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1. 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)

   There 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.

   We 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.

   Cell 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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2. Opposed bands of cilia in the nonfeeding larvae of the serpulid annelid Salmacina tribranchiata

   https://doi.org/10.1111/ivb.12285  

   Pernet, Bruno ( March 2020 , Invertebrate Biology)

   The nonfeeding planktonic larvae of marine invertebrates typically lack larval feeding structures. One puzzling exception to this generalization is the annelid clade Sabellidae, in which nonfeeding larvae possess ciliary bands (specifically, food groove and metatroch) that, to the best of our knowledge, have no function other than in feeding. Nishi and Yamasu (1992b,Bulletin of the College of Sciences, University of the Ryukyus,54, 107–121) published a scanning electron micrograph showing that nonfeeding larvae of the serpulid annelidSalmacina dysterialso possess food groove and metatrochal cilia. Here I demonstrate that nonfeeding larvae ofSalmacina tribranchiataalso bear ciliary bands identifiable as food groove and metatroch by position. High‐speed video of ciliary beat patterns shows that, together with the prototrochal cilia, these bands function in an opposed band system. The presence of feeding structures in nonfeeding annelid larvae is thus more widely distributed than previously recognized. The presence of feeding structures may make evolutionary transitions to planktotrophy more likely, and may underlie an inferred origin of larval feeding in the common ancestor of one of the two major clades of serpulid annelids, Serpulinae.

    

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3. Temperature influences immune cell development and body length in purple sea urchin larvae

   https://doi.org/10.1016/j.marenvres.2024.106705  

   Wilkins, Emily M ; Anderson, Audrey M ; Buckley, Katherine M ; Strader, Marie E ( November 2024 , Marine Environmental Research)

   Anthropogenic climate change has increased the frequency and intensity of marine heatwaves that may broadly impact the health of marine invertebrates. Rising ocean temperatures lead to increases in disease prevalence in marine organisms; it is therefore critical to understand how marine heatwaves impact immune system devel- opment. The purple sea urchin (Strongylocentrotus purpuratus) is an ecologically important, broadcast-spawning, omnivore that primarily inhabits kelp forests in the northeastern Pacific Ocean. The S. purpuratus life cycle in- cludes a relatively long-lived (~2 months) planktotrophic larval stage. Larvae have a well-characterized cellular immune system that is mediated, in part, by a subset of mesenchymal cells known as pigment cells. To assess the role of environmental temperature on the development of larval immune cells, embryos were generated from adult sea urchins conditioned at 14 C. Embryos were then cultured in either ambient (14 C) or elevated (18 C) seawater. Results indicate that larvae raised in an elevated temperature were slightly larger and had more pigment cells than those raised at ambient temperature. Further, the larval phenotypes varied significantly among genetic crosses, which highlights the importance of genotype in structuring how the immune system develops in the context of the environment. Overall, these results indicate that larvae are phenotypically plastic in modulating their immune cells and body length in response to adverse developmental conditions 

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4. Gut microbiota of dung beetles correspond to dietary specializations of adults and larvae

   https://doi.org/10.1111/mec.13901  

   Shukla, Shantanu P. ; Sanders, Jon G. ; Byrne, Marcus J. ; Pierce, Naomi E. ( November 2016 , Molecular Ecology)

   Vertebrate dung is central to the dung beetle life cycle, constituting food for adults and a protective and nutritive refuge for their offspring. Adult dung beetles have soft mandibles and feed primarily on nutritionally rich dung particles, while larvae have sclerotized mandibles and consume coarser dung particles with a higher C/N ratio. Here, using the dung beetlesEuoniticellus intermediusandE. triangulatus, we show that these morphological adaptations in mandibular structure are also correlated with differences in basic gut structure and gut bacterial communities between dung beetle life stages. Metagenome functional predictions based on 16SrDNAcharacterization further indicated that larval gut communities are enriched in genes involved in cellulose degradation and nitrogen fixation compared to adult guts. Larval gut communities are more similar to female gut communities than they are to those of males, and bacteria present in maternally provisioned brood balls and maternal ‘gifts’ (secretions deposited in the brood ball along with the egg) are also more similar to larval gut communities than to those of males. Maternal secretions and maternally provisioned brood balls, as well as dung, were important factors shaping the larval gut community. Differences between gut microbiota in the adults and larvae are likely to contribute to differences in nutrient assimilation from ingested dung at different life history stages.

    

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5. Microbiome analysis of monarch butterflies reveals effects of development and diet

   https://doi.org/10.1093/femsec/fiae143  

   Sanaei, Ehsan ; Chavez, Joselyne ; Harris, Erica_V ; Alcaide, Tiffanie_Y ; Baffour-Addo, Keisha ; Bugay, Mahal_J ; Adams, Kandis L. ; Zelaya, Anna ; de Roode, Jacobus_C ; Gerardo, Nicole_M ( November 2024 , FEMS Microbiology Ecology)

   Diet profoundly influences the composition of an animal’s microbiome, especially in holometabolous insects, offering a valuable model to explore the impact of diet on gut microbiome dynamics throughout metamorphosis. Here, we use monarch butterflies (Danaus plexippus), specialist herbivores that feed as larvae on many species of chemically well-defined milkweed plants (Asclepias sp.), to investigate the impacts of development and diet on the composition of the gut microbial community. While a few microbial taxa are conserved across life stages of monarchs, the microbiome appears to be highly dynamic throughout the life cycle. Microbial diversity gradually diminishes throughout the larval instars, ultimately reaching its lowest point during the pupal stage and then recovering again in the adult stage. The microbial composition then undergoes a substantial shift upon the transition from pupa to adult, with female adults having significantly different microbial communities than the eggs that they lay, indicating limited evidence for vertical transmission of gut microbiota. While diet did not significantly impact overall microbial composition, our results suggest that fourth instar larvae exhibit higher microbial diversity when consuming milkweed with high concentrations of toxic cardenolide phytochemicals. This study underscores how diet and developmental stage collectively shape the monarch’s gut microbiota.

    

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