Stickleback – The super fish

Darting through Cheney Lake in Anchorage, Alaska are thousands of small fish, about three inches in length, with three spiny projections that jut off the top of their bodies, pricking anything that dares touch them. The color of their scales varying in color depending on the season, sex, or population from which they descend. They gleam shiny silver, blue, or a dull brown, sometimes with a greenish hue. They’re named threespine stickleback, and they’ve become a powerhouse organism for study.  Found in nearly all Alaskan lakes and across most of the northern hemisphere, scientists have taken keen interest in these fish for the practical uses they hold for studying evolution and conducting research.

Threespine stickleback from Cheney Lake in Anchorage, Alaska during their reproductive stage of life. The fish with blue eyes is a reproductive male.

        At the University of Alaska Anchorage, Kat Milligan-Myhre, heads a laboratory of undergraduates, graduates, lab techs, and post docs who are all using threespine stickleback as a model organism for a variety of projects on host gut microbe interactions. The lab is able to study how the microbes within the gut of threespine stickleback, the host, affect a variety of things like development, physiology, behavior, and more. Milligan-Myhre developed a procedure that allows the lab to fertilize eggs of the fish and then make them free of all microbes. They can then add back in select microbes or none at all to study how the microbes are actually affecting the fish.

A 7-day-old transparent juvenile threespine stickleback. Milligan-Myhre has developed a protocol to rear threespine stickleback free of microbes until 14 days after the eggs they’ve hatched from have been fertilized.

        “Stickleback have a number of really cool qualities. One is that they are transparent so we can actually watch fluorescent microbes move around in the gut of a live stickleback,” said Milligan-Myhre, “We can make large amounts of genetically similar eggs from a single cross or a couple of crosses… with fish you can get 100 to up to 200, if you’re lucky, of genetically related fish. That allows us to have a lot of power so we can do some really good statistical analysis on these changes that we’re seeing when we treat these animals.”

Kelly Ireland and Kat Milligan-Myhre set traps for threespine stickleback in Cheney Lake in Anchorage, Alaska in May of 2017. The lab uses minnow traps that have a funnel and hole on either end of the trap that threespine stickleback then swim into and get trapped.

        They are studying a variety of populations from varying lakes across Alaska, but by far their most frequented lake of interest is Cheney Lake. The lake had threespine stickleback introduced to it in 2009 from a parental population found in Rabbit Slough, Alaska, by Frank Von Hippel, a former professor at UAA, who like Milligan-Myhre used them as a model organism. Von Hippel’s lab was interested primarily in the evolution of the fish, however.

Ryan Lucas, Emily Lescak, and Kelly Ireland of Kat Milligan-Myhre’s lab pull traps from Y Lake of the Talkeetna Lakes chain in Talkeetna, Alaska. The lab then does in field gut dissections to assess gut microbe composition within the threespine stickleback.

        “What really sets stickleback apart from zebrafish, which are the traditional go to fish model, is that we can take stickleback that have evolved in different environments and we can relate the environments in which they evolved to their physiological and genetic variation,” said Emily Lescak, former doctoral student of Von Hippel’s, currently working as a post-doctoral fellow in Milligan-Myhre’s lab, “Basically we can understand what selection pressures in the environment cause a fish to evolve in certain ways, so we can understand what sort of ecological pressures there are on fish populations.”

Threespine stickleback fish from Rabbit Slough, near Wasilla, Alaska. The Rabbit Slough population is anadromous meaning they’re born in freshwater, then travel to oceanic environments for most of their life, and then return to freshwater to mate.

 

       Incidentally there’s already evidence that the threespine stickleback Von Hippel introduced into Cheney Lake are already undergoing evolution from their anadromous (meaning the fish, like salmon, are born in freshwater, travel to the ocean, and then come back to the freshwater to mate) ancestral form, to freshwater forms. The threespine stickleback in Cheney Lake were introduced in 2009 after the Alaska Department of Fish and Game applied a Rotenone treatment in October, 2008, to the lake. Rotenone was used to eliminate northern pike that were introduced illegally. The Rotenone treatment wiped out all fish populations in the lake and allowed Fish and Game to restock Cheney Lake with rainbow trout, and Von Hippel to introduce threespine stickleback from a known population, Rabbit Slough. Milligan-Myhre’s lab has been collecting data on Cheney Lake and threespine stickleback from the lake monthly to assess the changes of the threespine stickleback population over time.

 

        “We can follow evolution in real time. That’s exciting,” said Milligan-Myhre.

        The lab is collaborating with a lab at Stony Brook University in New York to look at genetic differences as the population evolves. Milligan-Myhre’s lab hopes to also take a look at how as the population changes over time into their freshwater form the microbiota and threespine stickleback’s immune response to microbes also change.

Rachael Kramp an undergraduate student of Kat Milligan-Myhre’s lab, works with microbes from the guts of threespine stickleback from Cheney Lake in the anaerobic chamber of Milligan-Myhre’s lab at the University of Alaska Anchorage.

        The tools these fish offer are nearly limitless from using them as a model for biomedical research, as they have similar physiology to humans, to studying evolution, these fish also make great models for studying ecotoxicology, as well as, host microbe interactions, just to touch on a few of their benefits. The threespine stickleback came to be a model organism in the 1900s with the work of Nobel Prize laureates, Niko Tinbergen, Konrad Lorenz, and Karl von Frisch, because of the ease to which they could be manipulated in the lab, now in 2017 the threespine stickleback shows no signs of slowing down as being the model organism of many scientist’s dreams. In 2018, hundreds of researchers will even gather together for the 9th International Conference on Stickleback Behavior and Evolution in Kyoto, Japan. These prickly little fish may not seem like much to the majority of people, but to many scientists they are the crux of their entire careers.

 

Written by Kelly Ireland. Kelly Ireland is an undergraduate student doing research in Kat Milligan-Myhre’s lab.

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