Biology subjects

Bladen, J.

Publications and source records attributed to Bladen, J..

4 recordsLinked to original sources

bioRxiv2025

Drive, suppression, and escape from suppression of a selfish chromosome

Meiotic drivers are selfish chromosomes that are predicted to spark a rapid intragenomic arms-race with their suppressors. However, the long-term persistence of unsuppressed selfish chromosomes in natural populations violates these theoretical expectations. The Drosophila pseudoobscura Sex-Ratio (SR) chromosome exemplifies this problem, sometimes referred to as the "ancient gene drive paradox". Here, we reconstruct the evolutionary history of this SR chromosome and show that its genetic architecture and complexity has been shaped by a history of drive, suppression, and escape from suppression. Our results indicate that the current lack of resistance to the SR chromosome represents a transient condition awaiting the emergence of new suppressors. SIGNIFICANCEIntragenomic arms races triggered by selfish chromosomes are expected to drive rapid evolution through cycles of drive, suppression, and escape from suppression. Despite these expectations, some selfish chromosomes such as the D. pseudoobscura Sex-Ratio (SR) chromosome exist unsuppressed for extended periods of time. Despite the absence of suppression, we uncover currently segregating suppressors against the ancestral version and evidence of recent dynamic evolution on the SR chromosome. Todays SR chromosome thus represents a transient state in a surprisingly slow arms race. Taken together, the lack of suppressors against this selfish chromosome can be explained by mutational limits for the emergence of suppressors.

evolutionary biology↗

bioRxiv2024

Overdrive is essential for targeted sperm elimination by Segregation Distorter

Intra-genomic conflict driven by selfish chromosomes is a powerful force that shapes the evolution of genomes and species. In the male germline, many selfish chromosomes bias transmission in their own favor by eliminating spermatids bearing the competing homologous chromosomes. However, the mechanisms of targeted gamete elimination remain mysterious. Here, we show that Overdrive (Ovd), a gene required for both segregation distortion and male sterility in Drosophila pseudoobscura hybrids, is broadly conserved in Dipteran insects but dispensable for viability and fertility. In D. melanogaster, Ovd is required for targeted Responder spermatid elimination after the histone-to-protamine transition in the classical Segregation Distorter system. We propose that Ovd functions as a general spermatid quality checkpoint that is hijacked by independent selfish chromosomes to eliminate competing gametes.

genetics↗

bioRxiv2024

Transformation of meiotic drive into hybrid sterility in Drosophila

Hybrid male sterility is one of the fastest evolving intrinsic reproductive barriers between recently isolated populations. A leading explanation for the evolution of hybrid male sterility involves genomic conflicts with meiotic drivers in the male germline. There are, however, few examples directly linking meiotic drive to hybrid sterility. Here, we report that the Sex-Ratio chromosome of Drosophila pseudoobscura, which causes X-chromosome drive within the USA subspecies, causes near complete male sterility when moved into the genetic background of the Bogota subspecies. In addition, we show that this new form of sterility is genetically distinct from the sterility of F1 hybrid males in crosses between USA males and Bogota females. Our observations provide a tractable study system where non-cryptic drive within species is transformed into strong hybrid sterility between very young subspecies.

genetics↗

bioRxiv2019

A triple-hybrid cross reveals new a hybrid incompatibility locus between D. melanogaster and D. sechellia

Hybrid incompatibilities are the result of deleterious interactions between diverged genes in the progeny of two species. In Drosophila, crosses between female D. melanogaster and males from the D. simulans clade (D. simulans, D. mauritiana, D. sechellia) fail to produce hybrid F1 males. When attempting to rescue hybrid F1 males by depleting the incompatible allele of a previously identified hybrid incompatibility gene, we observed robust rescue in crosses of D. melanogaster to D. simulans or D. mauritiana, but no rescue in crosses to D. sechellia. To investigate the genetic basis of D. sechellia resistance to hybrid rescue, we designed a triple-hybrid cross to generate recombinant D. sechellia / D. simulans genotypes. We tested the ability of those genotypes to rescue hybrid males with D. melanogaster, and used whole genome sequencing to measure the D. sechellia / D. simulans allele frequency of viable F1 males. We found that recombinant genotypes were rescued when they contained two specific loci from D. simulans - a region containing previously identified Lethal hybrid rescue (Lhr), and an unknown region of chromosome 3L which we name Sechellia aversion to hybrid rescue (Satyr). Our results show that the genetic basis for the recent evolution of this hybrid incompatibility is simple rather than a highly dispersed effect. Further, these data suggest that fixation of differences at Lhr after the split of the D. simulans clade strengthened the hybrid incompatibility between D. sechellia and D. melanogaster.

evolutionary biology↗