Highlight—Tiny, Unseeing Mite Defies Expectations

For those who love and study insects and arachnids, they can see the underappreciated wonders of the biological realm. In the face of so much diversity, so much remains to be discovered. A recent study in Genome Biology Evolution is a case in point. Researchers sequencing the genome of a mite have found what might seem stranger than fiction: a mite that has retained genes important to sight, despite having no eyes, and has spread genes important for the development of body segments all over its genome, in stark contrast to most organisms, keeps these genes close together in a tidy line. Coauthor Stephen Richards, from the Baylor College of Medicine in Texas, says his “mind is still blown” when he reflects on this finding. “I always thought having the Hox genes all in a row was kind of important for animals, and apparently it’s not,” he says. In other arthropods whose genomes have been examined, Hox genes are collinear, with few to no intervening genes. But in their examined mite, Metaseiulus occidentalis, the genes aren’t just spaced apart, they’re on completely different gene scaffolds. In this mite, researchers also found an unusually high number of intron gains and losses, indicating that the evolutionary background of this arthropod (at least from a genome point of view) has been full of unexpected genetic gymnastics. “It really makes me wonder what’s been happening in this lineage,” says Richards. It’ll take the sequencing of other related animals to determine if this mite started out with orderly Hox genes (which is assumed to be the historical arrangement). Or, Richards floats an alternate possibility, perhaps “it is more basal in the mites?”