# General Topics > General Discussion & News > Press / News Items >  Peru poison frog reveals secret of monogamy

## John Clare

*BBC News (London, UK) 22 February 2010: Peru poison frog reveals secret of monogamy*

*The first monogamous amphibian has been discovered  living in the rainforest of South America.*
Genetic tests have  revealed that male and females of one species of Peruvian poison frog  remain utterly faithful. 
More surprising is the discovery that  just one thing - the size of the pools of water in which they lay their  tadpoles - prevents the frogs straying. 
That constitutes the best  evidence yet documented that monogamy can have a single cause, say  scientists. 
Details of the frog's sex life is to be  published in the journal The American Naturalist.
"This is the first discovery of a truly monogamous amphibian," says  biologist Dr Jason Brown, then of East Carolina University in  Greenville, North Carolina, who made the discovery with colleagues Dr  Victor Morales and Professor Kyle Summers. 
The monogamous frog  species _Ranitomeya imitator_, known as the mimic poison frog, is  already known to science. 
In recent years, Dr Brown and his  colleagues have extensively studied many of its habits, which were  filmed by the BBC natural history documentary series Life in Cold Blood.  
After mating, a female mimic poison frog lays her eggs on the  surface of leaves. 
The male frog then takes away the tadpoles  that hatch, carrying them one by one on his back to pools of water which  collect in bromeliad leaves high up in the branches of trees.



Each  of half a dozen babies are put into their own tiny pool, which he then  looks after. 
When the tadpoles become hungry, the male calls to  his female partner who arrives to lay a non-fertile egg in each pool,  which the tadpole eats as food. 


But while the male and female  frogs appear to act in unison, new experiments have revealed the extent  of their fidelity.
Many animals appear to be monogamous, with males and females forming  pairs that can often last a lifetime. 
But the recent explosion in  genetic analyses has revealed many of these so-called monogamous  relationships to be a sham. 
While many animals might stay  together and breed, they will often sneak off and cheat on their  partners when they get a chance. 
So Dr Brown and his colleagues  decided to check out the mimic poison frog more closely. 
They  sampled the DNA of many pairs of adult frogs, and the subsequent  generations of tadpoles they produced. 
Of 12 frog families, 11  had males and females that remained continually faithful to one another,  together producing all their offspring. In the twelfth family, a male  frog mated with two females. 
"Others have found evidence of  social monogamy in amphibians where parents remain paired, however they  didn't look at the genetics of these couples and their offspring to  confirm this," Dr Brown told the BBC. 
"Or they have looked at the  genetics and observed that they are actually promiscuous." 
So  that makes the mimic poison frog the first confirmed monogamous  amphibian. 
That contrasts with another closely related frog  called the variable poison frog, which the mimic poison frog imitates,  having a very similar colour pattern. 
Genetic tests on the  variable poison frog (_Ranitomeya variabilis)_ by the researchers  show it is promiscuous.
Further research by the team has also revealed why the two frogs,  similar in so many ways, are sexually very different. 
The  variable poison frog lays its eggs in much bigger pools of water, five  times as large on average than those used by the mimic poison frog. 
Also,  the female plays no part in their raising, leaving their care to the  male frog only. 
When the researchers moved tadpoles from both  species into different sized pools, they found that the tadpoles grew  quickly in the larger pools, which contain more nutrients, but could not  survive alone in smaller ones. 
That strongly suggests that  variable poison frogs don't need to stick together, as their tadpoles  can survive in larger pools without feeding from their mothers. 
Mimic  poison frogs have been forced to take a different path, however. 
Their  tadpoles cannot survive without the care of both their father and  mother, as there is too little natural food in their smaller pools.
So the adult frogs stick together. 
Overall, the researchers  believe they have found convincing evidence of an evolutionary chain of  causation: changing the breeding pool size forced the mimic poison frog  to change its system of parental care, with males and females working  together. That then culminated in social and genetic monogamy. 
If  the pools were bigger, the frogs wouldn't have to remain faithful, as  they wouldn't be tied by their need to work together to raise their  brood. 
"These frogs are truly devoted to their offspring, and to  each other," says Dr Brown, who is now studying at Duke University in  Durham, North Carolina, US. 

*Full article: BBC - Earth News - Peru poison frog reveals secret of monogamy*
(Photos used in this posting are not those from the BBC news article but are the same species, showing same behaviour.)

*Dr. Jason Brown's Article in the American Naturalist: A Key Ecological Trait Drove the Evolution of Biparental Care and Monogamy in an Amphibian*
Abstract: Linking specific ecological factors to the evolution of parental care  pattern and mating system is a difficult task of key importance. We  provide evidence from comparative analyses that an ecological factor  (breeding pool size) is associated with the evolution of parental care  across all frogs. We further show that the most intensive form of  parental care (trophic egg feeding) evolved in concert with the use of  small pools for tadpole deposition and that egg feeding was associated  with the evolution of biparental care. Previous research on two Peruvian  poison frogs (_Ranitomeya imitator_ and _Ranitomeya variabilis_)  revealed similar life histories, with the exception of breeding pool  size. This key ecological difference led to divergence in parental care  patterns and mating systems. We present ecological field experiments  that demonstrate that biparental care is essential to tadpole survival  in small (but not large) pools. Field observations demonstrate social  monogamy in _R. imitator_, the species that uses small pools.  Molecular analyses demonstrate genetic monogamy in _R. imitator_,  the first example of genetic monogamy in an amphibian. In total, this  evidence constitutes the most complete documentation to date that a  single ecological factor drove the evolution of biparental care and  genetic and social monogamy in an animal.

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