Population Genomics, Hybrid Sterility, & Gene Expression in the Anopheles gambiae Species Complex
Abstract
This dissertation explores the genomics of speciation in the An. gambiae
complex. The complex is comprised of eight recently diverged species and contains the
most important vectors of human malaria. Male F1 hybrids between these species are
completely sterile and females exhibit varying levels of sterility. I performed a
population genomic analysis of the three genetic clusters that comprise An. melas that
illuminated genome-wide divergence between them. This is suggestive of a pattern of
allopatric divergence with little to no gene flow.
I analyzed gene expression data to assess if dosage compensation occurs in males
of An. coluzzii, An. arabiensis, and An. quadriannulatus, in order to balance expression
between the hemizygous X chromosome and the autosomes. Dosage compensation is
acting in each species and is not influenced by hybridization. I identified male- and
female-biased genes in each parental species and mis-expressed genes in F1 hybrid
males that are involved in hybrid sterility. Mis-expressed genes are involved in mitosis,
spermatogenesis, and other physiological processes involved in the sterility phenotype.
An analysis of allele-specific expression found that An. coluzzii and An. arabiensis have
a high proportion of genes (~80%) that are conserved or compensatory in their
transcription. In contrast, An. coluzzii and An. quadriannulatus have a higher proportion
of genes that have diverged in trans-. These patterns may reflect higher levels of
historical and ongoing introgression between An. coluzzii and An. arabiensis than
between An. coluzzi and An. quadriannulatus.
Lastly, I performed a QTL analysis of sterility in a (An. coluzzi x An.
quadriannulatus) x An. quadriannulatus backcross to identify regions of the An. coluzzi
genome that are responsible for male sterility when introgressed into an An.
quadriannulatus genomic background. Five autosomal QTL were identified that interact
through epistatic interactions with each other and the X chromosome, which is
responsible for the majority of the variation observed in the sterility phenotype. Two
autosomal QTL of large effect are shared with the An. coluzzi x An. arabiensis cross, indicating that these regions of the An. coluzzii genome contribute to reproductive isolation between this species and multiple members of the An. gambiae species complex.
Subject
Anopheles gambiaeSpeciation
Hybrid Sterility
Gene Expression: Dosage Compensation: Transcription Regulation
Citation
Deitz, Kevin Canning (2017). Population Genomics, Hybrid Sterility, & Gene Expression in the Anopheles gambiae Species Complex. Doctoral dissertation, Texas A & M University. Available electronically from https : / /hdl .handle .net /1969 .1 /165721.