Journal of experimental zoology. Part B, Molecular and developmental evolution最新文献

Phoronida is a small group of marine animals, most of which are characterized by a long larval period and complex metamorphosis. As a result of metamorphosis, their body changes so much that their true anterior and posterior ends are very close to each other, and the intestine becomes long and U-shaped. Using histology and electron microscopy, we have shown that the elongation and change in shape of the digestive tract that occurs during metamorphosis in Phoronopsis harmeri larvae is accompanied by the formation of new parts and changes in ultrastructure. At the same time, our in situ hybridization data suggest that the posterior markers Cdx and Post2 are expressed in posterior tissues at larval stages, during metamorphosis, and in juveniles, and that changes in their expression correlate with remodeling of the posterior parts of the digestive tract. Our data may shed light on the evolution of body patterning in animals undergoing complex metamorphosis.

Colonial invertebrates consist of iterative semi-autonomous modules (usually termed zooids) whose lifespan is significantly shorter than that of the entire colony. Typically, module development begins with budding and ends with degeneration. Most studies on the developmental biology of colonial invertebrates have focused on blastogenesis, whereas the changes occurring throughout the entire zooidal life were examined only for a few tunicates. Here we provide the first description of transcriptomic changes during polypide development in the freshwater bryozoan Cristatella mucedo. For the first time for Bryozoa, we performed bulk RNA sequencing of six polypide stages in C. mucedo (buds, juvenile polypides, three mature stages, and degeneration stage) and generated a high-quality de novo reference transcriptome. Based on these data, we analyzed clusters of differentially expressed genes for enriched pathways and biological processes that may be involved in polypide budding, growth, active functioning, and degradation. Although stem cells have never been described in Bryozoa, our analysis revealed the expression of conservative "stemness" markers in developing buds and juvenile polypides. Our data also indicate that polypide degeneration is a complex regulated process involving autophagy and other types of programmed cell death. We hypothesize that the mTOR signaling pathway plays an important role in regulating the polypide lifespan.

Developmental plasticity, the ability of a genotype to produce different phenotypes in response to environmental conditions, has been subject to intense studies in the last four decades. The self-fertilising nematode Pristionchus pacificus has been developed as a genetic model system for studying developmental plasticity due to its mouth-form polyphenism that results in alternative feeding strategies with a facultative predatory and non-predatory mouth form. Many studies linked molecular aspects of the regulation of mouth-form polyphenism with investigations of its evolutionary and ecological significance. Also, several environmental factors influencing P. pacificus feeding structure expression were identified including temperature, culture condition and population density. However, the nutritional plasticity of the mouth form has never been properly investigated although polyphenisms are known to be influenced by changes in nutritional conditions. For instance, studies in eusocial insects and scarab beetles have provided significant mechanistic insights into the nutritional regulation of polyphenisms but also other forms of plasticity. Here, we study the influence of nutrition on mouth-form polyphenism in P. pacificus through experiments with monosaccharide and fatty acid supplementation. We show that in particular glucose supplementation renders worms non-predatory. Subsequent transcriptomic and mutant analyses indicate that de novo fatty acid synthesis and peroxisomal beta-oxidation pathways play an important role in the mediation of this plastic response. Finally, the analysis of fitness consequences through fecundity counts suggests that non-predatory animals have an advantage over predatory animals grown in the glucose-supplemented condition.

Developmental plasticity can affect traits directly related to survival, and some changes may promote or impair population persistence in changing environments. At the same time, it can also originate new complex phenotypes, surpassing species-specific boundaries. Therefore, plastic responses have the potential to participate in processes of micro and macroevolution. In this study, we evaluate plastic responses to different thermal regimes during development in traits related to survival and also used for taxonomic classification of two true-toad species, Rhinella icterica and Rhinella ornata. We raised tadpoles representing distinct operational taxonomic units (OTUs) at different temperatures, and the resulting phenotypic patterns suggest canalization in R. icterica and complex variation revealed by plasticity among R. ornata OTUs. Plastic responses to thermal regimes produced differences among the OTUs in traits associated with specific survival strategies of Rhinella species. Some changes surpassed taxonomic boundaries and rescued lineage-specific phenotypic patterns, establishing unusual phenotypic combinations for these species. Our results illustrate the contribution of developmental plasticity for processes involving phenotypic differentiation among species in traits directly related to survival.

What morphologies are more likely to appear during evolution is a central question in zoology. Here we offer a novel approach to this question based on first developmental principles. We assumed that morphogenesis results from the genetic regulation of cell properties and behaviors (adhesion, contraction, etc.). We used EmbryoMaker, a general model of development that can simulate any gene network regulating cell properties and behaviors, the mechanical interactions and signaling between cells and the morphologies arising from those. We created spherical initial conditions with anterior and dorsal territories. We performed simulations changing the cell properties and behaviors regulated in these territories to explore which morphologies may have been possible. Thus, we obtained a set of the most basic animal morphologies that can be developmentally possible assuming very simple induction and morphogenesis. Our simulations suggest that elongation, invagination, evagination, condensation and anisotropic growth are the morphogenetic transformations more likely to appear from changes in cell properties and behaviors. We also found some parallels between our simulations and the morphologies of simple animals, some early stages of animal development and fossils attributed to early animals.

Anurans are famous for having evolved a highly simplified skull through bone loss and fusion events. Nevertheless, their skeleton displays a rich morphological diversity associated with adaptations to diverse lifestyles and ecological niches. Here, we report larval skull ossification in the Andean toad Rhinella spinulosa (Bufonidae), and compare it to the phylogenetically distant genetic model organism Xenopus tropicalis (Pipidae). We find that the ossification timing of most skull bones is conserved between both species, except for the prootic and the angulosplenial that ossify at much later stages in R. spinulosa than X. tropicalis. We propose that a delayed lower jaw ossification in R. spinulosa is tightly related to the more extensive metamorphosis process observed in this species where the ventrally oriented mouth opening shifts anteriorly. We also report two conspicuous notches in the R. spinulosa frontoparietal bone mineralization front which are absent in X. tropicalis, and presumably represent evolutionary remnants of the coronal suture that separates the frontal and parietal bones in most vertebrates. As such notches have not been overtly reported in the literature, we examined the X. tropicalis sibling species Xenopus laevis, and were able to identify similar, albeit transient, indentations in the forming frontoparietal bone, suggesting that vestigial coronal sutures might exist in more frog species than anticipated. Taken together, we show that R. spinulosa represents an ideal organism to study heterochronic shifts and the mechanisms underlying cranial suture loss which drove anuran skull simplification.

Vertebrates acquired various novel traits that were pivotal in their morphological evolution. Domain shuffling, rearrangements of functional domains between genes, is a key molecular mechanism in deuterostome evolution. However, comprehensive studies focusing on early vertebrates are lacking. With advancements in genomic studies, the genomes of early vertebrate groups and cyclostomes are now accessible, enabling detailed comparative analysis while considering the timing of gene acquisition during evolution. Here, we compared 22 metazoans, including four cyclostomes, to identify genes containing novel domain architectures acquired via domain-shuffling (DSO-Gs), in the common ancestor of vertebrates, gnathostomes, and cyclostomes. We found that DSO-Gs in the common ancestor of vertebrates were associated with novel vertebrate characteristics and those in the common ancestor of gnathostomes correlated with gnathostome-specific traits. Notably, several DSO-Gs acquired in common ancestors of vertebrates have been linked to myelination, a distinct characteristic of gnathostomes. Additionally, in situ hybridization revealed specific expression patterns for the three vertebrate DSO-Gs in cyclostomes, supporting their potential functions. Our findings highlight the significance of DSO-Gs in the emergence of novel traits in the common ancestors of vertebrates, gnathostomes, and cyclostomes.

Ants are one of the most ecologically and evolutionarily successful groups of animals and exhibit a remarkable degree of phenotypic diversity. This success is largely attributed to the fact that all ants are eusocial and live in colonies with a reproductive division of labor between morphologically distinct queen and worker castes. Yet, despite over a century of studies on caste determination and evolution in ants, we lack a complete ontogenetic series from egg to adult for any ant species. We, therefore, present a developmental table for the Pharaoh ant Monomorium pharaonis, a species whose colonies simultaneously produce reproductive queens and completely sterile workers. In total, M. pharaonis embryonic, larval, and pupal development lasts 45 days. During embryogenesis, the majority of developmental events are conserved between M. pharaonis and the fruit fly Drosophila melanogaster. We discovered, however, two types of same-stage embryos before gastrulation: (1) embryos with internalized germ cells; and (2) embryos with germ cells outside of the blastoderm at the posterior pole. Moreover, we also found two-types of embryos following germ band extension: (1) embryos with primordial germ cells that will develop into reproductive queens; and (2) embryos with no germ cells that will develop into completely sterile workers. Together, these data show that queen and worker castes are already determined and differentiated by early embryogenesis. During larval development, we confirmed that reproductive and worker larvae proceed through three larval instars. Using anatomical and developmental markers, we can further discern the development of gyne (unmated queen) larvae, male larvae, and worker larvae as early as the 1st instar. Overall, we hope that the ontogenetic series we present here will serve as a blueprint for the generation of future ant developmental tables.

The comparative study of the four non-bilaterian phyla (Cnidaria, Placozoa, Ctenophora, and Porifera) provides insights into the origin of bilaterian traits. To complete our knowledge of the cell biology and development of these animals, additional non-bilaterian models are needed. Given the developmental, histological, ecological, and genomic differences between the four sponge classes (Demospongiae, Calcarea, Homoscleromorpha, and Hexactinellida), we have been developing the Oscarella lobularis (Porifera, class Homoscleromorpha) model over the past 15 years. Here, we report a new step forward by inducing, producing, and maintaining in vitro thousands of clonal buds that now make possible various downstream applications. This study provides a full description of bud morphology, physiology, cells and tissues, from their formation to their development into juveniles, using adapted cell staining protocols. In addition, we show that buds have outstanding capabilities of regeneration after being injured and of re-epithelization after complete cell dissociation. Altogether, Oscarella buds constitute a relevant all-in-one sponge model to access a large set of biological processes, including somatic morphogenesis, epithelial morphogenesis, cell fate, body axes formation, nutrition, contraction, ciliary beating, and respiration.