The European earwig exhibits a remarkable male-dimorphism in forceps morphology that is associated with alternative reproductive tactics under the control of a conditional evolutionarily stable strategy. Populations on the small, rocky islands of the Farnes off the Northumberland coast are known to sustain populations with dramatically higher morph ratios than observed on the UK mainland. A survey conducted of island and mainland sites around the UK showed that the dimorphic populations of the Farnes are similar to other islands and that mainland populations generally exhibit low morph ratios. Additionally, a correlation between morph ratio and population density was found lending support to the hypothesis that the ESS thresholds that define the morph ratios have diverged through local adaptation. A set of seven microsatellite markers are presented that were developed from a Farne island population of F. auricularia with one additional, previously published locus. These eight markers exhibit genetic variability within and between populations and as such can potentially be applied at a range of scales, from broad-scale phylogeography to within population parentage studies. A phylogeographic study of the UK populations using these markers suggests a single postglacial colonisation from mainland Europe and give further support to the local adaptation hypothesis of ESS threshold evolution. A study of ejaculate size in F. auricularia showed that the males transfer free sperm at a steady rate and that the morphs do not differ in the number of sperm per ejaculate. Measurements of change in body-mass were found to be ineffective measures of ejaculate size, but that macrolabic males lost more weight during copula than brachylabic males. This may be the result of differential investment in accessory ejaculate components between the morphs, as a result of the differing risk of sperm competition.

The evolution and maintenance of multiple phenotypes within populations is an interesting evolutionary and ecological question, and is becoming increasingly important for the restoration and conservation of partially migratory species. In particular, why individuals adopt a particular phenotype has been the focus of numerous research efforts. In the partially migratory species Oncorhynchys mykiss (commonly known as steelhead and rainbow trout), I found that sex plays a strong role in whether an individual adopts an anadromous or resident life history. I observed a higher frequency of females adopting the anadromous tactic throughout the species range, and I attributed this to the relationship between body size and reproductive success in females that is not present in males. I did not observe differences in female bias along gradients of latitude or migration distance, and I hypothesize that while the frequency of tactics among populations may change along these gradients, either the change is equal between males and females, or an interaction of latitude and migration distance may control changes. I did not observe a corresponding male bias in the one resident population I sampled, and suggest that this is the result of a high frequency of residents in that population. I propose that sex ratios could be a valuable metric for measuring frequency of life-history tactics in populations and could facilitate the investigation into the controls of life-history tactics across broad scales. / Graduation date: 2013