Biology subjects

Signor, S.

Publications and source records attributed to Signor, S..

3 recordsLinked to original sources

bioRxiv2018

Evolution of phenotypic plasticity in response to ethanol between sister species with different ecological histories (Drosophila melanogaster and D. simulans)

The contribution of phenotypic plasticity to adaptation is contentious, with contradictory empirical support for its role in evolution. Here I investigate the possibility that phenotype plasticity has contributed to adaptation to a novel resource. If phenotype plasticity contributes to adaptation, it is thought to evolve in a process termed genetic accommodation. Under this model, the initial response to the environment is widely variable due to cryptic genetic variation, which is then refined by selection to a single adaptive response. I examine the role of phenotypic plasticity in adaptation here by comparing two species of Drosophila that differ in their adaptation to ethanol (Drosophila melanogaster and D. simulans). Both species are human commensals with a recent cosmopolitan expansion, but only D. melanogaster is adapted to ethanol exposure. I measure phenotype plasticity in response to ethanol with gene expression and an approach that combines information about expression and alternative splicing. I find evidence for adaptation to ethanol through genetic accommodation, suggesting that the evolution of phenotype plasticity contributed to the ability of D. melanogaster to exploit a novel resource. I also find evidence that alternative splicing may be more important for the adaptive response to ethanol than overall changes in exon expression.

evolutionary biology↗

bioRxiv2017

Quantitative variation and evolution of spatially explicit morphogen expression in Drosophila

Robustness in development allows for the accumulation of neutral genetically based variation in expression, and here will be termed genetic stochasticity . This largely neutral variation is potentially important for both evolution and complex disease phenotypes. However, it has generally only been investigated as variation exhibited in the response to large genetic perturbations. In addition, work on variation in gene expression has similarly generally been limited to being spatial, or quantitative, but because of technical restrictions not both. Here we bridge these gaps by investigating replicated quantitative spatial gene expression using rigorous statistical models, in different genotypes, sexes, and species (Drosophila melanogaster and D. simulans). Using this type of quantitative approach with developmental data allows for effective comparison among conditions, including health versus disease. We apply this approach to the morphogenetic furrow, a wave of differentiation that sweeps across the developing eye disc. Within the morphogenetic furrow, we focus on four conserved morphogens, hairy, atonal, hedgehog, and Delta. Hybridization chain reaction quantitatively measures spatial gene expression, co-staining for all four genes simultaneously and with minimal effort. We find considerable variation in the spatial expression pattern of these genes in the eye between species, genotypes, and sexes. We also find that there has been evolution of the regulatory relationship between these genes. Lastly, we show that the spatial interrelationships of these genes evolved between species in the morphogenetic furrow. This is essentially the first population genetics of development as we are able to evaluate wild type differences in spatial and quantitative gene expression at the level of genotype, species and sex.

developmental biology↗

bioRxiv2017

Population genomics of Wolbachia and mtDNA in Drosophila simulans from California

Wolbachia pipientis is an intracellular endosymbiont in fecting many arthropods and filarial nematodes. Little is known about the short-term evolution of Wolbachia or its interaction with its host. Wolbachia is maternally inherited, resulting in co-inheritance of mitochondrial organelles such as mtDNA. Here I explore the short-term evolution of Wolbachia, and the relationship between Wolbachia and mtDNA, using a large inbred panel of Drosophila simulans infected with the Wolbachia strain wRi. I find reduced diversity relative to expectation in both Wolbachia and mtDNA, but only mtDNA shows evidence of a recent selective sweep or population bottleneck. I estimate Wolbachia and mtDNA titre in each genotype, and I find considerable variation in both phenotypes, despite low genetic diversity in Wolbachia and mtDNA. A phylogeny of Wolbachia and of mtDNA show that both trees are largely unresolved, suggesting a recent origin of the infection and a single origin. Using Wolbachia and mtDNA titre as a phenotype, we perform an association analysis with the nuclear genome and find several regions implicated in the phenotype, including one which contains four CAAX-box protein processing genes. CAAX-box protein processing can be an important part of host-pathogen interactions in other systems, suggesting interesting directions for future research.

evolutionary biology↗