rationale why a ribosome which initially was capable only of producing short non-coded peptides was advantageous and it forgoes issues related to maintaining a replicating RNA inside a lipid enclosure. I develop this model by proposing that the evolutionary selection for improved membrane anchors resulted in the emergence of primitive membrane pores which enabled obcells to gradually evolve into a cellular morphology. Moreover, I introduce a model of obcell production which advances that tRNAs developed from primers of the RNA world.

Tubule system of earliest shells as a defense against increasing microbial attacks

The evolutionary mechanism behind the early Cambrian animal skeletonization was a complex and multifaceted process involving environmental, ecological, and biological factors. Predation pressure, oxygenation, and seawater chemistry change have frequently been proposed as the main drivers of this biological innovation, yet the selection pressures from microorganisms have been largely overlooked. Here we present evidence that calcareous shells of the earliest mollusks from the basal Cambrian (Fortunian Age, ca. 539-529 million years ago) of Mongolia developed advanced tubule systems that evolved primarily as a defensive strategy against extensive microbial attacks within a microbe-dominated marine ecosystem. These high-density tubules, comprising approximately 35% of shell volume, enable nascent mineralized mollusks to cope with increasing microbial bioerosion caused by boring endolithic cyanobacteria, and hence represent an innovation in shell calcification. Our finding demonstrates that enhanced microboring pressures played a significant role in shaping the calcification of the earliest mineralized mollusks during the Cambrian Explosion.

Ecological Implications on Aquatic Food Webs Due to Effects of Pesticides on Invertebrate Predators in a Neotropical Region

Predation presents specific behavioral characteristics for each species, and the interaction between prey and predator influences the structuring of the food web. Concerning insects, predation can be affected in different ways, such as exposure to chemical stressors, e.g., pesticides. Therefore, analyses were carried out of the effects of exposure to insecticide fipronil and the herbicide 2,4-D on predation, parameters of food selectivity, and the swimming behavior of two neotropical predatory aquatic insects of the families Belostomatidae (giant water bugs) and larvae of Libellulidae (dragonfly). These predatory insects were exposed for 24 h to a commercial formulation of the chlorophenoxy herbicide, 2,4-D at nominal concentrations of 200, 300, 700, and 1400 μg L-1, and to a commercial formulation of the phenylpyrazole insecticide, fipronil at nominal concentrations of 10, 70, 140, and 250 µg L-1. In a control treatment, the insects were placed in clean, unspiked water. At the end of the exposure, the maximum swimming speed of the predators was evaluated. Afterward, the predators were placed in clean water in a shared environment for 24 h with several prey species, including the cladoceran Ceriodaphnia silvestrii, larvae of the insect Chironomus sancticaroli, the amphipod Hyalella meinerti, the ostracod Strandesia trispinosa, and the oligochaete Allonais inaequalis for 24 h. After this period, the consumed prey was counted. The results reveal that predators from both families changed prey consumption compared with organisms from the control treatment, marked by a decrease after exposure to fipronil and an increase in consumption caused by 2,4-D. In addition, there were changes in the food preferences of both predators, especially when exposed to the insecticide. Exposure to fipronil decreased the swimming speed of Belostomatidae individuals, possibly due to its neurotoxic effect. Exposure to the insecticide and the herbicide altered prey intake by predators, which could negatively influence the complex prey-predator relationship and the functioning of aquatic ecosystems in contaminated areas.

Animal cognition and culture mediate predator-prey interactions

Predator-prey ecology and the study of animal cognition and culture have emerged as independent disciplines. Research combining these disciplines suggests that both animal cognition and culture can shape the outcomes of predator-prey interactions and their influence on ecosystems. We review the growing body of work that weaves animal cognition or culture into predator-prey ecology, and argue that both cognition and culture are significant but poorly understood mechanisms mediating how predators structure ecosystems. We present a framework exploring how previous experiences with the predation process creates feedback loops that alter the predation sequence. Cognitive and cultural predator-prey ecology offers ecologists new lenses through which to understand species interactions, their ecological consequences, and novel methods to conserve wildlife in a changing world.

Towards the Big History of information. Approaching the origins of information behaviour

A palaeontological analysis of the evolutionary steps of Metazoa is tracing back the appearance and first steps of information behaviour as far as the Proterozoic Eon. Either the neural cell or the nervous system or the eyesight did not trigger the appearance of the information behaviour, but it did a novel way of diet. Carnivorous diet appeared on Earth slightly before the information behaviour as a completely new way of feeding - and what is more important: the application of light into the behavioural complexes as a radically innovative survival supporting tool. A genetic toolkit was ready for Metazoa, and the combination of the neural system, eyesight and carnivorous diet initiated the information behaviour. We provide an answer for this simple question: why did the carnivorous diet result in the first disruptive innovation in information behaviour? The junction of Big History, palaeontology and information history provides many challenging new aspects for further research.

On the evolutionary emergence of predation

In models for the evolution of predation from initially purely competitive species interactions, the propensity of predation is most often assumed to be a direct consequence of the relative morphological and physiological traits of interacting species. Here we explore a model in which predation ability is an independently evolving phenotypic feature, so that even when the relative morphological or physiological traits allow for predation, predation only occurs if the predation ability of individuals has independently evolved to high enough values. In addition to delineating the conditions for the evolutionary emergence of predation, the model reproduces stationary and non-stationary multilevel food webs with the top predators not necessarily having size superiority.

Variation of shell ornamentation with latitude and water depth-A case study using living brachiopods

As a potential anti-predatory defensive structure, the shell ornamentation of marine calcifiers is usually used to understand the macro coevolution of the interactions between predators and preys. Marine calcifiers' shell ornamentation complexity is generally believed to vary negatively with latitude and water depth. In this paper, we explored the association between shell ornamentation and latitude/bathymetry using the latest global database of living brachiopods. We found that (1) ~59% of living brachiopods species are characterized by smooth shells and that (2) there is no statistically significant linear trend, either positive or negative, between the ornamentation index and latitudes nor with water depths. Both findings are puzzling for living brachiopods as they are sharply contrasted to the patterns of fossil brachiopods whereby the latter, especially Paleozoic brachiopods, are known to exhibit (1) a much greater ornamentation diversity and (2) (at least for the geological periods that have been studied) a linear latitudinal gradient of ornamentation complexity existed. The reasons why living brachiopods have such a high proportion of smooth or weakly ornamented shells and fail to demonstrate an unequivocal linear latitudinal ornamentation gradient were explored and are linked to a multitude of potential factors rather than uniquely only to the predation pressure. Among these, the most plausible factor seems to be the cryptic (refuge-type) habitats (e.g., deep waters, cold polar regions, and submarine rock caves) that living brachiopods have been adapted to due to their low metabolism, where predation pressure is low, allowing brachiopods to enact the predator avoidance strategy rather than having to manufacture robust shell ornamentation to survive in an otherwise highly engaged predator-prey global marine ecosystem.

Savviness of prey to introduced predators

The prey naivety hypothesis posits that prey are vulnerable to introduced predators because many generations in slow gradual coevolution are needed for appropriate avoidance responses to develop. It predicts that prey will be more responsive to native than introduced predators and less responsive to introduced predators that differ substantially from native predators and from those newly established. To test these predictions, we conducted a global meta-analysis of studies that measured the wariness responses of small mammals to the scent of sympatric mammalian mesopredators. We identified 26 studies that met our selection criteria. These studies comprised 134 experiments reporting on the responses of 36 small mammal species to the scent of six introduced mesopredators and 12 native mesopredators. For each introduced mesopredator, we measured their phylogenetic and functional distance to local native mesopredators and the number of years sympatric with their prey. We used predator and prey body mass as a measure of predation risk. Globally, small mammals were similarly wary of the scent of native and introduced mesopredators; phylogenetic and functional distance between introduced mesopredators and closest native mesopredators had no effect on wariness; and wariness was unrelated to the number of prey generations, or years, since first contact with introduced mesopredators. Small mammal wariness was associated with predator-prey body mass ratio, regardless of the nativity. The one thing animals do not seem to recognize is whether their predators are native.

Methanosaeta and "Candidatus Velamenicoccus archaeovorus"

The phylum "Candidatus Omnitrophica" (candidate division OP3) is ubiquitous in anaerobic habitats but is currently characterized only by draft genomes from metagenomes and single cells. We had visualized cells of the phylotype OP3 LiM in methanogenic cultures on limonene as small epibiotic cells. In this study, we enriched OP3 cells by double density gradient centrifugation and obtained the first closed genome of an apparently clonal OP3 cell population by applying metagenomics and PCR for gap closure. Filaments of acetoclastic Methanosaeta, the largest morphotype in the culture community, contained empty cells, cells devoid of rRNA or of both rRNA and DNA, and dead cells according to transmission electron microscopy (TEM), thin-section TEM, scanning electron microscopy (SEM), catalyzed reporter deposition-fluorescence in situ hybridization (CARD-FISH), and LIVE/DEAD imaging. OP3 LiM cells were ultramicrobacteria (200 to 300 nm in diameter) and showed two physiological stages in CARD-FISH fluorescence signals: strong signals of OP3 LiM cells attached to Bacteria and to Archaea indicated many rRNA molecules and an active metabolism, whereas free-living OP3 cells had weak signals. Metaproteomics revealed that OP3 LiM lives with highly expressed secreted proteins involved in depolymerization and uptake of macromolecules and an active glycolysis and energy conservation by the utilization of pyruvate via a pyruvate:ferredoxin oxidoreductase and an Rnf complex (ferredoxin:NAD oxidoreductase). Besides sugar fermentation, a nucleotidyl transferase may contribute to energy conservation by phosphorolysis, the phosphate-dependent depolymerization of nucleic acids. Thin-section TEM showed distinctive structures of predation. Our study demonstrated a predatory metabolism for OP3 LiM cells, and therefore, we propose the name "Candidatus Velamenicoccus archaeovorus" gen. nov., sp. nov., for OP3 LiM. IMPORTANCE Epibiotic bacteria are known to live on and off bacterial cells. Here, we describe the ultramicrobacterial anaerobic epibiont OP3 LiM living on Archaea and Bacteria. We detected sick and dead cells of the filamentous archaeon Methanosaeta in slowly growing methanogenic cultures. OP3 LiM lives as a sugar fermenter, likely on polysaccharides from outer membranes, and has the genomic potential to live as a syntroph. The predatory lifestyle of OP3 LiM was supported by its genome, the first closed genome for the phylum "Candidatus Omnitrophica," and by images of cell-to-cell contact with prey cells. We propose naming OP3 LiM "Candidatus Velamenicoccus archaeovorus." Its metabolic versatility explains the ubiquitous presence of "Candidatus Omnitrophica" 3 in anoxic habitats and gives ultramicrobacterial epibionts an important role in the recycling and remineralization of microbial biomass. The removal of polysaccharides from outer membranes by ultramicrobacteria may also influence biological interactions between pro- and eukaryotes.

Evolution of behavioural control from chordates to primates

This article outlines a hypothetical sequence of evolutionary innovations, along the lineage that produced humans, which extended behavioural control from simple feedback loops to sophisticated control of diverse species-typical actions. I begin with basic feedback mechanisms of ancient mobile animals and follow the major niche transitions from aquatic to terrestrial life, the retreat into nocturnality in early mammals, the transition to arboreal life and the return to diurnality. Along the way, I propose a sequence of elaboration and diversification of the behavioural repertoire and associated neuroanatomical substrates. This includes midbrain control of approach versus escape actions, telencephalic control of local versus long-range foraging, detection of affordances by the dorsal pallium, diversified control of nocturnal foraging in the mammalian neocortex and expansion of primate frontal, temporal and parietal cortex to support a wide variety of primate-specific behavioural strategies. The result is a proposed functional architecture consisting of parallel control systems, each dedicated to specifying the affordances for guiding particular species-typical actions, which compete against each other through a hierarchy of selection mechanisms.

This article is part of the theme issue ‘Systems neuroscience through the lens of evolutionary theory’.

Vertebrate Taphonomy and Diagenesis: Implications of Structural and Compositional Alterations of Phosphate Biominerals

Biominerals are recorders of evolution and palaeoenvironments. Predation is one of the most frequent modes leading to the concentration of small vertebrates in fossil assemblages. Consumption by predators produces damages on bones and teeth from prey species, and one of the greatest challenges to taphonomists is differentiating original biological and secondary, geologically altered attributes of fossils. Excellent morphological preservation is often used to assume that the structure and composition of fossils are not modified. Nevertheless, during predation and fossilization, both the physical structure and chemical composition of enamel, dentine and bone are altered, the degree and extent of which varies from site to site, depending on the nature of the burial environment. A relationship between the surficial alterations and the compositional changes which take place during fossilization has yet to be established. Herein, I present a review of old and recent taphonomic studies that collectively reveal the wide diversity of microstructural and chemical changes that typically take place during fossilization of vertebrate remains, including common taphonomic biases and the challenges inherent to reconstructing the history of vertebrate fossil assemblages.

Dawn of complex animal food webs: A new predatory anthozoan (Cnidaria) from Cambrian

Cnidarians diverged very early in animal evolution; therefore, investigations of the morphology and trophic levels of early fossil cnidarians may provide critical insights into the evolution of metazoans and the origin of modern marine food webs. However, there has been a lack of unambiguous anthozoan cnidarians from Ediacaran assemblages, and undoubted anthozoans from the Cambrian radiation of metazoans are very rare and lacking in ecological evidence. Here, we report a new polypoid cnidarian, Nailiana elegans gen. et sp. nov., represented by multiple solitary specimens from the early Cambrian Chengjiang biota (∼520 Ma) of South China. These specimens show eight unbranched tentacles surrounding a single opening into the gastric cavity, which may have born multiple mesenteries. Thus, N. elegans displays a level of organization similar to that of extant cnidarians. Phylogenetic analyses place N. elegans in the stem lineage of Anthozoa and suggest that the ancestral anthozoan was a soft-bodied, solitary polyp showing octoradial symmetry. Moreover, one specimen of the new polyp preserves evidence of predation on an epifaunal lingulid brachiopod. This case provides the oldest direct evidence of macrophagous predation, the advent of which may have triggered the emergence of complex trophic/ecological relationships in Cambrian marine communities and spurred the explosive radiation of animal body plans.

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Polypoid animal from early Cambrian of China is a stem-group anthozoan cnidarian

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Anthozoan ancestor inferred to be soft-bodied, solitary polyp of octoradial symmetry

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The new anthozoan provides the oldest direct evidence of macrophagous predation

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Macrophagous predation may have triggered complex food webs in early Cambrian

The evolution of knowledge during the Cambrian explosion

Phillips et al. make a compelling case for a reversal in the current paradigm in "other minds" research by considering the representation of other people's knowledge more basic than the attribution of belief. Unfortunately, they only discuss primates. In this commentary, I argue that the representation of others' knowledge is an evolutionary ancient trait, first appearing during the Cambrian explosion.

Can scientific laws be discussed on philosophical grounds? a reply to naïve arguments on ‘predators’ proposed by Bramble (2021)

A recent paper by Bramble (2021) argues that given that predators inflict pain and fear on their prey we have the moral right to act to minimize these effects. The author proposes two alternatives. The first is to transform predators by ‘genetically modifying them so that their offspring gradually evolve into herbivores’. The second is simply ‘painlessly killing predators’, which is the title of Bramble’s essay. We address the misconceptions that Bramble uses as central in his arguments and present scientific reasoning to discuss the ethical implications of disregarding scientific knowledge when addressing animal welfare and animal rights. We conclude that both Bramble’s alternatives are nonsensical, not only from a scientific point of view, but also, and more importantly, from ethical grounds.

Symbiosis in the Cambrian: enteropneust tubes from the Burgess Shale co-inhabited by commensal polychaetes

The in situ preservation of animal behaviour in the fossil record is exceedingly rare, but can lead to unique macroecological and macroevolutionary insights, especially regarding early representatives of major animal clades. We describe a new complex ecological relationship from the middle Cambrian Burgess Shale (Raymond Quarry, Canada). More than 30 organic tubes were recorded with multiple enteropneust and polychaete worms preserved within them. Based on the tubicolous nature of fossil enteropneusts, we suggest that they were the tube builders while the co-preserved polychaetes were commensals. These findings mark, to our knowledge, the first record of commensalism within Annelida and Hemichordata in the entire fossil record. The finding of multiple enteropneusts sharing common tubes suggests that either the tubes represent reproductive structures built by larger adults, and the enteropneusts commonly preserved within are juveniles, or these enteropneusts were living as a pseudo-colony without obligate attachment to each other, and the tube was built collaboratively. While neither hypothesis can be ruled out, gregarious behaviour was clearly an early trait of both hemichordates and annelids. Further, commensal symbioses in the Cambrian may be more common than currently recognized.

Deciphering trophic interactions in a mid-Cambrian assemblage

Exceptionally preserved fossil sites have allowed specimen-based identification of trophic interactions to which network analyses have been applied. However, network analyses of the fossil record suffer from incomplete and indirect data, time averaging that obscures species coexistence, and biases in preservation. Here, we present a high-resolution fossil data set from Raymond Quarry member of the mid-Cambrian Burgess Shale (7,549 specimens, 61 taxa, ∼510 Mya) and formulate a measure of "preservation bias" that aids identification of assemblage subsets to which network analyses can be reliably applied. For these sections, abundance correlation network analyses predicted longitudinally consistent trophic and competitive interactions. Our analyses predicted previously postulated trophic interactions with 83.5% accuracy and demonstrated a shift from specialist interaction-dominated assemblages to ones dominated by generalist and competitive interactions. This approach provides a robust, taphonomically corrected framework to explore and predict in detail the existence and ecological character of putative interactions in fossil data sets.

Predators as Agents of Selection and Diversification

Predation is ubiquitous in nature and can be an important component of both ecological and evolutionary interactions. One of the most striking features of predators is how often they cause evolutionary diversification in natural systems. Here, we review several ways that this can occur, exploring empirical evidence and suggesting promising areas for future work. We also introduce several papers recently accepted in Diversity that demonstrate just how important and varied predation can be as an agent of natural selection. We conclude that there is still much to be done in this field, especially in areas where multiple predator species prey upon common prey, in certain taxonomic groups where we still know very little, and in an overall effort to actually quantify mortality rates and the strength of natural selection in the wild.

Intraguild predation between Pristionchus pacificus and Caenorhabditis elegans: a complex interaction with the potential for aggressive behaviour

The related nematodes Pristionchus pacificus and Caenorhabditis elegans both eat bacteria for nutrition and are therefore competitors when they exploit the same bacterial resource. In addition to competing with each other, P. pacificus is a predator of C. elegans larval prey. These two relationships together form intraguild predation, which is the killing and sometimes eating of potential competitors. In killing C. elegans, the intraguild predator P. pacificus may achieve dual benefits of immediate nutrition and reduced competition for bacteria. Recent studies of P. pacificus have characterized many aspects of its predatory biting behaviour as well as underlying molecular and genetic mechanisms. However, little has been explored regarding the potentially competitive aspect of P. pacificus biting C. elegans. Moreover, aggression may also be implicated if P. pacificus intentionally bites C. elegans with the goal of reducing competition for bacteria. The aim of this review is to broadly outline how aggression, predation, and intraguild predation relate to each other, as well as how these concepts may be applied to future studies of P. pacificus in its interactions with C. elegans.

Transitions in Brain Evolution: Space, Time and Entropy

How did brains evolve to become so complex, and what is their future? Brains pose an explanatory challenge because entropy, which inexorably increases over time, is commonly associated with disorder and simplicity. Recently we showed how evolution is an entropic process, building structures – organisms – which themselves facilitate entropy growth. Here we suggest that key transitional points in evolution extended organisms’ reach into space and time, opening channels into new regions of a complex multidimensional state space that also allow entropy to increase. Brain evolution enabled representation of space and time, which vastly enhances this process. Some of these channels lead to tiny, dead-ends in the state space: the persistence of complex life is thus not thermodynamically guaranteed.

Evolution of brain complexity is (counterintuitively) an entropy-enhancing process leading organisms to new regions of a space of states, which in turn allow access through channels to additional new spaces, and thus entropy to continue growing.

Step transitions in evolution have occurred as organisms acquired new abilities to reach out in space and time, vastly increasing the visitable space of states, and thereby access to new channels.

The ability of brains to represent space and time, culminating in human language and hence human technological civilisation, was an important set of transitions that magnified this process.

Continued evolution of biological complexity is not assured, because some newly accessible regions of the state space may be small and have no exits, resulting in extinction.

Predatory colponemids are the sister group to all other alveolates

Alveolates are a major supergroup of eukaryotes encompassing more than ten thousand free-living and parasitic species, including medically, ecologically, and economically important apicomplexans, dinoflagellates, and ciliates. These three groups are among the most widespread eukaryotes on Earth, and their environmental success can be linked to unique innovations that emerged early in each group. Understanding the emergence of these well-studied and diverse groups and their innovations has relied heavily on the discovery and characterization of early-branching relatives, which allow ancestral states to be inferred with much greater confidence. Here we report the phylogenomic analyses of 313 eukaryote protein-coding genes from transcriptomes of three members of one such group, the colponemids (Colponemidia), which support their monophyly and position as the sister lineage to all other known alveolates. Colponemid-related sequences from environmental surveys and our microscopical observations show that colponemids are not common in nature, but they are diverse and widespread in freshwater habitats around the world. Studied colponemids possess two types of extrusive organelles (trichocysts or toxicysts) for active hunting of other unicellular eukaryotes and potentially play an important role in microbial food webs. Colponemids have generally plesiomorphic morphology and illustrate the ancestral state of Alveolata. We further discuss their importance in understanding the evolution of alveolates and the origin of myzocytosis and plastids.

Glycan diversity in the course of vertebrate evolution

Vertebrates are estimated to have arisen over 500 million years ago in the Cambrian Period. Species that survived the Big Five extinction events at a global scale underwent repeated adaptive radiations along with habitat expansions from the sea to the land and sky. The development of the endoskeleton and neural tube enabled more complex body shapes. At the same time, vertebrates became suitable for the invasion and proliferation of foreign organisms. Adaptive immune systems were acquired for responses to a wide variety of pathogens, and more sophisticated systems developed during the evolution of mammals and birds. Vertebrate glycans consist of common core structures and various elongated structures, such as Neu5Gc, Galα1-3Gal, Galα1-4Gal, and Galβ1-4Gal epitopes, depending on the species. During species diversification, complex glycan structures were generated, maintained or lost. Whole-genome sequencing has revealed that vertebrates harbor numerous and even redundant glycosyltransferase genes. The production of various glycan structures is controlled at the genetic level in a species-specific manner. Because cell surface glycans are often targets of bacterial and viral infections, glycan structural diversity is presumed to be protective against infections. However, the maintenance of apparently redundant glycosyltransferase genes and investment in species-specific glycan structures, even in higher vertebrates with highly developed immune systems, are not well explained. This fact suggests that glycans play important roles in unknown biological processes.

Exploring abnormal Cambrian-aged trilobites in the Smithsonian collection

Biomineralised trilobite exoskeletons provide a 250 million year record of abnormalities in one of the most diverse arthropod groups in history. One type of abnormality-repaired injuries-have allowed palaeobiologists to document records of Paleozoic predation, accidental damage, and complications in moulting experienced by the group. Although Cambrian trilobite injuries are fairly well documented, the illustration of new injured specimens will produce a more complete understanding of Cambrian prey items. To align with this perspective, nine new abnormal specimens displaying healed injuries from the Smithsonian National Museum of Natural History collection are documented. The injury pattern conforms to the suggestion of lateralised prey defence or predator preference, but it is highlighted that the root cause for such patterns is obscured by the lumping of data across different palaeoecological and environmental conditions. Further studies of Cambrian trilobites with injuries represent a key direction for uncovering evidence for the Cambrian escalation event.

Competition-driven evolution of organismal complexity

Non-uniform rates of morphological evolution and evolutionary increases in organismal complexity, captured in metaphors like “adaptive zones”, “punctuated equilibrium” and “blunderbuss patterns”, require more elaborate explanations than a simple gradual accumulation of mutations. Here we argue that non-uniform evolutionary increases in phenotypic complexity can be caused by a threshold-like response to growing ecological pressures resulting from evolutionary diversification at a given level of complexity. Acquisition of a new phenotypic feature allows an evolving species to escape this pressure but can typically be expected to carry significant physiological costs. Therefore, the ecological pressure should exceed a certain level to make such an acquisition evolutionarily successful. We present a detailed quantitative description of this process using a microevolutionary competition model as an example. The model exhibits sequential increases in phenotypic complexity driven by diversification at existing levels of complexity and a resulting increase in competitive pressure, which can push an evolving species over the barrier of physiological costs of new phenotypic features.

We provide a theoretical proof-of-principle explanation for the empirically well-documented macroevolutionary pattern of punctuated changes in organismal complexity. According to such patterns, many phenotypic properties related to organismal complexity, such as body size, the development of new sensory or locomotive capabilities, etc., show long periods of relatively slow changes interrupted by intermittent bursts of rapid evolutionary changes. Building on earlier work, we argue that punctuated expansions in organismal complexity can be caused by a threshold-like response to growing ecological pressures in diversifying communities at an existing level of complexity. Acquisition of novel phenotypic features then allows a species to escape this pressure once the existing diversity reaches a certain threshold. Continuing our previous line of research on microevolutionary models for long-term evolution in high-dimensional phenotype spaces, we present a detailed quantitative description of this process based on a classic competition model. The resulting macro-evolutionary dynamics exhibit sequential increases in phenotypic complexity driven by the build-up of competitive pressures at an existing level of complexity, which allows the evolution of novel phenotypes despite substantial physiological costs.

Resynthesizing behavior through phylogenetic refinement

This article proposes that biologically plausible theories of behavior can be constructed by following a method of "phylogenetic refinement," whereby they are progressively elaborated from simple to complex according to phylogenetic data on the sequence of changes that occurred over the course of evolution. It is argued that sufficient data exist to make this approach possible, and that the result can more effectively delineate the true biological categories of neurophysiological mechanisms than do approaches based on definitions of putative functions inherited from psychological traditions. As an example, the approach is used to sketch a theoretical framework of how basic feedback control of interaction with the world was elaborated during vertebrate evolution, to give rise to the functional architecture of the mammalian brain. The results provide a conceptual taxonomy of mechanisms that naturally map to neurophysiological and neuroanatomical data and that offer a context for defining putative functions that, it is argued, are better grounded in biology than are some of the traditional concepts of cognitive science.

Ediacaran scavenging as a prelude to predation

Predation is one of the most fundamental ecological and evolutionary drivers in modern and ancient ecosystems. Here, we report the discovery of evidence of the oldest scavenging of shallowly buried bodies of iconic soft-bodied members of the Ediacara Biota by cryptic seafloor mat-burrowing animals that produced the furrow and levee trace fossil, Helminthoidichnites isp. These mat-burrowers were probably omnivorous, stem-group bilaterians that largely grazed on microbial mats but when following mats under thin sands, they actively scavenged buried Dickinsonia, Aspidella, Funisia and other elements of the Ediacara Biota. These traces of opportunistic scavengers of dead animals from the Ediacaran of South Australia represent a fundamental ecological innovation and a possible pathway to the evolution of macrophagous predation in the Cambrian. While the Ediacaran oceans may have had oxygen levels too low to support typical large predators, the Helminthoidichnites maker lived in and grazed on microbial mats, which may have provided a localized source of oxygen.

Implications of selective predation on the macroevolution of eukaryotes: evidence from Arctic Canada

Existing paleontological data indicate marked eukaryote diversification in the Neoproterozoic, ca. 800 Ma, driven by predation pressure and various other biotic and abiotic factors. Although the eukaryotic record remains less diverse before that time, molecular clock estimates and earliest crown-group affiliated microfossils suggest that the diversification may have originated during the Mesoproterozoic. Within new assemblages of organic-walled microfossils from the ca. 1150 to 900 Ma lower Shaler Supergroup of Arctic Canada, numerous specimens from various taxa display circular and ovoid perforations on their walls, interpreted as probable traces of selective protist predation, 150-400 million years before their first reported incidence in the Neoproterozoic. Selective predation is a more complex behavior than phagotrophy, because it requires sensing and selection of prey followed by controlled lysis of the prey wall. The ca. 800 Ma eukaryotic diversification may have been more gradual than previously thought, beginning in the late Mesoproterozoic, as indicated by recently described microfossil assemblages, in parallel with the evolution of selective eukaryovory and the spreading of eukaryotic photosynthesis in marine environments.

Reactive oxygen species may play an essential role in driving biological evolution: The Cambrian Explosion as an example

The Cambrian Explosion is one of the most significant events in the history of life; essentially all easily fossilizable animal body plans first evolved during this event. Although many theories have been proposed to explain this event, its cause remains unresolved. Here, we propose that the elevated level of oxygen, in combination with the increased mobility and food intake of metazoans, led to increased cellular levels of reactive oxygen species (ROS), which drove evolution by enhancing mutation rates and providing new regulatory mechanisms. Our hypothesis may provide a unified explanation for the Cambrian Explosion as it incorporates both environmental and developmental factors and is also consistent with ecological explanations for animal radiation. Future studies should focus on testing this hypothesis, and may lead to important insights into evolution.

Increase in predator-prey size ratios throughout the Phanerozoic history of marine ecosystems

The escalation hypothesis posits that predation by increasingly powerful and metabolically active carnivores has been a major driver of metazoan evolution. We test a key tenet of this hypothesis by analyzing predatory drill holes in fossil marine shells, which provide a ~500-million-year record of individual predator-prey interactions. We show that drill-hole size is a robust predictor of body size among modern drilling predators and that drill-hole size (and thus inferred predator size and power) rose substantially from the Ordovician to the Quaternary period, whereas the size of drilled prey remained stable. Together, these trends indicate a directional increase in predator-prey size ratios. We hypothesize that increasing predator-prey size ratios reflect increases in prey abundance, prey nutrient content, and predation among predators.

Antibiotics from predatory bacteria

Bacteria, which prey on other microorganisms, are commonly found in the environment. While some of these organisms act as solitary hunters, others band together in large consortia before they attack their prey. Anecdotal reports suggest that bacteria practicing such a wolfpack strategy utilize antibiotics as predatory weapons. Consistent with this hypothesis, genome sequencing revealed that these micropredators possess impressive capacities for natural product biosynthesis. Here, we will present the results from recent chemical investigations of this bacterial group, compare the biosynthetic potential with that of non-predatory bacteria and discuss the link between predation and secondary metabolism.

The 2.1 Ga old Francevillian biota: biogenicity, taphonomy and biodiversity

The Paleoproterozoic Era witnessed crucial steps in the evolution of Earth's surface environments following the first appreciable rise of free atmospheric oxygen concentrations ∼2.3 to 2.1 Ga ago, and concomitant shallow ocean oxygenation. While most sedimentary successions deposited during this time interval have experienced thermal overprinting from burial diagenesis and metamorphism, the ca. 2.1 Ga black shales of the Francevillian B Formation (FB2) cropping out in southeastern Gabon have not. The Francevillian Formation contains centimeter-sized structures interpreted as organized and spatially discrete populations of colonial organisms living in an oxygenated marine ecosystem. Here, new material from the FB2 black shales is presented and analyzed to further explore its biogenicity and taphonomy. Our extended record comprises variably sized, shaped, and structured pyritized macrofossils of lobate, elongated, and rod-shaped morphologies as well as abundant non-pyritized disk-shaped macrofossils and organic-walled acritarchs. Combined microtomography, geochemistry, and sedimentary analysis suggest a biota fossilized during early diagenesis. The emergence of this biota follows a rise in atmospheric oxygen, which is consistent with the idea that surface oxygenation allowed the evolution and ecological expansion of complex megascopic life.

Multiple micro-predators controlling bacterial communities in the environment

Predator-prey interactions are a main issue in ecological theory, including multispecies predator-prey relationships and intraguild predation. This knowledge is mainly based on the study of plants and animals, while its relevance for microorganisms is not well understood. The three key groups of micro-predators include protists, predatory bacteria and bacteriophages. They greatly differ in size, in prey specificity, in hunting strategies and in the resulting population dynamics. Yet, their potential to jointly control bacterial populations and reducing biomass in complex environments such as wastewater treatment plants is vast. Here, we present relevant ecological concepts and recent findings on micropredators, and propose that an integrative approach to predation at the microscale should be developed enabling the exploitation of this potential.

Elevated CO2 affects predator-prey interactions through altered performance

Recent research has shown that exposure to elevated carbon dioxide (CO2) affects how fishes perceive their environment, affecting behavioral and cognitive processes leading to increased prey mortality. However, it is unclear if increased mortality results from changes in the dynamics of predator-prey interactions or due to prey increasing activity levels. Here we demonstrate that ocean pCO2 projected to occur by 2100 significantly effects the interactions of a predator-prey pair of common reef fish: the planktivorous damselfish Pomacentrus amboinensis and the piscivorous dottyback Pseudochromis fuscus. Prey exposed to elevated CO2 (880 µatm) or a present-day control (440 µatm) interacted with similarly exposed predators in a cross-factored design. Predators had the lowest capture success when exposed to elevated CO2 and interacting with prey exposed to present-day CO2. Prey exposed to elevated CO2 had reduced escape distances and longer reaction distances compared to prey exposed to present-day CO2 conditions, but this was dependent on whether the prey was paired with a CO2 exposed predator or not. This suggests that the dynamics of predator-prey interactions under future CO2 environments will depend on the extent to which the interacting species are affected and can adapt to the adverse effects of elevated CO2.

The Cambrian conundrum: early divergence and later ecological success in the early history of animals

Diverse bilaterian clades emerged apparently within a few million years during the early Cambrian, and various environmental, developmental, and ecological causes have been proposed to explain this abrupt appearance. A compilation of the patterns of fossil and molecular diversification, comparative developmental data, and information on ecological feeding strategies indicate that the major animal clades diverged many tens of millions of years before their first appearance in the fossil record, demonstrating a macroevolutionary lag between the establishment of their developmental toolkits during the Cryogenian [(850 to 635 million years ago (Ma)], and the later ecological success of metazoans during the Ediacaran (635 to 541 Ma) and Cambrian (541 to 488 Ma) periods. We argue that this diversification involved new forms of developmental regulation, as well as innovations in networks of ecological interaction within the context of permissive environmental circumstances.

Conserved noncoding elements and the evolution of animal body plans

The genomes of vertebrates, flies, and nematodes contain highly conserved noncoding elements (CNEs). CNEs cluster around genes that regulate development, and where tested, they can act as transcriptional enhancers. Within an animal group CNEs are the most conserved sequences but between groups they are normally diverged beyond recognition. Alternative CNEs are, however, associated with an overlapping set of genes that control development in all animals. Here, we discuss the evidence that CNEs are part of the core gene regulatory networks (GRNs) that specify alternative animal body plans. The major animal groups arose >550 million years ago. We propose that the cis-regulatory inputs identified by CNEs arose during the "re-wiring" of regulatory interactions that occurred during early animal evolution. Consequently, different animal groups, with different core GRNs, contain alternative sets of CNEs. Due to the subsequent stability of animal body plans, these core regulatory sequences have been evolving in parallel under strong purifying selection in different animal groups.

The emergence of predators in early life: there was no Garden of Eden

Background

Eukaryote cells are suggested to arise somewhere between 0.85∼2.7 billion years ago. However, in the present world of unicellular organisms, cells that derive their food and metabolic energy from larger cells engulfing smaller cells (phagocytosis) are almost exclusively eukaryotic. Combining these propositions, that eukaryotes were the first phagocytotic predators and that they arose only 0.85∼2.7 billion years ago, leads to an unexpected prediction of a long period (∼1–3 billion years) with no phagocytotes – a veritable Garden of Eden.

Methodology

We test whether such a long period is reasonable by simulating a population of very simple unicellular organisms - given only basic physical, biological and ecological principles. Under a wide range of initial conditions, cellular specialization occurs early in evolution; we find a range of cell types from small specialized primary producers to larger opportunistic or specialized predators.

Conclusions

Both strategies, specialized smaller cells and phagocytotic larger cells are apparently fundamental biological strategies that are expected to arise early in cellular evolution. Such early predators could have been ‘prokaryotes’, but if the earliest cells on the eukaryote lineage were predators then this explains most of their characteristic features.