Coral Host-Symbiont Interactions

Palau Host-Symbiont Interactions

Project Description
The impact of climate change on species and species interactions hugely impacts the ecosystems in which they live, changing their productivity, stability and survival. This is particularly true in ecosystems supported by symbioses - e.g. forests, marshes, coral reefs - where foundational species live in tight association with symbiont partners. In these cases, adaptive genes in one partner must work in concert with adaptive genes in the other to promote holobiont fitness. This project aims to determine how genetic interactions between coral hosts and their symbionts impact coral fitness in the face of climate-induced heat waves. Until now, researchers have focused on fixed genus- or species-level differences between symbionts to predict their contribution to bleaching in warm conditions. However, this ignores population-level polymorphisms in the symbionts - the raw material upon which selection can act on a changing planet. We present preliminary evidence that alleles at specific loci in the host coral are linked to loci in the symbiont genome to form ‘matches’ (i.e. are highly correlated) and that individuals straying from the matching pattern tend to bleach more in experimental tests than individuals that are more matched. We propose to test the consistency and impact of partner matching across three species of corals in three thermally diverse habitats in Palau using high resolution genome sequencing, thermal phenotype testing, and common garden experiments. We will confirm if matching loci are related to heat resistance across species, and if they impact long term traits such as growth and fecundity. Working with local partners to transplant heat resistant corals into reefs with different heat stress patterns and different symbiont genetic neighborhoods will test outcomes of different reef restoration decisions, and promote increased success of local restoration planning.

For ecosystems dependent on symbioses, climate resilience depends on successful interactions between partners (i.e. GxGxE interactions). In corals, this variation has been investigated at the level of coral genetic variants (within or between species) or genus-level symbiont variants. Yet, despite a great deal of careful work, these data have not yet revealed strong impact of specific coral genes on bleaching variation. Our preliminary data show strong increases in the ability to identify coral genes that impact heat resilience when symbiont polymorphisms are taken into account. 

Project Summary

We are performing a large reciprocal transplant experiment across different reef environments in Palau that vary in how much heat stress they experience using three different species of Acropora. We transplanted 80 individuals per species per reef (n=240) to all three sites (total n colonies transplanted = 720) in duplicate, resulting in an experiment that is tracking the fates of over 4,000 coral nubbins. We are pairing this experiment with population-genomic data from the host and symbiont, allowing us to quantify how genetic variation in both hosts, symbionts, and their interactions impact holobiont performance across environments.