The source of microbial transmission influences niche colonization and microbiome development

Parent-Specific Transgenerational Immune Priming Enhances Offspring Defense-Unless Heat Stress Negates It All

Transgenerational immune priming (TGIP) adjusts offspring's immune responses based on parental immunological experiences. It is predicted to be adaptive when parent-offspring environmental conditions match, while mismatches negate those advantages, rendering TGIP potentially costly. We tested these cost-benefit dynamics in the pipefish Syngnathus typhle (Syngnathidae). Because of their unique male pregnancy, egg production and rearing occur in different sexes, providing both parents multiple avenues for TGIP. Parental bacteria exposure in our pipefish was simulated through vaccinations with heat-killed Vibrio aestuarianus before mating the fish to each other or to controls. The resulting offspring were exposed to V. aestuarianus in control or heat stress environments, after which transcriptome and microbiome compositions were investigated. Transcriptomic TGIP effects were only observed in Vibrio-exposed offspring at control temperatures, arguing for low costs of TGIP in non-matching microbiota environments. Transcriptomic phenotypes elicited by maternal and paternal TGIP had limited overlap and were not additive. Parentally induced transcriptomic responses were associated with immune functions, and specifically, the paternal response to the innate immune branch, possibly hinting at trained immunity. TGIP of both parents reduced the relative abundance of the experimental Vibrio in exposed offspring, showcasing its ecological benefits. Despite TGIP's significance in matching biotic environments, no TGIP-associated phenotypes were observed for heat-treated offspring, illustrating its limitations. Heat spikes caused by climate change thus threaten TGIP benefits, potentially increasing susceptibility to emerging marine diseases. We demonstrate the urgent need to understand how animals cope with climate-induced changes in microbial assemblages to assess their vulnerability in light of climate change.

The effect of parental age on the quantity and quality of offspring in Syngnathus typhle, a species with male pregnancy

Parental age impacts offspring quantity and quality. Most prior research focused on maternal age. Since in most organisms the mother produces the costly eggs plus provides all or most parental care, it is difficult to distinguish maternal effects mediated via the egg from later maternal care. Here, we addressed the effects of parental age on offspring in Syngnathus typhle, a pipefish with male pregnancy. The divide between one parent producing the eggs and the second parent being the exclusive provider of parental care facilitates a distinction between the effects of parental age on egg quality versus parental age on early development. We fully reciprocally crossed young and old mothers and young and old fathers and assessed impact of parental age combination on offspring number, offspring size, and offspring gene expression patterns. Neither parental combination significantly influenced offspring size or male gestation duration; however, they influenced the number of offspring. Paternal, but not maternal, age strongly affected the offspring gene expression. Offspring from old fathers exhibited substantial changes in the expression of genes related to cell cycle regulation, protein synthesis, DNA repair, and neurogenesis. Our findings thus highlight the importance of gestation, as opposed to gamete production, in shaping the parental contribution to offspring development.

The source of microbial transmission influences niche colonization and microbiome development

Early life microbial colonizers shape and support the immature vertebrate immune system. Microbial colonization relies on the vertical route via parental provisioning and the horizontal route via environmental contribution. Vertical transmission is mostly a maternal trait making it hard to determine the source of microbial colonization in order to gain insight into the establishment of the microbial community during crucial development stages. The evolution of unique male pregnancy in pipefishes and seahorses enables the disentanglement of both horizontal and vertical transmission, but also facilitates the differentiation of maternal versus paternal provisioning ranging from egg development, to male pregnancy and early juvenile development. Using 16S rRNA amplicon sequencing and source-tracker analyses, we revealed how the distinct origins of transmission (maternal, paternal and horizontal) shaped the juvenile internal and external microbiome establishment in the broad-nosed pipefish Syngnathus typhle. Our data suggest that transovarial maternal microbial contribution influences the establishment of the juvenile gut microbiome whereas paternal provisioning mainly shapes the juvenile external microbiome. The identification of juvenile key microbes reveals crucial temporal shifts in microbial development and enhances our understanding of microbial transmission routes, colonization dynamics and their impact on lifestyle evolution.