We reconstruct the phylogeny of the most speciose genus of cuckoo bees, genus Nomada Scopoli, 1770, using 221 species from throughout its distribution, yet with a strong emphasis on the West Palearctic. For phylogenetic reconstruction, we sequenced ultraconserved elements, allowing robust phylogenetic estimates with both concatenation and coalescent-based methods. By integrating extensive information on Nomada host records, we study macroevolutionary patterns of host associations, transitions, and phylogenetic conservatism. Using Bayesian divergence time estimates, we assess the historical biogeography of the genus, focusing on the West Palearctic. Our results show that Nomada likely originated in the Eastern Mediterranean and Near Eastern region, and likely expanded its range to a near-global distribution from there. We recovered long-standing phylogenetic conservatism in the host usage of Nomada and provided strong statistical evidence for an ancestral host association with Andrena and its most recent common ancestor. However, host transitions occurred multiple times independently in the natural history of Nomada, and species of the genus are brood parasites in at least 5 genera and 4 different families of bees in the Old World. At last, we systematically revise the taxonomy of the Old World Nomada by integrating morphological study with our well-supported phylogenetic estimates. We re-establish the genus Acanthonomada Schwarz, 1966, stat. res., as a distinct, second genus in the tribe Nomadini. We recognize 13 subgenera for Nomada, 9 of which are described as new: Afronomada Straka and Bossert, subgen. nov., Colliculla Straka, subgen. nov., Gestamen Straka, subgen. nov., Hungias Straka, subgen. nov., Mininomada Straka, subgen. nov., Nomacolla Straka, subgen. nov., Nomonosa Straka, subgen. nov., Plumada Straka, subgen. nov., and Profuga Straka, subgen. nov. Aside from the subgenus Nomada s.s., we reinstitute 3 previously synonymized subgenera: Heminomada Cockerell, 1902, stat. res., Holonomada Robertson, 1903, stat. res., and Hypochrotaenia Holmberg, 1886 stat. res. A total of 15 subgeneric names are formally synonymized with the newly established subgeneric concepts.

Graphical Abstract

Genetic introgression, allele exchange across species boundaries, is a commonly recognized feature of animal evolution. Under such a paradigm, contemporary contact zones provide first-hand insight into the geographic, phenotypic, and genetic details of introgression. Also, when mate choice phenotypes are conspicuous and variable in hybrids, contact zones provide potential insight into how sexual selection interacts with species boundary maintenance, particularly when postzygotic reproductive isolation is weak. The Habronattus americanus subgroup includes several recently evolved jumping spider species, with an estimated age of about 200,000 yr, and substantial evidence for hybridization and introgression. We explored a contact zone involving H. americanus (Keyserling, 1885) and H. kubai (Griswold, 1979) on Mount Shasta, CA, in alpine habitats that would have been unavailable (under ice) at the Last Glacial Maximum. We characterized morphological diversity within the contact zone, including the fine-scale geographic distribution of hybrid and parental individuals, and assessed genetic variation using ddRADseq data. Combined results indicate a lack of measured genomic differentiation between specimens with distinct morphologies, including individuals with phenotypes of the parental species. We identified a diverse array of hybrid morphologies, with phenotypic evidence for backcrossing, essentially forming a phenotypic bridge between parental taxa. The study area is characterized by more hybrid than parental individuals, with a significantly larger number of red-palped morphologies than white- and/or yellow-palped morphologies; the novel, white-palped phenotype is perhaps transgressive. Overall, these results contribute to a better understanding of the expected ebb and flow of lineage interactions during the early stages of speciation.

Graphical Abstract

Morphology has long been used to classify and identify living organisms. However, taxonomic descriptions are often limited to qualitative descriptions of size and shape, making identification difficult due to the subjective language used to describe complex shapes. Additionally, for some taxa, there are few reliable qualitative characters available for delimitation that have yet to be tested objectively in a phylogenetic context. Solifugae is one such example. The order, Solifugae, is recognized from the other arachnid orders by the possession of large, powerful jaws or chelicerae. Male cheliceral morphology is the leading diagnostic character system in solifuge systematics and is the basis for much of solifuge current taxonomy. Female chelicerae, on the other hand, are reportedly deeply conserved and much of the species identification is based on female operculum morphology. To elucidate patterns of chelicerae and opercula trait evolution within the solifuge family, Eremobatidae, we used a 2-dimenstional morphological analysis using an Elliptical Fourier approach for closed outlines, in addition to an analysis of traditionally used measures in a phylogenetic context. Using ancestral state reconstruction and ultra-conserved elements, we assessed the taxonomic utility of female cheliceral and opercular morphology, and we evaluated which male morphological characters reflect shared, derived ancestry. Investigation into ubiquitously used character sets, in addition to newly proposed characters herein, illustrates the complex evolution of traits with high levels of convergence. Our results provide taxonomic insight into future, higher level taxonomic revisions of Eremobatidae.