Researchers from the American Museum of Natural History and Louisiana State University have discovered that two groups of blind cave fishes now separated by about 6,000 miles of open ocean are each other’s closest relatives. These eyeless fishes, one group from Madagascar and the other from Australia, descended from a common ancestor before being separated by continental drift nearly 100 million years ago, the scientists say. Their study, which was published this week in the journal PLOS ONE, also identifies new species that add to existing biological proof for the existence of Gondwana, a prehistoric supercontinent that was part of Pangaea and contained all of today’s southern continents.
The cave fishes, of the genus Typhleotris in Madagascar and Milyeringa in Australia, are small—less than 100 millimeters long—and usually lack pigment, a substance that gives an organism its color and also provides protection from the sun’s ultraviolet radiation. These characteristics, coupled with a lack of eyes and enhanced sensory capabilities, are common in many cave organisms.
“I had seen the Australian form many years ago while caving in Cape Range National Park, well before I became an ichthyologist, but upon catching my first Malagasy Typhleotris I remember thinking how morphologically similar the two genera were despite being on opposite sides of the Indian Ocean,” said John Sparks, a curator in the Museum’s Division of Vertebrate Zoology and an author of the paper. “Given a high degree of morphological convergence in cavefishes in general, we needed DNA evidence to test this relationship, and sure enough, they were revealed to be each other's closest relative.”
The newfound genetic relationship between the trans-oceanic groups also is an exciting geological find. Sparks calls it a “remarkable example” of a phenomenon known as Gondwanan vicariance, the split in the geographical range of an organism when the southern supercontinent broke up in the Mesozoic.
One of the new species discovered by the researchers is a novelty among cave fishes because it is fully and darkly pigmented. Stranger yet, phylogenetic analysis showed that it evolved from a pigment-free ancestor.
"It has generally been thought that cave organisms are unable to evolve to live in other environments, in other words to ‘reverse’ their specializations for a subterranean life,” Sparks said. “Our results, and the fact that we have recently discovered new cave fish species in both Madagascar and Australia belonging to these genera, are intriguing from another perspective: they show that caves are not so-called 'evolutionary dead ends.’”
Funding for the research expedition was provided by the Constantine S. Niarchos Expedition Fund, established by the Stavros Niarchos Foundation to support the research of museum curators around the globe.
For more information about this study, click here to read the Museum’s press release.