Return of the prodigal son: morphology and molecular phylogenetic relationships of a new Antarctic fish leech (Hirudinea: Piscicolidae) imply a bipolar biogeographic pattern

Abstract

The bipolar distribution of fish leeches (Piscicolidae) has been considered and discussed by leech biologists for a long time. All cases of putative bipolar ranges of related taxa that occur in cold and temperate waters of both hemispheres and are absent in the tropics have been morphology-based hypotheses. Here, we present, for the first time, an instance of bipolar distribution substantiated by morphological and molecular data. The latter include the mitochondrial genes 12S rRNA, COI, ND1 and tRNA Leu, and the nuclear 28S rRNA. A new genus and species of Antarctic piscicolids, Austroplatybdellina prodiga, is described. The new leech was part of a Boreal-Arctic monophyletic group that is informally called ‘classic platybdellins’. That clade is the core of the non-monophyletic subfamily Platybdellinae. Austroplatybdellina prodiga gen. nov. sp. nov. was further classified as a member of a monophyletic group along with two Boreal genera, Crangonobdella and Beringobdella, which share a number of systematically important morphological features with its newly described relative. It is hypothesized that the Boreal ancestor of the new leech crossed warm tropical waters and colonized the Antarctic. The colonization was relatively recent as the low genetic distance between A. prodiga and its Boreal sister species suggests. This migration can be viewed as a return of a Boreal descendant of the Antarctic ancestor of Piscicolidae to the area of origin of the entire family, which follows from the basal position of the Antarctic Megaliobdella szidati in the family phylogenetic tree. This evolutionary scenario is reflected in the species epithet of the new leech. https://zoobank.org/urn:lsid:zoobank.org:pub:DA548F19-922A-4B5D-B7F1-4C3AF57B9824 https://zoobank.org/urn:lsid:zoobank.org:act:A35C365A-A475-4F3E-B28B-C799F618215D https://zoobank.org/urn:lsid:zoobank.org:act:BCE6411F-E38A-4A99-A726-DE5C33D9D658