Handicap principle implies emergence of dimorphic ornaments

Abstract

Species spanning the animal kingdom have evolved extravagant and costly ornaments to attract mating partners. Zahavi's handicap principle offers an elegant explanation for this: ornaments signal individual quality, and must be costly to ensure honest signalling, making mate selection more efficient. Here, we incorporate the assumptions of the handicap principle into a mathematical model and show that they are sufficient to explain the heretofore puzzling observation of bimodally distributed ornament sizes in a variety of species.

Does the handicap principle explain the evolution of dimorphic ornaments?

“…The selective maintenance of such male dimorphisms has been difficult to understand ( Simpson et al., 2011 ). Yet, a recent paper by Clifton et al (2016) concluded the evolution of male dimorphisms can be explained solely by the handicap principle ( Zahavi, 1975 ). It is not intuitively obvious how the handicap principle can selectively maintain male dimorphisms, and no verbal explanations were provided.…”

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Figure 1 Fitness curves with three different benefit functions (concave, linear and convex respectively). The cost function is the same as that in Clifton et al. (2016) with Grafen's handicap conditions.

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“…The approach used in constructing this new model appears to be based on calculating a ‘signalling equilibrium’ by searching only for the optimal signal intensity for signallers and keeping the receivers' evolutionary response fixed. Here we explore why the current shape of the receiver's response may not be the best response to the signaller's strategy described in the Clifton, Braun, and Abrams (2016) model. The authors argue that communication is ‘mostly honest, at least for large enough variance in health.’ This conclusion might apply to certain scenarios.…”

“…In summary, the model proposed by Clifton et al. (2016) to explain male dimorphisms is interesting, but several caveats should be considered.…”

“… Clifton et al. (2016) model the change in the distribution of male ornament size due to selection on the differential fitness effect of ornaments with different sizes.…”