Picture it. You are a larva, freshly hatched from an egg, and squirming around with just one goal. Survive. How best to survive? Well, you need food pronto; you’ve literally never been hungrier in your life!! You survey your options, in addition to the flour surrounding you there are a bunch of lush round eggs, some full siblings, some half siblings, and some of no relation at all. While flour alone may be sufficient for survival, cannibalising some eggs would provide you with an edge over the other larvae.
So now you have to choose. Will you become a cannibal, bettering your chances of survival? Does your relatedness to the egg affect the degree of cannibalism?
Are you… confused?
In 1980, Michael J. Wade decided to study the tendency of larvae from the coolest named beetle, the confused flour beetle (Tribolium confusm), to cannibalise eggs. He used it as a platform to investigate the conditions required for the evolutionary theory of kin selection.
Kin selection is defined as:
“Natural Selection in which an apparently disadvantageous characteristic increases in the population due to increased survival of individuals genetically related to those possessing the characteristic”
So here, larvae eat eggs due to a genetically inherited behaviour which you think would be bad for the population but since larvae that ate the eggs thrive, the behaviour has stuck around and even increased in the population.
In 1980 this theory was poorly defined, while it was agreed that the relatedness of individuals is important, there were many differing opinions to whether the breeding structure was important leading Wade to his big research question.
However, firstly I had a question of my own: Why bother developing evolutionary theories, they require such specific conditions that it does not seem to be realistic or applicable in nature?
It had really stumped me as it made the whole study of evolution seem rather redundant. Thankfully I have come up with an answer which is actually pretty simple, the experiments we all conduct give information on the present. Organisms in the present time, how they act and react, right at this moment. Developing evolutionary theories and taking the time to carefully refine them is all we have, it is the very best we can do to take what we see happening right now and use it, not only opening up the mystery of what occurred in ancient populations as species fought to survive but to also predict what will happen to populations in the future.
Now sense of importance restored, back to Wade and his big research question!
What is the role of population breeding structure in the evolution of social behaviour?
To test this Wade designed 3 different population structures which tested both the effect of the relatedness of individuals and the breeding structure on the evolution of the egg cannibalism behaviour.
Population Structure One is shown above. 5 larvae from each of the selected 15 mating pairs were put into separate vials; in both groups 45 fully related eggs (R=50) were offered over time and all beetles were allowed to mature then counted to determine the degree of cannibalism. If no cannibalism occurred, you would have 50 adults in each vial (5 larvae + 45 eggs). The mature beetles are then subjected to different breeding structures, either random or within-group mating. Larvae were again collected from 15 mating pairs and the experiment was repeated for 8 generations.
Population Structure Two is the same only half related eggs (R=25) were offered.
Population Structure Three is also the same but with non-related eggs (R=00) offered.
What Wade found…
At first glance the results seemed to be a bust with no trends in the rate of cannibalism for either breeding structure, there are fluctuations, but they are attributed to an uncontrollable aspect of environmental variation.
But don’t despair!
When Wade plotted the difference between the average cannibalism rate when eggs were related and when the eggs were not related, effectively normalising the results, theoretical expectations as predicted by the kin selection model were met!!
There was a lower cannibalism rate when larvae and egg are closely related, but only in the within-group breeding structure. Population structure did not seem to affect the cannibalism rate when random breeding occurs.
It turns out this all comes down to the variance of the genetic basis for this behaviour within the groups. It is either preserved (within-group mating) or destroyed (random mating).
Variance is essential for the ability of a behaviour to become pronounced, so it is no surprise that when random mating occurs there are no behavioural trends.
Furthermore, he concludes that population genetic models which assume random mating of individuals are inappropriate to the study of evolution of these traits.
To simply answer Wade’s question, population breeding structure DOES plays a critical role in determining how a social behaviour evolve and should be considered when studying the kin selection theory!
Let’s now take a moment to appreciate the irony that clarity is provided by none other than the confused flour beetle!
Maybe, just maybe, this wee beetle is not as confused as first suggested…
To read the full paper by Michael J Wade click here.