Natural epigenetic variation within and among six subspecies of the house sparrow, Passer domesticus

Epigenetic modifications can respond rapidly to environmental changes and can shape phenotypic variation in accordance with environmental stimuli. One of the most studied epigenetic marks is DNA methylation. In the present study, we used the methylationsensitive amplified polymorphism (MSAP) technique to investigate the natural variation in DNA methylation within and among subspecies of the house sparrow, Passer domesticus. We focused on five subspecies from the Middle East because they show great variation in many ecological traits and because this region is the probable origin for the house sparrow's commensal relationship with humans. We analysed house sparrows from Spain as an outgroup. The level of variation in DNA methylation was similar among the five house sparrow subspecies from the Middle East despite high phenotypic and environmental variation, but the non-commensal subspecies was differentiated from the other four (commensal) Middle Eastern subspecies. Further, the European subspecies was differentiated from all other subspecies in DNA methylation. Our results indicate that variation in DNA methylation does not strictly follow subspecies designations. We detected a correlation between methylation level and some morphological traits, such as standardized bill length, and we suggest that part of the high morphological variation in the native populations of the house sparrow is influenced by differentially methylated regions in specific loci throughout the genome. We also detected 10 differentially methylated loci among subspecies and three loci that differentiated between commensal or non-commensal status. Therefore, the MSAP technique detected larger scale differences among the European and non-commensal subspecies, but did not detect finer scale differences among the other Middle Eastern subspecies.