Trigonostigma hengeli pairing up with trigonostigma heteromorpha?

[fozziebear]

I'm witnessing some breeding behaviour with my rasboras whilst i have them in a small holding tank, funnily enough the only real pair that has formed are from different species, (harlequin and hengeli) will these actually breed? i can't find much information on the subject.

 

[AbbeysDad]

Saywhat? (bet you can't say that title 3 times quickly!)

I don't know the answer, however, often different, but closely related species in the same genus can breed (Guppies and Mollies, Swordtails and Platies) but for some others, if/when they produce hybrid offspring they are sometimes sterile.
I think that It's also rare, but possible for different species to uhm pair/engage (dating?), but not produce any offspring.

 

[fozziebear]

Definitely a mouthful , i know livebearers can cross breed no problem, was just wondering about rasboras really, mine have never showed any breeding behaviour before this in 4 years, just happy to see them courting and twirling together.

 

[Byron]

This is the primary reason that species of the same genus sometimes should not be kept together. It depends upon the species and genus, and while there is really no problem if two species should cross-breed, you have to be careful never to release any of the fry into the hobby. In other words, they remain in your tanks until death. We must be careful not to contaminate the gene pool of any species. I have cory species that have crossed and produced fry, but they will live out their lives in my tanks.

The background to your question may be interesting, so I'll summarize. The discovery in the 1970's of DNA has significantly altered our understanding of species relationships, which is why so many previous classifications (scientific names of fish species) have been and are being revised. The species is the most specific classification, and the next up is the genus (plural genera). Each of these designations can be considered a clade, which is a group of organisms that consists of its common ancestor and all lineal descendants. "Clade" comes from the Greek κλάδος ["klados" in our alphabet] which means branch.

A species obviously means all the organisms are as closely related as is possible to be. Species are organized into genera, and each genus may have from one to any number of species; a genus containing more than one species will be either monophyletic or polyphyletic.

Monophyletic means that the clade (genus) consists of a common ancestor and all species in that genus are descended from that ancestor. This means that each species will share a large number of traits; physiological traits include dentition, scale counts, fins, sometimes but not always external markings, etc. But usually there will be behaviourial traits too, where each species may show similar behaviours, aggressiveness, etc. So knowing the genus of a species can give us a fairly effective clue as to how this species will function and behave, similar to its close relatives.

A polyphyletic genus means that there are species in the classification that are not descended from the one common ancestor, but have one or more other ancestors. So that genus is not true, strictly speaking, hence the revisions as ichthyologists identify them by cladistic analysis using the DNA. Obviously these species will have more variance in physiology and behaviours, though the degree may vary; I'll come back to this below.

Now to the examples. Trigonostigma is a monophyletic genus; there are four described species, all of which descended from the one common ancestor and no other. And (so far as we know) there are no other species on earth that share this ancestor. So the species, Trigonostigma heteromorpha, T. espei, T. hengeli and T. somphongsi, are very closely related. [The latter species has a dark broad stripe (rather than the triangular mark common to the other three species) that runs laterally below an iridescent stripe; this species occurs in the basin and floodplain of the Menam River in Thailand and is very rare.] Being so closely related, these species might cross-breed. It is a basic premise in the hobby that species of cyprinids in monophyletic genera should never be housed together, simply to avoid this occurring; but again, provided they live their lives out in your tanks the problem of contamination of the gene pool should not arise. I should perhaps mention that one reason this is so important is that with the extinction of so many species in the wild, aquarium specimens of some of these may be the way to re-establish them; this is only viable if the species are kept pure genetically.

My next question would be, exactly what interaction are you seeing between these two species? Males displaying to one another cross-species is very common, and males displaying to females of their own or related species is also not uncommon. But how far does this actually go? If you witness the two fish depositing eggs and fertilizing them, that is one thing; but the "preliminaries" may not lead to actual spawning, though from the above it is always a possibility.

Although outside your initial question, I will just briefly comment on polyphyletic genera to complete the picture. Genera like Hyphessobrycon and Hemigrammus in the characidae family hold well over 100 described species, but it is now a certainty that these are not all related, so these are polyphyletic genera. Another example is Corydoras; in the older literature, the Corydoradinae family has three genera, Aspidoras, Brochis and Corydoras. Corydoras has more than 160 described species. Phylogenetic analysis to date has established there are actually nine different clades within Corydoras, so this genus is polyphletic; what this means is that this genus will eventually be broken into nine different genera, as there are nine distinct ancestors in the present genus.

This has already occurred with the "cory" species Corydoras barbatus ‘I & II’, C. prionotus, and C. macropterus. Britto (2003) determined that these three species were in fact a sister clade to the species in Aspidoras; to retain monophyly of both clades, he resurrected the genus Scleromystax. The species were assigned to Scleromystax, with S. barbatus the type species. [S. salmacis Britto & Reis, 2005 subsequently became the fourth species in the genus.] All species are endemic to small tributary streams in several coastal river basins in southern Brazil (Britto and Reis, 2005).

Brochis has already been invalidated. The genus Brochis, containing three species B. britskii, B. multiradiatus and B. splendens is now considered to be synonymous with Corydoras [Britto, 2003; Ferraris, 2007] and there are two or three other Corydoras species that are now known to have descended from the same ancestor as these three. These are thus now within Corydoras. But, when the nine lineages are finally sorted out, these species will almost certainly be in the genus Brochis, as this is the oldest name assigned to any of these species, and under the rules of the ICZN it takes precedence.

The last three paragraphs are not directly relevant but I though you and others might be interested in a more complete explanation.

 

[fozziebear]

Very informative, thanks a lot byron you answered pretty much everything i was thinking about, if they do spawn im not purposely raising the fry, so if any do survive it will be through luck rather than judgement, obviously i would never take hybrids anywhere near an LFS.

 

[AbbeysDad]

So did @Byron say "yes"? LOL ;-)

 

[fozziebear]

hahaha yeah from what i read he said that all 4 species are from the same ancestor which means they could all interbreed from what i know, mine are only exhibiting behaviours related to pairing though, ive only seen the hengeli try to hug the rock a few times, they are ignoring the java fern, and the other "pair" i thought was happening looks more like 2 males having squabbles.

 

[Byron]

Another thing to keep in mind that I didn't mention directly is that species tend not to cross-breed on their own (we're talking egg layers here, not livebearers). So with the two closely-related species in the same tank they might engage in this "preliminary" interaction but never follow through. Which is what I meant by seeing actual egg scattering or not.

One illustration comes to mind, the Marble Hatrchetfish, Carnegiella strigata. This species has a varied pattern depending upon its origin location, primarily with respect to the mid band across the keel. In some fish, this band is thicker and divides mid-way along the length, while in others it divides from its commencement more like an elongated "V." As well, the dark tone of the marbling on the first is black, whereas on the second (the "V") it is dark brown. At one time or another, five species were recognized, reorganized into two by Weitzman in 1960, C. strigata and C. vesca. Gery (1977) recognized the very close physiological structure and modified these into subspecies as C. strigata strigata and C. strigata fasciata respectively, and also noted that all species in this genus are polytipic, meaning that two or more distinct populations can be recognized within the species concept. Weitzman & Palmer in Reis, et al. (2003) considered the one single species C. strigata. All of this was without the benefit of phylogenetic analysis.

Phylogenetic analysis has now shown that while the genus Carnegiella is monophyletic, the species C. strigata is not. Examination of populations within the Negro and Uatuma blackwater rivers has revealed two monophyletic lineages within this species, with considerable genetic distance (10-12%) between them, making it probable that there are two distinct species within this complex (Schneider, et al, 2012; Abe, et al, 2013). It is not all that surprising to discover that these two lineages do correspond primarily with the afore-mentioned differences. Specimens collected and analyzed by these recent studies has revealed that in the one or two areas where they are both present, they never cross-breed. To cite from Schneider, et al (2012):

The occurrence of sympatry between the two C. strigata lineages in the Cajuri Stream, in the lower portion of the Negro River, suggest that, even when in contact, the lineages are probably reproductively isolated and demographically independent, since they coexist and do not share haplotypes. As the two lineages detected in C. strigata are clearly recognized as distinct genetic and ecological and geographical entities, they may be considered evolutionarily significant units (ESU). An ESU is defined as species and sub-specific categories that are reciprocally monophyletic, with significant allelic divergences that manifest in ecological distinctiveness (Moritz, 1994). This is extremely important because C. strigata is widely exploited as an ornamental fish in the middle and upper Negro River, which are the main areas of harvesting of ornamental fishes. As the protected areas of Anavilhanas National Park and Ja´u National Park exist in the lower portion of Negro River where the two lineages co-exist, it is to be hoped that exploitation under the same taxonomic denomination and loss of genetic diversity will be avoided.​

 

[fozziebear]

Your posts are like paying for learning Byron, without the paying part, thanks for taking the time to put this across, i assure you it is not wasted on me.

 

[Byron]

Your posts are like paying for learning Byron, without the paying part, thanks for taking the time to put this across, i assure you it is not wasted on me.

Thank you. This for me, as someone who absolutely loves research and ichthyology, is always fascinating, though I realize not everyone sees science the same way. But we have a totally scientific hobby, and understanding these things, even though rudimentary, can tell us a lot about the species and how to care for it. I must say though that much of my posts in this regard are simple cut/paste from profiles or articles I wrote over the past decade for other sites. So compiling a response is not as onerous as it would be if I had to pull out of my files these papers and read them again.

 

[fozziebear]

It leads to much more reading than just this though... opens up new avenues of intrigue for myself, from what i have read so far, they do occur in the wild together in places, but i cannot find any articles on crossbreeding in the species and for there to only be 4 distinct lineages then they cannot be crossbreeding in my own opinion, time will tell if eggs are actually scattered i would be pretty shocked.