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1. The reproductive microbiome and maternal transmission of microbiota via eggs in Sceloporus virgatus

   https://doi.org/10.1093/femsec/fiae011  

   Bunker, Marie E.; Weiss, Stacey L. (February 2024, FEMS Microbiology Ecology)

   Abstract Maternal transmission of microbes occurs across the animal kingdom and is vital for offspring development and long-term health. The mechanisms of this transfer are most well-studied in humans and other mammals but are less well-understood in egg-laying animals, especially those with no parental care. Here, we investigate the transfer of maternal microbes in the oviparous phrynosomatid lizard, Sceloporus virgatus. We compared the microbiota of three maternal tissues—oviduct, cloaca, and intestine—to three offspring sample types: egg contents and eggshells on the day of oviposition, and hatchling intestinal tissue on the day of hatching. We found that maternal identity is an important factor in hatchling microbiome composition, indicating that maternal transmission is occurring. The maternal cloacal and oviductal communities contribute to offspring microbiota in all three sample types, with minimal microbes sourced from maternal intestines. This indicates that the maternal reproductive microbiome is more important for microbial inheritance than the gut microbiome, and the tissue-level variation of the adult S. virgatus microbiota must develop as the hatchling matures. Despite differences between adult and hatchling communities, offspring microbiota were primarily members of the Enterobacteriaceae and Yersiniaceae families (Phylum Proteobacteria), consistent with this and past studies of adult S. virgatus microbiomes. 

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2. Microbiome maturation during a unique developmental window

   https://doi.org/10.1111/mec.15436  

   Videvall, Elin (May 2020, Molecular Ecology)

   Shortly after birth, mammals are colonized by a multitude of microbes derived from the mother and the environment. Studies in model organisms have demonstrated that the structure and composition of the gut microbiome of offspring steadily mature with increasing diversity during nursing and weaning (Sommer & Bäckhed, 2013). This period of microbiome assembly is critical for young mammals because the gut microbes they acquire will help train their immune system (Lathrop et al., 2011) with potential long‐lasting effects on their health (Cox et al., 2014). In an article in this issue ofMolecular Ecology, Stoffel et al. (2020) investigated the gut microbiota of northern elephant seals (Mirounga angustirostris) during a key developmental window. A month after giving birth, elephant seal mothers stop nursing their pups and return to the sea. As a consequence, their pups go from a diet of milk rich in fat to abruptly enter a post weaning fasting period which lasts for about two months while they remain with the colony. This particular life‐history trait therefore offered the authors a unique and exciting opportunity to evaluate intrinsic factors contributing to gut microbiota development in a wild marine mammal. 

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3. Microbiome composition and function within the Kellet’s whelk perivitelline fluid

   https://doi.org/10.1128/spectrum.03514-23  

   Daniels, Benjamin N.; Nurge, Jenna; De Smet, Chanel; Sleeper, Olivia; White, Crow; Davidson, Jean M.; Fidopiastis, Pat (March 2024, Microbiology Spectrum)

   Hom, Erik F. (Ed.)

   ABSTRACT Microbiomes have gained significant attention in ecological research, owing to their diverse interactions and essential roles within different organismal ecosystems. Microorganisms, such as bacteria, archaea, and viruses, have profound impact on host health, influencing digestion, metabolism, immune function, tissue development, and behavior. This study investigates the microbiome diversity and function of Kellet’s whelk (Kelletia kelletii) perivitelline fluid (PVF), which sustains thousands of developingK. kelletiiembryos within a polysaccharide and protein matrix. Our core microbiome analysis reveals a diverse range of bacteria, with theRoseobactergenus being the most abundant. Additionally, genes related to host-microbe interactions, symbiosis, and quorum sensing were detected, indicating a potential symbiotic relationship between the microbiome and Kellet’s whelk embryos. Furthermore, the microbiome exhibits gene expression related to antibiotic biosynthesis, suggesting a defensive role against pathogenic bacteria and potential discovery of novel antibiotics. Overall, this study sheds light on the microbiome’s role in Kellet’s whelk development, emphasizing the significance of host-microbe interactions in vulnerable life history stages. To our knowledge, ours is the first study to use 16S sequencing coupled with RNA sequencing (RNA-seq) to profile the microbiome of an invertebrate PVF.IMPORTANCEThis study provides novel insight to an encapsulated system with strong evidence of symbiosis between the microbial inhabitants and developing host embryos. The Kellet’s whelk perivitelline fluid (PVF) contains microbial organisms of interest that may be providing symbiotic functions and potential antimicrobial properties during this vulnerable life history stage. This study, the first to utilize a comprehensive approach to investigating Kellet’s whelk PVF microbiome, couples 16S rRNA gene long-read sequencing with RNA-seq. This research contributes to and expands our knowledge on the roles of beneficial host-associated microbes. 

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4. Reciprocal microbiome transplants differentially rescue fitness in two syntopic dung beetle sister species (Scarabaeidae: Onthophagus )

   https://doi.org/10.1111/een.13031  

   Parker, Erik_S; Moczek, Armin_P; Macagno, Anna_L_M (March 2021, Ecological Entomology)

   1. Microbial symbionts play a crucial role in the development, health, and homeostasis of their hosts. However, the eco‐evolutionary conditions shaping these relationships and the evolutionary scale at which host–microbiome interactions may diverge warrant further investigation, especially in non‐model systems. This study examines the impact of reciprocal gut microbiome transplants between two ecologically very similar, sympatric, and syntopic dung beetle sister species. 2.Onthophagus vaccaandOnthophagus mediuswere specifically used to compare the growth, development, and fitness outcomes of individuals that were either (i) reared in the presence of a microbiome provided by a mother of the same species (“self‐inoculated”), (ii) forced to develop with a microbiome derived from a heterospecific mother (“cross‐inoculated”), or (iii) reared without a maternally transmitted microbiome. 3. This study found that individuals reared in the absence of a maternally derived gut microbiome incur detrimental changes in survival, as well as in several metrics signalling normative development. Furthermore, such negative effects are only partly rescued through inoculation with a heterologous microbiome. 4. Collectively, this study's results suggest that inoculation with a species‐specific, maternally transmitted microbiome is critical for normative development, that the significance of maternally derived microbiota for host survival differs across species, and that the phenotypic outcomes resulting from host–microbiome interactions may diverge even between closely related, ecologically similar host species. 

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5. Vertically transmitted microbiome protects eggs from fungal infection and egg failure

   https://doi.org/10.1186/s42523-021-00104-5  

   Bunker, M. E.; Elliott, G.; Heyer-Gray, H.; Martin, M. O.; Arnold, A. E.; Weiss, S. L. (December 2021, Animal Microbiome)

   Abstract Background Beneficial microbes can be vertically transmitted from mother to offspring in many organisms. In oviparous animals, bacterial transfer to eggs may improve egg success by inhibiting fungal attachment and infection from pathogenic microbes in the nest environment. Vertical transfer of these egg-protective bacteria may be facilitated through behavioral mechanisms such as egg-tending, but many species do not provide parental care. Thus, an important mechanism of vertical transfer may be the passage of the egg through the maternal cloaca during oviposition itself. In this study, we examined how oviposition affects eggshell microbial communities, fungal attachment, hatch success, and offspring phenotype in the striped plateau lizard, Sceloporus virgatus , a species with no post-oviposition parental care. Results Relative to dissected eggs that did not pass through the cloaca, oviposited eggs had more bacteria and fewer fungal hyphae when examined with a scanning electron microscope. Using high throughput Illumina sequencing, we also found a difference in the bacterial communities of eggshells that did and did not pass through the cloaca, and the diversity of eggshell communities tended to correlate with maternal cloacal diversity only for oviposited eggs, and not for dissected eggs, indicating that vertical transmission of microbes is occurring. Further, we found that oviposited eggs had greater hatch success and led to larger offspring than those that were dissected. Conclusions Overall, our results indicate that female S. virgatus lizards transfer beneficial microbes from their cloaca onto their eggs during oviposition, and that these microbes reduce fungal colonization and infection of eggs during incubation and increase female fitness. Cloacal transfer of egg-protective bacteria may be common among oviparous species, and may be especially advantageous to species that lack parental care. 

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