acropora cervicornis

Abstract

The plastic ability for a range of phenotypes to be exhibited by the same genotype allows organisms to respond to environmental variation and may modulate fitness in novel environments. Differing capacities for phenotypic plasticity within a population, apparent as genotype by environment interactions (GxE), can therefore have both ecological and evolutionary implications. Epigenetic gene regulation alters gene function in response to environmental cues without changes to the underlying genetic sequence and likely mediates phenotypic variation. DNA methylation is currently the most well described epigenetic mechanism and is related to transcriptional homeostasis in invertebrates. However, evidence quantitatively linking variation in DNA methylation with that of phenotype is lacking in some taxa, including reef-building corals. In this study, spatial and seasonal environmental variation in Bonaire, Caribbean Netherlands was utilized to assess relationships between physiology and DNA methylation profiles within genetic clones across different genotypes of Acropora cervicornis and A. palmata corals. The physiology of both species was highly influenced by environmental variation compared to the effect of genotype. GxE effects on phenotype were only apparent in A. cervicornis. DNA methylation in both species differed between genotypes and seasons and epigenetic variation was significantly related to coral physiological metrics. Furthermore, plastic shifts in physiology across seasons were significantly positively correlated with shifts in DNA methylation profiles in both species. These results highlight the dynamic influence of environmental conditions and genetic constraints on the physiology of two important Caribbean coral species. Additionally, this study provides quantitative support for the role of epigenetic DNA methylation in mediating phenotypic plasticity in invertebrates.

Contact details:

Francesca Virdis (Reef Renewal Bonaire) ->  francesca@reefrenewalbonaire.org

Serena Hackerott (FIU) -> shack013@fiu.edu

Full text available here: https://pubmed.ncbi.nlm.nih.gov/37454286/

Abstract

The plastic ability for a range of phenotypes to be exhibited by the same genotype allows organisms to respond to environmental variation and may modulate fitness in novel environments. Differing capacities for phenotypic plasticity within a population, apparent as genotype by environment interactions (GxE), can therefore have both ecological and evolutionary implications. Epigenetic gene regulation alters gene function in response to environmental cues without changes to the underlying genetic sequence and likely mediates phenotypic variation. DNA methylation is currently the most well described epigenetic mechanism and is related to transcriptional homeostasis in invertebrates. However, evidence quantitatively linking variation in DNA methylation with that of phenotype is lacking in some taxa, including reef-building corals. In this study, spatial and seasonal environmental variation in Bonaire, Caribbean Netherlands was utilized to assess relationships between physiology and DNA methylation profiles within genetic clones across different genotypes of Acropora cervicornis and A. palmata corals. The physiology of both species was highly influenced by environmental variation compared to the effect of genotype. GxE effects on phenotype were only apparent in A. cervicornis. DNA methylation in both species differed between genotypes and seasons and epigenetic variation was significantly related to coral physiological metrics. Furthermore, plastic shifts in physiology across seasons were significantly positively correlated with shifts in DNA methylation profiles in both species. These results highlight the dynamic influence of environmental conditions and genetic constraints on the physiology of two important Caribbean coral species. Additionally, this study provides quantitative support for the role of epigenetic DNA methylation in mediating phenotypic plasticity in invertebrates.

Abstract Coral reefs are some of the most diverse and valuable ecosystems worldwide. Since the 1970’s the coral populations of Acropora spp. around Bonaire Island have been declining due to White Band Disease (WBD) and due to heavy storms and hurricanes (i.e., hurricane Lenny in 1999). Acropora cervicornis is one of the species selected as restoration target because its critically endangered status according to the IUCN red list and its ecological value as reef builder. Promoting genetic diversity is key to aid the recovery of degraded populations and give this species higher chance to survive in the long-term. In this study, we measure growth and healing, as phenotypic traits of propagated corals to assess the different genotype performance in the nursery phase. Linear length and tissue regeneration have been monitored for 8 weeks for 10 different genotypes (n=5), respectively with in situ measurement and image analysis. The preliminary results suggest that some individual fragments can grow up to one centimeter per week and achieve complete tissue regeneration from cutting and handling damage in 15 days. Being able to determinate the differences in performance from various coral genotypes can help nursery based coral restoration to be more performant. Indeed, selecting coral genotypes that can grow and regenerate faster is a considerable advantage for coral restoration practitioners that could therefore optimize their outplanting efforts.

Abstract:

Knowledge gaps remain regarding the drivers of active coral restoration success that may impede our ability to effectively restore coral reef communities. Publications about ecological development of Acropora outplants on natural reefs reveal that long term survival is low and that growth and survivorship is negatively correlated with increased density, competition by other species and sedimentation. Freshly deployed artificial reefs have the potential to relieve corals from some of the stressors by facilitating a clean, competitor free environment. Especially the relieve from the prominent Dictyota macro-algae species wich we assumed to be a main competitor, might benefit the corals. Here, we conducted a field experiment of one year to investigate growth and survival of nursery-raised Acropora cervicornis corals outplants for two types of reefs as substrate: natural patch reefs and originally clean algae-free artificial reefs, and simultaneously investigated the effects of depth and position of attachment to the reefs on these variables.

Significant differences in survival between reef types up to 53 days after outplanting indicated that corals did benefit from clean artificial reef substrate in the early stages. However, after that time, survival of corals on both reef types converged so that no significant differentiation could be made. Final survival after a year was 50% ± 10.20% on natural patch reefs, while the survival on the artificial reefs plots decreased to 49.17% ± 13.86. Initial cleanliness of the substrate seemed to be not important to survival in the long run in the current study. However, in combination with other survival improving practices, overcoming initial losses of outplanted corals by using clean artificial substrates has potential to improve survival in the long run.

Instantaneous growth rates of Acropora cervicornis were .00379 day-1 (sd = .00129 day-1 ) and .00636 day-1 (sd = .00100 day-1 ) on artificial reefs and natural patch reefs respectively. These rates were affected by all variables under scrutiny. Place of attachment within the artificial reefs had the strongest effect, followed by the reef type for which confidence intervals were wider. Depth was found to have an effect but only very minimal over the small range of 15 to 18.6 meters. Acropora cervicornis grew faster on the natural patch reefs. The hypothesis that the absence of an established benthic community on artificial reefs might have a positive effect on coral growth rate cannot be supported. Differential growth rates are possibly induced by differences in water flow rates within reefs and are possibly the combined result of differential flow rates and overall nutrient availability between reef types. More investigation into the drivers for growth is necessary to confidently deduce the most important factors for growth on the two reef types