Abstract
Climate adaptation is surprisingly rarely reported as a cause for the build-up of reproductive isolation between diverging populations. In this review, we summarize evidence for effects of climate adaptation on pre- and postzygotic isolation between emerging species with a particular focus on pied (Ficedula hypoleuca) and collared (Ficedula albicollis) flycatchers as a model for research on speciation. Effects of climate adaptation on prezygotic isolation or extrinsic selection against hybrids have been documented in several taxa, but the combined action of climate adaptation and sexual selection is particularly well explored in Ficedula flycatchers. There is a general lack of evidence for divergent climate adaptation causing intrinsic postzygotic isolation. However, we argue that the profound effects of divergence in climate adaptation on the whole biochemical machinery of organisms and hence many underlying genes should increase the likelihood of genetic incompatibilities arising as side effects. Fast temperature-dependent co-evolution between mitochondrial and nuclear genomes may be particularly likely to lead to hybrid sterility. Thus, how climate adaptation relates to reproductive isolation is best explored in relation to fast-evolving barriers to gene flow, while more research on later stages of divergence is needed to achieve a complete understanding of climate-driven speciation.
Highlights
The process of speciation is often seen as a gradual build-up of a combination of pre- and postzygotic reproductive barriers between genetically diverging populations (Coyne and Orr 2004)
Adaptation to different climatic conditions often relies on physiological traits and may appear morphologically cryptic. This may lead to an underestimation of the role of climate adaptation in the gradual build-up of reproductive isolation
We reviewed the evidence of climate adaption in the buildup of reproductive isolation between populations with a particular emphasis on studies using collared and pied flycatchers as a model system for speciation research
Summary
The process of speciation is often seen as a gradual build-up of a combination of pre- and postzygotic reproductive barriers between genetically diverging populations (Coyne and Orr 2004). This difference in climate adaptation, in turn, matches a number of differences in life-history traits. We are planning to explore the physiological and genomic background to the observed trade-off between competitive ability (i.e. signalled by plumage traits) and tolerance to harsh environment in Ficedula flycatchers by, for example, measuring metabolic rate and performing genomewide association mapping These are necessary steps to explore whether divergence in climate adaptation relates to the build-up of genetic incompatibilities. Disturbed epistatic interactions (i.e. due to lack of a co-evolutionary history) between genes underlying divergent climate adaptation may have fundamental effects on hybrid fertility and viability
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