Cryptic or underworked? Taxonomic revision of the Antistrophus rufus species complex (Cynipoidea, Aulacideini)

Cryptic species present challenges across many subdisciplines of biology. Not all “cryptic” species, however, are truly cryptic; many are simply underexplored morphologically. We examined this idea for the Antistrophus rufus species complex, which previously contained three species thought to be morphologically cryptic. To determine whether the A. rufus complex are truly cryptic species, we assessed species boundaries of members of the A. rufus species complex using morphological, ecological, and DNA barcode data, and tested whether a set of 50 morphological characters could adequately diagnose these species. We revealed that this complex includes five species, and that there are useful phenotypic diagnostic characters for all members of this species complex. This enabled redescription of four species and the description of Antistrophus laurenae Nastasi, sp. nov., which induces externally inconspicuous galls in stems of Silphium integrifolium Michx., a host not associated with other members of the complex. We use these new diagnostic characters to construct a key to the five species of the rufus complex. We conclude that the A. rufus complex was not a true case of cryptic species. Our Bayesian analysis of DNA barcode data suggests possible cospeciation of members of the rufus complex and their Silphium host plants, but further study is necessary to better understand the evolution of host use in the lineage.