While it has been suggested that histone modification can facilitate animal responses to rapidly changing environments, few studies have profiled whole-genome histone modification patterns in introduced species, leaving its role in invasiveness unclear. Here, we screen genome-wide patterns of two important histone modifications, trimethylated Histone H3 Lysine 4 (H3K4me3) and trimethylated Histone H3 Lysine 27 (H3K27me3), in adult thorax muscles of a notorious invasive pest, the Oriental fruit fly Bactrocera dorsalis (Hendel) (Diptera: Tephritidae), using Chromatin Immunoprecipitation with high-throughput sequencing (ChIP-seq). We identified active, repressed and poised promoters, featured by the occupancy of H3K4me3, H3K27me3 and bivalent histone modifications that were respectively annotated with unique genes key to muscle development and structure maintenance. In addition, we found H3K27me3 occupied the entire body of genes, with the average enrichment was almost constant. When comparing to the closely related indigenous Drosophila species, while we found highly conserved histone modifications patterns of distribution and function between the two species, we identified more genes and putative motifs modified by histone modifications that may regulate insect flight capacity and invasiveness compared to D. melanogaster. These findings provide the first evidence of histone modification signature in an invasive species, and will be useful for future studies of epigenetic regulation of invasiveness under global climate change.

While adaptation is commonly thought to result from selection on DNA sequence-based variation, recent studies have highlighted an analogous epigenetic component as well. However, the extent to which these adaptive mechanisms to adaptation to environmental heterogeneity are redundant or complementary remains unclear. To address the underlying genetic and epigenetic mechanisms and their relationship underlying environmental adaptation, we screened the genomes and epigenomes of nine global populations of a predominately sessile marine invasive tunicate, Botryllus schlosseri. We detected clear population genetic and epigenetic differentiation, which were both significantly influenced by local environments, and the minimum annual sea surface temperature (T_min) was simultaneously identified as the top explanatory variable for both types of variation. However, there remain some degree of difference in population structure patterns between two levels, suggesting a certain level of autonomy in epigenetic variation. From the functional perspective, a set of functional genes and biological pathways were shared between two levels, indicating a conjoint contribution of genetic and epigenetic variation to environmental adaptation. Moreover, we also detected genetic- or epigenetic-specific genes/pathways in relation to a wide variety of core processes potentially underlying adaptation to local environmental factors, suggesting the partly independent relationship between two mechanisms. We infer that complementary genetic and epigenetic routes to adaptation are available in this system. Collectively, these mechanisms may facilitate population persistence under environmental changes and sustain successful invasions in novel but contrasting environments.