Regarding the info on interbreeding Byron (which was useful and interesting) - I have told my lfs about the possibility of me getting some hybrid cories and as I really don't want any more panda's they have still offered to take them in. One staff member said no problem, they can go into our display tank but the other made a valid point that I wanted to share ... If they can interbreed in a fish tank they can interbreed in the wild. We can't possibly know if that is where all the different cory types have come from and we all get excited about wild caught fish... happily paying much more money because it's a species caught in the wild that we've never seen before - how do we know if it's a new species or a hybrid? .... something to think on maybe?
Before I respond to your question about the species, I must say that it is sad to hear that your store is willing to take in possible hybrids; this is something that we as hobbyists should never condone or encourage. Keeping pure strains of fish is extremely important biologically, environmentally and ecologically. Although not likely to be needed in the case of panda corys, there are other species of tropical fish that are extinct or close to extinction in nature, and aquarium fish could well be the source of re-introduced species. It is one thing to confine experimental hybrids to one's aquarium, but quite another matter to release it to the hobby. Enough on that, now to your species.
Hybridization among corys in their habitats is very probably non-existent. For one thing, the species rarely mix, and even when they are known to, cross-breeding has never been documented. When we confine fish to the very small and enclosed space of an aquarium, they can be affected in ways that would absolutely never occur naturally. Sometimes the offspring are sterile, which is one way of nature telling us it is not "natural," as such fish would never survive in the wild but die out. But in terms of geography, many species of cory, especially those now being discovered for the first time, are endemic to one specific stream or creek, and found no where else. Each of these species descended from ancestors, and this is where we get into phylogenetics. As for the many species, this is an example of Darwin's discovery of natural selection at work. And it is occurring with many different Amazonian species besides corys. You can be assured that these new species are not hybrids, and phylogenetic analysis confirms this.
Phylogenetic analysis became possible after the discovery of DNA in (I believe) the 1970's, and over the past two or three decades has become more and more standard as part of the process in describing species.
Phylogeny is sometimes referred to as the natural relationships and is an attempt to construct the history of all life based on the evidence from both living and fossil organisms. This allows us to trace a fish back to its original ancestor
. Fishbase lists 159 valid species in the genus Corydoras, and new species are being discovered and described regularly. Phylogenetic analysis allows ichthyologists to ascertain just where each of these species fits.
A genus (plural genera) is a grouping of one or more species that share identical properties. Prior to the discovery of DNA and development of phylogenetics, ichthyologists used physical characteristics to classify species into genera. Dentition was a major factor, along with fin ray numbers, internal physiological characteristics such as bone structure, and so forth. Outward appearance was considered but was often of less importance. Thinking only of corys, all species in the genera
Aspidoras, Corydoras and
Brochis have the same general appearance, and they also share a number of identical characteristics beyond this. These genera are thus classified in a family, here known as the Callichthyidae [family names always end in "dae"]. But because there are many other species that share these characteristics but also have significant variances, the family was divided into subfamilies, and our corys and their closest cousins are in the subfamily Corydoradinae [subfamilies end in "nae"].
With the benefit of phylogenetics, we now see that some of these fish are not so closely related, in spite of their general outward appearance, but certain others are. Thus, we have suggestions that instead of three genera, there should be nine.
Brochis as I mentioned previously has already been invalidated as a distinct genus. In spite of their different physical characteristics--"brochis" fish are larger with a rather higher profile, and the dorsal on the three
Brochis species has between 10 and 18 rays, while on all "corydoras" species it has 6 to 8 rays--the three species are now
Corydoras. As you can see, in the new classification these outward physical characteristics are not of prime significance in classification.
The present genus Corydoras with its 159 species is termed polyphyletic because all of the species did not descend from the same common ancestor, and conversely all of the descendants of an individual ancestor are not included.
Classification now aims for monophyletic genera, which is a taxon (group of organisms) that forms a clade, meaning that it consists of an ancestral species and all its descendants.
The variety of "cory" species, many having very similar colour patterns, all evolved independantly from some ancestor. Allopatric speciation, also termed geographic speciation, occurs when populations of a species become isolated, to the degree that influences or prevents genetic interchange. Distinct species, or sometimes subspecies, may occur; or the species may remain basically intact genetically and form variants. This has occurred with many fish, especially those that have a widespread range. The Blackwing Hatchetfish, Carnegiella marthae, is now known to have at least three cryptic species, but further sampling will be required before ichthyologists can be certain these are variants (as presently held), subspecies or distinct species. This is what seems to have occurred with many of the species now being discovered as collectors enter areas of the rainforest previously never explored, at least for fish.
This has been lengthy, but feel free to question and I will do my best.
Byron.
