New species has its anus behind its head

An image of the new species showing the lack of eyes. This specimen had its flesh cleared and researchers stained the bones to show the skeleton. Photo courtesy of: Chakrabarty et al.

In the dark caves of southern Indiana in the United States, scientists have discovered a new species of cavefish that are blind, pinkish, and have their anus behind their heads. This peculiar new cavefish is the first to be described in North America in 40 years, and researchers have named it Amblyopsis hoosieri or Hoosier cavefish, after the Indiana University’s men’s basketball team and a common name for any resident of Indiana.

It all began when Matthew L. Niemiller, a postdoctoral researcher at the University of Kentucky, was studying the Northern cavefish (Amblyopsis spelaea), in Indiana and Kentucky. He found that the fish on either side of the Ohio River seemed to belong to two genetically different groups – one in the north in Indiana, and one in Kentucky in the south. Could these two groups be two different species?

To find out, he teamed up with Prosanta Chakrabarty and Jacques A. Prejean from Louisiana State University. After several hours of crawling through muddy dark caves in wetsuits, they collected 30 fish specimens from Indiana and 11 from Kentucky. A detailed examination revealed that the ones from Indiana were indeed a new species of Amblyopsis, the researchers report in a new study published in Zookeys.

The Hoosier cavefish. Photo by: Chakrabarty et al.

The Hoosier cavefish and the northern cavefish differ in many ways, both in appearance and in their genes. While the new species has a plump, fleshy, and wrinkly body, the northern cavefish has a thin, svelte figure with tighter skin. But what is perhaps most interesting, is the presence of its anus behind its head at the bottom of its body.

“The anus behind the head might help them get the eggs into their gill chamber, where we know they brood their young, another strange behavior,” said Chakrabarty.

Adapted to the complete darkness of caves, the Hoosier cavefish has no pigmentation on its body, and no eyes, like the Northern cavefish. But despite the lack of eyes, the Hoosier cavefish has a functional rhodopsin gene (responsible for the perception of light), while the Northern cavefish does not.

“The rhodopsin gene is oddly functional in the new species although it isn’t helping with vision as it does for us, because the animal lacks working eyes,” said Chakrabarty. “That tells me that some of the DNA is playing catch-up with the changes in the body.”

While the rather odd location of its anus has garnered the Hoosier cavefish plenty of publicity lately, this group of cavefish remains largely threatened. The Northern cavefish is listed as Vulnerable on the IUCN Red List, and Hoosier cavefish could be at greater risk of extinction, the researchers write.

Some of the threats to the caves they live in include groundwater pollution from pesticide and fertilizer use, sedimentation due to agriculture, quarrying, over-collection of specimens for scientific studies and commercial cave tours. But many of these caves are now protected.

“Several cave systems inhabited by Hoosier cavefish are located on state and federally-owned land, such as Spring Mill State Park in Lawrence Co., Indiana, and the Hoosier National Forest,” said Niemiller. “Consequently, access to caves on these properties are regulated and restricted.”

So what does it take to trudge through dark caves and collect tiny blind fish? The researchers tell us below.

Q & A WITH MATTHEW NIEMILLER, AND PROSANTA CHAKRABARTY

Prosanta Chakrabarty holding a blind crawfish from the caves in Alabama. Photo by: Prosanta Chakrabarty.

Mongabay: : What triggered your interest in cavefish research?

Matthew Niemiller: I saw my first cavefish in 2004 while I was working on my Master’s thesis at Middle Tennessee State University. I was studying the phylogenetics and conservation of Tennessee cave salamanders at the time, and was fascinated every time I encountered a cavefish. Needless to say, I was fascinated enough to devote my Ph.D. dissertation to studying their ecology and evolution. But I didn’t see my first Hoosier cavefish until 2007.

Prosanta Chakrabarty: For me it was a trip as a postdoctoral fellow at the American Museum of Natural History to Madagascar in 2008, where we went to some caves and sinkholes where no scientists had ever been before. I had never been to caves and I found them thrilling. Each one was different. Some had species no one had even seen before. The caves were all just stunningly beautiful and serene places (besides all the 20 feet Nile crocodiles) – you never knew what you would see just beyond the illumination of your headlamp.

Mongabay: : What’s a typical day in a cave like?

Matthew Niemiller examining some cave fauna. Photo by: Prosanta Chakrabarty.

Matthew Niemiller: A typical cave trip to study cavefishes starts with a stop at Burger King in the morning for a ham-egg-and-cheese croissant and an orange juice. I need to get some fuel in me because I won’t eat or drink much at all when I am in a cave. There isn’t a worse feeling than crawling through cave streams with 55 Fahrenheit water temperatures in a wetsuit, then having the realization that you need to use the bathroom.

Every cave is different. Some are quite easy to explore and don’t really require you to even to get in the water (except to catch a cavefish, of course). Other caves require wearing a full wetsuit and wading, crawling and even swimming in the cave stream. A typical trip might last from 2 to 10 hours depending on the amount of passage we are exploring. I attempt to document every species I encounter and pay particular attention that are known or thought to be rare or endangered. I record the number of individuals encountered and other life history or ecological data from some species, including body size, evidence of disease or parasites, and possible threats. Threats might include evidence that a septic system is leaking into the cave system or large amounts of trash have washed into the cave.

Prosanta Chakrabarty: Matt and I just went caving in Northern Alabama this past weekend and spent five hours in the cave. He was counting all the cave organisms that he saw, and I was focusing on the fish. But I also enjoyed seeing the many crayfish, crickets and salamanders that are also found in the darkness of the caves. We only saw three cavefish in the entire five hours, but it was worth it.
Sometimes we were crawling with our bellies on the water with our backs near the ceiling, but most often you can stand upright through the larger passages. It can be quite muddy in places and you can see the breakdowns, which are places where part of the cave has fallen apart and either a new passage is born or an opening is closed off. You can’t help but think about the great amount of time that it took to form this subterranean passage.

Distribution of Amblyopsis spelaea and Amblyopsis hoosieri in the Mitchell Plain and Crawford-Mammoth Uplands of Indiana and Kentucky. Image courtesy of Chakrabarty et al.

Citations:

Chakrabarty P, Prejean JA, Niemiller ML (2014) The Hoosier cavefish, a new and endangered species (Amblyopsidae, Amblyopsis) from the caves of southern Indiana. ZooKeys 412: 41–57. doi: 10.3897/zookeys.412.7245

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