Host-shift speciation in Antarctic symbiotic invertebrates: further evidence from the new amphipod species Lepidepecreella debroyeri from the Ross Sea?

Lepidepecreella debroyeri n. sp. (Amphipoda, Lysianassoidea) is described from specimens collected at Terra Nova Bay (Ross Sea, Antarctica) in the framework of several scientific expeditions of the Italian National Antarctic Research Program. This amphipod is an obligate parasite of the regular sea urchin Sterechinus neumayeri (Meissner, 1900) and also occurs at diving depths. L. debroyeri n. sp. shares with Lepidepecreella andeep Berge, Vader & Lockhart, 2004, an abyssal species described for the Weddell Sea, an almost identical morphology and ecological traits, being both associated with sea urchins of two different families. This close relationship could be the result of a host-shift phenomenon that occurred during the high number of glacial cycles, possibly rendering the preferred host unavailable. L. debroyeri n. sp. shows a high degree of variation in terms of sex ratio and population structure between different host specimens, a fact that could be related to a great mobility of this small parasitic amphipod. The new amphipod species is itself the subject of a hyperparasitic interaction, carrying tantulocarid crustaceans on the pleopods. This represents the first record of a symbiotic interaction between a tantulocarid and an amphipod for the Southern Ocean.