North American velvet ants form one of the world's largest known Müllerian mimicry complexes

Abstract

Color mimicry is often celebrated as one of the most straightforward examples of evolution by natural selection, as striking morphological similarity between species evolves in response to a shared predation pressure. Recently, a large North American mimetic complex was described that included 65 species of Dasymutilla velvet ants (Hymenoptera: Mutillidae). Beyond those 65 species, little is known about how many species participate in this unique Müllerian complex, though several other arthropods are thought to be involved as Müllerian mimics (spider wasps) and Batesian mimics (beetles, antlions, and spiders; see references in). Müllerian mimicry is similarity in appearance or phenotype among harmful species, while Batesian mimicry is similarity in which not all species are harmful. Here, we investigate the extent of the velvet ant mimicry complex beyond Dasymutilla by examining distributional and color pattern similarities in all of the 21 North American diurnal velvet ant genera, including 302 of the 361 named species (nearly 84%), as well as 16 polymorphic color forms and an additional 33 undescribed species. Of the 351 species and color forms that were analyzed (including undescribed species), 336 exhibit some morphological similarities and we hypothesize that they form eight distinct mimicry rings (Figure 1A; Supplemental Information). Two of these eight mimicry rings, red-headed Timulla and black-headed Timulla, were not documented in earlier assessments of mimicry in velvet ants, and are newly described here. These findings identify one of the largest known Müllerian mimicry systems worldwide and provide a novel system to test hypotheses about aposematism and mimicry, especially those regarding the evolution of imperfect mimicry.