Evo-devo Approach Research Articles

Transcriptomic analyses in the gametophytes of the apomictic fern Dryopteris affinis

Main conclusionA novel genomic map of the apogamous gametophyte of the fern Dryopteris affinis unlocks oldest hindrance with this complex plant group, to gain insight into evo-devo approaches.The gametophyte of the fern Dryopteris affinis ssp. affinis represents a good model to explore the molecular basis of vegetative and reproductive development, as well as stress responses. Specifically, this fern reproduces asexually by apogamy, a peculiar case of apomixis whereby a sporophyte forms directly from a gametophytic cell without fertilization. Using RNA-sequencing approach, we have previously annotated more than 6000 transcripts. Here, we selected 100 of the inferred proteins homolog to those of Arabidopsis thaliana, which were particularly interesting for a detailed study of their potential functions, protein–protein interactions, and distance trees. As expected, a plethora of proteins associated with gametogenesis and embryogenesis in angiosperms, such as FERONIA (FER) and CHROMATING REMODELING 11 (CHR11) were identified, and more than a dozen candidates potentially involved in apomixis, such as ARGONAUTE family (AGO4, AGO9, and AGO 10), BABY BOOM (BBM), FASCIATED STEM4 (FAS4), FERTILIZATION-INDEPENDENT ENDOSPERM (FIE), and MATERNAL EFFECT EMBRYO ARREST29 (MEE29). In addition, proteins involved in the response to biotic and abiotic stresses were widely represented, as shown by the enrichment of heat-shock proteins. Using the String platform, the interactome revealed that most of the protein–protein interactions were predicted based on experimental, database, and text mining datasets, with MULTICOPY SUPPRESSOR OF IRA4 (MSI4) showing the highest number of interactions: 16. Lastly, some proteins were studied through distance trees by comparing alignments with respect to more distantly or closely related plant groups. This analysis identified DCL4 as the most distant protein to the predicted common ancestor. New genomic information in relation to gametophyte development, including apomictic reproduction, could expand our current vision of evo-devo approaches.

Consciousness as Telos: An Evo-Devo Approach

Consciousness as Telos: An Evo-Devo Approach

Wing pattern diversity in Eunica butterflies (Nymphalidae: Biblidinae): phylogenetic analysis implies decoupled adaptive trends in dorsal sexual dimorphism and ventral eyespot evolution.

Butterfly eyespots are wing patterns reminiscent of vertebrate eyes, formed by concentric rings of contrastingly coloured scales. Eyespots are usually located close to the wing margin and often regarded as the single most conspicuous pattern element of butterfly wing colour displays. Recent efforts to understand the processes involved in the formation of eyespots have been driven mainly by evo-devo approaches focused on model species. However, patterns of change implied by phylogenetic relationships can also inform hypotheses about the underlying developmental mechanisms associated with the formation or disappearance of eyespots, and the limits of phenotypic diversity occurring in nature. Here we present a combined evidence phylogenetic hypothesis for the genus Eunica, a prominent member of diverse Neotropical butterfly communities, that features notable variation among species in eyespot patterns on the ventral hind wing surface. The data matrix consists of one mitochondrial gene region (COI), four nuclear gene regions (GAPDH, RPS5, EF1a and Wingless) and 68 morphological characters. A combined cladistic analysis with all the characters concatenated produced a single most parsimonious tree that, although fully resolved, includes many nodes with modest branch support. The phylogenetic hypothesis presented corroborates a previously proposed morphological trend leading to the loss of eyespots, together with an increase in the size of the conserved eyespots, relative to outgroup taxa. Furthermore, wing colour pattern dimorphism and the presence of androconia suggest that the most remarkable instances of sexual dimorphism are present in the species of Eunica with the most derived eyespot patterns, and are in most cases accompanied by autapomorphic combinations of scent scales and "hair pencils". We discuss natural and sexual selection as potential adaptive explanations for dorsal and ventral wing patterns.

Morphogenesis of fruit as a subject matter for the carpological studies

In this review, the concept of fruit morphogenesis is treated in the context of implementation of the evo-devo approach in carpology. A new viewpoint on the fruit morphogenesis is proposed and justified, comprising the pre-anthetic, as well as post-anthetic periods of fruit development, id est, development of the gynoecium, and development of the fruit itself. It is proposed to recognize ontogenetical (individual) and evolutionary (historical) aspects of fruit morphogenesis, the first of them we can study directly, while the second aspect can be only hypothesized or treated as a theoretical model of fruit evolution in consequence of some presumed changes in the individual fruit morphogenesis. In this article these aspects are named as "ontomorphogenesis" and "phylomorphogenesis" of the fruit, correspondingly. Our concept of ontomorphogenesis of the fruit involves four components that could not be brought together, such as changes in the morphological structure of the gynoecium, abscission of the extragynecial floral parts and the style, histogenesis of the fruit wall and other fruit parts, and terminal stages of the fruit morphogenesis (dehiscence, splitting, or abscission). The current state of studies of these components in the individual and evolutionary contexts is discussed. By examining the patterns of fruit evolution, we should consider factors acting at both the post-anthetic and pre-anthetic periods of fruit ontomorphogenesis.

The Hazards of Regeneration: From Morgan's Legacy to Evo-Devo.

In his prominent book Regeneration (1901), T.H. Morgan's collected and synthesized theoretical and experimental findings from a diverse array of regenerating animals and plants. Through his endeavor, he introduced a new way to study regeneration and its evolution, setting a conceptual framework that still guides today's research and that embraces the contemporary evolutionary and developmental approaches.In the first part of the chapter, we summarize Morgan's major tenets and use it as a narrative thread to advocate interpreting regenerative biology through the theoretical tools provided by evolution and developmental biology, but also to highlight potential caveats resulting from the rapid proliferation of comparative studies and from the expansion of experimental laboratory models. In the second part, we review some experimental evo-devo approaches, highlighting their power and some of their interpretative dangers. Finally, in order to further understand the evolution of regenerative abilities, we portray an adaptive perspective on the evolution of regeneration and suggest a framework for investigating the adaptive nature of regeneration.

The developmental origins of heterodonty and acrodonty as revealed by reptile dentitions.

Despite the exceptional diversity and central role of dentitions in vertebrate evolution, many aspects of tooth characters remain unknown. Here, we exploit the large array of dental phenotypes in acrodontan lizards, including EDA mutants showing the first vertebrate example of positional transformation in tooth identity, to assess the developmental origins and evolutionary patterning of tooth types and heterodonty. We reveal that pleurodont versus acrodont dentition can be determined by a simple mechanism, where modulation of tooth size through EDA signaling has major consequences on dental formula, thereby providing a new flexible tooth patterning model. Furthermore, such implication of morphoregulation in tooth evolution allows predicting the dental patterns characterizing extant and fossil lepidosaurian taxa at large scale. Together, the origins and diversification of tooth types, long a focus of multiple research fields, can now be approached through evo-devo approaches, highlighting the importance of underexplored dental features for illuminating major evolutionary patterns.

The role of ontogeny in wood diversity and evolution.

Evolutionary developmental biology (evo-devo) explores the link between developmental patterning and phenotypic change through evolutionary time. In this review, we highlight the scientific advancements in understanding xylem evolution afforded by the evo-devo approach, opportunities for further engagement, and future research directions for the field. We review evidence that (1) heterochrony-the change in rate and timing of developmental events, (2) homeosis-the ontogenetic replacement of features, (3) heterometry-the change in quantity of a feature, (4) exaptation-the co-opting and repurposing of an ancestral feature, (5) the interplay between developmental and capacity constraints, and (6) novelty-the emergence of a novel feature, have all contributed to generating the diversity of woods. We present opportunities for future research engagement, which combine wood ontogeny within the context of robust phylogenetic hypotheses, and molecular biology.

A tale of two leeches: Toward the understanding of the evolution and development of behavioral neural circuits.

In the animal kingdom, behavioral traits encompass a broad spectrum of biological phenotypes that have critical roles in adaptive evolution, but an EvoDevo approach has not been broadly used to study behavior evolution. Here, we propose that, by integrating two leech model systems, each of which has already attained some success in its respective field, it is possible to take on behavioral traits with an EvoDevo approach. We first identify the developmental changes that may theoretically lead to behavioral evolution and explain why an EvoDevo study of behavior is challenging. Next, we discuss the pros and cons of the two leech model species, Hirudo, a classic model for invertebrate neurobiology, and Helobdella, an emerging model for clitellate developmental biology, as models for behavioral EvoDevo research. Given the limitations of each leech system, neither is particularly strong for behavioral EvoDevo. However, the two leech systems are complementary in their technical accessibilities, and they do exhibit some behavioral similarities and differences. By studying them in parallel and together with additional leech species such as Haementeria, it is possible to explore the different levels of behavioral development and evolution.

Egg Microinjection and Efficient Mating for Genome Editing in the Firebrat Thermobia domestica.

The firebrat Thermobia domestica is an ametabolous, wingless species that is suitable for studying the developmental mechanisms of insects that led to their successful evolutionary radiation on the earth. The application of genetic tools such as genome editing is the key to understanding genetic changes that are responsible for evolutionary transitions in an Evo-Devo approach. In this article, we describe our current protocol for generating and maintaining mutant strains of T. domestica. We report a dry injection method, as an alternative to the reported wet injection method, that allows us to obtain stably high survival rates in injected embryos. We also report an optimized environment setting to mate adults and obtain subsequent generations with high efficiency. Our method underlines the importance of taking each species' unique biology into account for the successful application of genome editing methods to non-traditional model organisms. We predict that these genome editing protocols will help in implementing T. domestica as a laboratory model and to further accelerate the development and application of useful genetic tools in this species.

In the Spotlight-Postdoc.

Maryna Lesoway received the 1st place for a Postdoctoral Oral Presentation at the 2019 meeting of the Pan-American Society for Evolutionary Developmental Biology. She is a recipient of Whitman Center Early Career Investigator Awards at the Marine Biological Laboratory, Woods Hole (2017, 2018), of an Emerging Models Grant of the Society for Developmental Biology (2017), and of an EDEN: Evo-Devo-Eco Network Research Exchange Award (2011) Website: https://marynalesoway.com With whom and where did you study? Right now, I am working with Jonathan Henry in Illinois, where we've been building infrastructure to support growing marine animals like calyptraeids (slipper snails) in non-marine labs, and digging into the sexual development of these crazy snails. Before that, I did my PhD in Biology as a student in the Neotropical Environment Option, a joint program between McGill University in Montreal and the Smithsonian Tropical Research Institute in Panama. This gave me the opportunity to build a project combining my interests in larval biology with EvoDevo approaches. At McGill, I was supervised by Ehab Abouheif, who taught me everything I know about eco-evo-devo. At STRI, I was supervised by Rachel Collin, who showed me the diversity of the calyptraeids and what a great system they are to work with. Before that, I did a Master's degree at the University of Victoria with Louise Page, who introduced me to EvoDevo and patiently taught me microscopy and imaging. What got you interested in Biology? When did you know EvoDevo was for you? It started with an undergraduate field course. In school, I had always liked my biology classes, but until that point I was planning to go into medicine, because that's what smart kids who were good at biology did. I had taken all the invertebrate biology courses offered at the University of Calgary during my bachelor's degree, so I signed up to take Invertebrate Biology at the Bamfield Marine Sciences Center (BC, Canada) too. It didn't hurt that there was a scholarship to help with the costs. That summer, it was taught by Sally Leys (University of Alberta), and it was the first time I encountered living invertebrates in their natural habitat—such a difference from the preserved specimens in my lab courses in landlocked Calgary! It was also the first time that I designed my own research project (I spent a long time looking for penis-fencing behavior in the local flatworms) and realized that research was a career option. I wrote the MCAT that same summer, but applied to graduate school instead of medical school. What makes an EvoDevo lab particularly welcoming? In my experience, the best places to work have a diversity of people, organisms, and approaches. EvoDevo labs usually have this feature by default. There are many ways to do and think about EvoDevo, and it is this openness to new things—new models, new tools, new approaches—that makes it exciting to work in an EvoDevo lab. The best labs that I've worked in have been collaborative and supportive, and excited about the biology of the whole organism. I love working with people who share tools and ideas. That's how we advance the field the fastest—by collaboration, and not by competition. What is the biggest challenge you face as a postdoc? What are issues that you feel the discipline still needs to address? The hardest part of being a postdoc is the uncertainty of what happens next. The academic job market is hard, and what with the COVID-19 pandemic, US immigration issues, and everything else going on in the world, it just got much harder. On a career level, I worry about how long it takes to build new tools and techniques in nontraditional models, especially in such a competitive environment. Experiments can take longer in new models because you often have to start from scratch, and making multi-species comparisons only adds to this. Expectations (often my own) can be unrealistic. I have also been told by that I haven't specialized enough on a single area of research and that this will make it difficult to be hired. I don't believe that, but sometimes it can feel like search committees are only excited about interdisciplinarity in theory. I've also been thinking a lot more about equity and social justice issues. These are big challenges that have not been seriously addressed in academia. As a white woman I am not an underrepresented minority in biology, so the challenge is how I can use my privilege to change structural issues.

Housing microbial symbionts: evolutionary origins and diversification of symbiotic organs in animals.

In many animal hosts, microbial symbionts are housed within specialized structures known as symbiotic organs, but the evolutionary origins of these structures have rarely been investigated. Here, I adopt an evolutionary developmental (evo-devo) approach, specifically to apply knowledge of the development of symbiotic organs to gain insights into their evolutionary origins and diversification. In particular, host genetic changes associated with evolution of symbiotic organs can be inferred from studies to identify the host genes that orchestrate the development of symbiotic organs, recognizing that microbial products may also play a key role in triggering the developmental programme in some associations. These studies may also reveal whether higher animal taxonomic groups (order, class, phylum, etc.) possess a common genetic regulatory network for symbiosis that is latent in taxa lacking symbiotic organs, and activated at the origination of symbiosis in different host lineages. In this way, apparent instances of convergent evolution of symbiotic organs may be homologous in terms of a common genetic blueprint for symbiosis. Advances in genetic technologies, including reverse genetic tools and genome editing, will facilitate the application of evo-devo approaches to investigate the evolution of symbiotic organs in animals. This article is part of the theme issue 'The role of the microbiome in host evolution'.

Searching for Models for Psychological Science: A Possible Contribution of Simulation.

The problem of the theoretical precariousness of psychology requires defining, at an epistemological level, its concepts and languages and the use of models for finding core concepts and building more or less 'hard' theories. After reviewing some main aims and models of psychology, and comparing them with those of other sciences, the commentary deals with the possibility of simulating life as a tool for building evolutionary psychological models. In particular, evolutionary and developmental robotics and the evo-devo models can simulate the simultaneous adaptation effects of the phylogenetic and ontogenetic development of the embodied mind in response to the characteristics of the environment. The simulation using Artificial Intelligence and robotics could contribute significantly to the definition, experimentation, and validation of the models that make up the theories of psychology in its different domains, enhancing the interdisciplinarity with other sciences that study the same objects. Further studies, both epistemological and empirical, are suggested to confirm whether this evo-devo approach can be integrated with "evolutionary psychology" and contribute to a unifying meta-theory of psychological science.

PEATmoss (Physcomitrella Expression Atlas Tool): a unified gene expression atlas for the model plant Physcomitrella patens.

Physcomitrella patens is a bryophyte model plant that is often used to study plant evolution and development. Its resources are of great importance for comparative genomics and evo-devo approaches. However, expression data from Physcomitrella patens were so far generated using different gene annotation versions and three different platforms: CombiMatrix and NimbleGen expression microarrays and RNA sequencing. The currently available P. patens expression data are distributed across three tools with different visualization methods to access the data. Here, we introduce an interactive expression atlas, Physcomitrella Expression Atlas Tool (PEATmoss), that unifies publicly available expression data for P. patens and provides multiple visualization methods to query the data in a single web-based tool. Moreover, PEATmoss includes 35 expression experiments not previously available in any other expression atlas. To facilitate gene expression queries across different gene annotation versions, and to access P. patens annotations and related resources, a lookup database and web tool linked to PEATmoss was implemented. PEATmoss can be accessed at https://peatmoss.online.uni-marburg.de.

CASE REPORT: HUMAN DIGASTRIC SARTORIUS MUSCLE WITH AN EVO‐DEVO APPROACH

INTRODUCTIONHox genes are essential in the fixation of the anteroposterior axes in symmetrical individuals. During mammal evolution of the musculoskeletal system's paired appendages there has been expresión HOX genes; for example, Tbx4 genes determine the identity of hind limbs when paired paraxial mesoderm originates hypaxial and epaxial muscles. From an ontogenetic perspective, muscle embryology has myogenic hierarchical control genes such as Myf5, MyoD, myogenin and MRF4, when linked with diversity controlling genes like Kdm5, Med13, Tcfap4 Atrophin1, Rere, Elongin‐B, ZBTB20, AF10/AF17, Kdm2, Sin3A justify muscular morphological diversity, loss or duplication. Once this is understood trough an evolutionary perspective, one may understand sartorius muscle diversity in mammals. In the case of ruminants, this muscle has a morphology with two superior heads. Interestingly enough, the same sartorius morphology has been documented in humans like an anatomical variant. The present case aims to describe this anatomical variant with an EVO‐DEVO approach.REPORT CASEDuring the course of a second year anatomy class, at La Universidad de La Sabana, the class professor, when exploring the corpse of a 40 year old male, noticed a digastric belly sartorius muscle on the left lower limb, while also noticing an uncommonly thick sartorium on the right lower limb. [Figure 1]. When it came to the digastric sartorius muscle, both bellies ran parallel to each another, however they were covered by different fascia. The medial head originated from the superior border of the anterior superior iliac crest. The lateral head had its classical origin. Both heads had the classical muscular insertion.DiscussionIn natural populations, there are reports of morphological left – right differences, however, reports of individuals with asymmetric morphologies are rare, suggesting the possibility that asymmetric individuals might arise as a result of imperfect development. This may be reflected by the genome's instability due to interactions with environmental factors or “noise”. The stability of the genome is an intrinsic capacity of an organism to resist external disturbances that may occur during natural development and growth. In this case report, the obvious sartorius muscles asymmetry is evidence that invites us to consider the Evo‐Devo perspective. Such idea suggests the possibility that any disturbance during early ontogeny of the lower limb might have occurred as consequence of the genome's lack of buffer capacity. This reminds us, that myogenic control and diversity genes define an individual's symmetry when they are buffered.ConclusionA molecular Evo‐Devo approach should be started in ontogenical manner in order to explain the asymmetry cases that might be found.Support or Funding InformationPROSEIMThis abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Evolution and Regulation of Limb Regeneration in Arthropods.

Regeneration has fascinated both scientists and non-scientists for centuries. Many organisms can regenerate, and arthropod limbs are no exception although their ability to regenerate is a product shaped by natural and sexual selection. Recent studies have begun to uncover cellular and molecular processes underlying limb regeneration in several arthropod species. Here we argue that an evo-devo approach to the study of arthropod limb regeneration is needed to understand aspects of limb regeneration that are conserved and divergent. In particular, we argue that limbs of different species are comprised of cells at distinct stages of differentiation at the time of limb loss and therefore provide insights into regeneration involving both stem cell-like cells/precursor cells and differentiated cells. In addition, we review recent studies that demonstrate how limb regeneration impacts the development of the whole organism and argue that studies on the link between local tissue damage and the rest of the body should provide insights into the integrative nature of development. Molecular studies on limb regeneration are only beginning to take off, but comparative studies on the mechanisms of limb regeneration across various taxa should not only yield interesting insights into development but also answer how this remarkable ability evolved across arthropods and beyond.

The Comparative Method in Biology and the Essentialist Trap

The comparative method is at the centre of a complex view of biology, according to which organisms are seen as historical products. This is a dynamic view of nature, where genotypes and phenotypes change over evolutionary time under the influence of natural selection. Organisms (species) and groups of them (clades) are defined by their uniqueness, and their comparison provides insight into patterns of diversification. The alternative, mechanistic approach is enormously powerful, and has led to our understanding of basic molecular mechanisms underlying biological processes. However, because of intrinsic practical difficulties, this latter approach has only been applied to a very small cohort of animal systems, the so-called “model systems”. While this approach has been enormously productive, it has brought with it as a by-product a narrow view of biological diversity; and the assumption that with just a handful of well-studied animals we “understand” development and evolution. Nothing could be further from the truth, as indicated by many recent studies, which have shown that the development of animals is highly plastic. The lack of appreciation of this simple fact has brought me (and others) to see the field of developmental biology as caught within an “essentialist trap” from which many contemporary evo-devo approaches try to free it.

Expression of vasa, piwi, and nanos during gametogenesis in Typosyllis antoni (Annelida, Syllidae).

Although model species have proven to be crucial for developmental biology, the evo-devo approach requires a broader picture across phylogeny. Herein, we try to expand the range of studied annelids by presenting a transcriptome of Typosyllis antoni as a tool for the study of developmental and evolutionary processes in Syllidae. Moreover, we provide homologs of the stem-cell markers vasa, piwi, and nanos, and investigate their expression patterns in gamete-producing individuals for the first time in this group. We found no expression in females, while there is a distinct expression pattern in males. Based on this data, we argue that spermatogenesis starts in the gonads and finishes in the coelomic cavity, and it occurs simultaneously in a large number of segments. Surprisingly, no expression of the stem-cell markers was found in the segment addition zone of these reproducing animals (stolonizing). Preliminary explanations like a lack of growth during stolonization, or the absence of a common genetic program between germ and somatic stem cells, are discussed. Finally, no reservoir of primordial cells has been detected, suggesting a possible epigenic origin of the Primordial Germ Cells of this species, though this hypothesis needs to be further investigated.

Nasal polyposis (or chronic olfactory rhinitis)

The concept of chronic rhinosinusitis with or without polyps is founded on the structural and functional unicity of the pituitary mucosa and its united response to environmental aggression by allergens, viruses, bacteria, pollution, etc. The present review sets this concept against the evo-devo three-nose theory, in which nasal polyposis is distinguished as specific to the olfactory nose and in particular to the non-olfactory mucosa of the ethmoid, which is considered to be not a sinus but rather the skull-base bone harboring the olfactory mucosa. The evo-devo approach enables simple and precise positive diagnosis of nasal polyposis and its various clinical forms, improves differential diagnosis by distinguishing chronic diseases of the respiratory nose and those of the paranasal sinuses, hypothesizes an autoimmune origin specifically aimed at olfactory system auto-antigens, and supports the surgical concept of nasalization against that of functional sinus and ostiomeatal-complex surgery. The ventilation function of the sinuses seems minor compared to their production, storage and active release of nitric oxide (NO) serving to oxygenate arterial blood in the pulmonary alveoli. This respiratory function of the paranasal sinuses may indeed be their most important. NO trapped in the ethmoidal spaces also accounts for certain radiographic aspects associated with nasal polyposis.

Evolution and development of handedness: An Evo-Devo approach.

Hand preference is a sensorimotor skill whose development both reflects and promotes the development of hemispheric lateralization for manual and cognitive functions. Extensive comparative, crosscultural, and paleoanthropological evidence demonstrates the prevalence of limb lateralized preferences across vertebrate species and the prevalence of right-handedness within hominid evolution. Many reviews of the evolution and development of human handedness have proposed adaptive explanations for its evolution. However, during the last 3 decades a new approach to understanding evolution (the Extended Evolutionary Synthesis-EES) provided a persuasive alternative to the conventional (Neo-Darwinian Synthetic Theory-ST) evolutionary and developmental accounts. EES combines modern evolutionary and developmental research (Evo-Devo) in ways that alter understanding of natural selection, adaptation, and the role of genes in development and evolution. These changes make obsolete all past accounts of the evolution and development of lateralization and handedness because EES/Evo-Devo requires new study designs. The developmental trajectories of any structural or functional trait must be specified so that it may be related to variations in the developmental trajectories of other traits. First, we describe how the EES/Evo-Devo differs from the conventional ST, particularly for understanding of how traits develop. Then, we apply Evo-Devo to the study of handedness development in infancy and its relation to the development of other cognitive functions. Finally, we argue that identifying the development of atypical traits would benefit from knowledge of the range of individual differences in typical developmental trajectories of hand-use preference and their relation to variations in the developmental trajectories of cognitive functions.

Outflow tract septation and the aortic arch system in reptiles: lessons for understanding the mammalian heart

BackgroundCardiac outflow tract patterning and cell contribution are studied using an evo-devo approach to reveal insight into the development of aorto-pulmonary septation.ResultsWe studied embryonic stages of reptile hearts (lizard, turtle and crocodile) and compared these to avian and mammalian development. Immunohistochemistry allowed us to indicate where the essential cell components in the outflow tract and aortic sac were deployed, more specifically endocardial, neural crest and second heart field cells. The neural crest-derived aorto-pulmonary septum separates the pulmonary trunk from both aortae in reptiles, presenting with a left visceral and a right systemic aorta arising from the unseptated ventricle. Second heart field-derived cells function as flow dividers between both aortae and between the two pulmonary arteries. In birds, the left visceral aorta disappears early in development, while the right systemic aorta persists. This leads to a fusion of the aorto-pulmonary septum and the aortic flow divider (second heart field population) forming an avian aorto-pulmonary septal complex. In mammals, there is also a second heart field-derived aortic flow divider, albeit at a more distal site, while the aorto-pulmonary septum separates the aortic trunk from the pulmonary trunk. As in birds there is fusion with second heart field-derived cells albeit from the pulmonary flow divider as the right 6th pharyngeal arch artery disappears, resulting in a mammalian aorto-pulmonary septal complex. In crocodiles, birds and mammals, the main septal and parietal endocardial cushions receive neural crest cells that are functional in fusion and myocardialization of the outflow tract septum. Longer-lasting septation in crocodiles demonstrates a heterochrony in development. In other reptiles with no indication of incursion of neural crest cells, there is either no myocardialized outflow tract septum (lizard) or it is vestigial (turtle). Crocodiles are unique in bearing a central shunt, the foramen of Panizza, between the roots of both aortae. Finally, the soft-shell turtle investigated here exhibits a spongy histology of the developing carotid arteries supposedly related to regulation of blood flow during pharyngeal excretion in this species.ConclusionsThis is the first time that is shown that an interplay of second heart field-derived flow dividers with a neural crest-derived cell population is a variable but common, denominator across all species studied for vascular patterning and outflow tract septation. The observed differences in normal development of reptiles may have impact on the understanding of development of human congenital outflow tract malformations.