Concepedia

The Great American Schism: Divergence of Marine Organisms After the Rise of the Central American Isthmus

Annual Review of Ecology Evolution and Systematics · 2008 · 542 citations · 113 references

TL;DR

The Central American Isthmus, completed 2.8 Myr ago after a 12‑Myr formation, altered Pacific‑Atlantic currents, salinity, temperature, and primary productivity, initiating independent evolutionary trajectories that have led to divergence among surviving marine species. The study uses the precisely dated isthmus event to examine molecular divergence between species pairs on its two coasts. The authors sequenced 38 DNA regions in 9 echinoid, 38 crustacean, 42 fish, and 26 mollusc clades with amphi‑isthmian subclades. Molecular data show that 34 clades diverged during final isthmus closure, 73 earlier, and 8 retained post‑closure gene flow; reproductive isolation is complete only in sea urchin Diadema, while adaptive divergence in life‑history traits—such as increased maternal provisioning in Caribbean invertebrates—has arisen in response to lower primary productivity.

Abstract

After a 12-million-year (My) process, the Central American Isthmus was completed 2.8 My ago. Its emergence affected current flow, salinity, temperature, and primary productivity of the Pacific and the Atlantic and launched marine organisms of the two oceans into independent evolutionary trajectories. Those that did not go extinct have diverged. As no vicariant event is better dated than the isthmus, molecular divergence between species pairs on its two coasts is of interest. A total of 38 regions of DNA have been sequenced in 9 clades of echinoids, 38 of crustaceans, 42 of fishes, and 26 of molluscs with amphi-isthmian subclades. Of these, 34 are likely to have been separated at the final stages of Isthmus completion, 73 split earlier and 8 maintained post-closure genetic contact. Reproductive isolation has developed between several isolates, but is complete in only the sea urchin Diadema. Adaptive divergence can be seen in life history parameters. Lower primary productivity in the Caribbean has led to the evolution of higher levels of maternal provisioning in marine invertebrates.