Pipefish and Parenthood

You are never alone. Your microbiome is composed of trillions of microbes living in and on your body and playing key roles in everything from digestion to immune system modulation. Where do all these microbes come from? Some were transmitted vertically from your mother’s microbiome as you made your way through the birth canal. Other microbes were, and continue to be, transmitted horizontally from the microbe-rich environment we all inhabit. Naturally, this complicates efforts to determine the origin of microbes found in different body niches. But a new study from Kiel University and the GEOMAR Helmholtz Centre for Ocean Research sheds light on microbial colonization patterns by investigating the pipefish microbiome.      

Pipefish and their seahorse cousins are well-known for their bizarre male pregnancy. Instead of carrying a pregnancy to term, a pipefish mother will deposit her eggs into the father’s pouch, leaving the father to protect and nurture his offspring as they develop into fully-fledged juveniles. As a result of this outlandish pregnancy, young pipefish are colonized by microbes via both maternal and paternal vertical transmission, a fact the researchers leveraged to design two fascinating experiments.

In the first experiment, the team sampled microbes from unfertilized eggs, females, males, pouches and the young developing inside them at different pregnancy stages. In the second experiment, microbes were sampled from juveniles during the first 12 days after their release from the paternal pouch. To identify the microbes present in each sample, the researchers sequenced copies of the 16rRNA gene, a gene commonly used for bacterial characterization. The microbial compositions of the various samples were then compared, revealing intriguing insights into microbial colonization patterns.

Before getting pregnant, male and female pipefish harbored sex-specific microbiomes. But when eggs were deposited into their pouches, the males acquired a feminized microbial composition, indicating interparental transmission. Interestingly, male microbiomes reverted to their sex-specific composition as the males settled into pregnancy, lending credence to the idea that being an involved father is not a threat to one’s masculinity. Microbial colonization in offspring, as it turns out, is also sex-specific. Paternal microbes were mostly found to inhabit the external microbiome of juveniles, while maternal microbes made up the internal microbiome and eventually formed the all-important gut microbiome. These remarkable findings demonstrate that niche colonization is transmission route dependent, paving the way for further research on microbiome establishment patterns.

Source: Tanger, I. S., Stefanschitz, J., Schwert, Y., & Roth, O. (2024). The source of microbial transmission influences niche colonization and microbiome development. Proceedings of the Royal Society B, 291(2016), 20232036.‏