Date Published: 5 June 2018

Bright colours on some frogs both warn predators and act as camouflage

The strikingly bright yellow colours on poison dart frogs also have a camouflage function according to a recent study involving fieldwork in the jungles of Guiana, also known as French Guiana (located on the north Atlantic coast of South America - see map), followed by laboratory visual search experiments and computer modelling in the UK.

The research was conducted by scientists at Bristol University's School of Biological Sciences and School of Experimental Psychology, both based in Bristol, England 1. They considered how the 'dyeing dart frog', also known as the 'dyeing poison frog' and scientifically as Dendrobates tinctorius benefits from the effects of its colouration, both (a) warning its predators against attacking it and (b) helping to conceal the frog by also having a camouflage function.

More about Poison Dart Frogs

The dyeing dart frog which was the subject of this study is a species of poison dart frog, of which there are many subfamilies and genera. Poison dart frogs generally are small (1.5cm - 6cm length), brightly coloured and endemic to humid, tropical environments including rainforests in Central and South America

Poison dart frogs in general (various species) are well known for their deadly toxins and bright colours. Many poison dart frogs secrete lipophilic alkaloid toxins through their skin, approx. 28 structural classes of alkaloids being known in poison frogs 2,3. To take an extreme example, has been suggested that the most poisonous dart frog known, the golden poison frog Phyllobates terribilis, has enough toxin to kill about ten to twenty men or about ten thousand mice 4. Poison dart frogs' notoriety for deadly toxins and bright colours has made them a popular example of 'warning coloration' in biology.

The dyeing dart frog (see photo) is highly toxic and warns its predators with a yellow-and-black pattern.

Research outcome

The recent research suggests that the bright yellow colour pattern on Dendrobates tinctorius does not merely indicate 'danger' (to possible predators of this frog), but also has a camouflage effect. The explanation for this apparently contradictory finding is that although highly conspicuous at close range, the particular colours and their arrangement on the frog enable its overall pattern to visually 'blend together' to form background-matching camouflage when viewed from a distance.

The scientists interpreted this interesting aspect of the colours and pattern on this type of frog as enabling members of the species to "get the best of both worlds". That is, they have effective camouflage until a predator is close enough to discover such a frog. From that situation the frog then benefits from its bright, highly salient, 'warning' colouration in a different way, specifically the possibility that its bright colours might dissuade the predator from harming that individual frog.

The lead author Dr Jim Barnett completed this research while based Bristol University (England) and is now working at McGill University in Canada. He explained that:

"Effective as warning signals are, it's not necessarily the best strategy to be maximally conspicuous.
_Certain predators have evolved tolerance of toxins that would be deadly for humans, and some individual predators may have not encountered the warning signal prey before (a dangerous mistake for the predator, but also for the frog).
_So, colour patterns that could be distinctive close-up, but work as camouflage from a distance, would provide a clear advantage
."

Co-author Prof Innes Cuthill added that:

" How many other animals use 'distance-dependent coloration' to balance competing evolutionary pressures is yet to be explored.
_Being able to signal when close to a would-be mate, whilst remaining inconspicuous to more distant predators would seem beneficial. So too for human applications such as military camouflage, where recognition by allies is as important as concealment from foes. Also, signage that only need be clear at the distance where the information is needed, but might be distracting if detected earlier
."

Further details about this research are described in the recent paper by Barnett et.al. 5.

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