Just why do unusual things persist?

Rare traits persist in a population because predators detect common forms of prey more easily.

Rare traits may offer protection, especially for salamanders

Researchers writing in the journal BMC Ecology found that birds will target salamanders that look like the majority - even reversing their behavior if a trait that was previously in the minority becomes the majority.

A team from the University of Tennessee studied the effects of the prevalence of a dorsal stripe among a group of model salamanders on the foraging behavior of a flock of Blue Jays.

Lead researcher Benjamin Fitzpatrick, said: “Maintenance of variation is a classic paradox in evolution because both selection and drift tend to remove variation from populations. If one form has an advantage, such as being harder to spot, it should replace all others. Likewise, random drift alone will eventually result in loss of all but one form when there are no fitness differences. There must therefore be some advantage that allows unusual traits to persist”.

The authors placed a selection of food-bearing model salamanders into a field for six days, with striped models outnumbering the unstriped by nine to one, or vice versa. On test days, the numbers were evened out. In each case, Blue Jays were more likely to attack the models that had been most prevalent over the previous six-day period. According to Fitzpatrick, “We believe that the different colour forms represent different ways of blending in on the forest floor. Looking for something cryptic takes both concentration and practice. Predators concentrating on finding striped salamanders might not notice unstriped ones”.

He concludes: “Thus, the maintenance of color variation in terrestrial salamanders might be explained by the oldest and most obvious hypothesis - rare form advantage arises because predators tend to overlook rare prey.”