Comparative Evolutionary Developmental Biology Research Articles

Invention sharing is the mother of developmental biology.

Here we release Part 2 of this special issue, following Part 1 in October. In the preface of Part 1, we proposed the title “Invention sharing is the mother of developmental biology” as a novel adage in place of the classic one by Jonathan Swift, "Necessity is the mother of invention", to promote the formation of research platforms for comparative evolutionary developmental biology (Ogino et al., 2021). To further convince researchers of this title, Part 2 releases two method articles and two protocols as follows. Yamanaka et al. (2022) established culture and microinjection methods for embryos of false clownfish, one of the most popular anemonefish, and demonstrated the effectiveness of RNA injection into the yolk sac as a convenient misexpression tool. These methods are expected to open the way for reverse genetics in this and related anemonefish species, and may reveal the molecular mechanisms of sex change and brilliant color pattern formation. Tagami et al. (2022) showed that RNA interference (RNAi) effectively suppresses zygotic β-catenin activity after the mid-blastula transition (MBT) in the Xenopus embryo. In contrast with other model animals, the RNAi technique had not been successfully applied in Xenopus due to the lack of an essential component of the RISC complex, Argonaute2 (Ago2), at stages earlier than the MBT. However, this study revives it as a tool for gene knock-down in later stages. Tokanai et al. (2022) provide an easy and rapid staining protocol for confocal microscopic observation and reconstruction of three-dimensional images of echinoderm (sea lily, sea urchin, and sand dollar) larvae and juveniles. This protocol uses Nile blue and benzyl alcohol/benzyl benzoate (BABB) to obtain strong and stable fluorescent staining signals and clear opaque backgrounds, which could be applicable to other organisms with untransparent tissues. Hiraga et al. (2022) provide a high-throughput screening protocol for CRISPR/Cas9-mediated genome editing in a nematode Pristionchus pacificus. The use of co-injection markers that induce a certain “roller” phenotype and fluorescent protein expression allow researchers to perform quick visual screening of desired mutants and comparative studies with Caenorhabditis elegans. We hope the above articles convince the readers that sharing methods and protocols among researchers using different organisms would move science forward by inspiring new ambitious ideas and exciting collaborations.

Invention sharing is the mother of developmental biology.

Invention sharing is the mother of developmental biology.

A practical staging atlas to study embryonic development of Octopus vulgaris under controlled laboratory conditions

BackgroundOctopus vulgaris has been an iconic cephalopod species for neurobiology research as well as for cephalopod aquaculture. It is one of the most intelligent and well-studied invertebrates, possessing both long- and short-term memory and the striking ability to perform complex cognitive tasks. Nevertheless, how the common octopus developed these uncommon features remains enigmatic. O. vulgaris females spawn thousands of small eggs and remain with their clutch during their entire development, cleaning, venting and protecting the eggs. In fact, eggs incubated without females usually do not develop normally, mainly due to biological contamination (fungi, bacteria, etc.). This high level of parental care might have hampered laboratory research on the embryonic development of this intriguing cephalopod.ResultsHere, we present a completely parameter-controlled artificial seawater standalone egg incubation system that replaces maternal care and allows successful embryonic development of a small-egged octopus species until hatching in a laboratory environment. We also provide a practical and detailed staging atlas based on bright-field and light sheet fluorescence microscopy imaging for precise monitoring of embryonic development. The atlas has a comparative section to benchmark stages to the different scales published by Naef (1928), Arnold (1965) and Boletzky (2016). Finally, we provide methods to monitor health and wellbeing of embryos during organogenesis.ConclusionBesides introducing the study of O. vulgaris embryonic development to a wider community, this work can be a high-quality reference for comparative evolutionary developmental biology.

Prospects for a General Theory of Evolutionary Novelty.

Novelty is a topic of broad interest, with two distinct approaches within evolutionary biology. The dominant approach since Darwin has been transformationist, with novelty arising through gradual changes in morphology. The Modern Synthesis emphasized the importance of ecological opportunity rather than the source of variation, and this view has many adherents today. Yet, since well before Darwin, an alternative view has held that novelties could arise by rapid changes and many not necessarily be connected to ecological opportunity. The rise of comparative evolutionary developmental biology since 1990 has led to a resurgence of these arguments. Many case studies have documented novelties and there have been rigorous efforts to define the attributes of novelty, but there have been few attempts at a more general model. In contrast, studies of technological innovation have been replete with qualitative models since the 1930s. In this article I consider several possibilities for constructing a general model of novelty and innovation: (1) A general formal theory. (2) Commonalities between different levels, such as genes and morphology, but with sufficient differences between domains that any formal theory would be level specific. (3) Commonalities across levels but for various reasons developing a formal theory even within domains is improbable. A final alternative is that novelty and innovation may be so deeply historical that any general framework is impossible. I conclude that a common conceptual framework can be developed and serve as the foundation for simulation studies, but the importance of feedbacks and potentiating factors renders a formal model implausible.

Eric Davidson and deep time.

Eric Davidson had a deep and abiding interest in the role developmental mechanisms played in generating evolutionary patterns documented in deep time, from the origin of the euechinoids to the processes responsible for the morphological architectures of major animal clades. Although not an evolutionary biologist, Davidson's interests long preceded the current excitement over comparative evolutionary developmental biology. Here I discuss three aspects at the intersection between his research and evolutionary patterns in deep time: First, understanding the mechanisms of body plan formation, particularly those associated with the early diversification of major metazoan clades. Second, a critique of early claims about ancestral metazoans based on the discoveries of highly conserved genes across bilaterian animals. Third, Davidson's own involvement in paleontology through a collaborative study of the fossil embryos from the Ediacaran Doushantuo Formation in south China.

Development of the embryo, larva and early juvenile of Nile tilapia Oreochromis niloticus (Pisces: Cichlidae). Developmental staging system

We described the developmental stages for the embryonic, larval and early juvenile periods of Nile tilapia Oreochromis niloticus to elucidate sequential events of craniofacial development. Craniofacial development of cichlids, especially differentiation and morphogenesis of the pharyngeal skeleton, progresses until about 30 days postfertilization (dpf). Because there is no comprehensive report describing the sequential processes of craniofacial development up to 30 dpf, we newly defined 32 stages using a numbered staging system. For embryonic development, we defined 18 stages (stages 1-18), which were grouped into seven periods named the zygote, cleavage, blastula, gastrula, segmentation, pharyngula and hatching periods. For larval development, we defined seven stages (stages 19-25), which were grouped into two periods, early larval and late larval. For juvenile development until 30 dpf, we defined seven stages (stages 26-32) in the early juvenile period. This developmental staging system for Nile tilapia O. niloticus will benefit researchers investigating skeletogenesis throughout tilapia ontogeny and will also facilitate comparative evolutionary developmental biology studies of haplochromine cichlids, which comprise the species flocks of Lakes Malawi and Victoria.

Endless Forms Most Beautiful. Sean B. Carroll. (2005, W. W. Norton.) $25.95. ISBN 0-393-06016-0

Endless Forms Most Beautiful. Sean B. Carroll. (2005, W. W. Norton.) $25.95. ISBN 0-393-06016-0. In the run-up to the completion of the sequencing of the human genome, many biologists engaged in a modern-day parlor game (via the internet) of guessing the likely number of genes. The genome of Drosophila had already come in at some 13,000–14,000 genes, and since some theories suggested that two whole-genome duplications (albeit with some subsequent gene loss) had occurred between the last common ancestor of Drosophila and vertebrates, guesstimates of 60,000 to 80,000 were common. The announcement in 2003 that the draft human genome sequence indicated a relatively paltry 20,000–25,000 genes was met with some incredulity (and a few refuse to believe it to this day). How could humans, in all our diversity of cell types and complexity of neurons, require essentially the same number of genes as a fly, or worse, a worm (the nematode Caenorhabditis elegans)? I half expected Republicans in Congress to demand that NIH find the missing genes to assuage this affront. That the astonishing morphological diversity of the animal kingdom can be constructed from such a limited number of genes is indeed remarkable, but far more surprising has been the elucidation, over the past two decades, of the developmental mechanisms underlying the construction of this diversity. Sean Carroll, professor at the University of Wisconsin, Madison, and an investigator at the Howard Hughes Medical Institute, has been at the forefront of this revolution since its inception. In Endless Forms Most Beautiful, Carroll brings this story to a general readership in an insightful and enthusiastic fashion, weaving together a childhood friend’s fascination with horror movies; mutant lambs born with a single eye after their mother ate a lily, Veratrum californicum, which secretes cyclopamine; and master regulator genes responsible for major components of body patterning. More importantly, however, Carroll uses these studies in comparative evolutionary developmental biology (known to initiates as evo-devo) to argue for its central role in what he believes is an emerging new evolutionary synthesis. Over the whole the range of topics, Carroll’s writing is witty and engaging, and pulls the reader into the intricacies of Hox genes, Pax-6 as a master gene controller for eye formation, what the Cambrian ‘‘big bang’’ of animal evolution says about the evolution of development, and a remarkable chapter on making black animals, or more prosaically, the evolution of dark coloration. Carroll focuses on four questions: the developmental rules underlying the generation of animal form, the specific mechanisms for generating these forms, how animal diversity has evolved over time, and the developmental explanations underlying large-scale trends in the evolution of form. Throughout the book Carroll moves seamlessly from discussing the morphology of living and fossil animals to the developmental mechanisms underlying them. The first section of the book moves from a discussion of the diversity of animal architecture, including the importance of serial homology and modularity, through the aforementioned discussion of master control genes, to the range of genetic techniques that underlies the genetic toolkit of metazoan development. This background