Loe, L. E. | Search bioRxiv

bioRxiv2024

Arctic greening drives changes in the diet and gut microbiome of a resident herbivore with consequences for fitness

Rapid climate warming is "greening" the tundra due to higher plant productivity, particularly of deciduous shrubs and grasses, potentially changing the nutritional base for herbivores. However, the consequences for herbivores are unclear. Although the gut microbiome is an essential factor, mediating the capacity to adapt to dietary change, few studies have investigated the effect of annual changes in the diet-gut microbiome nexus on fitness traits. In a model system, the Svalbard reindeer, a species experiencing the greatest rate of climate warming on Earth, we investigate how climate-induced changes in diet and the gut microbiome impact reindeer body mass. Using high-resolution DNA metabarcoding, we quantified diet and microbiome composition in rumen samples from 97 animals culled in October from 1998 to 2004 in four different valleys. Overall diet diversity and grass consumption were significantly higher following warmer summers, while intake of the dwarf shrub Salix polaris increased with the maximum normalised difference vegetation index (NDVI). The proportion of Salix had a significant positive effect on autumn body mass, which in turn increases ovulation rates and overwinter survival. There was a significant positive effect of Salix on the microbiome diversity, while between-year variation in Bacteroidota, the most common bacteria phylum, was also significantly, positively related to maximum NDVI. However, a structural equation model revealed that the direct "path" effect of the proportion of Salix in the diet on reindeer body mass was stronger than the indirect path effect, mediated through the gut microbiome. Our results suggest a positive impact of climate-driven Arctic greening on Svalbard reindeer fitness, operating through a change in diet composition, partially mediated by the changes in the gut microbiome. These findings advance our understanding of the mechanistic underpinnings of Arctic warming on herbivore populations and contribute to the debate about the importance of the diet-gut microbiome nexus in facilitating species resilience in the face of climate change.

ecology↗

bioRxiv2022

Contrasting genomic consequences of anthropogenic reintroduction and natural recolonisation in high-arctic wild reindeer

Anthropogenic reintroduction can supplement natural recolonisation in reestablishing a species distribution and abundance. However, both reintroductions and recolonisations can give rise to population bottlenecks that reduce genetic diversity and increase inbreeding, potentially causing accumulation of genetic load and reduced fitness. Most current populations of the endemic high-arctic Svalbard reindeer (Rangifer tarandus platyrhynchus) originate from recent reintroductions or recolonisations following regional extirpations due to past overharvesting. We investigated and compared the genomic consequences of these two paths to reestablishment using whole-genome shotgun sequencing of 100 Svalbard reindeer across their range. We found little admixture between reintroduced and natural populations. Two reintroduced populations, each founded by 12 individuals around four decades (i.e. 8 reindeer generations) ago, formed two distinct genetic clusters. Compared to the source population, these populations showed only small decreases in genome-wide heterozygosity and increases in inbreeding and lengths of runs of homozygosity. In contrast, the two naturally recolonised populations without admixture possessed much lower heterozygosity, higher inbreeding, and longer runs of homozygosity, possibly caused by serial population bottlenecks and/or fewer or more genetically related founders than in the reintroduction events. Naturally recolonised populations can thus be more vulnerable to the accumulation of genetic load than reintroduced populations. This suggests that in some organisms even small-scale reintroduction programs based on genetically diverse source populations can be more effective than natural recolonisation in establishing genetically diverse populations. These findings warrant particular attention in the conservation and management of populations and species threatened by habitat fragmentation and loss.

genomics↗