Ecological genetics of populations experiencing changing environmental conditions
Abstract
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.