New Species of Lobsters Prompt Re-Analysis of Kiwaid Biogeographical History

Recently two new species of kiwaid squat lobsters were found on hydrothermal vents in the Pacific Ocean and in the Pacific sector of the Southern Ocean. Finding these two new species had prompted the re-analysis of the kiwaid bio-geographical history. These squat lobsters are commonly known as "Yeti crabs." The yeti crabs get most of their nutrition from chemosynthetic episymbiotic bacteria growing on setae on their ventral surface and appendages. All but one species of kiwaid have been collected from hydrothermal vents. The other species, Kiwa puravida, was collected from cold seeps on the Pacific continental slope near Costa Rica. All the species were found in the Pacific or the Pacific sector of the Southern Ocean; however one species, Kiwa tyleri, is found in mass amounts at vents on the East Scotia Ridge in the Atlantic sector of the Southern Ocean.

Figure 1: Photos of known Yeti crabs.
 A) Kiwa puravida B) Kiwa sp. Galapagos Microplate C) Kiwa araonae D) Kiwa hirsuta E) Kiwa tyleri (F) Kiwa sp. SWIR
Scale bars are an approximation and represent 10 mm.

The first new species to be discovered was found on hydrothermal vents on the Galapagos Microplate and is called Kiwa sp. GM. The Galapagos Microplate is a distinct spreading system between the Galapagos Rift and the northern and southern portions of the East Pacific Rise. The second species is known as Kiwa araonae. This species is found on vents on the Australian-Antarctic Ridge in the southwest Pacific sector of the Southern Ocean. The discovery of this species widens the original known range of the Yeti crabs by ~6,500 km. This discovery suggests that the spread of the Yeti crabs is more complicated than previously believed. This discovery also suggests that the original seep-to-vent evolutionary progression may be wrong.

Figure 2: Map showing locations of kiwaids and the Cretaceous stem lineage fossil Pristinaspina gelasina in relation to land-masses and mid-ocean ridges.
Kiwaid are: i) Kiwa puravida, ii) Kiwa sp. GM, iii) Kiwa hirsuta, iv) Kiwa araonae, v) Kiwa tyleri, vi) Kiwa sp. SWIR.
Abbreviations are: NEPR = Northern East Pacific Rise; SEPR = Southern East Pacific Rise; GR = Galapagos Rift; GM = Galapagos Microplate; PAR = Pacific-Antarctic Ridge; AAR = Australian-Antarctic Ridge; CR = Chile Rise; ESR = East Scotia Ridge; AmAR = American-Antarctic Ridge; SWIR = Southwest Indian Ridge; CIR = Central Indian Ridge; SEIR = Southeast Indian Ridge; MAR = Mid-Atlantic Ridge.

The researchers found through many tests that Kiwaidae most likely originated in the Pacific. The researchers also found that the pattern of divergence could be closely linked to the evolution and movement of mid-ocean spreading ridges supporting hydrothermal vent habitats. Kiwaids, minus the one species mentioned earlier, are found only at hydrothermal vents along with BEAST analysis indicates that the common ancestor most likely inhabited the vents. They found that in other vent-associated taxa appeared consistent with movement and evolution of active spreading ridges. While there are puzzling reasons to why there are Yeti crabs are in certain areas there is also puzzling questions to why they are not in other areas.

Figure 3: The present-day configuration of mid-ocean ridges in the tropical East Pacific and the location of all currently known kiwaids

Yeti crabs are expected to be in areas such as vents along both the Galapagos Rift and the southern EPR, however they are absent from these. These vents have been majorly explored and no kiwaids have been found in them to this day. This study was done to include the two newest species and add on to a report previously done that included the previous four species. The research recently done does support the earlier inference to East Pacific origin. The research also shows that the divergence estimates are broadly similar to previous studies. 

Source for paper and figures 1-3:
Roterman CN, Lee WK, Liu X, Lin R, Li X, et al. (2018) "A New Yeti Crab Phylogeny: Vent Origins with Indications of Regional Extinction in the East Pacific." PLOS ONE 13(3):e0194696

http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0194696