Differential DNA methylation in Pacific oyster reproductive tissue in response to ocean acidification

Genome-wide DNA methylation patterns in bumble bee (Bombus vosnesenskii) populations from spatial-environmental range extremes

Unraveling molecular mechanisms of adaptation to complex environments is crucial to understanding tolerance of abiotic pressures and responses to climatic change. Epigenetic variation is increasingly recognized as a mechanism that can facilitate rapid responses to changing environmental cues. To investigate variation in genetic and epigenetic diversity at spatial and thermal extremes, we use whole genome and methylome sequencing to generate a high-resolution map of DNA methylation in the bumble bee Bombus vosnesenskii. We sample two populations representing spatial and environmental range extremes (a warm southern low-elevation site and a cold northern high-elevation site) previously shown to exhibit differences in thermal tolerance and determine positions in the genome that are consistently and variably methylated across samples. Bisulfite sequencing reveals methylation characteristics similar to other arthropods, with low global CpG methylation but high methylation concentrated in gene bodies and in genome regions with low nucleotide diversity. Differentially methylated sites (n = 2066) were largely hypomethylated in the northern high-elevation population but not related to local sequence differentiation. The concentration of methylated and differentially methylated sites in exons and putative promoter regions suggests a possible role in gene regulation, and this high-resolution analysis of intraspecific epigenetic variation in wild Bombus suggests that the function of methylation in niche adaptation would be worth further investigation.

The mechanisms and factors that induce trained immunity in arthropods and mollusks

Besides dividing the organism's immune system into adaptive and innate immunity, it has long been thought that only adaptive immunity can establish immune memory. However, many studies have shown that innate immunity can also build immunological memory through epigenetic reprogramming and modifications to resist pathogens' reinfection, known as trained immunity. This paper reviews the role of mitochondrial metabolism and epigenetic modifications and describes the molecular foundation in the trained immunity of arthropods and mollusks. Mitochondrial metabolism and epigenetic modifications complement each other and play a key role in trained immunity.

Experimental DNA Demethylation Reduces Expression Plasticity and Thermal Tolerance in Pacific Oysters

Increasing seawater temperatures pose a great threat to marine organisms, especially those settled in fluctuating intertidal areas. DNA methylation, which can be induced by environmental variation, can influence gene expression and mediate phenotypic plasticity. However, the regulatory mechanisms of DNA methylation in gene expression-mediated adaptation to environmental stress have rarely been elucidated. In this study, DNA demethylation experiments were conducted on a typical intertidal species, the Pacific oyster (Crassostrea gigas), to determine the direct role of DNA methylation in regulating gene expression and adaptability under thermal stress. The global methylation level and the expression level of DNA methyltransferases (DNMT1, DNMT3a) showed an accordant variation trend under high temperatures, supporting that the genomic methylation status was catalyzed by DNMTs. DNA methylation inhibitor 5-Azacytidine (5-Aza) effectively inhibited DNA methylation level and decreased methylation plasticity at the 6th hour in thermal conditions. In total, 88 genes were identified as candidate DNA methylation-regulated thermal response genes; they exhibited reduced expression plasticity in response to heat stress, possibly caused by the decreased methylation plasticity. Post-heat shock, the thermal tolerance indicated by the survival curve was reduced when oysters were pretreated with 5-Aza, meaning that DNA demethylation negatively affected thermal adaptation in oysters. This study provides direct evidence for the crucial role of DNA methylation in mediating stress adaptation in marine invertebrates and contributes to the theoretical foundations underlying marine resource conservation and aquaculture.

Latitudinal variation and plasticity in response to temperature in Geukensia demissa

As global temperatures warm, species must adapt to a changing climate or transition to a different location suitable for their survival. Understanding the extent to which species are able to do so, particularly keystone species, is imperative to ensuring the survival of key ecosystems. The ribbed mussel Geukensia demissa is an integral part of salt marshes along the Atlantic coast of North America. Spatial patterns of genomic and phenotypic divergence have been previously documented, although their link with coastal environmental variation is unknown. Here, we study how populations of G. demissa in the northern (Massachusetts) and southern (Georgia) portions of the species range respond to changes in temperature. We combine assays of variation in oxygen consumption and RNA transcriptomic data with genomic divergence analyses to identify how separate populations of G. demissa may vary in distinct thermal environments. Our results show differences in constitutive oxygen consumption between mussels from Georgia and Massachusetts, as well as shared and disparate patterns of gene expression across temperature profiles. We also find that metabolic genes seem to be a strong component of divergence between these two populations. Our analysis highlights the importance of studying integrative patterns of genomic and phenotypic variation in species that are key for particular ecosystems, and how they might respond to further changes in climate.