The link between immunity and life history traits in scleractinian corals

Immunity is an important biological trait that influences the survival of individuals and the fitness of a species. Immune defenses are costly and likely compete for energy with other life-history traits, such as reproduction and growth, affecting the overall fitness of a species. Competition among these traits in scleractinian corals could influence the dynamics and structural integrity of coral reef communities. Due to variability in biological traits within populations and across species, it is likely that coral colonies within population/species adjust their immune system to the available resources. In corals, the innate immune system is composed of various pathways. The immune system components can be assessed in the absence (constitutive levels) and/or presence of stressors/pathogens (immune response). Comparisons of the constitutive levels of three immune pathways (melanin synthesis, antioxidant and antimicrobial) of closely related species of Scleractinian corals allowed to determine the link between immunity and reproduction and colony growth. First, we explored differences in constitutive immunity among closely related coral species of the genus Meandrina with different reproductive patterns (gonochoric vs. hermaphrodite). We then compared fast-growing branching vs. slow-growing massive Porites to test co-variation between constitutive immunity and growth rates and morphology in corals. Results indicate that there seems to be a relationship between constitutive immunity and sexual pattern with gonochoric species showing significantly higher levels of immunity than hermaphrodites. Therefore, gonochoric species maybe better suited to resist infections and overcome stressors. Constitutive immunity varied in relation with growth rates and colony morphology, but each species showed contrasting trends within the studied immune pathways. Fast-growing branching species appear to invest more in relatively low cost pathways of the immune system than slow-growing massive species. In corals, energetic investments in life-history traits such as reproduction and growth rate (higher energy investment) seem to have a significant impact on their capacity to respond to stressors, including infectious diseases and coral bleaching. These differences in energy investment are critical in the light of the recent environmental challenges linked to global climate change affecting these organisms. Understanding physiological trade-offs, especially those involving the immune system, will improve our understanding as to how corals could/will respond and survive in future adverse environmental conditions associated with climate change.