|Map showing locations of kiwaids and the Cretaceous stem lineage fossil Pristinaspina gelasina in relation to land-masses and mid-ocean ridges.|
in Roterman, Lee, Liu, et al., 2018.
The recent discovery of two new species of kiwaid squat lobsters on hydrothermal vents in the Pacific Ocean and in the Pacific sector of the Southern Ocean has prompted a re-analysis of Kiwaid biogeographical history. Using a larger alignment with more fossil calibrated nodes than previously, we consider the precise relationship between Kiwaidae, Chirostylidae and Eumunididae within Chirostyloidea (Decapoda: Anomura) to be still unresolved at present. Additionally, the placement of both new species within a new “Bristly” clade along with the seep-associated Kiwa puravida is most parsimoniously interpreted as supporting a vent origin for the family, rather than a seep-to-vent progression. Fossil-calibrated divergence analysis indicates an origin for the clade around the Eocene-Oligocene boundary in the eastern Pacific ~33–38 Ma, coincident with a lowering of bottom temperatures and increased ventilation in the Pacific deep sea. Likewise, the mid-Miocene (~10–16 Ma) rapid radiation of the new Bristly clade also coincides with a similar cooling event in the tropical East Pacific. The distribution, diversity, tree topology and divergence timing of Kiwaidae in the East Pacific is most consistent with a pattern of extinctions, recolonisations and radiations along fast-spreading ridges in this region and may have been punctuated by large-scale fluctuations in deep-water ventilation and temperature during the Cenozoic; further affecting the viability of Kiwaidae populations along portions of mid-ocean ridge.
|Fig 2. Map showing locations of kiwaids and the Cretaceous stem lineage fossil Pristinaspina gelasina in relation to land-masses and mid-ocean ridges.|
Kiwaid representations are: i) Kiwa puravida ii) Kiwa sp. GM, iii) Kiwa hirsuta, iv) Kiwa araonae v) Kiwa tyleri vi) Kiwa sp. SWIR. Land shapes and ridge positions are modified from the InterRidge Vents Database 2.1 static map (vents-data.interridge.org/maps). Areas of mid-ocean ridge in light blue denote unexplored regions that may support Kiwaidae. Spreading ridge abbreviations are as follows: 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. Photograph of K. puravida modified from Thurber et al.  and Kiwa hirsuta modified from Muséum National D’Histoire Naturelle (MNHN) crustacean collection–credit Noémy Mollaret
This study is an augmentation of Roterman et al.  through the addition of more kiwaids, longer alignments and more fossil calibrations. Tree topologies produced here modify some of the inferences of the previous study. The sister-phyly of Kiwaidae and Chirostylidae within Chirostyloidea is placed in doubt, as are the previous inferences of a seep-to-vent evolutionary progression and a Northern Hemisphere origin for Kiwaidae. Current analyses do support the earlier inference for an East Pacific origin, however, and divergence estimates are broadly similar to previous analyses. Age estimates for the MRCA of Kiwaidae indicate an origin long after the PETM, around the Eocene-Oligocene boundary at a time of deep-water cooling and increased ventilation in the Pacific. Likewise, the rapid radiation of a newly defined Bristly clade appears synchronous with another transition to cooler and more ventilated conditions in the East Pacific during the Middle Miocene. The distribution, diversity, tree topology and divergence timing of vent-associated Kiwaidae in the Pacific is consistent with a pattern of regional extinctions, recolonisations and radiations along fast-spreading ridges over the last 40 million years. This pattern may have been punctuated by large-scale fluctuations in deep-water ventilation and temperature during the Cenozoic; further affecting the viability of Kiwaidae populations along large areas of mid-ocean ridge. The exploration of new vent and seep systems in the Pacific and beyond will help to better resolve the biogeographic history of Kiwaidae and provide new insights into the long-term resilience of metapopulations inhabiting deep-sea chemosynthetic ecosystems.
Christopher Nicolai Roterman, Won-Kyung Lee, Xinming Liu, Rongcheng Lin, Xinzheng Li and Yong-Jin Won. 2018. A New Yeti Crab Phylogeny: Vent Origins with Indications of Regional Extinction in the East Pacific. PLoS ONE. 13(3): e0194696. DOI: 10.1371/journal.pone.0194696