Divergent Evolutionary Profile of MULE Transposons in Arthropods

Mutator-like elements (MULEs) are a major DNA transposon superfamily. The evolutionary profiles of MULE transposons and their impact on arthropod genomes remain largely unexplored. Here, we define the evolutionary landscape-including distribution, diversity, structure, and activity-of MULE transposons across 4268 assembled arthropod genomes. Systematic analysis reveals a divergent evolutionary profile. From the sampled genomes, 222 arthropod species harbor MULE transposons, comprising 322 distinct elements. Phylogenetic analysis divides arthropod MULE transposons into twelve clades. The majority of species (164) carry only one type of MULE transposon, while 51 species contain two or three types, and a few host multiple types (4-9). Copy numbers vary significantly, ranging from 5 to 88 per species. Structural variation is pronounced: full-length MULEs range from 1.4 kb to 10.0 kb, with most falling between 2.5 kb and 5.0 kb. Low Kimura divergence in several species suggests recent MULE activity, noteworthy because most transposons are expected to be inactive. Collectively, our results show that MULEs are widely distributed yet phylogenetically structured across arthropods, with lineage-specific expansions and recent activity in several species.