Epigenetic Regulation in Seasonal Migrants
Keywords:
photoperiod, migratory phenotype, histone modification, Zugunruhe, Ficedula hypoleuca, Sylvia atricapilla, circadian clock, seasonal migration, ChIP-seq, RRBS, migratory birds, DNA methylation, epigeneticsAbstract
Seasonal migration in birds requires profound physiological transformations -- hyperphagia, fat deposition, gonadal
regression, altered circadian rhythms, and directional orientation programming -- that must be precisely timed relative to
photoperiod cues and executed reversibly across multiple annual cycles. Epigenetic mechanisms, including DNA
methylation, histone modification, and non-coding RNA regulation, have emerged as candidate molecular switches
mediating these reversible seasonal phenotype transitions in a photoperiod-responsive manner. This study characterised
genome-wide DNA methylation dynamics (RRBS; reduced representation bisulfite sequencing) and histone modification
profiles (ChIP-seq; H3K4me3, H3K27me3, H3K27ac) across three physiological states -- pre-migratory (Zugunruhe),
mid-migration, and post-breeding -- in three long-distance migratory passerine species (Ficedula hypoleuca pied
flycatcher, Acrocephalus scirpaceus reed warbler, Sylvia atricapilla Eurasian blackcap) sampled at standardised ringing
stations (n = 284 individuals per species; n = 28 per state per species for RRBS/ChIP-seq). Differentially methylated
regions (DMRs) between pre-migratory and post-breeding states numbered 4,284 +- 842 per species, with significant
enrichment at circadian clock genes (CLOCK, BMAL1, PER2: mean DMR enrichment 8.4x above genome background; p
< 0.001), hypothalamic neuropeptide genes (GnRH, NPY, VIP: 6.4x; p < 0.001), and fat deposition pathway genes
(PPAR-gamma, fatty acid synthase: 5.8x; p = 0.002). H3K4me3 active promoter marks showed significant gain at
migratory fat deposition genes during the pre-migratory state (fold enrichment 4.2 +- 0.8; p < 0.001), while H3K27me3
repressive marks increased at gonadal development genes consistent with post-breeding gonadal regression. Blackcap
(S. atricapilla) showed the largest DMR count and the strongest epigenetic regulation of migratory orientation genes
among the three species, consistent with its documented capacity for rapid migratory route evolution over 30+ years in
central European wintering populations. These results identify epigenetic regulation of circadian and metabolic pathways
as a key molecular mechanism of migratory phenotype switching and suggest that epigenetic plasticity may facilitate
rapid adaptation of migratory timing and routes under climate change.
