Abstract
The speed at which species adapt depends partly on the rates of beneficial adaptation generation and how quickly they spread within and among populations. Natural rates of adaptation of corals may not be able to keep pace with climate warming. Several interventions have been proposed to fast‐track thermal adaptation, including the intentional translocation of warm‐adapted adults or their offspring (assisted gene flow, AGF) and the ex situ crossing of warm‐adapted corals with conspecifics from cooler reefs (hybridization or selective breeding) and field deployment of those offspring. The introgression of temperature tolerance loci into the genomic background of cooler‐environment corals aims to facilitate adaptation to warming while maintaining fitness under local conditions. Here we use research on selective sweeps and connectivity to understand the spread of adaptive variants as it applies to AGF on the Great Barrier Reef (GBR), focusing on the genus Acropora. Using larval biophysical dispersal modeling, we estimate levels of natural connectivity in warm‐adapted northern corals. We then model the spread of adaptive variants from single and multiple reefs and assess if the natural and assisted spread of adaptive variants will occur fast enough to prepare receiving central and southern populations given current rates of warming. We also estimate fixation rates and spatial extent of fixation under multiple release scenarios to inform intervention design. Our results suggest that thermal tolerance is unlikely to spread beyond northern reefs to the central and southern GBR without intervention, and if it does, 30+ generations are needed for adaptive gene variants to reach fixation even under multiple release scenarios. We argue that if translocation, breeding, and reseeding risks are managed, AGF using multiple release reefs can be beneficial for the restoration of coral populations. These interventions should be considered in addition to conventional management and accompanied by strong mitigation of CO2 emissions.
Highlights
The increasing pace and severity of environmental change has degraded ecosystems around the world and heightened the need for management interventions to support adaptation or restoration of species (Lindenmayer, Piggott, & Wintle, 2013; van Oppen, Oliver, Putnam, & Gates, 2015; Rinkevich, 2014)
Our biophysical dispersal predictions generally support findings from previous models exploring southern reefs repopulating northern reefs against prevailing currents; our model uniquely explores the possibility for potentially bleaching resistant corals to re‐seed central and southern reefs under scenarios of southwards gene flow
Limited connectivity to the central and southern sectors of the Great Barrier Reef (GBR) is confirmed by our southward biophysical models and by the strong genetic evidence presented in previous studies (Ayre & Hughes, 2004; Lukoschek et al, 2016; van Oppen, Peplow, Peplow, Kininmonth, & Berkelmans, 2011)
Summary
The increasing pace and severity of environmental change has degraded ecosystems around the world and heightened the need for management interventions to support adaptation or restoration of species (Lindenmayer, Piggott, & Wintle, 2013; van Oppen, Oliver, Putnam, & Gates, 2015; Rinkevich, 2014). Estimates of model‐based connectivity suggest some dispersal occurs between major regions on the GBR (Treml & Halpin, 2012) and has been supported by further genetic and modeling data showing some acroporid coral species exhibit low differentiation (Lukoschek, Riginos, & Oppen, 2016; Matz, Treml, Aglyamova, & Bay, 2018; van Oppen, Bongaerts, et al, 2011; Shinzato, Mungpakdee, Arakaki, & Satoh, 2015). Together, this evidence supports that some level of gene flow occurs and that natural penetrance of PALs is possible. Regional differentiation has been detected in a number of species from the Caribbean, the Red Sea, and Western Australia
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