Many poisonous frogs in South America have articles like “the poison in this one frog is deadly enough to kill a hundred men” but there shouldn’t have been any evolutionary pressure to become that poisonous. Nothing especially large was eating frogs that would require them to become so poisonous. Soo is there any evidence of breeding progressively poisonous frogs for their poison for arrow heads? If that was even a real practice. Hopefully this is the correct subreddit. Thanks in advance.
There is a bit of twist - the frog does not produce its own poison, so they cannot be bred to be more poisonous. I will focus on the family Dendrobatidae which make up the poison dart frogs of Central and South America.
Most ants use formic acid as a weak form of chemical defense, but some tropical species use much more potent chemicals such as pulimiotoxin and batrachotoxin. Researchers found that not only do poison dart frogs use the same poison as found in these toxic ants, but that the frogs themselves regularly consume these ants (Saporito 2004). The mechanism is that frogs consume poisonous arthropods and accumulate increasing concentrations of the toxins; contrariwise, dart frogs raised in captivity have no poison and are harmless (Clark 2005).
How the frogs manage to harmlessly consume these toxins is unknown, although one theory is that particular proteins help with this (Nature 2021). Since all tested species of Dendrobatidae can consume noxious arthropods this trait is apparently ancestral to the lineage, while only some of these species actually express the toxin through their skin glands (Darst 2005). It is this latter subset of frogs which can both consume toxic arthropods and express the sequestered poison which are actually used by Indigenous communities in tropical America.
As for dart gun use, the frogs are hunted rather than bred. For instance, some Emberá hunters in Colombia will kill frogs and place them on a spit, or simply rub a dart over a live captured frog (Myers 1978). There is no evidence of any dart frog breeding before the modern exotic animal trade developed; these hunters obtain their frogs by capturing them.
Sources
Clark, Valerie C., et al. “Convergent Evolution of Chemical Defense in Poison Frogs and Arthropod Prey between Madagascar and the Neotropics.” Proceedings of the National Academy of Sciences of the United States of America, vol. 102, no. 33, 2005, pp. 11617–22. JSTOR, http://www.jstor.org/stable/3376319.
Darst, Catherine R., et al. “Evolution of Dietary Specialization and Chemical Defense in Poison Frogs (Dendrobatidae): A Comparative Analysis.” The American Naturalist, vol. 165, no. 1, 2005, pp. 56–69. JSTOR, https://doi.org/10.1086/426599.
“An Absorbing Tale: Poison Dart Frogs Might Have a ‘toxin Sponge.’” Nature (London), vol. 596, no. 7871, 2021, pp. 166–166, https://doi.org/10.1038/d41586-021-02104-6.
Myers, Charles, et al. "A Dangerously Toxic New Frog (Phyllobates) Used by Emberá Indians of Western Colombia, with Discussion of Blowgun Fabrication and Dart Poisoning". Bulletin of the AMNH ; V. 161, Article 2.
Saporito, Ralph A., et al. “Formicine Ants: An Arthropod Source for the Pumiliotoxin Alkaloids of Dendrobatid Poison Frogs.” Proceedings of the National Academy of Sciences of the United States of America, vol. 101, no. 21, 2004, pp. 8045–50. JSTOR, http://www.jstor.org/stable/3372448.