Diet, adaptation and the evolution of assortative mating in Ceratitis capitata

Abstract The action of natural selection in establishing barriers to gene flow between populations, or reproductive isolation, is increasingly understood to be a primary driver of speciation and thus biodiversity. ‘Ecological speciation’ is now supported by evidence from numerous studies in a range of natural populations. However, experimental tests of the role of divergent natural selection in the establishment of reproductive isolation are still scant. To address this omission, the role of larval diet in imposing divergent selection and causing ecological adaptation and reproductive isolation was tested. These tests were conducted on the Mediterranean fruit fly (Ceratitis capitata, Wiedemann) (medfly) model system, which has been relatively under-utilised in the experimental study of speciation. Using manipulative experiments and experimental evolution, the three major components of ecological speciation were examined. Firstly a source of divergent selection was established through quantification of the consequences of alteration in specific dietary nutrients during the development of medfly larvae. Following this, similar selective pressures were used as the basis of experimental evolution of medfly populations reared on divergent developmental diets. Divergence between these populations was assayed at several time points during evolution, in real time, using tests for sexual isolation. After 60 generations of experimental evolution a form of reproductive isolation between populations had evolved. The mechanism that may have led to the evolution of this isolation was also explored, through further mating tests, and also the quantification of male courtship behaviour. The genetic basis of the phenotypes associated with adaptation and sexual isolation was explored using transcriptomic sequencing and differential expression analysis of genes expressed in males from the two experimental regimes. A range of candidate genes was identified as differentially expressed, including genes associated with oxidative phosphorylation and chemosensation. Taken together, the results of this research present a novel example of how divergent ecological selection pressure can lead to the evolution of sexual isolation in experimental populations.

Name dc:type.qualificationname

phd

Level dc:type.qualificationlevel

doctoral

Grantor dc:publisher.institution

University of East Anglia

Year dc:date.issued

2015

Author dc:creator

• Nash, William

Language dc:language

en