Happening right now under the sea off SA ... evolution!
Study of little critter on west and east coasts challenges a long-held belief about the evolution of marine species
The dramatic temperature range along SA’s coastline is driving the evolution of new species, scientists believe.
An international study led by a University of Johannesburg zoologist has found that the different temperatures on the west and east coasts cause new species to evolve even if they are not isolated from similar fish nearby.
The critter responsible for the finding, which challenges a long-held belief that new marine species can evolve only in isolated environments, is the Knysna sand goby.
A team led by Peter Teske from the Centre for Ecological Genomics and Wildlife Conservation at UJ caught 312 examples of the tiny fish over two years in the mouths of nine estuaries between Langebaan in the west and Durban in the east.
Before releasing the fish, they used fingernail scissors to snip off part of their pectoral fins, and subjected 109 samples to DNA tests.
The team discovered that while the goby’s regional populations are similar, they showed differences in nine genes affected by water temperature. The rest of the genes showed no identifiable differences.
“Each regional goby population is already adapted to its preferred thermal habitat, and migrants that disperse into nearby regions that are too warm or too cold will not do as well as the locals,” said Teske, whose colleagues in the study included Sophie von der Heyden, from the Evolutionary Genomics Lab at Stellenbosch University.
With sea temperatures around SA ranging from 10ºC to 25ºC, the areas that provided Teske’s sample came from ocean regions classified as cool-temperate, warm-temperate, subtropical and tropical.
The study, published in the journal Proceedings of the Royal Society B, said SA’s coastline provided “a unique opportunity for studying the importance of incipient environmentally driven parapatric speciation in the sea”.
Parapatric speciation occurs when two sub-populations of a species, such as the Knysna sand goby, evolve reproductive isolation from one another while continuing to exchange genes.
Teske said that over time the rest of the sand goby’s genome would “catch up” with the genes affected by sea temperature.
“Even later, the new species will also change morphologically [that is, in its form and structure]. Only then will they be recognisable without the help of genetic methods.”
The results have important implications for the management of threatened or exploited species, and fish stocks around the world.
Co-researcher Luciano Beheregaray, from Flinders University in Adelaide, Australia, said: “When several very young species that already cannot live in each others’ habitats are all treated as a single species, this can result in the over-fishing of locally adapted stocks, or the extinction of a rare species that has been mistaken for its more abundant neighbour.”