Oceans Around the World – The Sunda and Sahul Shelves

Notes on several key papers regarding biodiversity hotspots in and around the Sunda Shelf.

Article 1: Crandall 2008

Vicariance patterns as a result of Pleistocene sea-level changes in the Sunda Shelf area should be present in both invertebrates and their ectosymbionts. Highly variable results across many different studies have spurred the authors to explore a more closely linked hypothesis: That patterns of genetic variation found in marine invertebrates (in this case, two seastars) should closely match that of their ectosymbionts (a mollusk and crustacean). Most of the four species did show at least some genetic structure, but it was not concordant across species, with each species displaying a different pattern of range expansion most likely due to differences in dispersal, and adult survivability.

Source: https://www.ncbi.nlm.nih.gov/pubmed/19067797

Map of Sunda and Sahul.

Map of Sunda and Sahul. CC 3.0 By Maximilian Dörrbecker (Chumwa). Wikimedia Commons.

Article 2: Crandall 2012

Sea-level changes during the end of the Last Glacial Maximum (LGM) should correspond closely with population range expansions of marine species. Prior to sea-level rises, the Sunda shelf and neighboring shelves were well above the ocean. Beginning roughly 20,000 years ago sea-levels began to rise rapidly, covering the Sunda shelf under water and facilitating the rapid expansion of marine species into this new habitat. The authors suggest that since the genetic signal of this sea-level rise is present in so many species, this event can be used as a means of calibrating the heterogeneous rate of mutation rates of lineages through time, that is, that younger lineages tend to have higher mutation rates. The authors proclaim strong support for the idea of time dependency of molecular clocks. This is an important understanding because correlating the time of geologic events with species/population events is a critical aspect of marine phylogeography.


Article 3: Kraus 2012

Here the authors investigate a genus of freshwater crab, Parathelphusa, for its historical biogeographic distributions in the Sunda region and the relation of those distributions to Pleistocene sea-level changes. The authors suggest that if Pleistocene-aged sea-level changes are responsible for the diversification of Parathelphusa clades throughout the Sunda region, then the rate of speciation should have greatly increased during that time. However, the authors find that most clades have Miocene or Pliocene origins, all with origins from Borneo although some speciation events did occur during the end of the Pleistocene, although rarely and via sporadic dispersal events as there have been no recent land-bridge connections.


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