Celebrating Sculpin Speciation

Merry Christmas everyone! Since you all have been good little nerds and scientists this year you get a brand new blog post in your stocking. Not only is it our first post in a while, but I'm excited to introduce you to our first ever guest writer.

Brian Harmon (Harmonus fishnerdii)

Brian is currently pursuing the glamorous world of graduate studies at the University of Nebraska. He's a sarcasm enthusiast and passionate advocate for (less than) charismatic (usually micro) fauna. So with out further ado let's get this post started!

Some fish are delicious, others put up a heck'uva fight, a few are particularly weird, aesthetically pleasing, or a critical keystone species. Then there are freshwater sculpins. These cryptic fish pretty much just sit on the bottom, doing nothing. All the time. If they don't swim they just sink, I mean c'mon, even we hydrodynamically challenged humans float. 

A sculpin taking a break from a hard day of... sitting on a different rock.

A true trophy of a sculpin is about 110mm (that's like 4 inches for those who deny the superiority of the metric system) so sculpins don't exactly attract much of a following from the fishing or environmentalist crowds. Actually they don't really have any following, except for a couple of fish nerds here and there. And yet, despite rarely being seen, they are all over North America and Europe, even in super remote and highly polluted waters.

A good day's haul of trophy sculpins.

Now that I have lowered the expectations for this month's Depth and Taxa, it's time to explain why sculpins are an amazing group of fish to study. 

The majestic sculpin. 

Courtesy and permission of Jason Ching

Sculpins present one of those philosophically challenging dinner-table appropriate conversations (especially since you don't want to eat them): what exactly is a species? Now, we drop species names all the time. Even here in this blog, scientific names get thrown around like it's no big deal. Yet it turns out the first man responsible for our modern definition and naming of species, Carl Linnaeus, had it pretty easy. When you have to start at square one, you pick the obvious animals. And it turns out telling the difference between an elephant and a rhinoceros isn't too difficult. And even this guy ran into all kinds of trouble. 

The Hamburg Hydra: one of many "species" Linnaeus debunked 
Courtesy: wikipedia Commons

So let's use a non-aquatic example most people are familiar with: lions and tigers. And a hypothesis: species cannot produce offspring with one another. Except clearly delineated species like lions and tigers can produce offspring: ligers (and the lesser known tigons). "Okay, okay, but they're sterile" you say. Well not... completely. Ever heard of the litigon? Now ligers and litigons are a bit of an odd example because tigers and lions don't meet in the wild.

"Ligers, and tigons, and pizzly bears, oh my!"
Courtesy: Wikipedia Commons

Well here is where freshwater sculpins come back into the story. Freshwater sculpins are notoriously difficult to tell apart unless you like counting fin rays and chin pores under a microscope. And if you're a sane human-being, you don't. 

No, please, you id this one.

Sculpins also don't move much. Which means isolated pockets of different species can be found within the same, rather small river system. Often these pockets overlap. Thus biologists face a challenging puzzle: how do we separate species that look nearly identical and whose ranges overlap?

Modern DNA analysis has gone a long way to solving that problem, while at the same time providing new challenges. For example, the cleverly named and ubiquitous slimy sculpin (Cottus cognatus) seems to coexist with just about every other sculpin species. However, recently biologists discovered the slimy sculpin is not one species but multiple, unidentified species. One newly identified group of previously "slimy" sculpins has been renamed the cedar sculpin (Cottus schitsuumsh). Just try pronouncing that. (Or go here to learn how). Oh and here is the kicker. They live in the same places as slimy sculpins.

A range map for slimy sculpins. Cedar sculpins are limited to western Montana,
 an area also occupied by slimy sculpins
Courtesy: The state of Montana

And they may hybridize with slimy sculpins, producing hybrids that can breed again. Further adding to this confusion is that one of the many species that coexists with slimy and cedar sculpins, the mottled sculpin (C. bairdi) is actually the Rocky Mountain sculpin (C.bondi) because the long-described mottled sculpin doesn't exist in Montana. So just how many species (and which?!) are we talking about?

So.. wait a minute. what defines a species? Well we will add one more group of fish into the mix. Rift Valley African Cichlids (sick-lids) to help explain. A single species of cichlids first colonized Lake Victoria about 10,000 years ago. Within that geologically tiny amount of time, hundreds of species... well... speciated. Many of these species are more closely related to one another than humans are to each other, and yet we are one species, while they are many. Turns out many of their behaviors and visual differences exist specifically to identify exactly who they should mate with. Side note: wouldn't that be nice? 

One of many, many, cichlid species
Courtesy: Wikipedia commons.

Humans introduced the Nile perch (Lates niloticus) into Lake Victoria for food. The introduction of a novel predator drove many of the cichlids to extinction. Many of those left began hybridizing due to changes in population numbers and environmental conditions caused by the Nile perch. Those hybrids continue to propagate, creating, you guessed it, the begins of new species.

A Nile perch. Fun fact: Linnaeus described it, and lions, and tigers. 
Courtesy: Wikipedia commons.

So I leave you with the ever-infuriating question of what exactly constitutes a species? Is it a specific level of genetic difference, producing only sterile hybrids, not producing hybrids very often? Or is the concept of a species a messy continuum that we humans have tried to neatly categorize? Though we can be fairly certain sculpins and elephants are not the same species, we can't figure out how many sculpin species we are talking about.

The closest thing I could find to an elephant-sculpin hybrid. 
Trust me, I looked far too hard.
Courtesy: Wikipedia commons.

It turns out, scientists argue about what is or is not a species all the time. Whether a population of fish is a different species often depends on whether you are a lumper or a splitter. And here's why it matters. Conserving species for the future is a challenging proposition full of trade-offs and hard choices. If we want to save species for future generations, what do we do when we aren't even really sure what the definition for species is? Think it over, and when this dilemma starts to get too hard, go id some sculpins. Maybe start here for a free guide on some more aesthetically pleasing marine sculpins!

Your first challenge.

Thanks once again to Brian Harmon for breaking the seal on guest posts here at Depth and Taxa. If you're an aspiring scientist or educator and you'd like to be featured on this blog contact our editor at patrick@nwnhc.com.

References:

Columbia Slimy Sculpin — Cottus cognatus. Montana Field Guide. Montana Natural Heritage Program and Montana Fish, Wildlife and Parks. Accessed via: http://FieldGuide.mt.gov/speciesDetail.aspx?elcode=AFC4E02080. Last accessed: 12/14/15.

Goldschmidt, T. 1996. Darwin's dreampond. The MIT Press.

USDA Forest Service, news release. Accessed via: http://www.fs.fed.us/rmrs/news/releases/content/?id=14-01-29. Last accessed: 11/15/2015.



Rocky Mountain Sculpin — Cottus bondi. Montana Field Guide. Montana Natural Heritage Program and Montana Fish, Wildlife and Parks. Accessed via: http://FieldGuide.mt.gov/speciesDetail.aspx?elcode=AFC4E02380. Last accessed: 11/15/2015