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1. The early actinopterygian genus Rhadinichthys redefined, the type species ornatissimus redescribed, and the species bearsdeni introduced

   https://doi.org/10.1017/S1755691024000136  

   MO, Yunyan; CARON, Abigail M; COATES, Michael I (October 2024, Earth and Environmental Science Transactions of the Royal Society of Edinburgh)

   ABSTRACT Rhadinichthysis one of the most wide-ranging and speciose genera of Palaeozoic actinopterygians. A classic variety of ‘palaeoniscoid’,Rhadinichthysspecies are generally small (~10–15 cm) and known mostly from dermal skeletal remains that show features commonplace among early ray-finned fishes. For this reason, the genus has long been considered a poorly diagnosed wastebasket taxon in need of revision and rarely included in systematic analyses. In the present work, syntypes ofRhadinichthys ornatissimus, the type species, are re-examined and supplemented with better-preserved material from other localities in the Scottish Midland Valley. A neotype is nominated and a more precise diagnosis presented with a suite of genus-level apomorphies. Unexpectedly, these traits are also evident in the monotypic Lower Carboniferous actinopterygian genusWoodichthys, which the neotype ofR. ornatissimusclosely resembles. As a result, the genusWoodichthysis subsumed within the redefinedRhadinichthys, and the singleWoodichthysspecies is reassigned asR. bearsdeni, comb. nov., bringing with it a set of endoskeletal data. Some of these data are new, derived from μCT scans of the skull of theR. bearsdeniholotype, yielding renderings that update the original description of its skull table, parasphenoid, neurocranium, and otoliths. Further new data concerning the hyoid arch are obtained from a new specimen ofR. bearsdenifrom a site close by the original Bearsden locality. Redefined in this way,Rhadinichthyspresents a data-rich operational taxonomic unit better suited for systematic studies. However, in so doing, it also releases a cluster of fossil species no longer anchored to a genus and now in need of rediagnoses. 

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2. Comparisons of cell proliferation and cell death from tornaria larva to juvenile worm in the hemichordate Schizocardium californicum

   https://doi.org/10.1186/s13227-022-00198-1  

   Bump, Paul; Khariton, Margarita; Stubbert, Clover; Moyen, Nicole E.; Yan, Jia; Wang, Bo; Lowe, Christopher J. (June 2022, EvoDevo)

   Abstract BackgroundThere are a wide range of developmental strategies in animal phyla, but most insights into adult body plan formation come from direct-developing species. For indirect-developing species, there are distinct larval and adult body plans that are linked together by metamorphosis. Some outstanding questions in the development of indirect-developing organisms include the extent to which larval tissue undergoes cell death during the process of metamorphosis and when and where the tissue that will give rise to the adult originates. How do the processes of cell division and cell death redesign the body plans of indirect developers? In this study, we present patterns of cell proliferation and cell death during larval body plan development, metamorphosis, and adult body plan formation, in the hemichordateSchizocardium californium(Cameron and Perez in Zootaxa 3569:79–88, 2012) to answer these questions. ResultsWe identified distinct patterns of cell proliferation between larval and adult body plan formation ofS. californicum. We found that some adult tissues proliferate during the late larval phase prior to the start of overt metamorphosis. In addition, using an irradiation and transcriptomic approach, we describe a genetic signature of proliferative cells that is shared across the life history states, as well as markers that are unique to larval or juvenile states. Finally, we observed that cell death is minimal in larval stages but begins with the onset of metamorphosis. ConclusionsCell proliferation during the development ofS. californicumhas distinct patterns in the formation of larval and adult body plans. However, cell death is very limited in larvae and begins during the onset of metamorphosis and into early juvenile development in specific domains. The populations of cells that proliferated and gave rise to the larvae and juveniles have a genetic signature that suggested a heterogeneous pool of proliferative progenitors, rather than a set-aside population of pluripotent cells. Taken together, we propose that the gradual morphological transformation ofS. californicumis mirrored at the cellular level and may be more representative of the development strategies that characterize metamorphosis in many metazoan animals. 

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3. Genes with spiralian-specific protein motifs are expressed in spiralian ciliary bands

   https://doi.org/10.1038/s41467-020-17780-7  

   Wu, Longjun; Hiebert, Laurel S.; Klann, Marleen; Passamaneck, Yale; Bastin, Benjamin R.; Schneider, Stephan Q.; Martindale, Mark Q.; Seaver, Elaine C.; Maslakova, Svetlana A.; Lambert, J. David (August 2020, Nature Communications)

   Abstract Spiralia is a large, ancient and diverse clade of animals, with a conserved early developmental program but diverse larval and adult morphologies. One trait shared by many spiralians is the presence of ciliary bands used for locomotion and feeding. To learn more about spiralian-specific traits we have examined the expression of 20 genes with protein motifs that are strongly conserved within the Spiralia, but not detectable outside of it. Here, we show that two of these are specifically expressed in the main ciliary band of the molluscTritia(also known asIlyanassa). Their expression patterns in representative species from five more spiralian phyla—the annelids, nemerteans, phoronids, brachiopods and rotifers—show that at least one of these,lophotrochin, has a conserved and specific role in particular ciliated structures, most consistently in ciliary bands. These results highlight the potential importance of lineage-specific genes or protein motifs for understanding traits shared across ancient lineages. 

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4. Evidence for a Parabasalian Gut Symbiote in Egg-Feeding Poison Frog Tadpoles in Peru

   https://doi.org/10.1007/s11692-023-09602-7  

   Weinfurther, K. D.; Stuckert, A. M. M.; Muscarella, M. E.; Peralta, A. L.; Summers, K. (April 2023, Evolutionary Biology)

   Abstract We report preliminary evidence of a symbiotic parabasalian protist in the guts of Peruvian mimic poison frog (Ranitomeya imitator) tadpoles. This species has biparental care and egg-feeding of tadpoles, while the relatedR. variabilisconsumes the ancestral detritus diet in their nursery pools. Each species’ diet was experimentally switched, in the field and lab. Analyses of gut gene expression revealed elevated expression of proteases in theR. imitatorfield egg-fed treatment. These digestive proteins came from parabasalians, a group of protists known to form symbiotic relationships with hosts that enhance digestion. Genes that code for these digestive proteins are not present in theR. imitatorgenome, and phylogenetic analyses indicate that these mRNA sequences are from parabasalians. Bar-coding analyses of the tadpole microbiomes further confirmed this discovery. Our findings indicate the presence of parabasalian symbiotes in the intestines of theR. imitatortadpoles, that may aid the tadpoles in protein/lipid digestion in the context of an egg diet. This may have enabled the exploitation of a key ecological niche, allowingR. imitatorto expand into an area with ecologically similar species (e.g.,R. variabilisandR. summersi). In turn, this may have enabled a Müllerian mimetic radiation, one of only a few examples of this phenomenon in vertebrates. 

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5. Correlated and decoupled evolution of adult and larval body size in frogs

   https://doi.org/10.1098/rspb.2020.1474  

   Phung, Tung X.; Nascimento, João C.; Novarro, Alexander J.; Wiens, John J. (August 2020, Proceedings of the Royal Society B: Biological Sciences)

   The majority of animal species have complex life cycles, in which larval stages may have very different morphologies and ecologies relative to adults. Anurans (frogs) provide a particularly striking example. However, the extent to which larval and adult morphologies (e.g. body size) are correlated among species has not been broadly tested in any major group. Recent studies have suggested that larval and adult morphology are evolutionarily decoupled in frogs, but focused within families and did not compare the evolution of body sizes. Here, we test for correlated evolution of adult and larval body size across 542 species from 42 families, including most families with a tadpole stage. We find strong phylogenetic signal in larval and adult body sizes, and find that both traits are significantly and positively related across frogs. However, this relationship varies dramatically among clades, from strongly positive to weakly negative. Furthermore, rates of evolution for both variables are largely decoupled among clades. Thus, some clades have high rates of adult body-size evolution but low rates in tadpole body size (and vice versa). Overall, we show for the first time that body sizes are generally related between adult and larval stages across a major group, even as evolutionary rates of larval and adult size are largely decoupled among species and clades. 

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