Reduced thermal tolerance of massive coral species in a highly variable environment.

Coral bleaching events are increasing in frequency and severity, resulting in widespread losses in coral cover. However, branching corals native to highly variable (HV) thermal environments can have higher bleaching resistance than corals from more moderate habitats. Here, we investigated the response of two massive corals, Porites lobata and Goniastrea retiformis, from a moderately variable (MV) and a low variability (LV) pool transplanted into a HV pool on Ofu Island in American Samoa. Paired transplant and native ramets were exposed to an acute thermal stress after 6 and 12 months of exposure to the HV pool to evaluate changes in thermal tolerance limits. For both species, photosynthetic efficiency and chlorophyll loss following acute heat stress did not differ between ramets transplanted into the HV pool and respective native pool. Moreover, HV native P. lobata exhibited the greatest bleaching susceptibility compared to MV and LV natives and there was no effect of acute heat stress on MV P. lobata. There was also a thermal anomaly during the study, where Ofu's backreef thermal regime surpassed historical records-2015 had 8 degree heating weeks (DHW) and 2016 had up to 5 DHW (in comparison to less than or equal to 3 over the last 10 years)-which may have exceeded the upper thermal limits of HV native P. lobata. These results strongly contrast with other research on coral tolerance in variable environments, potentially underscoring species-specific mechanisms and regional thermal anomalies that may be equally important in shaping coral responses to extreme temperatures.

Comparison of synganglion neuropeptides, neuropeptide receptors and neurotransmitter receptors and their gene expression in response to feeding in Ixodes scapularis (Ixodidae) vs. Ornithodoros turicata (Argasidae).

Illumina GAII high-throughput sequencing was used to compare expressed genes for female synganglion neuropeptides, neuropeptide receptors and neurotransmitter receptors of the soft tick Ornithodoros turicata with the hard tick Ixodes scapularis. Gene ontology molecular level three mapping revealed no significant differences amongst the same categories represented in O. turicata and I. scapularis. Transcripts predicting 22 neuropeptides or their receptors in the O. turicata synganglion were similar to annotations for 23 neuropeptides or receptors previously identified from I scapularis, with minor exceptions. A transcript predicting ecdysis triggering hormone receptor was identified in O. turicata; transcripts encoding for proprotein convertase and glycoprotein B were identified in both species. Transcripts predicting the same neurotransmitter receptors were found in the synganglion of both species. Gene expression of the transcripts showed numerous differences in response to feeding. Major differences were observed in expression of genes believed important in regulating slow vs. rapid feeding, blood water elimination, cuticle synthesis plasticity and in signalling reproductive activity. Although the glutamate receptor was strongly upregulated in both species, the gamma aminobutyric acid receptor, which inhibits glutamate, was upregulated significantly only in I. scapularis. These differences are consistent with the slow vs. rapid action of the pharyngeal pump in the two species.

Protein expression and genetic structure of the coral Porites lobata in an environmentally extreme Samoan back reef: does host genotype limit phenotypic plasticity?

The degree to which coral reef ecosystems will be impacted by global climate change depends on regional and local differences in corals' susceptibility and resilience to environmental stressors. Here, we present data from a reciprocal transplant experiment using the common reef building coral Porites lobata between a highly fluctuating back reef environment that reaches stressful daily extremes, and a more stable, neighbouring forereef. Protein biomarker analyses assessing physiological contributions to stress resistance showed evidence for both fixed and environmental influence on biomarker response. Fixed influences were strongest for ubiquitin-conjugated proteins with consistently higher levels found in back reef source colonies both pre and post-transplant when compared with their forereef conspecifics. Additionally, genetic comparisons of back reef and forereef populations revealed significant population structure of both the nuclear ribosomal and mitochondrial genomes of the coral host (F(ST) = 0.146 P < 0.0001, F(ST) = 0.335 P < 0.0001 for rDNA and mtDNA, respectively), whereas algal endosymbiont populations were genetically indistinguishable between the two sites. We propose that the genotype of the coral host may drive limitations to the physiological responses of these corals when faced with new environmental conditions. This result is important in understanding genotypic and environmental interactions in the coral algal symbiosis and how corals may respond to future environmental changes.