Posted on | July 8, 2011 | Comments Off
Researchers have demonstrated that Hawaiʻi is not an evolutionary dead end for marine species. Mānoa Postdoctoral Fellow Christopher Bird and researchers at the Hawaiʻi Institute of Marine Biology have shown that Hawaiʻi hosts three limpets (cone shaped marine snails, locally known as ʻopihi) that defy classification as dead-enders.
Why there are so many species in the sea and how new species form remains a central question in marine biology. Below the waterline, about 30 percent of Hawaiʻi’s marine species are endemic—being found only in Hawaiʻi and nowhere else on Earth—one of the highest rates found worldwide. But where did this diversity of species come from?
Hawaiʻi is famous for its adaptive radiations (the formation of many species with specialized lifestyles from a single colonist) above the water line. Still, spectacular examples of adaptive radiations such as Hawaiian honeycreeper birds and fruit flies are not found in Hawaiian waters. Marine species were thought to colonize Hawaiʻi and eventually diverge into an isolated native species, but were doomed to an evolutionary “dead end” with no further specialization and speciation.
The standard explanation for three species of ʻopihi is that Hawaiʻi was independently colonized three times. However, using DNA, fossil and geologic evidence, Bird has shown that Hawaiʻi was successfully colonized only once by Japanese limpets, approximately 5 million years ago. The ʻopihi then speciated within the Hawaiian Archipelago along an ecological gradient, as they invaded deeper habitats, forming the three species that people observe today.
Bird proposes that differences in the timing of sperm and egg production and the ability to survive at particular shore levels led to the ʻopihi radiation. While ʻopihi may look similar to the untrained eye, Bird demonstrates that each species possesses novel evolutionary adaptations that confer an advantage at a particular shore level, a hallmark signature of natural selection and adaptive radiation.
“The research on ʻopihi give us better insight to the processes that produce biodiversity, especially in the ocean where the speciation process is not well understood,” says Bird. Prior to this report, no marine radiations had been found in Hawaiʻi.