Microbiome reduction and endosymbiont gain from a switch in sea urchin life-history

Animal gastrointestinal tracts harbor a microbiome that is integral to host function, yet species from diverse phyla have evolved a reduced digestive system or lost it completely. Whether such changes are associated with alterations in the diversity and/or abundance of the microbiome remains an untested hypothesis in evolutionary symbiosis. Here, using the life-history transition from planktotrophy (feeding) to lecithotrophy (non-feeding) in the sea urchin Heliocidaris, we demonstrate that the lack of a functional gut corresponds with a reduction in microbial community diversity and abundance as well as the association with a diet-specific microbiome. We also determine that the lecithotroph vertically transmits a Rickettsiales that may complement host nutrition through amino acid biosynthesis and influence host reproduction. Our results indicate that the evolutionary loss of a functional gut correlates with a reduction in the microbiome and the association with an endosymbiont. Symbiotic transitions can thus accompany life-history transitions in the evolution of developmental strategies.Funding provided by: Human Frontier Science Program AwardCrossref Funder Registry ID: Award Number: RGY0079/2016Funding provided by: National Science FoundationCrossref Funder Registry ID: http://dx.doi.org/10.13039/100000001Award Number: IOS 1456778Funding provided by: National Institutes of HealthCrossref Funder Registry ID: http://dx.doi.org/10.13039/100000002Award Number: R01 AI132581Funding provided by: Australian Research CouncilCrossref Funder Registry ID: http://dx.doi.org/10.13039/501100000923Award Number: DP120102849Total DNA extraction Ampylificaiton of the 16S rRNA gene for bacteria using primers for the V3/V4 region Sequencing via MiSe