Josh's Frogs strongly recommends against mixing different species and morphs of poison dart frogs in captivity. Not only would we recommend against mixing Dendrobates tinctorius with Dendrobates auratus, but we would also recommend against mixing Dendrobates tinctorius 'Azureus' with Dendrobates tinctorius 'Cobalt'. There are several reasons for this.
1. Different species/morphs of poison dart frogs can crossbreed/hybridize.
Many closely related species of dart frogs are capable of breeding with each other. For instance, Dendrobates tinctorius, Dendrobates auratus, Dendrobates leucomelas, and Dendrobates truncatus are all closely related and can breed together and produce offspring. When different species breed together and produce offspring, it is called hybridization and the resulting offspring are called hybrids.
Among many species of dart frogs, distinct populations exist that are represented by different colors and patterns in adult animals. These separate, distinct populations do not breed together in the wild, but may readily do so in captivity. Breeding of two different populations of dart frogs is called crossbreeding, and the resulting offspring are called crosses.
In the picture above, you can see Phyllobates terribilis 'Mint' (white frogs), P. terribilis 'Yellow' (yellow frog) and P. bicolor (2 yellow orange frogs on the right). All of these frogs are capable of breeding together. If a Mint and Yellow terribilis produced offspring, they would be called crossbreeds. If a Mint or Yellow terribilis bred with a bicolor, the resulting offspring would be called hybrids. Note the relatively skinny bicolor on the far right - when a smaller species or morph of dart frog is housed with a larger and more aggressive morph/species, the less aggressive animal may not get enough food.
Although hybrids/crosses are typically outwardly healthy, they are generally frowned upon in the dart frog community. Hybrids and crosses are generally sterile, and therefore (luckily) incapable of reproduction. Breeding poison dart frogs (and the related behaviors) is one of the most rewarding parts of their ownership. Hybrids/crosses tend to vary quite a bit in appearance, but are typically quite ugly when compared to the wild types that produced them. Sometimes, hybrids/crosses resemble one parent so closely they could be mistaken for a 'pure' morph/species of dart frog, and sold (intentionally or otherwise) as such, thus polluting the few precious bloodlines in the hobby. Once a hybrid/cross is produced, there is no going back and making the animals 100% wild type again - the phenotypic (appearance) and genotypic (genetic) integrity of the animal is lost. With many dart frog populations at risk in the wild, the last thing we should do as responsible hobbyists is reduce the captive gene pool.
2. Poison Dart Frogs are very territorial animals, and can be very aggressive towards each other.
It's hard to think of any species of frog as being aggressive, but poison dart frogs certainly are! Poison dart frogs tend to be relatively peaceful when young, but can become increasingly aggressive with age - especially after reaching sexual maturity (around 10-12 months with most species). Within a pair or group of the same species/morph, the aggression is typically dissipated among the animals, and they can generally tolerate it without issue. When different species or morphs of dart frogs are housed together the size and aggression differences present tend to allow one or two frogs to glean the upper hand, leaving the 'losers' to slowly perish if not removed. True, a large vivarium (like the size of a large zoo exhibit) and dense plantings can reduce the stress experienced in a mixed tank, but even the largest of mixed vivaria typically experience loss of several frogs before the resident frog population stabilizes. The zoo exhibit pictured in this article measured approximately 5'x3'x5', or about 560 gallons. The exhibit contained about 20 frogs, providing about 28 gallons of space per frog - much more than the often cited 5-10 gallons of space per frog cited for home vivaria.
3. Mixing non-sympatric animals may expose all animals involved to new and harmful microorganisms.
Sympatric animals are those animals that occur together in the wild, such as zebras and giraffes on the African savannah. Therefore, non-sympatric animals are those that do not naturally live in the same region. Because these different species do not occur naturally together, either may carry different diseases, bacteria, viruses, or other microorganisms that they evolved to handle, but the other species may not be able to. Many of the different species and morphs of dart frogs available in the hobby are from different regions and countries from other commonly available species. Mixing species/morphs from different areas puts the frogs at risk.
In the vivarium pictured above, it contains Epipedobates anthonyi (Ecuador), Phyllobates terribilis and bicolor (Colombia), Dendrobates auratus (Panama), and Dendrobates tinctorius (Suriname). These different species would not naturally encounter each other in the wild, and could potentially convey different parasites or diseases to other animals that have not evolved to naturally cope with it.