Discrete morphological variation within conspecific males puzzled Darwin, and still fascinates evolutionary biologists today. Known as male dimorphism, this phenomenon reflects alternative mating tactics (AMTs) among males: the large male morphs typically guard females or reproductive territories and have more elaborate weaponry; the small male morphs normally sneak copulations and have reduced weaponry. Male dimorphism is particularly common among arthropods, and generally results from a conditional strategy in which the expression of distinct male morphs depends on the status of individuals. In this thesis I firstly review the occurrence of male dimorphism and AMTs in insects, and also provide an overview of how current theory explains their evolution. I then move on to investigate empirically some of the several unanswered questions about the genetic architecture and the evolution of male dimorphism. Firstly, using the bulb mite Rhizoghyphus echinopus as a model system, I show that there is genetic variation for the switchpoint that links male morph expression to the status of individuals, which is an important prediction of quantitative genetics models that explain the genetics of such dimorphisms. Secondly, I disentangle the sources of heritability of male morph in R. echinopus, showing that this trait is strongly influenced by a paternal effect that could either be linked to the Y chromosome of males or an indirect genetic effect that is environmentally transmitted. Next, I use the dung beetle Onthophagus taurus to investigate the importance of maternal effects for the ecology of male dimorphism. I demonstrate that female O. taurus perceive population density and respond by changing the phenotype of their offspring, through a new type of maternal effect that represents a transgenerational response of AMTs to demography.
|Qualification||Doctor of Philosophy|
|Publication status||Unpublished - 2012|