Curious about Trichomycterus distribution

[bekateen]

Hi All,

This is nothing more than an exercise in curiosity: I recently looked at the distribution map for the genus

Trichomycterus

, and I couldn't help notice the bimodal distribution of the species we have here on PC.

My curiosity is about what could be responsible for such a split in this map. Right off the top, I'm aware that there are several factors to consider, a few of which I'll list here:

1. To begin with, I realize that the PC list of species in this genus is profoundly incomplete. I've read that this genus is a very speciose genus (about 200 spp), so it's my expectation that a lot of the relevant species are missing from the Cat-e-Log (31 appear in the Cat-e-Log); if they were all to be added, maybe the bimodal distribution would disappear, or at least perhaps a bridge would form along the Andes to connect the more northern and southern groups together.
2. I realize that many of these spp are mountain stream spp, so of course it's reasonable to expect their absence from much of the flat lands. But barring my first point, why aren't there more species running along the Andes? Why are the areas of Bolivia and southern Peru so vacant? Is it that many fish aren't collected there?
3. And if they are mostly montane in their distribution, how is it that they cut across southern Brazil as seen in the distribution map? Again, is it merely an artifact of where species tend to get collected for geopolitical reasons? Or are there biogeographical issues involved?
4. Finally, relevant perhaps to no more than the lack of representation in the Cat-e-Log but should not be relevant to the real distribution of the genus, this genus is not very common in the pet trade, so I understand a lack of info on them as a group.

I'd like to get more info from you experts. I suppose the answers may be really straightforward and I just don't know them due to my naiveté. So if anyone feels like humoring me to explain, or wants to share the curiosity, I'd like to hear back from you.

Cheers, Eric

[Bas Pels]

While I am unable to answer any of your questions, I would like to point out that there is a genus of cichlids - Australoheros - which are found in Southern Brasil, Uruguay, Paraguay and Argentina. Their closest living ralatives are the Central American cichlids.

No relative is found in between, but the recent described genus Mesoheros is also thought of as coming from central America, and now found in the Pacific coast areas of Ecuador, and Colombia. These are, however, not close relatives of Australoheros

I just wanted to point out that there is another group of fishes with a rather similar distribution

[bekateen]

Thanks Bas Pels,

Maybe it doesn't answer the question, but it does add to the story. If there are other fish, catfish or not, that have the same distribution, then it might provide clues to explain why or how the pattern developed.

Cheers, Eric

[Jools]

It's mostly to do with the fact that all the species have not been entered and those that have been entered are either from the few species we see in the hobby or species we have pictures of for one reason or another.

That said, if we put them all in, I'd suggest that while more widespread, they're going to be a lot more of them closer to where there are more universities and/or studies made of these fishes.

Jools

[bekateen]

That said, if we put them all in, I'd suggest that while more widespread, they're going to be a lot more of them closer to where there are more universities and/or studies made of these fishes.

[coelacanth]

I can think of others that have a similar distribution, Salminus is one genus that springs to mind, gymnocharacine and stevardine tetras, there's another characid genus that I can't quite recall.

[Acanthicus]

As Jools stated already, the map doesnt show the real distribution of the genus. CentralBrazil is full of Trichomycterus, so is Bolivia and there is even one species endemic to a small tributary of lago Titicaca in Bolivia, which is missing in the map as well.

cheers, Daniel

[bekateen]

Thanks to all of you for your feedback. Yes, I suspected it was mostly an artifact of an incomplete database (my point #1), but it is helpful to me to hear this from others with more experience than myself.

Perhaps it is nothing more than coincidental, but it is odd none-the-less. Even if the other areas where the group is not currently found in our database (geographic regions connecting the two distribution areas together) are not well sampled or well represented in the aquarium pet industry, there are certainly plenty of fish of other groups from the same locations which are present in the pet trade. So it's not because nobody would ever come across these fish.

Thanks for the cerebral distraction. The way my mind works is to look for patterns and then ask if there's any meaning to them. And of course patterns can develop by sheer coincidence, even if the probability of them developing is extremely low. But without following up with questions, we run the risk of overlooking something of interest, which otherwise is not inherently obvious. So for example, some of you mentioned other fish taxa which have similar distributions to the one shown above. If they are not as speciose as Trichomycterus, what is the explanation for their broken distribution? ... Just something to ponder when the mind is idling.

Cheers, Eric

[racoll]

As Jools said, the pattern is not biogeographic, and certainly an artefact of the species richness and how much taxonomic work has been done on the group in each area. You certainly do get them in the central Amazon (although not super abundant and they seem to prefer the upland streams), but they're a difficult group and there are few experts and lots of species.

Isolated coastal drainages tend to be more tractable, as species are usually endemic and there is less diversity.

See GBIF: http://www.gbif.org/species/2339002

[bekateen]

Thanks racoll, I often forget to check GBIF, even though it is a wonderful resource.

Cheers, Eric