Population structure and clonal prevalence of scleractinian corals (Montipora capitataandPorites compressa) in Kaneohe Bay, Oahu

Abstract

20As the effects of anthropogenic climate change grow, mass coral bleaching events are expected to 21 increase in severity and extent. Much research has focused on the environmental stressors 22 themselves, symbiotic community compositions, and transcriptomics of the coral host. Globally, 23 fine-scale population structure of corals is understudied. This study reports patterns of population 24 structure and clonal prevalence found in Montipora capitata and Porites compressa in Kaneohe 25 Bay, Oahu. Generated using ddRAD methods, genetic data reveals different patterns in each taxa 26 despite them being exposed to the same environmental conditions. STRUCTURE and site-level 27 pairwise FST analyses suggest population structure in M. capitata resembling isolation by distance. 28 Mantel tests show strong, significant FST correlations in M. capitata in relation to geographic 29 distance, water residence time, and salinity and temperature variability (range) at different time 30 scales. STRUCTURE did not reveal strong population structure in P. compressa. FST correlation 31 was found in P. compressa in relation to yearly average sea surface height. We also report high 32 prevalence of clonal colonies in P. compressa in outer bay sites exposed to storms and high energy 33 swells. Amongst only outer bay sites, 7 out of 23 sequenced individuals were clones of other 34 colonies. Amongst all 47 sequenced P. compressa individuals, 8 were clones. Only one clone was 35 detected in M. capitata. Moving forward, it is crucial to consider these preexisting patterns relating 36 to genetic diversity when planning and executing conservation and restoration initiatives. 37Recognizing that there are differences in population structure and diversity between coral taxa, 38 even on such small-scales, is important as it suggests that small-scale reefs must be managed by 39 species rather than by geography. 40 41 adaptation 43 44 Rapid climate change due to anthropogenic carbon emissions is one of the greatest threats 45 to global marine biodiversity (Cheung et al. 2009). Within the past few decades, coral bleaching 46 events have increased in occurrence and severity to the point where they are becoming 47 commonplace (Hughes et al. 2003). Despite bleaching being a widely-known impact of climate 48 change, the pathways by which it occurs remain poorly understood. 49 A large proportion of research has focused on the role of zooxanthellae, dinoflagellate 50 algae of the genus Symbiodinium that form symbiotic relationships with coral, in mediating the 51 bleaching response. In a zooxanthellae driven response, thermal bleaching is caused by or begins 52 when photosystems within the symbiont cells become damaged by heat and sunlight and cells are 53 subsequently ejected by the coral host (Jones et al. 1998, Warner et al. 1999). In addition to 54 symbiont-related mechanisms of coral bleaching, bleaching can be a physiological response of the 55 coral, in which case genetic variation among coral could affect their response. Some evidence 56e...

Host-symbiont coevolution, cryptic structure, and bleaching susceptibility, in a coral species complex (Scleractinia; Poritidae)

“…Previous work on corals has found partitioning by depth 24 , 25 , and correlation with fine scale environmental differences such as temperature variation associated with proximity to shore 26 , 27 . In the genus Porites , which is one of the most abundant corals in the tropics, there are several examples of morphologically distinct ‘species’ that genetic studies have been unable to resolve, consistent with phenotypic polymorphism, incipient speciation, hybridization between species 10 , 28 , or epigenetic differences 29 .…”

“…In Hawaiʻi, similar strong genetic structure was found between different sampling locations on the island of Oʻahu 10 , and between nearshore and offshore populations of P. lobata exposed to contrasting anthropogenic stress across the main Hawaiian Islands 31 , 32 . In addition, recent work found cryptic genetic structure within P. compressa in Kāneʻohe Bay that was correlated to annual average sea surface height 25 . The branching ( P. compressa ) and mounding ( P. lobata ) corals in this species complex, have a fairly continuous range of intermediate morphologies that can occur in the same habitat, ruling out phenotypic plasticity (Fig.…”

“…1 B). We were particularly interested in determining if this variation in bleaching susceptibility was related to the cryptic genetic structure that previous work has found to be associated with nearshore/offshore habitat differences 10 , 25 , 30 – 32 . In addition, we sought to identify candidate outlier loci that differentiated bleached and unbleached colonies.…”

Genomic signatures of clonality in the deep water kelp Laminaria rodriguezii

“…Over the last few years, RAD-sequencing has been used to study partially clonal species, such as the moss Syntrichia caninervis (Baughman et al, 2017), the tussock species (Kobresia tibetica andBlysmus sinocompressus , Ning et al, 2018), the Cardamine (Kobresia tibetica and Blysmus sinocompressus , Tsujimoto et al, 2020) and scleractinian corals (Montipora capitate ,Porites compressa in Locatelli & Drew, 2019; Leptopsammia pruvoti in Boscari et al, 2019). These studies have enabled the detection of multilocus lineages (MLLs) for determining the spatial architecture of clonal lineages.…”

“…Notably, the threshold was defined from the distribution of pairwise genetic distance in admitting that the first peak of small distance was derived from somatic mutations or genotyping errors within genets, and the second peak of long-distance represented variation between genets (Meirmans & Tienderen, 2004). Sometimes, a fixed threshold of similarity was applied to collapse individuals in MLLs following the logic that clonal individuals should be nearly 100% identical (Locatelli & Drew, 2019). However, this is not a universal trend, especially when the background of genotyping errors is high enough to confuse the identification of closely related genotypes, or if independent somatic mutations are numerous enough to accentuate the differences beyond the detection threshold.…”