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...

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.



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?

[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.