Ecological genetics of populations experiencing changing environmental conditions
A major goal in evolutionary biology is to understand how ecological factors shape the phenotypic and genetic variation that we observe in natural populations and in this thesis I examine how rapid changes in temperature have influenced phenotypic and genetic variation in morphological and life history traits in long-term studies of great tits. In Chapter 1 I review what is known about the effects of environmental change on natural populations, and outline the quantitative genetic framework that is available to study genetic variation in natural populations. Much focus on the effects of climate change has concerned species’ phenology, far less attention has been given to other traits. In Chapter 2 I examine the effects changing environmental conditions have had on the proportion of females that produce second broods. Temperature operates mainly through indirect effects (such as food abundance) but may also have more direct effects. In Chapter 3 I show that over a 36 year period body size have declined in line with predictions from Bergmann’s rule and I explore the genetic basis of this decline and the environmental factors involved. Although we can learn much from population level responses, there is a great deal of additional information to be gained by studying between-individual responses. In Chapter 4 I therefore compare the multivariate pattern of between-individual variation in phenotypic plasticity and its genetic basis for laying date and clutch size, in two great tit populations. Environmental changes may also directly affect the expression of genetic variance as well as the strength of selection acting on a trait, and in Chapter 5 I show that, for laying date, the environment induces a positive covariance between strength of selection and the expression of additive genetic variance, something that may enhance the rate of adaptation. Finally, in Chapter 6 I discuss and summarise the wider implications of the findings from this thesis.