Genetic structure is stronger across human-impacted habitats than among islands in the coralPorites lobata

Abstract

We examined genetic structure in the lobe coral Porites lobata among pairs of highly variable and high-stress nearshore sites and adjacent less variable and less impacted offshore sites on the islands of Oʻahu and Maui, Hawai'i. Using an analysis of molecular variance framework, we tested whether populations were more structured by geographic distance or environmental extremes. The genetic patterns we observed followed isolation by environment, where nearshore and adjacent offshore populations showed significant genetic structure at both locations (AMOVA FST = 0.04 ~ 0.19, P < 0.001), but no significant isolation by distance between islands.In contrast, a third site with a less impacted nearshore site showed no significant structure. Strikingly, corals from the two impacted nearshore sites on different islands over 100km apart with similar environmentally stressful conditions were genetically closer (FST ~ 0, P = 0.733) than those within a single location less than 2 km apart (FST = 0.041~0.079, P < 0.01). Our results suggest that ecological boundaries appear to play a strong role in forming genetic structure in the coastal environment, and that genetic divergence in the absence of geographical barriers to gene flow may be explained by disruptive selection across contrasting habitats.# 1

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

“…Very recent or ongoing diversification driven by selection would also be a parsimonious explanation for the cryptic genetic structure found in the mitochondrial genome, which was also resolved at a finer scale by the genome-wide SNP data. Previous studies on this species complex have uncovered strong and unexpected genetic structure associated with nearshore and offshore differences in Samoa 30 , and in Hawaiʻi 31,32 . Gene ontology enrichment analysis of the most highly differentiated (nearly alternatively fixed) loci between the mitochondrial clades (B and C) were significantly enriched for processes involving phosphorus as well as mitochondrial electron transport, and chemosensory and olfactory behavior.…”

“…1B). 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][31][32] . In addition, we sought to identify candidate outlier loci that differentiated bleached and unbleached colonies.…”

Isotopic approaches to estimating the contribution of heterotrophic sources to Hawaiian corals

“…Kāne‘ohe Bay is a semi‐enclosed body of water and the corals in this bay can be exposed to greater amounts of terrestrial runoff than at other sites, potentially affecting their isotopic composition. Indeed, even the genetic structure of Hawaiian Porites corals is known to differ along gradients of anthropogenic influence (Tisthammer et al 2020). Changes in the concentration of DIM are also important considerations, as natural seasonal fluctuations and variation in anthropogenic influence can affect the fractionation of δ 13 C and δ 15 N used for photosynthesis (Swart et al 2005, further explanation of fractionation values used in the mixing models is included in the Supporting Information).…”

Small‐scale genetic structure of coral populations in Palau based on whole mitochondrial genomes: Implications for future coral resilience

“…Genetic differentiation can also be seen for corals living across environmental gradients such as depth or water quality where selection might be acting (Eckert et al, 2019; Tisthammer et al, 2020). For instance, Selmoni et al (2020) compared polymorphism levels in A. digitifera across nearly 8000 SNPs from two broad sampling areas in Okinawa and the Yaeyama Islands approximately 500 km away, and found 18 loci that seemed to have a high association with coral bleaching alerts and with latitude.…”