The Dendrobatidae are themselves a diverse family, with somewhere in the area of two hundred currently recognised species. Many of these have only recently been recognised: nearly half of the currently known species have been named since 1985 (Grant et al. 2006). There are also ninety or so species in the closely related family Aromobatidae that were historically treated as dendrobatids and still may be in some sources. The Dendrobatidae are currently divided between three subfamilies: about half the species belong to the subfamily Dendrobatinae, a bit less than a quarter to the Colostethinae, and close to sixty species are placed in the genus Hyloxalus that forms its own subfamily (Grant et al. 2006).
Members of the Dendrobatidae are best known, of course, for their remarkable toxicity, associated with bright, striking warning colours. The name 'arrow-poison frog' reflects this trait as an arrow scraped across a frog's skin would pick up some of the frog's own lethality. The toxin, comprising various alkaloids, is not produced directly by the frog itself but is instead acquired through its arthropod diet. Most of the alkaloids sequestered by arrow-poison frogs come from ants (Darst et al. 2005) but other potential sources include beetles, millipedes and oribatid mites. However, not all dendrobatids are toxic and colourful. In fact, these features are largely characteristic of the Dendrobatinae only. Members of the Colostethinae and Hyloxalus are mostly cryptic in coloration and largely do not sequester alkaloids. The distinction is not an unshakeable rule: some non-dendrobatine dendrobatids are quite colourful in their own right and a handful of colostethines (members of the genus Epipedobates) are toxic, having seemingly evolved the ability to secrete alkaloids independently of the dendrobatines. Laboratory studies indicate that at least some non-toxic colostethines are able to consume alkaloid-bearing prey without ill effects, suggesting that alkaloid resistance is ancestral for the family as a whole.
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More characteristic of dendrobatids as a whole is their breeding behaviour. As a rule, dendrobatids are more or less terrestrial, not habitually living in water, though many species are found alongside the margins of water bodies and may dive into the water to escape danger. Others will be found among leaf litter or be completely arboreal. Eggs are laid in damp terrestrial locations such as under leaves; males may deposit their sperm before or after the female deposits her eggs. Hatching tadpoles are then carried on the back of one of the parents to a suitable body of water such as a pool or stream. In members of the Dendrobatinae, tadpoles are deposited in phytotelmata, water-filled hollows in vegetation (such as in the cenre of bromeliads or holes in trees). Adelphobates castaneoticus, found in Pará in Brazil, has a habit of using the fallen husks of Brazil nuts. In some species, tadpoles are transferred one at a time; in others, groups of tadpoles will be carried en masse. In most genera, the male parent is the primary or sole transporter of tadpoles. Females of some species may also carry tadpoles; in others, a female finding an unattended cache of eggs will simply eat them. In the dendrobatine genus Oophaga, tadpole transport is the sole responsibility of the female. Following deposition, developing tadpoles of many species live on a diet of detritus. Others, particularly among the phytotelm-inhabiting species, are carnivorous, feeding on insects and other aquatic vertebrates, or even on their own siblings. In the aforementioned Oophaga, the transporting female will also lay a deposit of unfertilised eggs at the same time as she drops off the tadpoles. As well as providing food for the developing larvae, these eggs may also carry a shot of alkaloids to provide a head start in developing their defenses.
Despite their often bright colours, many dendrobatids are poorly known due to cryptic habits and many species are only found in restricted ranges. As well as the usual threats to their survival from habitat destruction and the like, many dendrobatid species are threatened by collection for the pet trade. Their bright colours make dendrobatids popular specimens and captive individuals lose their toxicity if not provided with the prey from which alkaloids are derived. Unfortunately, about a quarter of dendrobatid species are currently recognised as endangered, many severely so. The highest diversity of endangered species is in the northern Andean region, in Venezuela, Colombia and Peru, which is also the centre of diversity for the family as a whole (Guillory et al. 2019). Urgent action may be required if we are to preserve these tiny, shiny, toxic beauties.
REFERENCES
Darst, C. R., P. A. Menéndez-Guerrero, L. A. Coloma & D. C. Cannatella. 2005. Evolution of dietary specialization and chemical defense in poison frogs (Dendrobatidae): a comparative analysis. American Naturalist 165 (1): 56–69.
Grant, T., D. R. Frost, J. P. Caldwell, R. Gagliardo, C. F. B. Haddad, P. J. R. Kok, D. B. Means, B. P. Noonan, W. E. Schargel & W. C. Wheeler. 2006. Phylogenetic systematics of dart-poison frogs and their relatives (Amphibia: Athesphatanura: Dendrobatidae). Bulletin of the American Museum of Natural History 299: 1-262.
Guillory, W. X., M. R. Muell, K. Summers & J. L. Brown. 2019. Phylogenomic reconstruction of the Neotropical poison frogs (Dendrobatidae) and their conservation. Diversity 11: 126.
The paper I have linked should clear up the auratus thing. It is so contradictory that I can only imagine the toxins cause mental incapacity at very low doses. "I did not note any effect from handling them myself."
ReplyDeletehttps://www.biodiversitylibrary.org/page/4413562#page/643/mode/1up
So is it saying there is variation? I had wondered if the misnomer might have been from looking at a preserved specimen that may have lost coloration.
DeleteThe toxin being diet-derived, it does seem that levels can potentially fluctuate over time (the Darst et al. study I cited noted this as a potential complication in measurements). It might be that the author of your link just got lucky. On the other hand, the super-strong batrachotoxins that are the most notorious of the arrow-poison frog toxins are found only in members of the genus Phyllobates, not in Dendrobates.