Natural hybrids in Amazon & Orinoco Basins

[apistomaster]

I came across a short publication about the prevalence of natural hybrids and occurrences of the genera, Cichla, in both the Amazonas and Orinoco Basins. I thought it is interesting as it may relate to Hypancistrus. I make no claims of expertise in this subject but perhaps it will have more meaning to more qualified PC members than myself.
https://sites.google.com/site/stuartcwi ... ridization

[MatsP]

I'm also no expert, but I don't really see what this article adds to what we already know - that fish can hybridise with fertile offspring.

I also believe that Cichla are significantly more mobile than Loricariidae - I would expect, in rainy season in particular, that Cichla will move over rather large areas, where I expect Loricariidae to be relatively stationary. From what I understand, there is no evidence that Loricariidae move very far at all.

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Mats

[apistomaster]

Hi Mats,
What you say may be true but none the less the Genus Hypancistrus came to inhabit both the Orinoco and Amazon Basins. Presumably not by hitching rides.
I came across the short piece while considering completely unrelated fish but it seemed to have a little relevance to any genus or species which are naturally found in either river basin. I assume they did not spontaneously arise independently in two different major river systems.

[MatsP]

Hi Mats,
What you say may be true but none the less the Genus Hypancistrus came to inhabit both the Orinoco and Amazon Basins. Presumably not by hitching rides.
I came across the short piece while considering completely unrelated fish but it seemed to have a little relevance to any genus or species which are naturally found in either river basin. I assume they did not spontaneously arise independently in two different major river systems.

Yes, my point wasn't that they don't move at all, but rather that populations are relatively stationary. Of course, fish populate spaces which are suitable habitat. And yes, I agree that Hypancistrus are (most likely) related between Rio Orinoco and Rio Negro, which is connected by the Casiquaire channel. But this migration to populate new places, as far as I understand, is not a quick migration, but something that takes time.

What I'm trying to say is that the "natural hybrids" are much more likely in species that travel large distances, than in fish that are relatively stationary, as those that travel are more likely to meet similar fish from a different species. If all types of Hypancistrus (just to give one example, many other Loricariidae are similar) were to travel great distances from where they were born, I'd expect to see absolutely no differences. Yet, we have distinctly different markings, body shapes, fin shapes. They are a young genera, so they are still closely related, and I'm not saying they don't naturally hybridise where they ocurr side by side, but I also don't buy the "all the Hypancistrus from Rio Xingu are one great mix of L260 crossed with L66 crossed with L333 crossed with L250", or whatever people tend to say.

And before someone attacks the fact that I have no evidence to prove this, I would argue that there is no evidence of the contrary either. And I'm not sure recent DNA testing of these fish will prove me right, but I'm also not confident that the DNA testing is sufficiently "wide-based" to show proper differences between groups that are subtly different.

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Mats

[apistomaster]

I think I poorly chose the title of this topic. I didn't even spell "Natural" correctly.
Like I said, I was looking into another family of fishes and thought this would be just a tidbit for those who are interested in the dispersal of certain genera of fishes into the two river basins while others remained indigenous to one or the other basin. Like no Discus ever came to populate the Orinoco but became speciated into three species within solely the Amazon Basin. There are many such examples going only one way while many others ended up well represented in both.
I was not trying to prove any point or be argumentative. Just wanted to share something I came across that I found interesting.
You did touch on the geological connection which is entirely relevant to what I am looking into; that being the role the Cassaquire River/connection has played in the dispersal of several aquaristically important families of fishes between the Rio Negro and Orinoco drainages.

[Suckermouth]

I'm guessing this website is actually information from Willis et al. 2010 talking about gene flow in Cichla across the Casiaquiare. I haven't read that one in a while but for those that are able to dig that up they can read more about the topic.

[Bijn]

What I'm trying to say is that the "natural hybrids" are much more likely in species that travel large distances, than in fish that are relatively stationary, as those that travel are more likely to meet similar fish from a different species.

I'm not so sure about that. Maybe species that travel large distances have a bigger area of distribution and have genus members that are separated by big natural barriers while "not so mobile" species have a smaller area of distribution with less "space" between a different species in their genus. Maybe the effort they have to make and the bad luck they have to have is relatively seen the same in both type of species.

I also have no evidence to prove this.

[MatsP]

What I'm trying to say is that the "natural hybrids" are much more likely in species that travel large distances, than in fish that are relatively stationary, as those that travel are more likely to meet similar fish from a different species.

I'm not so sure about that. Maybe species that travel large distances have a bigger area of distribution and have genus members that are separated by big natural barriers while "not so mobile" species have a smaller area of distribution with less "space" between a different species in their genus. Maybe the effort they have to make and the bad luck they have to have is relatively seen the same in both type of species.

I also have no evidence to prove this.

Exactly, Hypancistrus (and a large portion of other Loricariidae) are MUCH smaller than Cichla ("Peacock Bass", a large predatory cichlid, many of these reach 2-3ft/60-100cm at full growth), and as we all know, Loricariidae aren't the greatest swimmers. The Loriicariidae also live in areas that are rich in natural barrier. There are some smaller Loricarriidae with wide distribution, and some of the larger ones certainly have large distribution - but large distribution doesn't necessarily mean large movements of the fish as such. I'd expect that predatory fish move further to find prey than fish that live on little invertebrates at the bottom of the lake/river.

And finally, you don't get variation if everything gets mixed up all the time. If you paint with water colours and don't rinse the brush when moving from colour to colour, you eventually end up with a brown-grey mix-up of all the colours on every block of colour. Same would apply to the Hypancistrus, you'd probably have something that is indistinctly brown/grey with some not so easy to describe lines/spot pattern. They clearly have been separated for some time - at least in some areas. I expect the L129/L340 didn't separate so long ago, so they are fairly similar [and I'd possibly expect them to be the same species - or "just split" (we're talking geological time here - so ranges of 10000-1M years].

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Mats

[Mike_Noren]

Dams (which wipe out previously impassable rapids and falls) and canals have removed a lot of previously existing barriers to dispersal, not to mention that people are actively introducing Cichla to various places all around Brazil, which increases the probability that populations previously isolated from each other will come in to contact.

Continuous gene flow, even at a very low level, will homogenize the gene pools, prohibiting speciation and cause already distinct species to coalesce. That interbreeding will rapidly homogenize gene pools is why hybrids in nature are rare. The only time one get long-lived hybrid zones is when the hybridization does not lead to homogenization of the gene pools: hooded crow and carrion crow interbreed and have viable hybrid offspring, yet remain distinct because the hybrids have lowered fitness (outbreeding depression).

EDIT: The original link doesn't make much sense. What article is it referring to?

[dw1305]

Hi all,
Purely as a hunch my money would be on their being a very large number of genetically distinct Hypancistrus species, possibly including many that are cryptic, and not distinguishable on morphological grounds. I'd also guess the same applies to the smaller Panaque species -"Panaqolus", and that they are not that closely related to the larger species.

The other scenario would be that their are relatively few variable species, and that the "species" we have named are convenient "pigeon holes" within the range of variation, this could be due to speciation being ongoing or continuous gene flow.

It doesn't help for either Hypancistrus or Panaque, but I think people should have access to "Molecular phylogeny of the Neoplecostominae and Hypoptopomatinae (Siluriformes: Loricariidae) using multiple genes" CA Cramer, SL Bonatto… - Molecular Phylogenetics and Evolution, (2011) <http://www.sciencedirect.com/science/ar ... 0311000030> Which is well worth a read, and gives an example of an approach you could use to get nearer to the "answer".

cheers Darrel

[apistomaster]

I'm guessing this website is actually information from Willis et al. 2010 talking about gene flow in Cichla across the Casiaquiare. I haven't read that one in a while but for those that are able to dig that up they can read more about the topic.

Hi Milton,
I have recently been receiving a flurry of papers from friends written by Willis et al. Including a lot about Cichla specie distribution and molecular genetic data indicating the amount and directions of gene flows.
I have just begun wading through and trying to understand these and similar papers.
I do not have any formal training in this field but have learned a little over the years.
I'm still in that zone where a little knowledge is kind of dangerous to use in public.
I am not trying to pretend I know more than I do.