|GIRIBET, GONZALO - Harvard University|
|BUCKMAN-YOUNG, REBECCA - Harvard University|
|COSTA, CRISTIANO - Universidade De Sao Paulo|
|BAKER, CAITLIN - Harvard University|
|BENAVIDES, LIGIA - Harvard University|
Submitted to: Invertebrate Systematics
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/15/2018
Publication Date: N/A
Interpretive Summary: The research study by Giribet et al. investigates evolutionary relationships among a rare group of invertebrate animals known as velvet worms (Phylum Onychophora). Velvet worms are an ancient group of worm-like animals that occur throughout the tropics and in a few, distantly separated areas in the southern hemisphere. The group has been of great scientific interest because of its rarity, geographic distribution, and presumed inability to disperse great distances, a feature that makes them useful for studying how the landscape has changed over geological time and how those changes have influenced evolutionary patterns. Despite great interest, little is known about velvet worm diversity and biology, primarily because they are so rarely encountered. The group currently includes two families and ~40 species. Using molecular data from several genes and a diverse sampling of species, many of which were recently collected, Giribet et al. present the most comprehensive estimation of velvet worm relationships to date. The authors also use fossil evidence to examine the timing of velvet worm diversification, which allows them to test a theory, called the Eurogondwana dispersal theory, that isolated species found in NE India arrived there recently via long-distance movement through ancient Europe. Based on the new results, the authors refute the Eurogondwana idea and suggest instead that the Indian species arrived via an ancient movement of land preceding the collision of India with Asia. The results of the study also show that the classification system used to name major groups of velvet worms within one of the families is flawed and is in need of revision. Overall, the study presents a major advancement in understanding of the global diversity and evolution of velvet worms.
Technical Abstract: Only Onychophorans or velvet worms are cryptic but extremely charismatic terrestrial invertebrates that have often been the subject of interesting biogeographic debates. Despite great interest, a well-resolved and complete phylogeny of the group and a reliable chronogram have been elusive due to their broad geographic distribution, paucity of samples, and challenging molecular composition. Here we present a comprehensive phylogenetic analysis of Onychophora including lineages previously unsampled or poorly sampled in molecular phylogenetic analyses and analyse them using a series of nested datasets designed to increase the amount of information available for the relevant taxa. These include a dataset with outgroups, one restricted to the ingroup taxa, and three other datasets for Peripatopsidae, Peripatidae and Neopatida (= the Neotropical Peripatidae). Comparing our results to those of Cyphophthalmi we contemplate an alternative to the previous hypothesis that velvet worms reached SE Asia via Eurogondwana, and instead propose that they reached SE Asia by rafting in the Sibumasu terrain, as they diverged from the other peripatids in the Triassic. Our phylogenetic results support the reciprocal monophyly of both families as well as an early division between East and West Gondwana, also in both families, each beginning to diversify between the Permian and the Jurassic. Peripatopsidae clearly supports paraphyly of South Africa with respect to southern South America (Chile) and a sister group relationship of the SE Asian/New Guinean Paraperipatus to the Australian/New Zealand taxa. The latter includes a clade that divides between Western Australia and East Australia and two sister clades of trans- Tasman species (one oviparous and one viviparous). This pattern supports matrotrophic viviparity as the plesiomorphic state in Peripatopsidae and clearly shows that oviparity is secondarily derived in velvet worms. Biogeographical explanations of these patterns are discussed. Peripatidae finds a sister group relationship between the SE Asian Eoperipatus and the West Gondwanan clade, which divides into the African Mesoperipatus and Neopatida. The latter shows a well-supported split between the Pacific Oroperipatus (although it is unclear whether they form one or two clades) and a sister clade that includes the members of the genera Peripatus, Epiperipatus, Macroperipatus and representatives of the monotypic genera Cerradopatus, Plicatoperipatus and Principapillatus. However, Peripatus, Epiperipatus, and Macroperipatus are not monophyletic, and all the species from the monotypic genera are always related to geographically close species. The same goes for the type species of Macroperipatus (from Trinidad, and sister group to other Trinidad and Tobago species of Epiperipatus) and Epiperipatus (from French Guiana, and related to other Guyana shield species of Epiperipatus and Peripatus). Geographic structure within Neopatida is largely obscured by a compressed backbone, but many well-supported instances of generic non-monophyly reject the current taxonomic framework, which relies on anatomical characters with little phylogenetic information.