Specialized dispersal morphs are well known from a large number of taxa, and, often, different phenotypes may coexist in one population. More dispersive types have often been found to be less fecund, as shown e.g. for the sand field cricket Gryllus firmus (among others Roff et al. 1999).

It was thus postulated that there is a trade-off between dispersal ability, i.e. the maintenance of a flight apparatus which reduces dispersal mortality, and fertility. To our knowledge, this hypothesis has never been validated theoretically. Furthermore it is unclear what specific conditions promote the evolution of such dispersal polymorphisms.

Therefore, we use an individual-based simulation approach to analyze the relevance of various key-factors (environmental conditions, life-history attributes, genetic system) for the evolution of dispersal strategies.

Results/Conclusions

We will demonstrate that a dispersal mortality – fertility trade-off may lead to a dimorphism in dispersal propensity.

A clear dimorphism between dispersive and non-dispersive animals that respectively did and did not reduce their fertility in order to minimize dispersal costs evolved only in diploid systems. The form of the functional relationship between dispersal mortality and the fertility trade-off, as well as the amount of linkage disequilibrium between dispersal-relevant traits, were of decisive importance to the stability of the dimorphism.

The dimorphism reported here is an emergent model property, while the underlying trait is quantitative and not assumed to be a threshold trait.

Reference:

Roff DA, Tucker J, Stirling G and Fairbairn DJ (1999) The evolution of threshold traits: effects of selection on fecundity and correlated response in wing dimorphism in the sand cricket. Journal of Evolutionary Biology 12 (3): 535-546.