Sarah F Worsley, Zoe Crighton, Chuen Zhang Lee , Terry Burke, Jan Komdeur, Hannah L Dugdale , David S Richardson

Conservation translocations are an increasingly common tool used to help combat species extinction and global biodiversity loss. However, their success is dependent on a wide range of abiotic and biotic factors. To date, the potential role of host-associated microbiomes in translocation success has been overlooked despite their fundamental contribution to host health and fitness. Here, we use faecal samples collected from the last remnant (source) population on Cousin Island, and all four translocated populations (established between 1988-2011), of the Seychelles warbler (Acrocephalus sechellensis) to evaluate whether translocations have long-term impacts on the vertebrate gut microbiome. Gut microbiome alpha diversity was lower in all translocated populations compared to the source population on Cousin Island. Gut microbiome composition also varied, with several short-chain fatty acid producing bacterial families being lost from the core microbiome in some translocated populations; such taxa have been implicated to play an important role in maintaining host metabolic health. Furthermore, the two translocated populations that were established the longest time ago, and with the fewest individuals, had reduced inter-individual gut microbiome variability compared to the source population. While it was not possible to directly assess the specific drivers of these differences, it is likely that size of the founding population, subsequent loss of host genetic variation and environmental factors play a role in shaping gut microbiome variation amongst these populations. Future work should assess whether taxonomic gut microbiome variation translates into differences in gut microbiome function and the consequences this has for individual host and population fitness, and long-term resilience to environmental change.