Symbiont genotype influences holobiont response to increased temperature

Area of Science:

• Marine biology
• Ecology
• Evolutionary biology

Background:

• Coral reefs face significant threats from warming oceans and coral bleaching.
• Evolutionary rescue through host and/or symbiont adaptation is a potential mechanism for reef persistence.
• Jellyfish are valuable model systems for studying cnidarian mutualisms and symbiont evolution.

Purpose of the Study:

• To investigate the adaptive potential of the microalgal endosymbiont Symbiodinium microadriaticum in the upside-down jellyfish Cassiopea xamachana to increased temperatures.
• To quantify trait variation among different algal genotypes under varying thermal conditions.
• To assess the impact of symbiont genotype on host fitness and development in response to temperature stress.

Main Methods:

• Quantified trait variation in five Symbiodinium microadriaticum genotypes across three temperatures (26°C, 30°C, 32°C).
• Assessed host fitness and developmental timing in Cassiopea xamachana infected with different algal genotypes.
• Analyzed the relationship between algal genotype, temperature, and physiological responses.

Main Results:

• All algal genotypes exhibited positive growth rates, but respiration and photosynthesis decreased with rising temperatures.
• Algal genotype influenced host asexual reproduction and developmental timing, with responses varying independently of genetic similarity.
• Different temperatures favored distinct algal genotypes, impacting overall host fitness.

Conclusions:

• Symbiodinium microadriaticum possesses adaptive potential to thermal stress, crucial for host resilience.
• The eco-evolutionary dynamics between hosts and symbionts are critical for understanding species survival in changing marine environments.
• Understanding genotype-specific responses is key to predicting the future of coral reef ecosystems.