Biology subjects

Davey, J. W.

Publications and source records attributed to Davey, J. W..

3 recordsLinked to original sources

bioRxiv2018

Ancestral admixture and structural mutation define global biodiversity in fission yeast

Mutation and recombination are key evolutionary processes governing phenotypic variation and reproductive isolation. We here demonstrate that biodiversity within all globally known strains of Schizosaccharomyces pombe arose through admixture between two ancestral lineages. Initial hybridization occurred [~]20 sexual outcrossing generations ago consistent with recent, human-induced migration at the onset of intensified transcontinental trade. Species-wide phenotypic variation was explained near-exclusively by strain-specific arrangements of alternating ancestry components with evidence for transgressive segregation. Reproductive compatibility between strains was likewise predicted by the degree of shared ancestry. Over 800 structural mutations segregating at low frequency had overall little effect on the introgression landscape. This study sheds new light on the population history of S. pombe and illustrates the importance of hybridization as a creative force in generating biodiversity.

evolutionary biology↗

bioRxiv2018

Sexually dimorphic gene expression and transcriptome evolution provides mixed evidence for a fast-Z effect in Heliconius

Sex chromosomes have different evolutionary properties as compared to the autosomes due to their hemizygous nature. In particular, recessive mutations are more readily exposed to selection, which can lead to faster rates of molecular evolution. Here, we report patterns of gene expression and molecular evolution in the sex chromosomes of a group of tropical butterflies. We first improved the completeness of the Heliconius melpomene reference annotation, a neotropical butterfly with a ZW sex determination system. Then we sequenced RNA from male and female whole abdomens and female ovary and gut tissue to identify sex and tissue specific gene expression profiles in H. melpomene. Using these expression profiles we compare sequence divergence and polymorphism, the strength of positive and negative selection and rates of adaptive evolution for Z and autosomal genes between two species of Heliconius butterflies, H. melpomene and H. erato.\n\nWe show that the rate of adaptive substitutions is higher for Z as compared to autosomal genes, but contrary to expectation it is also higher for male as compared to female biased genes. There is therefore mixed evidence that hemizygosity influences the rate of adaptive substitutions. Additionally, we find no significant increase in the rate of adaptive evolution or purifying selection on genes expressed in ovary tissue, a heterogametic specific tissue. Together our results provide limited support for fast-Z evolution. This contributes to a growing body of literature from other ZW systems that also provide mixed evidence for a fast-Z effect.

evolutionary biology↗

bioRxiv2016

Recombination Suppression is Unlikely to Contribute to Speciation in Sympatric Heliconius Butterflies

Mechanisms that suppress recombination are known to help maintain species barriers by preventing the breakup of co-adapted gene combinations. The sympatric butterfly species H. melpomene and H. cydno are separated by many strong barriers, but the species still hybridise infrequently in the wild, with around 40% of the genome influenced by introgression. We tested the hypothesis that genetic barriers between the species are reinforced by inversions or other mechanisms to reduce between-species recombination rate. We constructed fine-scale recombination maps for Panamanian populations of both species and hybrids to directly measure recombination rate between these species, and generated long sequence reads to detect inversions. We find no evidence for a systematic reduction in recombination rates in F1 hybrids, and also no evidence for inversions longer than 50 kb that might be involved in generating or maintaining species barriers. This suggests that mechanisms leading to global or local reduction in recombination do not play a significant role in the maintenance of species barriers between H. melpomene and H. cydno.\n\nAuthor SummaryIt is now possible to study the process of species formation by sequencing the genomes of multiple closely related species. Heliconius melpomene and Heliconius cydno are two butterfly species that have diverged over the past 2 million years and have different colour patterns, mate preferences and host plants. However, they still hybridise infrequently in the wild and exchange large parts of their genomes. Typically, when genomes are exchanged, chromosomes are recombined and gene combinations are broken up, preventing species from forming. Theory predicts that gene variants that define species might be linked together because of structural differences in their genomes, such as inverted pieces of chromosomes that will not be broken up when the species hybridise. However, in this paper, we use deep sequencing of large crosses of butterflies to show that there are no long chromosome regions that are not broken up during hybridisation, and no long chromosome inversions anywhere between the two genomes. This suggests that hybridisation is rare enough and mate preference is strong enough that inversions are not necessary to maintain the species barrier.

evolutionary biology↗