Biologists have long been fascinated with the origin and maintenance of the diversity of life. What determines how new species are created and maintained? Speciation is the evolution of barriers to interbreeding between groups; it can start when certain populations within a group become adapted to different environments, but for speciation to complete, other barriers to interbreeding, such as mate choice, must form.
Studies of speciation in natural populations usually focus on obligately sexual species. However, a wealth of reproductive modes exist across the tree of life, from complete asexuality to obligate bisexual reproduction. A facultatively sexual reproductive mode, in which species reproduce both sexually and asexually, is common in fungi, plants and animals, and is found in ecologically and economically important groups including disease causing organisms, crop pests and primary producers.
Sex affects the speciation process: by mixing up gene combinations it produces the genetic variation on which selection can act, facilitating early stages of speciation. However, it also erodes associations between barriers, and this can slow speciation down. Understanding how facultative sex impacts the speciation process will fill an important gap in speciation research, with implications for fundamental speciation theory, as well as for how we understand the evolution and spread of facultatively sexual pests and diseases.
Work in our lab aims to understand the impact of reproductive mode on speciation, with a focus on facultatively sexual monogonont rotifers and experimental evolution. Long-term experimental speciation in the lab provides a powerful tool for tackling intractable questions in evolutionary biology (White, Snook and Eyres, 2020; White et al, in press), and facultatively sexual rotifers are ideal for answering questions about reproductive mode. By recording phenotypes indicating local adaptation and reproductive isolation, and combining these with sequencing populations before and after long-term experimental speciation in the lab, we are able to examine how sex impacts the progress and outcome of speciation, and its genomic architecture.
The specific approach taken in this PhD can be tailored to the particular interests of the student, and could include experimental evolution, genomics, behavioural assays, and modelling to understand the roles of strength and directionality of selection, drift, or gene flow in driving speciation, or a more detailed look at the functional basis of reproductive isolation between experimentally diverged populations. The successful candidate will have the opportunity to gain experience and training in state of the art genomic techniques and molecular and aquatic laboratory work. In addition, there is scope within the PhD to develop fieldwork-based projects related to these topics with our international collaborators.
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