Mechanisms of reef coral resistance to future climate change

Abstract

Reef corals are highly sensitive to heat, yet populations resistant to climate change have recently been identified. To determine the mechanisms of temperature tolerance, we reciprocally transplanted corals between reef sites experiencing distinct temperature regimes and tested subsequent physiological and gene expression profiles. Local acclimatization and fixed effects, such as adaptation, contributed about equally to heat tolerance and are reflected in patterns of gene expression. In less than 2 years, acclimatization achieves the same heat tolerance that we would expect from strong natural selection over many generations for these long-lived organisms. Our results show both short-term acclimatory and longer-term adaptive acquisition of climate resistance. Adding these adaptive abilities to ecosystem models is likely to slow predictions of demise for coral reef ecosystems.

Mechanisms of Thermal Tolerance in Reef-Building Corals across a Fine-Grained Environmental Mosaic: Lessons from Ofu, American Samoa

“…Genetic architecture refers to the number, effect size, and distribution of genes that control a phenotypic trait (Gagnaire and Gaggiotti, 2016) and can range from a few genes of large effect (oligogenic) to many genes of small effect (polygenic) (Jain and Stephan, 2017). Data from Ofu indicate that thermal tolerance is a polygenic trait, where a number of alleles of small effect across many different cellular pathways are responsible for elevated thermal tolerance of the HV pool corals Palumbi et al, 2014). Polygenic traits are a common feature of high gene flow species and occur widely in marine populations (Limborg et al, 2012;Hale et al, 2013;Pespeni et al, 2013;Laporte et al, 2015;Barney et al, 2017).…”

“…This is accomplished through two fundamentally different pathways depending on the duration of preconditioning (Figure 5). Short-term acclimation is attained through reduced expression of stress response genes under acute heat stress (Bay and Palumbi, 2015), whereas long-term acclimatization involves a shift in baseline expression under control conditions, referred to as "frontloading" (Barshis et al, 2013;Palumbi et al, 2014). The dampening of stress response genes following short-term preconditioning has also been reported in studies on A. millepora from the Great Barrier Reef, which showed a lesser magnitude response of genes associated with apoptotic signaling to acute heat stress following 10 days of preconditioning (Bellantuono et al, 2012a).…”

Plasticity in thermal tolerance has limited potential to buffer ectotherms from global warming

“…As a result, organisms across the globe will be more likely to experience temperatures beyond their physiological limits unless they can in some way buffer themselves from environmental change [2,3]. One mechanism that could greatly reduce the risk of overheating is physiological plasticity in thermal tolerance, such as the reversible changes in thermal tolerance known as acclimation (if measured in the laboratory) or acclimatization (if measured in the field) [4][5][6][7]. For example, the upper thermal tolerance limits of many organisms increase (within individuals) as mean body temperatures rise, meaning that physiological adjustments can potentially compensate for the negative consequences of rising habitat temperatures [8].…”

pH homeostasis during coral calcification in a free ocean CO 2 enrichment (FOCE) experiment, Heron Island reef flat, Great Barrier Reef

“…This pH modification is thought to occur predominantly by the biologically mediated action of Ca-ATPase ion transporters that exchange 2H + for Ca 2+ (13,14), but how such biological controls are affected by changes in the ambient marine environment is still poorly understood. It is also becoming increasingly apparent that the natural level of environmental variability to which coral reef systems are subjected to also influences their potential to adapt and/or acclimatize to environmental change (15)(16)(17). Understanding how corals living in dynamic environments physiologically respond to large diel and seasonal changes in seawater…”