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Truncation selection is when a breeder selects for animals that exhibit a value for a trait that is above a certain threshold. What is it called when nature selects for a value of a trait that is above a certain threshold? I want to say natural truncation selection, but I don't see any mention of that. To clarify, what I mean is, what is it called when, as a result of natural selection, all perish but those with a value for a particular trait that exceeds a particular threshold.

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  • $\begingroup$ The term that comes to my mind is directional selection, but I'm not sure that's what you're asking about? $\endgroup$ – rachelette Jan 21 '18 at 15:27
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Truncation selection

The term truncation selection has been used a lot in theory papers because it is a simple model and because it is of interest to breeders. Truncation selection is most likely more common in a breeding setting than in nature and from wikipedia, truncation selection is defined as specific to breeding

In animal and plant breeding, truncation selection is a standard method in selective breeding in selecting animals to be bred for the next generation

However, as much as the definition fail to repeat animal or plant instead of just animal, IMO it fails to recognize that such notion could as well exist in nature. I would personally not be shock to read a paper talking about truncation selection in wild populations.

Threshold model

If you really want to avoid talking about truncation selection, then you can eventually picture the phenotypic trait as a liability factor (as it is done in sex determination literature, see Perrin and Beukeboom's book) and selection acting as a threshold on this factor. Note that the concept of threshold and threshold model is very common and everyone will understand what you mean.

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  • $\begingroup$ "If you really want to avoid talking about truncation selection, then you can eventually picture the phenotypic trait as a liability factor (and it is done in sex determination literature, see Perrin and Beukeboom's book) and selection acting as a threshold on this factor." Can you expound on what you mean by this? $\endgroup$ – sterid Oct 23 '17 at 7:20
  • $\begingroup$ In the sex determination literature, sex is often considered as a threshold trait on some liability factor. For example in humans, SRY create TDF and TDF is the liability factor. If TDF is at a high enough concentration, it will be a male, otherwise a female. Similarly, you can picture fitness as a threshold trait where your continuous phenotype of interest (heigh or whatever) is the liability factor. $\endgroup$ – Remi.b Oct 23 '17 at 11:50
  • $\begingroup$ Would you define "liability factor" please? $\endgroup$ – sterid Oct 23 '17 at 23:55
  • $\begingroup$ I won't be able to cite you a nice neat definition, but I mainly encountered this term in the sex determination literature and it is some factor (protein concentration typically) which depending on its value will affect a phenotypic trait based on a threshold model. I am not sure the term is always used like this though. Sorry, I can't give you more info on that. If interested you might want to have a look at this book. $\endgroup$ – Remi.b Oct 23 '17 at 23:59

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