Begging signals are honest in mimic poison frogs

I know many children who bug their parents incessantly when they want something. A new pair of trainers that all the cool kids at school have. A newly released computer game, which is far better than the one released last week. Perhaps a tasty chocolate treat before dinner? I’m sure many of us have been guilty of this at some point, and we hope our poor parents have since forgiven us.

But can we honestly say that we really needed those things that we begged so much for?

This puzzle also applies to begging in young animals. An obvious example is a nest full of the brightly coloured open mouths of hungry chicks. These begging signals stimulate food provisioning by parents that, by preventing starvation, ensure their young survive and pass on their own genes to future generations.

But parents have to balance their offspring’s needs with that of their own, because feeding young is costly. They expend precious energy finding the food, make themselves vulnerable to predators, and they are unable to eat the food themselves – a high price if food levels are already low.

Because of this dilemma, parents will lower how much effort they put into feeding their young if they think that they’re not really hungry.

 

800px-Carrion_Crow_Nest_16-05-10_(4612735510)
A nest of begging carrion crow (Corvus corone) chicks. Wikipedia Commons

 

The begging signals of hungry young therefore have to make the parents truly believe that they are hungry. That is, they have to be reliable signals of need. They have to tell the parents that: “I am truly hungry and if you don’t feed me I will die and therefore your genes will not survive” or something similar. Begging will only persist in nature if this occurs – as an “Evolutionary Stable Strategy” (ESS) – because otherwise the benefits of begging would be lost.

Over the years, three main hypotheses have been suggested about how the reliability of begging signals is achieved.

These are:

  1. Begging intensity reflects offspring need.
  2. Begging is costly.
  3. Parents provide the correct amount of food in accordance with offspring need (1).

A study published in Animal Behaviour today has tested these hypotheses in the tadpole offspring of mimic poison frogs, Ranitomeya imitator. In a series of experiments, the study by graduate researcher Miho Yoshioka and Professor Kyle Summers at East Carolina University found evidence for all three of these hypotheses.

800px-R._imitator_Chazuta
Mimic poison frog (Ranitomeya imitator). Wikipedia Commons

The team found that:

  1. Tadpoles that were given less food increased begging behaviour = signalling need.
  2. Tadpoles that were experimentally made to beg by the researchers suffered a cost (e.g. showed slower rates of growth).
  3. Parents were more likely to feed tadpoles that were fed a non supplemented diet as opposed to siblings fed a supplemented diet.

The researchers conclude that begging signals in R. imitator are honest and may predict differences in degree of parental food provisioning to offspring.

So, next time you ask your parents for something you don’t absolutely need… think again. You might actually ruin your chances of them getting you something you really do need.

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