Australia: Scientists discover rst hybrid sharkJuliet Eilperin, Washington PostThursday, January 5, 2012Scientists have identi ed the rst-ever hybrid shark o the coast of Australia, a discovery that suggests some shark species mayrespond to changing ocean conditions by interbreeding with one another.A team of 10 Australian researchers identi ed multiple generations of sharks that arose from mating between the common black-tip shark (Carcharhinus limbatus) and the Australian blacktip (Carcharhinus tilstoni), which is smaller and lives in warmer watersthan its global counterpart."To nd a wild hybrid animal is unusual," the scientists wrote in the journal Conservation Genetics. "To nd 57 hybrids along 2,000km (1,240 miles) of coastline is unprecedented."James Cook University Professor Colin Simpfendorfer, one of the papers co-authors, emphasized in an e-mail that he and his col-leagues "dont know what is causing these species to be mating together." They are investigating factors including the two spe-cies close relationship, shing pressure and climate change.Australian blacktips con ne themselves to tropical waters, which end around Brisbane, while the hybrid sharks swam more than1,000 miles south to cooler areas around Sydney. Simpfendorfer said this may suggest the hybrid species has an evolutionary ad-vantage as the climate changes.As a result, he wrote, "We are now seeing individuals carrying the more tropical species genes in more southerly areas. In a chang-ing climate, this hybridization may therefore allow these species to better adapt to di erent conditions."The researchers - who had been working on a government-funded study of the structure of shark populations along Australiasnortheast coast - rst realized something unusual was going on when they found sh whose genetic analysis showed they wereone kind of blacktip but their physical characteristics, particularly the number of vertebrae they had, were those of another. Sharkscientists often use vertebrae counts to distinguish among species.The team also found that several sharks that genetically identi ed as Australian blacktips were longer than the maximum lengthtypically found for the species. Australian blacktips reach 5.2 feet; common blacktips in that part of the world reach 6.6 feet.