Trout phylogeny

[DonCooksey]

The thread on Sagehen Creek and hybrids between brook and brown trout got me trying to remember the relatedness of different salmonid groups and why some do hybridize but not others. I couldn't remember, so I just read some papers on the topic. For anyone interested, I'll paste in a phylogenetic tree below that seems to be consistent with most of the recent molecular data.

Char and Brook trout (Salvelinus) are now thought to be more closely related to the pacific salmon/steelhead/rainbow/cutthroat/golden trout group (Oncorhynchus) than to the Salmo group (atlantic salmon and brown trout).

Maybe you all knew this or have discussed it previously on the board, but I thought some might find it interesting. After reviewing the phylogeny, it makes more sense to me now why we can get viable hybrids between species like cutthroats, rainbows, and goldens in the genus Oncorhynchus and only rare and infertile hybrids between brook and brown trout. I'd like to catch one of those tiger trout sometime, though... :twisted:

Another interesting thing is that the more recent phylogeny suggests that anadromy evolved independently at least twice. Previously, it was thought that Oncorhynchus and Salmo were "sister" taxa, and that anadromy in both groups was due to common ancestry.

http://img.photobucket.com/albums/v649/DonCooksey/salmonidphylogeny.jpg

From Oakley and Phillips (1999) Molecular Phylogenetics and Evolution, 11:381–393

Thanks for the tree, I'm sure it will come in useful someday!

[Adam Grace]

That went right over my head, but thanks for the info.

[DonCooksey]

Sorry, I didn't mean to start a technical discussion - I just didn't realize that all of the pacific salmon (chum, pink, kokanee, chinook, and coho) are closely related to steelhead/rainbows, as well as cutthroat and goldens (all of the above are in the same genus). That whole group is also more closely related to char (brook trout, Dolly Varden, char) than to the atlantic salmon/brown trout group (Salmo).

If you do want to get technical, the length of the horizontal lines connecting each cluster on the tree indicate genetic relatedness. Shorter lines mean they are more closely related. The bottom cluster shows that chum, pink, and kokanee salmon form a related group. You can ignore the numbers; they just indicate statistical significance of the groupings.

[Adam Grace]

Thanks for the simplification.

[FishFiend]

I think this is a great topic, but maybe that is because I 'm a fish biologist. I love fish!

[DocEsox]

Geez, I've missed some fun stuff by just recently finding this forum. Love discussing the taxonomy of trouts. Someone stated in the Sagehen thread that tiger trout are sterile hybrids produced in hatcheries.....this is true. From my reading there has been very few verified natural crosses between brookies and browns. Of course, this would have been absolutely impossible historically as brown trout are an introduced interloper to the Western hemisphere. The fish in the Sagehen thread is definitely a brookie....tiger trout generally are brownish yellow with large vermiculations covering the entire body and no spotting at all.....although there is great variation.

Interesting reference to anadromy as all three genus....Oncorhynchus, Salvelinus and Salmo....have anadramous forms. Obviously most Atlantic salmon (Salmo salar) are anadramous, although there are landlocked versions. Even the brown trout has developed several anadramous strains.....although only one in North America. Obviously, steelhead (both O. mykiss irideus and O. mykiss gairdneri) are anadramous as well as some strains of coastal cutthroat trout (O. clarki clarki) although the cutthroat only spend a limited part of each year in the ocean. Salvelinus, the charrs, have developed a few anadramous forms. The arctic charr while primarily lacustrine has a subspecies which has considerable anadromy (S. alpinus erthyrinus). As does the Northern Dolly Varden (S. malma malma) which is almost completely anadramous here in Alaska. Some of its close cousins, the Southern Dolly Varden, are anadramous too. Anadromy isn't as peculiar as you might think.

Sorry.....love trout taxonomy........

Brian

[flyfishnevada]

I just didn't realize that all of the pacific salmon (chum, pink, kokanee, chinook, and coho) are closely related to steelhead/rainbows, as well as cutthroat and goldens (all of the above are in the same genus). That whole group is also more closely related to char (brook trout, Dolly Varden, char) than to the atlantic salmon/brown trout group (Salmo).

Considering the many of the char, the pacific salmon and the rainbow/cutthroat/golden all evolved on this sid eof the continental divide and the Brown and atlantic salmon on the other side it kind of makes sense. It doesn't explain how the brook trout would up on the other side, but considering the ability to interbreed with browns and the similarity of the atlantic and pacific varieties, they must have had a common ancestor maybe when the continents were closer and things were quite differetn geologically.

But what the heck do I know? :D

[DocEsox]

The continental divide wasn't really one of the dividing lines. About 20 million years ago the genus Oncorhynchus and Salmo diverged from a common progenitor.....Oncorhynchus being isolated in the north Pacific Ocean and Salmo in the north Atlantic Ocean. Then about 5 million years ago the genus Oncorhynchus divided from a common progenitor into the salmon and trout groups. About 2 million years ago rainbow trout and cutthroat then seperated from a common progenitor. The charrs, genus Salvelinus branched off from a common progenitor of Oncorhynchus sometime after the Salmo genus had separated. But Salvelinus has a holarctic distribution....it's development is seen from the north and spreads south....has little to do with east or west.

Brook trout's native distribution is all on the northeastern side of North America....they have no natural distribution in the west. The charr's best distinguishing characteristic is their adaption to living in cold waters. The arctic char is the northernmost known freshwater fish and can actually actively feed in water below freezing. Another interesting charr, the Bull trout, is the only one with a distinctly western native distribution. What's fascinating with them, is though they are virtually indistinguishable from Dolly Varden and Arctic char morphologically, the later two are not their closest genetic relation. Bull trout, genetically, are most closely related to the white spotted charr of the Far East and the stone charr of the Kamchatka Peninsula....go figure that one out.

Sorry if I get into this a bit too much....

Brian

[Hairstacker]

Brian, this is fascinating stuff, I don't think you "get into this a bit too much" at all. I had thought the continental divide WAS the major cause of the divergence of the Western vs. Eastern fishes . . . . Very interesting to learn that's not the case. Please don't hesitate to get into it further if you feel inclined to do so, as I'm just trying to learn here. :)

[DonCooksey]

Brian:

Any chance that there could have been migration/exchange between Pacific and Atlantic fish populations through the northwest passage during warm periods between ice ages?

[Digger]

I hope there's not going to be a test on this!?

[DonCooksey]

No worries. Finals are still a few weeks off yet. :lol:

[DocEsox]

Perhaps I was a bit rash to infer the continental divide didn't have anything to do with species and their radiation....it just had little to do with the branching of the salmonidae family of fishes. The CD was considered to be formed by about 60 to 70 million years ago.....long before the salmonids we know today started branching out. Came across a recent publication outlining the current thinking on separation of the genus Salmo from Oncorhynchus. Most believe that it was cooling of the Arctic Ocean about 15 million years ago (ma) that seperated the common progenitor of Salmo and Oncorhynchus into Pacific and Atlantic oceans and the fish were forced to migrate south.....this ultimately lead to their subsequent divergences in the Atlantic and Pacific. This means that each group developed anadromy independently.

I haven't found much information on exactly where it is felt that the genus Salvelinus branched from Oncorhynchus....only that it was after the separation of Salmo from Oncorhynchus and after pacific salmon branched off the rest of the Oncorhynchus genus leading to trout. Nearly all the recent, detailed phylogenetic studies show that Salvelinus is indeed the sister taxa to Oncorhynchus....not Salmo. Although it is interesting there are a few, though rare, natural Salvelinus X Salmo hybrids (which are all sterile) with tiger trout but no known Salvelinus X Oncorhynchus hybrids.

Salvelinus, as mentioned before, developed exclusively from a north to south direction as they are the most cold adapted salmonid. The common progenitor for the Charrs developed into 3 lineages, of which 2 are exclusively North American and monophyletic (only 1 full species)…this would be lake trout and brook trout. The third is arctic charr which has an uncertain lineage and is polyphyletic having numerous subspecies and strains….all of which have still not been delineated or organized completely…..these include arctic charr (3 main North American subspecies), dolly varden (a north and south subspecies) and bull trout. Brook trout evolved only in the northeast which is their entire native range. They exist farther south than any other charr as they have developed an ability to live in water which is warmer than any other charr, similar to the temperature range of rainbow trout.

The continental divide does have some issues with speciation during and since the last glacial age which ended 10,000 or so years ago. The original cutthroat progenitor first invaded the west coast probably in the Columbia River drainage. They spread deep into the Rocky Mountains and as time progressed they were cut off from the ocean. This lead to geographic isolation which then gave rise to the 14 subspecies of cutthroat. With only a few exceptions these developed without other salmonids around and is why they are so susceptible to replacement by nonnative species….they did not evolve in a competitive ecosystem. The only subspecies which did was coastal cutthroat trout (O. clarkii clarkii) and because they evolved with rainbow they were able to keep their reproductive isolation and their was little hybridization. But stocking with nonnative rainbows can break down the barriers of reproductive isolation…..we have really screwed things up with so many of these fish by not understanding what was going on when for decades we threw stocked trout everywhere. All subspecies of cutthroat have been reduced to just a fraction of their original native ranges….two are extinct and a couple of others pretty darn close to extinct.

Rainbows developed later beginning with redband trout and the most recent evolution being the coastal rainbow trout (Oncorhynchus mykiss iredeus).

Study hard….the test will be sometime next month……. ;-)

Brian