Uncovering developmental diversity in the field.

Many developmental biologists seldom leave the lab for research, relying instead on establishing colonies of traditional and emerging model systems. However, to fully understand the mechanisms and principles of development and evolution, including the role of ecology and the environment, it is important to study a diverse range of organisms in context. In this Perspective, we hear from five research teams from around the world about the importance and challenges of going into the field to study their organisms of interest.

Divergence time estimates for the hypoxia-inducible factor-1 alpha (HIF1α) reveal an ancient emergence of animals in low-oxygen environments.

Unveiling the tempo and mode of animal evolution is necessary to understand the links between environmental changes and biological innovation. Although the earliest unambiguous metazoan fossils date to the late Ediacaran period, molecular clock estimates agree that the last common ancestor (LCA) of all extant animals emerged ~850 Ma, in the Tonian period, before the oldest evidence for widespread ocean oxygenation at ~635-560 Ma in the Ediacaran period. Metazoans are aerobic organisms, that is, they are dependent on oxygen to survive.

Comparing dormancy in two distantly related tunicates reveals morphological, molecular, and ecological convergences and repeated co-option.

Many asexually-propagating marine invertebrates can survive extreme environmental conditions by developing dormant structures, i.e., morphologically simplified bodies that retain the capacity to completely regenerate a functional adult when conditions return to normal.

The Genome of the "Sea Vomit" .

Tunicates are the sister group of vertebrates and thus occupy a key position for investigations into vertebrate innovations as well as into the consequences of the vertebrate-specific genome duplications. Nevertheless, tunicate genomes have not been studied extensively in the past, and comparative studies of tunicate genomes have remained scarce. The carpet sea squirt , commonly known as "sea vomit", is a colonial tunicate considered an invasive species with substantial ecological and economical risk.

From the individual to the colony: Marine invertebrates as models to understand levels of biological organization.

The developmental and evolutionary principles of coloniality in marine animals remain largely unexplored. Although many common traits have evolved independently in different groups of colonial animals, questions about their significance for colonial life histories remain unanswered. In 2018 (Nov.

The "Mexican dancer" in Ecuador: molecular confirmation, embryology and planktotrophy in the sea slug .

, otherwise known as the "Mexican dancer", aries in adult size and color across its geographical distribution in Ecuador. Because of morphological variation and the absence of genetic information for this species in Ecuador, we analyzed mtDNA sequences in three populations (Ballenita, La Cabuya, and Mompiche) and confirmed that individuals from the three locations belonged to and that there was no population structure that could explain their morphological differences. Next, we analyzed general aspects about the reproductive biology and embryology of this species.

Putative stem cells in the hemolymph and in the intestinal submucosa of the solitary ascidian .

Background: In various ascidian species, circulating stem cells have been documented to be involved in asexual reproduction and whole-body regeneration. Studies of these cell population(s) are mainly restricted to colonial species. Here, we investigate the occurrence of circulating stem cells in the solitary a member of the Styelidae, a family with at least two independent origins of coloniality.

Colonial ascidians strongly preyed upon, yet dominate the substrate in a subtropical fouling community.

Higher diversity and dominance at lower latitudes has been suggested for colonial species. We verified this pattern in species richness of ascidians, finding that higher colonial-to-solitary species ratios occur in the tropics and subtropics. At the latitudinal region with the highest ratio, in southeastern Brazil, we confirmed that colonial species dominate space on artificial plates in two independent studies of five fouling communities.

Modular co-option of cardiopharyngeal genes during non-embryonic myogenesis.

Background: In chordates, cardiac and body muscles arise from different embryonic origins. In addition, myogenesis can be triggered in adult organisms, during asexual development or regeneration. In non-vertebrate chordates like ascidians, muscles originate from embryonic precursors regulated by a conserved set of genes that orchestrate cell behavior and dynamics during development.

De novo neurogenesis in a budding chordate: Co-option of larval anteroposterior patterning genes in a transitory neurogenic organ.

During metamorphosis of solitary ascidians, part of the larval tubular nervous system is recruited to form the adult central nervous system (CNS) through neural stem-like cells called ependymal cells. The anteroposterior (AP) gene expression patterning of the larval CNS regionalize the distribution of the ependymal cells, which contains the positional information of the neurons of the adult nervous system. In colonial ascidians, the CNS of asexually developed zooids has the same morphology of the one of the post-metamorphic zooids.

Nonprotein-Coding RNAs as Regulators of Development in Tunicates.

Tunicates, or urochordates, are a group of small marine organisms that are found widely throughout the seas of the world. As most plausible sister group of the vertebrates, they are of utmost importance for a comprehensive understanding of chordate evolution; hence, they have served as model organisms for many aspects of the developmental biology. Current genomic analysis of tunicates indicates that their genomes evolved with a fast rate not only at the level of nucleotide substitutions but also in terms of genomic organization.

Convergent Acquisition of Nonembryonic Development in Styelid Ascidians.

Asexual propagation and whole body regeneration are forms of nonembryonic development (NED) widespread across animal phyla and central in life history and evolutionary diversification of metazoans. Whereas it is challenging to reconstruct the gains or losses of NED at large phylogenetic scale, comparative studies could benefit from being conducted at more restricted taxonomic scale, in groups for which phylogenetic relationships are well established. The ascidian family of Styelidae encompasses strictly sexually reproducing solitary forms as well as colonial species that combine sexual reproduction with different forms of NED.

Vascular budding in Symplegma brakenhielmi and the evolution of coloniality in styelid ascidians.

Individuals of colonial animals (e.g. zooids) are in continuous turnover.

Deviating from the Norm: Peculiarities of Aplysia cf. californica Early Cleavage Compared to Traditional Spiralian Models.

Spiralia represents one of the main clades of bilaterally symmetrical metazoans (Bilateria). This group is of particular interest due to the remarkable conservation of its early developmental pattern despite of the high diversity of larval and adult body plans. Variations during embryogenesis are considered powerful tools to determine ancestral and derived characters under a phylogenetic framework.

Automated detection of ncRNAs in the draft genome sequence of a colonial tunicate: the carpet sea squirt Didemnum vexillum.

Background: The colonial ascidian Didemnum vexillum, sea carpet squirt, is not only a key marine organism to study morphological ancestral patterns of chordates evolution but it is also of great ecological importance due to its status as a major invasive species. Non-coding RNAs, in particular microRNAs (miRNAs), are important regulatory genes that impact development and environmental adaptation. Beyond miRNAs, not much in known about tunicate ncRNAs.

Evolutionary Developmental Biology (Evo-Devo) Research in Latin America.

Famous for its blind cavefish and Darwin's finches, Latin America is home to some of the richest biodiversity hotspots of our planet. The Latin American fauna and flora inspired and captivated naturalists from the nineteenth and twentieth centuries, including such notable pioneers such as Fritz Müller, Florentino Ameghino, and Léon Croizat who made a significant contribution to the study of embryology and evolutionary thinking. But, what are the historical and present contributions of the Latin American scientific community to Evo-Devo? Here, we provide the first comprehensive overview of the Evo-Devo laboratories based in Latin America and describe current lines of research based on endemic species, focusing on body plans and patterning, systematics, physiology, computational modeling approaches, ecology, and domestication.

Evolution of flatworm central nervous systems: Insights from polyclads.

The nervous systems of flatworms have diversified extensively as a consequence of the broad range of adaptations in the group. Here we examined the central nervous system (CNS) of 12 species of polyclad flatworms belonging to 11 different families by morphological and histological studies. These comparisons revealed that the overall organization and architecture of polyclad central nervous systems can be classified into three categories (I, II, and III) based on the presence of globuli cell masses -ganglion cells of granular appearance-, the cross-sectional shape of the main nerve cords, and the tissue type surrounding the nerve cords.

The significance and scope of evolutionary developmental biology: a vision for the 21st century.

Evolutionary developmental biology (evo-devo) has undergone dramatic transformations since its emergence as a distinct discipline. This paper aims to highlight the scope, power, and future promise of evo-devo to transform and unify diverse aspects of biology. We articulate key questions at the core of eleven biological disciplines-from Evolution, Development, Paleontology, and Neurobiology to Cellular and Molecular Biology, Quantitative Genetics, Human Diseases, Ecology, Agriculture and Science Education, and lastly, Evolutionary Developmental Biology itself-and discuss why evo-devo is uniquely situated to substantially improve our ability to find meaningful answers to these fundamental questions.

Evolution and development of budding by stem cells: ascidian coloniality as a case study.

The evolution of budding in metazoans is not well understood on a mechanistic level, but is an important developmental process. We examine the evolution of coloniality in ascidians, contrasting the life histories of solitary and colonial forms with a focus on the cellular and developmental basis of the evolution of budding. Tunicates are an excellent group to study colonial transitions, as all solitary larvae develop with determinant and invariant cleavage patterns, but colonial species show robust developmental flexibility during larval development.

Host-finding behaviour in the nematode Pristionchus pacificus.

Costs and benefits of foraging have been studied in predatory animals. In nematodes, ambushing or cruising behaviours represent adaptations that optimize foraging strategies for survival and host finding. A behaviour associated with host finding of ambushing nematode dauer juveniles is a sit-and-wait behaviour, otherwise known as nictation.

Early lineage specification of long-lived germline precursors in the colonial ascidian Botryllus schlosseri.

In many taxa, germline precursors segregate from somatic lineages during embryonic development and are irreversibly committed to gametogenesis. However, in animals that can propagate asexually, germline precursors can originate in adults. Botryllus schlosseri is a colonial ascidian that grows by asexual reproduction, and on a weekly basis regenerates all somatic and germline tissues.

Whole body regeneration in a colonial ascidian, Botrylloides violaceus.

Colonial ascidians are the only chordates to undergo whole body regeneration (WBR), the ability to form an entirely new individual from the peripheral vasculature. Here we describe WBR in Botrylloides violaceus, a colonial ascidian that reliably regenerates after ablation of all zooids and buds of young colonies. During early regeneration several buds develop within the tunic vasculature, but only one continues development into a complete zooid.

Man is but a worm: chordate origins.

The origin of chordates remains one of the major puzzles of zoology, even after more than a century of intense scientific inquiry, following Darwin's "Origin of Species". The chordates exhibit a unique body plan that evolved from a deuterostome ancestor some time before the Cambrian. Molecular data gathered from phylogenetics and developmental gene expression has changed our perception of the relationships within and between deuterostome phyla.