Restricted gene flow and local adaptation highlight the vulnerability of high‐latitude reefs to rapid environmental change

Abstract

Global climate change poses a serious threat to the future health of coral reef ecosystems. This calls for management strategies that are focused on maximizing the evolutionary potential of coral reefs. Fundamental to this is an accurate understanding of the spatial genetic structure in dominant reef-building coral species. In this study, we apply a genotyping-by-sequencing approach to investigate genome-wide patterns of genetic diversity, gene flow, and local adaptation in a reef-building coral, Pocillopora damicornis, across 10 degrees of latitude and a transition from temperate to tropical waters. We identified strong patterns of differentiation and reduced genetic diversity in high-latitude populations. In addition, genome-wide scans for selection identified a number of outlier loci putatively under directional selection with homology to proteins previously known to be involved in heat tolerance in corals and associated with processes such as photoprotection, protein degradation, and immunity. This study provides genomic evidence for both restricted gene flow and local adaptation in a widely distributed coral species, and highlights the potential vulnerability of leading-edge populations to rapid environmental change as they are locally adapted, reproductively isolated, and have reduced levels of genetic diversity.

Adaptation to reef habitats through selection on the coral animal and its associated microbiome

“…The coral heat-stress response is also known to involve chaperones, such as HSPs, and the ubiquitin system (Csaszar, Seneca, & van Desalvo et al, 2008;Maor-Landaw et al, 2014;Voolstra et al, 2009). Further, a growing body of evidence supports local adaptation to different environmental factors, including temperature, involves selection on genes in the ubiquitin system (Barshis et al, 2010;Bay & Palumbi, 2014;Jin et al, 2016;Thomas, Kennington, Evans, Kendrick, & Stat, 2017 Sequence types C42 and C1 were also present in our and the previous studies, and, as expected for the higher resolution amplicon next-generation sequencing method, we observed additional sequence types previously reported from cloning methods (Sampayo et al, 2009; Figure 6). These co-occurring sequence types likely represent single but distinct Symbiodinium types in P. damicornis colonies on the reef flat versus the slope.…”

“…The coral heat‐stress response is also known to involve chaperones, such as HSPs, and the ubiquitin system (Csaszar, Seneca, & van Oppen, ; DeSalvo, Sunagawa, Voolstra, & Medina, ; Desalvo et al., ; Maor‐Landaw et al., ; Voolstra et al., ). Further, a growing body of evidence supports local adaptation to different environmental factors, including temperature, involves selection on genes in the ubiquitin system (Barshis et al., ; Bay & Palumbi, ; Jin et al., ; Lundgren et al., ; Thomas, Kennington, Evans, Kendrick, & Stat, ). Our results on P. damicornis are consistent with previous findings and highlight the prevalent role of the ubiquitin system in the coral acclimatization and adaptive responses to environmental differences.…”

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

“…Certainly, the extreme temperature profiles of the HV pool are not unique to Ofu; corals are found in a variety of extreme environments and are exposed to temperatures that would cause bleaching in their conspecifics from other areas (Coles and Riegl, 2013;Kline et al, 2015;Richards et al, 2015;Camp et al, 2017). Wide variation in thermal tolerance and genetic divergence has been reported across latitudes and at large-spatial scales (Middlebrook et al, 2008;Howells et al, 2013;Dixon et al, 2015;Thomas et al, 2017), and it is becoming increasingly clear that locally adapted thermally tolerant pockets of corals exist at fine-spatial scales within a variety of coral reef systems (Goreau and Macfarlane, 1990;Barshis et al, 2010;Castillo et al, 2012;Kenkel et al, 2013bKenkel et al, , 2015Schoepf et al, 2015). For example, Porites astreiodes colonies from the thermally variable inshore patch reef environment of south Florida have greater thermal tolerance than offshore populations less than 10 km away (Kenkel et al, 2013a).…”

High Latitude Corals Tolerate Severe Cold Spell

“…For example high latitude conditions suppress reef building processes and limit corals to distinct communities (Kleypas et al, 1999). Furthermore, these populations are locally adapted, reproductively isolated and have low genetic diversity (Ayre and Hughes, 2004;Miller and Ayre, 2008;Noreen et al, 2009;Thomas et al, 2017). Similar to what has been observed in low latitude corals, cold stress, such as can be expected during unusually cold MCS, could be limiting for corals and symbionts and induce bleaching in high latitude corals.…”