The Madeleine Brand Show for January 26, 2012

Marine biologist Pat Krug talks hybrid sharks

University of Queensland, Australia

Dozens of sharks showing DNA from both the Australian blacktip shark and the common blacktip shark, making them the first-discovered inter-species hybrid shark.

We’ve created hybrids before: a liger is the offspring of a male lion and tigress. A mule is the offspring of a male donkey and a mare. Now researchers have discovered a natural hybrid, the first union between two different shark species- the Australian blacktip shark and its Indo-Pacific ocean relative.

Cal State LA Marine Biologist Pat Krug said scientists have recently discovered more hybrids, partly because of improved genetic techniques in the lab. The question, said Krug, is whether there are more hybrids than ever before, or are biologists just getting better at finding them. If there are more hybrids than before, could global warming be playing a part?

"Species move around trying to track their comfort zone, so maybe one or both of these species moved into waters they didn't used to occupy, where they ran into each other, and maybe not knowing better, made sweet shark love and had hybrid babies," Krug said.

With sharks, Krug said the concern might not be global warming.

"The sharks have been around, pretty much unchanged, for a few hundred million years. So I think the bigger threat to sharks is actually fishing," he said.

Humans fish for the same food that sharks eat. Krug said that studies show that placing limits on fishing in certain areas allows small fish to repopulate, and in turn leads to a huge increase in shark biomass. It could be that the two shark species swam farther looking for food and ended up "mingling."

Krug said hybridization occurs more commonly than some may think; different plant species interact all the time, for example. "If you remember your old high school biology class, where you learn what makes a species a species is it doesn't breed with other species – well that’s just not true," Krug added. In almost any organism, species can hybridize. Krug said the question is whether or not they do, and how the hybrids fair.

"These rare events that cause an exchange of genes between species can be really important evolutionary engines of innovation, and sources of novelty that you just wouldn't see coming. These hybrids could persist and become their own species," he said.

Princeton researchers Peter and Rosemary Grant studied a male Galapagos island finch that was blown to another island. "He sang a very weird song but [a local female] dug it, so they got together and they made hybrid offspring," Krug explained.

The father's sons learned his foreign song, and his daughters inherited their mother's affection for the song. The offspring interbred within themselves for many generations, and Krug said that in time, they can evolve into their own species.

Our new shark friends seem to be forging their own path. Researchers found larger populations of the hybrid shark about 1,200 miles further south of both parent species, in much cooler waters.

"They are survivors, and it remains to be seen what the fate of these wacko hybrids is," Krug said.

Guest:

Pat Krug, marine biologist and professor at California State University Los Angeles


With contributions by Andrea Wang

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