Individual variation in growth and physiology of symbionts in response
to temperature
Abstract
In many cases, understanding species level responses to climate change
requires understanding variation among individuals in response to such
change. For species with strong symbiotic relationships, such as many
coral reef species, genetic variation in symbiont responses to
temperature may affect the response to increased ocean temperatures. To
assess variation among symbiont genotypes, we examined the population
dynamics and physiological responses of genotypes of Breviolum
antillogorgium in response to increased temperature. We found broad
temperature tolerance across genotypes, with all genotypes showing
positive growth at 26, 30, and 32 C. Genotypes differed in the
magnitude of the response of growth rate and carrying capacity to
increasing temperature, suggesting that natural selection could favor
different genotypes at different temperatures. However, the historical
temperature at which genotypes were reared was not a good predictor of
temperature response, suggesting a lack of adaptation to temperature
over hundreds of generations. We found increased photosynthetic rates
and decreased respiration rates with increasing temperature, and
differences in physiology among genotypes, but found no significant
differences in the response of different genotypes to temperature. In
species with such broad thermal tolerance, selection experiments on
symbionts outside of the host may not yield results sufficient for
evolutionary rescue from climate change.