Integrative taxonomy and ecology of the cryptic species complex of Aphodius fimetarius (Linnaeus, 1758) and Aphodius pedellus (de Geer, 1774) (Coleoptera: Aphodiidae)

Species in cryptic complexes are, per definition, difficult to identify using morphological characters. One such complex was recently detected in the dung beetle Aphodius fimetarius (Linnaeus, 1758) sensu lato, an abundant dung beetle with a wide distribution. While the two component taxa, Aphodius fimetarius sensu stricto and Aphodius pedellus (de Geer, 1774) exhibit distinctly different karyotypes, the validity of subtle morphological characters proposed to distinguish between them has been debated. Given the variability and minor interspecific differences in external characters, the large-scale distribution of respective taxa remained unknown, as did potential differences in ecology and habits. In this study, we ask how A. fimetarius and A. pedellus can best be distinguished, whether the use of different types of characters (karyotypes, DNA sequences and morphological traits) results in consistent species identification, where these species occur and whether they exhibit ecological differences. In total, we inspected a total material of 4224 individuals from across the globe, of which 183 were examined for both mtDNA sequences and morphology, 129 for both morphology and karyotype, and 8 for all three types of characters including the recently proposed neotype of Aphodius fimetarius. As a marker gene, we sequenced a 590 bp region of the cytochrome c oxidase I gene for 183 individuals. Overall, DNA sequences offered a clear-cut distinction between taxa: sequences of A. fimetarius and A. pedellus differed by an average pairwise distance of 8.2%, whereas variation within species was only 0.9% for A. fimetarius and 0.5% for A. pedellus. Both taxa were found to be globally distributed, with major sympatry within Central and Southern Europe and mixed patterns of sympatry within the US. Northern areas of Europe, Asia and North America are dominated by A. pedellus alone. Within A. pedellus, patterns of sequence diversity were indicative of a recent population expansion. In the western US, the phenology of a population of A. fimetarius was observed to significantly differ from that of a sympatric population of A. pedellus, thereby revealing an ecological difference between the two cryptic taxa. Overall, we conclude that all types of characters offered a consistent classification of the two species. Thus, the laborious karyotyping techniques used to originally establish the presence of two cryptic taxa can now be substituted by characters more easily applied to large ecological materials. Using this approach of integrative taxonomy, we were able to establish the global distribution and species-specific ecology of these ecologically important cryptic taxa.