Book Description

This thesis addresses questions concerning the evolution of body colour in threespine sticklebacks (Gasterosteus aculeatus). Chapter 2 examines natural selection of colour in sticklebacks by investigating the possible divergence of cryptic colouration between a species pair. I determined that the upper body colour of benthics matched the littoral background (benthics habitat) colour more closely than did the upper body colour of limnetics, suggesting that in their own habitat benthics are more cryptically coloured than the limnetic species. Furthermore, I found that benthics exhibited a greater degree of colour plasticity and consistency in this plasticity than limnetics, which is likely an adaptive response to the greater spectral heterogeneity of the littoral zone. Chapter 3 examines sexual selection of colour in sticklebacks by investigating whether UV is a secondary sexual character on the abdomen of four stickleback populations. Using colour measurements taken from reproductive males and females during the breeding season and individuals from the non-breeding season, I found that UV did not exhibit striking patterns of sexually dimorphism or seasonality on the abdomen, suggesting that UV is not a secondary sexual character on this part of the body in these populations. The Priest benthic population, however, exhibited significant sexual dimorphism and borderline significant seasonality, leaving open the possibility that UV may be a secondary sexual character in this population.