Abstract
Rising ocean temperatures associated with global climate change induce breakdown of the symbiosis between coelenterates and photosynthetic microalgae of the genus Symbiodinium. Association with more thermotolerant partners could contribute to resilience, but the genetic mechanisms controlling specificity of hosts for particular Symbiodinium types are poorly known. Here, we characterize wild populations of a sea anemone laboratory model system for anthozoan symbiosis, from contrasting environments in Caribbean Panama. Patterns of anemone abundance and symbiont diversity were consistent with specialization of holobionts for particular habitats, with Exaiptasia pallida/S. minutum (ITS2 type B1) abundant on vertical substrate in thermally stable, shaded environments but E. brasiliensis/Symbiodinium sp. (ITS2 clade A) more common in shallow areas subject to high temperature and irradiance. Population genomic sequencing revealed a novel E. pallida population from the Bocas del Toro Archipelago that only harbors S. minutum. Loci most strongly associated with divergence of the Bocas‐specific population were enriched in genes with putative roles in cnidarian symbiosis, including activators of the complement pathway of the innate immune system, thrombospondin‐type‐1 repeat domain proteins, and coordinators of endocytic recycling. Our findings underscore the importance of unmasking cryptic diversity in natural populations and the role of long‐term evolutionary history in mediating interactions with Symbiodinium.
Highlights
Rising ocean temperatures threaten the persistence of coral reef ecosystems, invaluable hotspots of marine biodiversity that support the health and economy of human communities (Ferrario et al, 2014; Moberg & Folke, 1999)
This study offers a fine-scale view into ecological and evolutionary dynamics of wild Exaiptasia sea anemones
Markers present in candidate symbiosis-related genes were among the most highly differentiated in our dataset, pointing to intraspecific variation in host specificity associated with divergence from the globally distributed population
Summary
Rising ocean temperatures threaten the persistence of coral reef ecosystems, invaluable hotspots of marine biodiversity that support the health and economy of human communities (Ferrario et al, 2014; Moberg & Folke, 1999). It is impossible to maintain large laboratory populations, propagate genetically controlled lines, or create different host–symbiont combinations Because of these challenges, the sea anemone Exaiptasia pallida (Grajales & Rodríguez, 2014), commonly called “Aiptasia,” is emerging as a laboratory model system for studying coral symbiosis, at the cellular level (Goldstein & King, 2016; Weis et al, 2008). The sea anemone Exaiptasia pallida (Grajales & Rodríguez, 2014), commonly called “Aiptasia,” is emerging as a laboratory model system for studying coral symbiosis, at the cellular level (Goldstein & King, 2016; Weis et al, 2008) These fast-growing anemones reproduce sexually through broadcast-spawning and asexually through pedal laceration, allowing large populations of genetically identical individuals to be propagated, experimentally bleached, and reinfected with cultured symbionts. We further analyze 2bRAD-Seq data to investigate locus-specific patterns of host differentiation that could suggest potential roles in adaptation to local environments
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