Unmasking alpha diversity, cladogenesis and biogeographical patterning in an ancient panarthropod lineage (Onychophora: Peripatopsidae: Opisthopatus cinctipes) with the description of five novel species.

Abstract

Speciation and biogeographical patterning in the velvet worm Opisthopatus cinctipes was examined under a null hypothesis that numerous discrete lineages are nested within the species. A total of 184 O.cinctipes specimens, together with a single specimen of each of the two congeneric point endemic sister species (O.roseus and O.herbertorum), were collected throughout the forest archipelago in the Eastern Cape, KwaZulu-Natal and Mpumalanga provinces of South Africa. All specimens were sequenced for two partial mitochondrial DNA loci (COI and 12S rRNA), while a single specimen from each locality was sequenced for the nuclear 18S rRNA locus. Evolutionary relationships were assessed using maximum-likelihood and Bayesian inferences, while divergence time estimations were conducted using BEAST. A Bayesian species delimitation approach was undertaken to explore the number of possible novel lineages nested within Opisthopatus, while population genetic structure was examined for the COI locus using ARLEQUIN. Phylogenetic results revealed that O.cinctipes is a species complex comprising seven geographically discrete and statistically well-supported clades. An independent statistical approach to species delimitations circumscribed ca. 67 species. Results from divergence time estimation and rate constancy tests revealed near constant net diversification occurring throughout the Eocene and Oligocene with subdivision of ranges during the Miocene. Gross morphological characters such as leg pair number within O.cinctipes were invariant, while dorsal and ventral integument colour was highly polymorphic. However, scanning electron microscopy revealed considerable differences both between and within clades. The caveats associated with both morphological and algorithmic delineation of species boundaries are discussed. The five novel Opisthopatus species are described.